Tf 125 motor bucket thingy

[layton]

Well, I thought it would be a good idea to tear Into this motor while I am stuck at home, was just going to check top end but the left hand main bearing didn't feel right so split the cases found rust on the bearing and putting where the oil seal sits. I got the motor in unknown condition no wonder it wouldn't idle.. looks like it's been sucking air and running lean... it has rooted the top end also anyone for ideas on what to do

Lost cause or?...

I am thinking of polishing crank end and adding a washer to space the oil seal out throw new main bearings in new small end bearing and piston with a rebore.

[layton]

Turned crank in the lathe slowly with some 2000 grit paper and this is the result, does anybody have a workshop manu for a tf/ts 125 motor? I can't seem to find one

[TZ350]

.
You might be able to polish that oil seal surface on the crank up some more. Usually the mag side bearing is a tight fit on the crank. But the hot trick is to polish the crank until a new bearing is just a slip fit. this does away with any power robbing side loading as the engine heats up and the cases expand. It does not matter much that the crank spins inside the bearing. A race engine is not going to do the hours of service that a road/farm bike does.

[TZ350]

345234

I see some decent engineering machinery in the background.

If you are into a bit of two stroke tuning page 2000 on the ESE thread is worth a look. https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner/page2000

[layton]

.
You might be able to polish that oil seal surface on the crank up some more. Usually the mag side bearing is a tight fit on the crank. But the hot trick is to polish the crank until a new bearing is just a slip fit. this does away with any power robbing side loading as the engine heats up and the cases expand. It does not matter much that the crank spins inside the bearing. A race engine is not going to do the hours of service that a road/farm bike does.
Ah, nice that sounds like a plan. I read on one of the other posts about pressing some slugs Into the crank for vibration I plan to up the rpms did you press the slugs into the big holes or smaller ones?
What's the best thing to do with the bore, and piston? Go for something like a rg500 piston like others have done or keep it simple? Bore or buy a new cylinder?

I am just getting into 2 stroke engines so I will have many questions but will start on that thread, thanks.

Yep.. good ol little myford the drill press makes it look tiny... I haven't actually used it much since getting a bigger harrison lathe but still nice to use for smaller bits.

[speedpro]

You need to measure the bore. A quick hone and a new piston may be all it needs. Bearings are dirt cheap from your local bearing shop and you may be able to get new seals there as well. Ask about "seal savers". These are nothing to do with Greenpeace but very thin sleeves that are slid onto shafts over where the seals run. A slug of aluminium goes in the big hole on each crank wheel. If you have it all apart and the bearings you can see aren't good there may also be damage on the big end bearing as well. It may be worth giving it a go but if it fails and you are really unlucky it could send bits of cage up the bore and into the cylinder. A crank rebuild might be worth doing depending on what you want to achieve.

The slugs of aluminium worked really well for me. Others seem to have had less spectacular results.

[layton]

I did think about a speedi sleeve, I'll see what happens with a slip fit on the bearing.

The bore measures 56.20mm

I made a quick jig for the crank shaft works quite well actually.. I do have a granite surface plate but missing the tooling may be a good excuse to buy some bits and pieces. I am looking forward to rebuilding this engine as it's the first time I have tried something like this, lots to learn.

I seem to of misplaced my 50-75 mm micrometer so was measured with a telescope gauge and a digital caliper not ideal345286

[speedpro]

Nice little jig. With a few more bits you will be able to check the balance factor as well. It's real easy.

[TZ350]

.
Use the Google "site:" search term to find all the posts about "balance factor" and how to check it posted on the ESE thread.

Copy and paste this line into your Google search bar:-

balance factor site:https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner

345305

[layton]

Cool, looks easy enough to balance it using this stand, the boy and I where bored today so made a engine stand.. there isnt much I can do until shops are open again so filling time in

[mr bucketracer]

I'm going to have another go at a tf engine
I have a heap of 1981 cr125 pistons at that 56mm range

[layton]

I'm going to have another go at a tf engine
I have a heap of 1981 cr125 pistons at that 56mm range

What size are they, and what rod size? Want to part with a few if they will work? I am looking to upgrade similar to what F5 Dave has done at the TF engine he built.

[husaberg]

What size are they, and what rod size? Want to part with a few if they will work? I am looking to upgrade similar to what F5 Dave has done at the TF engine he built.

I thhave a heap of Cr125M pistons her in various sizes 56mm and up they are 14mm pins

[layton]

At nice, perfect saves changing the rod.

The TF piston measures approx 66.50 mm dome to skirt and 56mm across

What's a cr piston in comparison

[husaberg]

Sorry replied as a PM
about 59mm to edge of piston 61 or 62 if top of crown
pined at 5 and 7 oclock
center of pin to edge of crown 28.5mm
But dont those Suzukis have a 19mm big end pin i would get rid of that and replace with a 20mm pin.

later ones like pro X will be thinner single rings and likely more available and lighter
http://www.pro-x.com/wp-content/uploads/2015/01/2015_TECH.pdf

[layton]

Yep.. 19mm big end, why change it? I am not bothered about what I end up using just after some guidance on what I should be doing with the piston/rod

So I was looking at the motor today half assembled and came to come to the conclusion after reading some bits and pieces that i should be looking to machine the reed valve down and cut the back of the cylinder and put a 45 degree bevel on the crank to help stuck fuel into the transfer ports, is this in the right track? I had to assemble half some bits to visualize what was happening 345326

[husaberg]

Yep.. 19mm big end, why change it? ]

19mm is only used by suzuki on a few bikes so the better silver flat cadge big ends are not available.
build it right once it will last. The better parts are not expensive likely cheaper than oem

[layton]

Good call on the big end its reasonably worn, couldn't sleep so went and pressed it apart. I swear the press is the most scary pieces of equipment in the garage.

345330
345331345332

[husaberg]

Good call on the big end its reasonably worn, couldn't sleep so went and pressed it apart. I swear the press is the most scary pieces of equipment in the garage.

345330
345331345332

Cool stuff before you machine the pin hole read through the catalogs and decide what piston and rod combo you want, preferably chose a inexpensive easily obtainable piston and rod combo to suit
I would have to check with Ken but if the cylinder is on std bore you might be able to use a KT100S overbore piston that is available up to i think 56.5mm? but they are not just restricted to .25mm sizes you can hone to bore.
if not you could go with a rod combo that suits 15mm pin pistons and use any of the modern overbore pistons.

i will give you some links
https://www.tkrj.co.jp/
http://www.mitaka.co.uk/MDP.htm
http://www.mitaka.co.uk/pistons.htm
http://www.pro-x.com/wp-content/uploads/2015/01/2015_TECH.pdf
http://www.mingyang-group.2u.com.tw/pdf/CAPT-conrod.pdf
http://www.mingyang-group.2u.com.tw/pdf/CAPT-Motorcycle.pdf
https://www.royalrods.com.tw/ebook/index.htm
http://www.strikeproducts.com.au/technical.asp
345349
as a rule modern 125 are 54x54 and have 15mm SM pins
older ones are 16mm pin for Yam and 22mm big ends With SE 14-15mm for others with 20m or 22mm BE pins depending on year.
kawaskis have a lot of dished tops.
the tkrj site will list the std dimensions for the ts125 your engine is based on.

vertex and Woosner offer pistons as well as Weisco try an go with something common
use the catalogs for sizes rather than makes.

the pro X catalog has the silver lated flat cadges you want at resonable prices.
on a 50mm stroke these will run all day at 14K

Is the crankpin length 52 or 56mm?

[TZ350]

.
I think the TS rod is 100mm CC.

If its any help. Team ESE have used these rods:-

RGV250 105mm CC
RD 350 110mm CC
RD 400 115mm CC

And all of them have done a few miles being spun up to 13,000 rpm on the track.

The rod kits all have 22mm big end pins and can run the silver plated flat big end bearing. Little end bearings can be found to suit 14,15 and 16mm pins.

[layton]

The pin is 56mm on a TF the rod is 100MM CC

You fellas know a lot more then me on this subject, what would you recommend for rod and piston?

I also dont have the tooling to bore the crank out, does anybody here have the tools to do it? I will get somebody else to bore the hole out.

[mr bucketracer]

The pin is 56mm on a TF the rod is 100MM CC

You fellas know a lot more then me on this subject, what would you recommend for rod and piston?

I also dont have the tooling to bore the crank out, does anybody here have the tools to do it? I will get somebody else to bore the hole out.I just parted a crank and the prox rod runs a stepped pin . Makes it easy to press together

[husaberg]

The pin is 56mm on a TF the rod is 100MM CC

You fellas know a lot more then me on this subject, what would you recommend for rod and piston?

I also dont have the tooling to bore the crank out, does anybody here have the tools to do it? I will get somebody else to bore the hole out.
if you wish to run a 22mm pin as the TS185er has one of those
then run any rod that suit the piston you will run.


i am not sure i have a CR125M one to measure for length.
okay they are 55mm long 20mm
They run 100mm centers as well and a 14mm pin
They only have a copper M cage though so that needs to be replaced with a silver flat cadge from pro x .
for a 20mm big end pin and 14 or 16mm pin you can run a GT250 m/a or K/l s they have these sizes and are 110mm long but they still need the cage changed.

there are plenty of others in between for length.
345385

I would suggest find the piston you want and work backwards.

[mr bucketracer]

Cr125 piston vs tf 345361is there to much cut away been part piston port

[husaberg]

Cr125 piston vs tf 345361is there to much cut away been part piston port

The early cr ones are not reed so pre 78 at least is 56mm and long skirts. They went cylinder reed around then 78-79 and i think 54mm in about 84-85 then case reed about 87.
the CR125M pistons i have are very much like a H100 in dimensions only bigger bore and thinner rings

[speedpro]

Cr125 piston vs tf 345361is there to much cut away been part piston port

The CR piston with the cutaway is probably OK. It will increase the port timing but the timing stock is horrendously conservative, as suits the bike's original purpose.

In my opinion it would be better to use a full skirt piston and take the piston port down to achieve the desired port timing. This will result in increased port area as well which it needs. Once the piston port is where it should be you will probably have gone into the reed valve area by busting out the bottom of the barrel. I had great success in completely removing the reed valve and filling the whole area with devcon. The end result was 200 degree piston port timing, plenty of port area, nice smooth intake port matched to a round slide 32mm Mikuni.

You are going to have to plan the whole thing before you start machining and grinding. If you machine the piston port down and then drop the cylinder because of a short piston causing excessive transfer port timing you end up with excessive piston port timing. A bit of devcon would fix it but I prefer to have as little filler in the intake port as possible, in case it falls out. The exhaust ports in those cylinders is a bit limited as well. The main problem with the ports though is the old style transfer ports and the angles entering the cylinder. If you correct the roof angles towards modern numbers it will raise the port which isn't a bad thing and scavenging will improve markedly, helped by a good pipe.

In order I would look at:
Rod and piston combination
Transfer porting
Transfer timing or T/A if you want to get that serious. T/A is Time/Area.
Exhaust timing or T/A
Piston port timing

The exhaust port is already too big at the pipe flange. If you do port it to get the port timing, only take out the minimum amount at the cylinder face and don't remove alloy further down the port. With the single exhaust port there is going to be a limitation on the blowdown T/A. Blowdown is how much the exhaust port is open before the transfers open. Raising the transfers will increase the transfer T/A but reduce blowdown T/A. Raising the revs will increase the blowdown T/A required.

It's going to do your head in at the start.

Do you have an update for the 750?

[layton]

The CR piston with the cutaway is probably OK. It will increase the port timing but the timing stock is horrendously conservative, as suits the bike's original purpose.

In my opinion it would be better to use a full skirt piston and take the piston port down to achieve the desired port timing. This will result in increased port area as well which it needs. Once the piston port is where it should be you will probably have gone into the reed valve area by busting out the bottom of the barrel. I had great success in completely removing the reed valve and filling the whole area with devcon. The end result was 200 degree piston port timing, plenty of port area, nice smooth intake port matched to a round slide 32mm Mikuni.

You are going to have to plan the whole thing before you start machining and grinding. If you machine the piston port down and then drop the cylinder because of a short piston causing excessive transfer port timing you end up with excessive piston port timing. A bit of devcon would fix it but I prefer to have as little filler in the intake port as possible, in case it falls out. The exhaust ports in those cylinders is a bit limited as well. The main problem with the ports though is the old style transfer ports and the angles entering the cylinder. If you correct the roof angles towards modern numbers it will raise the port which isn't a bad thing and scavenging will improve markedly, helped by a good pipe.

In order I would look at:
Rod and piston combination
Transfer porting
Transfer timing or T/A if you want to get that serious. T/A is Time/Area.
Exhaust timing or T/A
Piston port timing

The exhaust port is already too big at the pipe flange. If you do port it to get the port timing, only take out the minimum amount at the cylinder face and don't remove alloy further down the port. With the single exhaust port there is going to be a limitation on the blowdown T/A. Blowdown is how much the exhaust port is open before the transfers open. Raising the transfers will increase the transfer T/A but reduce blowdown T/A. Raising the revs will increase the blowdown T/A required.

It's going to do your head in at the start.

Do you have an update for the 750?
Is is alot to take in but I will just have to sit down and do some more reading on the subject, but thanks for the Input it is much appreciated!

The 750 hasn't been touched for about 10 months we only recently finished a big renovation on the house and got 3 phase in the shed for my toys I have had no spare time or money to get started on the bike again, I need to throw wads on cash at it now, like get the seat done a decent ignition system brake rotors engine internals lights finish the fabrication then tear it down and finish everything properly, also I am not too happy with the exhaust collector its messy and needs to be redone. This bucket project came about because I was at the go kart track one weekend and it spiked my interest got the frame and motor for a couple of hundred and thought it would be a quick side project before I got stuck into the 750 again but it has turned into more then that as usual.. no big deal I need to sort some other bits in the shed and get parts to spark abit of motivation again.. it was always a long term project with no real end date I will get it finished but am in no rush to push and be unhappy with the result. I like to try and have only one thing happening at once this little bucket thing wont be a big or expensive job it is what it is and I just want something reasonable to jump on give death and do maintenance when its needed so what husa said about do it once do it right is what I will try to do.

345368345369

This is currently where it sits, will have to read my posts on what I was up to last time as it's been awhile.

Here is the bike assembled I thought I was almost done the only reason I pulled it apart was to give me something to do during this lockdown... I was only going to paint it and check the top end out then bearings where falling apart on disassemble and broken bits falling out and it pretty much went south from there, need to fix that ugly exhaust pipe but apart from that it's all good, have all the other bits - nylon, clipons ect345370345371

[mr bucketracer]

Prox rod kit tf 100- 125345390

[layton]

Prox rod kit tf 100- 125345390

This looks like a much easier option then boring the crank out, I will have to price one up, also like you said far better to assemble with the shoulder.

Thanks for the pic. Had a look at the pro x website and the dimensions are perfect for a good piston selection.

[husaberg]

Prox rod kit tf 100- 125345390


This looks like a much easier option then boring the crank out, I will have to price one up, also like you said far better to assemble with the shoulder.

Thanks for the pic. Had a look at the pro x website and the dimensions are perfect for a good piston selection.

that rod is ProX Con.Rod Kit RM125 ’84-86 + CR125 ’83-84
https://www.pro-x.com/prox-connecting-rod-dimensions-brand/prox-connecting-rod-dimensions-suzuki/
But how do you know its a Pro x Pin Scott?

the Pin from the Cr125m is about the right length and Samarin still make the pins in the right size for 20mm

KT.204 EC • KTM 125 EXC SX 89/97 (110 19 26 14,8 20 56 15x19x20P 20x26x15.EC
HO.220 ECM • Honda 125 CR 85/87 88/07 104 19 28 16 22 54 15-19-18P 22-28-16-EC
http://www.samarin.net/?productos=&accion=buscar&idtipo=9&idmarca=&a=&c=&f=&jaula_piston=&b=&d=&l=&jaula_ciguenal=&Submit=BUSCAR&paginas=13&&id=192

or 22mm
http://www.samarin.net/?productos=&accion=buscar&idtipo=9&idmarca=&a=&c=&f=&jaula_piston=&b=&d=&l=&jaula_ciguenal=&Submit=BUSCAR&paginas=16&&id=211
KW.224 EC • Kawasaki 125 KX 2003/2006 (Reforzada) 104 19 29 17 22 56 15x19x20P 22x29x17EC

YA.207 EC • Yamaha 125 YZ 86 /00 - 01/04 (Reforzada) 105 20 29 17 22 54,5 15x20x18P 22x29x17.EC
YA.210 EC • Yamaha 125 TZR (Reforzada) 105 21 29 17 22 56 16x21x20P 22x29x17.EC
YA.215 EC • Yamaha 200 Quad Blaster (Reforzada) 110 20 29 17 22 56,4 16x20x20P 22x29x17EC

[mr bucketracer]

that rod is ProX Con.Rod Kit RM125 ’84-86 + CR125 ’83-84
https://www.pro-x.com/prox-connecting-rod-dimensions-brand/prox-connecting-rod-dimensions-suzuki/
But how do you know its a Pro x Pin Scott?

the Pn from the Cr125m is about the right length and Samarin still make the pins in the right size for 20mm

http://www.samarin.net/?productos=&accion=buscar&idtipo=9&idmarca=&a=&c=&f=&jaula_piston=&b=&d=&l=&jaula_ciguenal=&Submit=BUSCAR&paginas=13&&id=192

or 22mm
http://www.samarin.net/?productos=&accion=buscar&idtipo=9&idmarca=&a=&c=&f=&jaula_piston=&b=&d=&l=&jaula_ciguenal=&Submit=BUSCAR&paginas=16&&id=211

KT.204 EC • KTM 125 EXC SX 89/97 (110 19 26 14,8 20 56 15x19x20P 20x26x15.ECthe trouble is . I just pulled apart some rods . And out the blue this was in one of them . Now did some one modify this or was it part of a kit ? . Easy to use a stelight tip cutter to machine the pin down or buy one of my dad's cylindrical grinders to grind both ends down lol

[husaberg]

the trouble is . I just pulled apart some rods . And out the blue this was in one of them . Now did some one modify this or was it part of a kit ? . Easy to use a stelight tip cutter to machine the pin down or buy one of my dad's cylindrical grinders to grind both ends down lol

A few Kawasaki triples and some others had two diameter pins but they were not common does the pin have any markings.
my thoughts would be bore out crank fit std pin rinse ad reapeat.rather than make custon pin and have to do that again.

[mr bucketracer]

A few Kawasaki triples and some others had two diameter pins but they were not common does the pin have any markings.
my thoughts would be bore out crank fit std pin rinse ad reapeat.rather than make custon pin and have to do that again.boring out the hole really is like 10 Times
The work

[husaberg]

boring out the hole really is like 10 Times
The work

Than making a custom pin and getting it heat treated each time?
Powroll did all their strokers by boring and sleeving the pin holes than by offset pins?

[mr bucketracer]

Than making a custom pin and getting it heat treated each time?
Powroll did all their strokers by boring and sleeving the pin holes than by offset pins?na machining 2 ends of a crank pin down

[F5 Dave]

Did the crank wheels on the TF. And the MB. But only after breaking ground down pins twice, both times at Ruapuna. Despite huge radius. Easy rebuild after that, if ever required.

[layton]

How did you go about boring the hole out?? Would you use a rgv rod and yammy again?

[F5 Dave]

I cheated and gave it to Mike, dad of Rogan. Any decent toolmaker should do the job with precision. In the MB case we destroyed it by doing the bore offset. Actually did this with my RG and Derbi engine as wel the TF was just central and bigger.

[mr bucketracer]

I would not get to carried away . Just get a rod kit online . Last 3 I got were 17usd each . Mate got them somewhere. Hucky is a master at finding this stuff . With the barrel packed up 2mm and machine top of barrel . Ex port at around 24mm from top . Open the intack up for a 32mm carb and run a mx 125 exhaust . 186 degrees ex no more . Dont laugh dave (-: but you will get a good torquey power

[layton]

It is alot of info to process.. I think I am just waiting for somebody to give me a push on what to get and be done with it, anyway cleaned up the rough bits in the exhaust port still needs some more work, cleaned up transfer ports and drilled and tapped exhaust bolts for M8 as the M6 holes where almost stuffed.

Hard to clean these ports up without sanding drums currently have wet n dry paper wrapped around a rod poking out of the die grinder, far from ideal.

345403345404

What are peoples thoughts of removing the reed valve and filling the hole up? Seems like a good idea from what I have been reading.

[TZ350]

345406 Bad old style copper coated "W" big end bearing. These are prone to breaking up when revved hard.

345405 Good new style silver plated flat big end bearing. These are much more reliable.

It is the flat bearing that was important in making my rod choice. At the time only RGV250's had them but other rod kits do now. So you might be able to find a 19mm B/E flat bearing rod kit.

My motor has a rotary valve and I used longer and longer rods to get as much volume in the crankcase as possible. Big crankcase volumes seem to suit RV engines, reed valvers not so much.

Also the longer rod allowed the barrel to be moved up/down until the transfer timing was in the right place. Then the inlet and exhaust can be ported to get the required timing there.

I also favored rods with 22mm big end pins because I de stroked my motors by having the 19mm B/E bored out and offset to reduce the stroke so I could run some re bored cylinders I had as 110cc water coolers.

The last TS125 I saw made a very reliable 22 RWHP and did not suffer to badly from heat fade. I myself have made much more power but the waste heat load was to much for the air cooling fins to cope with. A torquey 22hp looks a good choice.

I would think a standard TS rod kit and 22 RWHP at 10,000 RPM would be plenty reliable and a very good ride.

345407

This is Ricks NF4 with his 22hp TS125 engine in it. Very reliable and super competitive with Rick and his son Will taking turns riding it.

345410

I chased hp thinking that was the answer but it turns out that its holding corner speed that wins races. I never really got very good at that..... :laugh:

[mr bucketracer]

Keep it simple345409

[TZ350]

345418 This is Yow Lings setup and I think this engine is now in Diesel Pigs bike.

An indispensable tool for 2T engine tuning is a good timing wheel.


I would not get to carried away . Just get a rod kit online . With the barrel packed up 2mm and machine top of barrel . Ex port at around 24mm from top . Open the intake up for a 32mm carb and run a mx 125 exhaust . 186 degrees ex (Duration) no more. You will get a good torquey power

Mr Bucketracers engine layout looks to be a pretty reliable plan.


In my opinion it would be better to use a full skirt piston and take the piston port down to achieve the desired port timing. This will result in increased port area as well which it needs. I had great success in completely removing the reed valve and filling the whole area with devcon. The end result was 200 degree piston port timing, plenty of port area, nice smooth intake port matched to a round slide 32mm Mikuni.


Speedpro had a pretty competitive engine and it ran 200 deg inlet duration and 200 deg exhaust duration, and my guess is that the transfers were around 130 - 132 duration.

345419

Both Mr Bucketracer and Speedpro have used stepped pins. Kawasaki also used stepped pins on some of their bikes. Speedpro made his pin offset to reduce the engines stroke so he could run a water cooled head. At the time air cooled capacity was 125cc and for water cooled 2T's max capacity was 100cc. With a re bored cylinder it is now a max capacity of 110cc for water cooled 2T's.

[layton]

345418 This is Yow Lings setup and I think this engine is now in Diesel Pigs bike.

An indispensable tool for 2T engine tuning is a good timing wheel.



Mr Bucketracers engine layout looks to be a pretty reliable plan.



Speedpro had a pretty competitive engine and it ran 200 deg inlet duration and 200 deg exhaust duration, and my guess is that the transfers were around 130 - 132 duration.

345419

Both Mr Bucketracer and Speedpro have used stepped pins. Kawasaki also used stepped pins on some of their bikes. Speedpro made his pin offset to reduce the engines stroke so he could run a water cooled head. At the time air cooled capacity was 125cc and for water cooled 2T's max capacity was 100cc. With a re bored cylinder it is now a max capacity of 110cc for water cooled 2T's.


Right, so I have been reading "2 stroke performance tuning" its actually a good book, starting to get more of a grasp of what's being said. I have emailed around asking about a flat silver cage bearing for the 19mm pin, will have to wait and see what comes back, not too bothered if I have to get the crank bored out its just more time.

What do you fellas use to change the port sizes? Does a 90 degree die grinder fit inside the bore or do you use those little 90 degree dentist type drills or just long reach bits through the intake?

Thanks for the pics and comments it has helped put a few things in perspective and I now have a better idea of what to shoot for.

[F5 Dave]

The TF has super long twisted exhaust port and you need to be able to reach the whole way, not just the big near the windows. I bought a really long flame bit with like a 7mm (guess) shaft for the big collet of my die grinder. It was actually too long so I cut at least an inch off the shaft.

Dip it in diesel (just heard this) or crc (what I used to use) to keep it clear. Diesel makes more sense so looking forward to trying it. Learn to use the bit carefully with stroking arcs, don't go too fast or you work harden the material, avoid chatter and never ever get it fully trapped by its diameter or bad things will happen. I.e. use the tip to widen the hole until it's big enough to fit the bit with some room.

Vivid pen for large area removal. You can take metal out but putting it back is much harder. Measure, cut measure. Repeat.

[mr bucketracer]

Cool thing about this sport you can let your mind run wild . No road racing class left in nz to do this . He I'd mine short stock crank and tf bottom end I'm going to use it in so I can run a 56mm piston for a 110 . I had a RGv top end on this but something new going on. 345430345431

[speedpro]

I used a stock rod in my TS125/100. At the time I was using the TS, Suzuki had superseded most of the early TS rods with the later RM rods. The 125 & 100 were the same stroke as I recall. I balanced the crank with a slug of aluminium in each big hole. The original aircooled motor was 200 degrees on exhaust and piston ports and around 132 degrees on the transfers but they were much better angled than stock. That motor made a huge fat 19.9hp, see dyno chart purple trace, and lasted well, apart from the pistons which I replaced every 2nd meeting. I was using RG400 rear pistons if I recall correctly with just the top ring. TS125ER gearboxes are better than others but still not great. Clutches, despite being garbage, work OK with just screwing the springs in a bit. On my bike anyway. Use C3 clearance main bearings on the crank and plastic cage bearings if you can get them.
In the end I went full crankcase reed valve with a sleeved down RGV250 watercooled cylinder. Quite disappointing, but fun to build.

[mr bucketracer]

I enjoyed having a ride on that bike down south. Nice easy bike to ride . Which you keeped it . Saw the engine for sale in Steve green's mag for like 200 bucks . To cheap

[TZ350]

Right, so I have been reading "2 stroke performance tuning" its actually a good book, starting to get more of a grasp of what's being said.

Yes, I cut my teeth on Bells 2 stroke performance tuning book. But it has a serious flaw about maybe one of the most important aspects of 2T tuning. If it mentions it at all, it does not go into "blow down time area" in any detail.

"blow down time area" is the amount of area of the exhaust port uncovered before the transfers open and the time it takes to uncover that amount of exhaust port real estate at any RPM (time). So "blow down time area" is RPM dependent and gets smaller as the RPM increases.

Pretty soon "blow down time area" is to small to allow all the combustion gases to blow down in the time available. All things being equal, available "blow down time area" is the single limiting factor on 2T power and RPM.

"specific time area" is another modern concept not touched on in the book. "specific time area" is the "specific" "time/area" a port needs to do its job at any specific RPM/Power. So you chose your target power and the rpm to achieve it and from that you get your "specific time area".

After that it is a reality check to see if you can mechanically spin the engine fast enough and cut ports big enough to match. And in the case of the transfer/exhaust port balance if you can achieve the "blow down time area" required there. It is all a juggling act. Bells 2 stroke performance tuning book is a very through piece of work for its time and gave a useful guiding range of port timings but not much about the all important "blow down time area".

For my own projects I cheat a bit and use EngMod2T for working all this out.

[TZ350]

.
When a 2T has been run for extended periods at high RPM and the "blow down time area" has become insufficient you will see carbon buildup and staining in the transfer ports. Running out of "blow down time area" is the reason you can hold a 2T's throttle wide open and the engine RPM will build up then plateau.

Speedpro told me about a time he held the throttle wide open and when the engine rpm reached the plateau he could look down the carb and see flames dancing around in the crankcase.

[layton]

.
When a 2T has been run for extended periods at high RPM and the "blow down time area" has become insufficient you will see carbon buildup and staining in the transfer ports. Running out of "blow down time area" is the reason you can hold a 2T's throttle wide open and the engine RPM will build up then plateau.

Speedpro told me about a time he held the throttle wide open and when the engine rpm reached the plateau you could look down the carb and see flames dancing around in the crankcase.


Funny you mention that, yesterday I had read up to the expansion chambers section in the book took a breather had a play on YouTube and somebody mentioned the blow down time and I thought????? So i googled it and it's pretty much a key ingredient, as the nelson Kart track is quite small I will probably do some bits different i dont need all out top horsepower as it wouldn't be used very often, looking forward to getting a degree wheel, an the bottom end back together. I have been looking at small 90 degree die grinders around 80ish$ on aliexpress

https://m.aliexpress.com/item/32836825739.html?src=google&_randl_currency=NZD&_randl_shipto=NZ&src=google&albch=shopping&acnt=494-037-6276&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&gclsrc=aw.ds&&albagn=888888&albcp=9444695485&albag=99457316601&trgt=296904914040&crea=en32836825739&netw=u&device=m&albpg=296904914040&albpd=en32836825739&gclid=CjwKCAjwvtX0BRAFEiwAGWJyZF_konDBszXlJt59gACX pmx2kj1XJH-nZfgg1YUC-KSJdu07ZkfLjBoCT5kQAvD_BwE

Might be good for the small transfers ?

[F5 Dave]

Do not touch the transfers.

Lift them to where you want them to be but it is far easier to mess things up than improve them.

[mr bucketracer]

Do not touch the transfers.

Lift them to where you want them to be but it is far easier to mess things up than improve them.this .......

[layton]

if you wish to run a 22mm pin as the TS185er has one of those
then run any rod that suit the piston you will run.


i am not sure i have a CR125M one to measure for length.
okay they are 55mm long 20mm
They run 100mm centers as well and a 14mm pin
They only have a copper M cage though so that needs to be replaced with a silver flat cadge from pro x .
for a 20mm big end pin and 14 or 16mm pin you can run a GT250 m/a or K/l s they have these sizes and are 110mm long but they still need the cage changed.

there are plenty of others in between for length.
345385

I would suggest find the piston you want and work backwards.

Well, i must say.. i have been sorting though parts lists for hours and have come back to the TS185 rod multiple times it seems like the best choice as it comes with the right size B.E pin, it is 10mm longer but i can put a spacer under the cylinder and adjust the ports right? you found that almost instantly and it took me days :facepalm: i also looked at the RGV rods, YZ125 01 - 04, and the KX 125 03 - 08
Ø Small End (A) Ø Big End (B) Center to Center (C) Width Small End (D) Width Big End (E) Total Length (F) Eye to Eye Center (G) Ø Big End Pin (H) Length Big End Pin (I) Washers Remarks

ProX Con.Rod Kit TS125ER’81 A18.00 B25.00 C100.00 D18.00 E16.00 F129.60 G78.50 H19.00 I56.00 19 x 34.5 x 1.0

ProX Con.Rod Kit RGV250 20.00 28.00 105.00 16.40 16.40 136.70 81.00 22.00 47.00 None

ProX Con.Rod Kit YZ125 ’01-04 19.00 29.00 105.00 16.00 17.00 138.00 81.00 22.00 54.50 22 x 37 x 1.0

ProX Con.Rod Kit KX125 ’03-08 19.00 29.00 104.00 17.00 17.00 137.00 80.00 22.00 55.00 22 x 42 x 1.0 Barreled Rod

ProX Con.Rod Kit TS185 21.00 28.00 110.00 17.00 17.00 143.00 85.50 22.00 56.00 22 x 39 x 1.0

[husaberg]

Well, i must say.. i have been sorting though parts lists for hours and have come back to the TS185 rod multiple times it seems like the best choice as it comes with the right size B.E pin, it is 10mm longer but i can put a spacer under the cylinder and adjust the ports right? you found that almost instantly and it took me days :facepalm: i also looked at the RGV rods, YZ125 01 - 04, and the KX 125 03 - 08
Ø Small End (A) Ø Big End (B) Center to Center (C) Width Small End (D) Width Big End (E) Total Length (F) Eye to Eye Center (G) Ø Big End Pin (H) Length Big End Pin (I) Washers Remarks

ProX Con.Rod Kit TS125ER’81 A18.00 B25.00 C100.00 D18.00 E16.00 F129.60 G78.50 H19.00 I56.00 19 x 34.5 x 1.0

ProX Con.Rod Kit RGV250 20.00 28.00 105.00 16.40 16.40 136.70 81.00 22.00 47.00 None

ProX Con.Rod Kit YZ125 ’01-04 19.00 29.00 105.00 16.00 17.00 138.00 81.00 22.00 54.50 22 x 37 x 1.0

ProX Con.Rod Kit KX125 ’03-08 19.00 29.00 104.00 17.00 17.00 137.00 80.00 22.00 55.00 22 x 42 x 1.0 Barreled Rod

ProX Con.Rod Kit TS185 21.00 28.00 110.00 17.00 17.00 143.00 85.50 22.00 56.00 22 x 39 x 1.0


i would go with the TKRJ or Pro X but swap out the big end bearing for a flat cadge silver plated, plus silver plated washers buy a couple for spares at the same time.
there are other rods in 104mm length that will also work, but longer likely gives you more room for a decent inlet.
Just find the piston you want and work backwards to get the rod that suits.
But shit its your money just get a hooker........and a 2m ruler......plus 500mls of hand sanitiser

[TZ350]

... it seems like the best choice as it comes with the right size B.E pin, it is 10mm longer but i can put a spacer under the cylinder and adjust the ports right?

Yes, being able to adjust the cylinder height to get the best possible port timing is the way to go.

345484345485345486345483

Maching the top of the cylinder and or using a longer rod with spacers under the cylinder is a common way to get the port timing in the right place.

If you are cunning and imaginative you can also make the spacer act as an extra cooling fin.

[TZ350]

Cool thing about this sport you can let your mind run wild . No other road racing class left in nz to do this .

345487



Being able to let your mind run wild is what I love about Bucket racing.

[layton]

]
If you are cunning and imaginative you can also make the spacer act as an extra cooling fin.

Cool, that is good. i did read ya thread about the measures you took to cool that motor. very interesting experiment very out of the box but hey, if it works it works right?

now to do the same thing with a piston.... urggghh :doh::doh:

Honestly, i have no clue what that pipe is coming from the auto oiler???!? i meant to ask about it but forgot. looks like a cool little motor.

[TZ350]

Honestly, i have no clue what that pipe is coming from the auto oiler???!? i meant to ask about it but forgot. looks like a cool little motor.

I think that is one of Scott's old motors. The auto oilier has been replaced with a home made water pump. The engine had a sleeved RGV cylinder on it for 100cc.

Team ESE have used a lot of Kawasaki KX125 (56mm) pistons early 80's I think. Purchased of eBay. They are a dished top and Weisco ones come in over sizes. We will have used domed ones too. I will look in the shed tomorrow and see if there are any packets with details I can photograph for you.

345488345489

With a dished piston and the head heavily skimmed back we got a compact combustion chamber with the plug electrodes pretty much in the center of it.

There are drawbacks with dished pistons, but you work with what you have got.

[layton]

I think that is one of Scott's old motors. The auto oilier has been replaced with a home made water pump. The engine had a sleeved RGV cylinder on it for 100cc.

Ah, cool. i was going to run the bike as it was "stock" for abit to get a feel for how it all works and slowly chip away at learning how to tune a 2 stroke engine as things needed work, but after this lockdown and being bored, i thought meh lets check the top end out " due to it being difficult to start" ... i jumped down the rabbit hole head first. so i am looking to build a decent bottom end as a solid building block and try different combos in the top half as time goes by.

anything to get me in the ballpark will be great. i do want to get rid of the offset plug and o-ring the head but only because i am in this far already. i take it the only real way to do that is weld the head up and re-shape it ? any other heads that bolt on?

[TZ350]

.
I could not find a dished Kawasaki KX125 piston, only this empty box.

345491

The "5650" in the part number means 56mm piston 0.5mm oversize and CW16 means 16mm piston pin clips.

345492 The box's and pistons are probably mixed up.

This is a collection of different 56mm Yamaha YZ125 pistons. Flat top and shallow dome, 16mm pin.

I understand that Buckets is called Buckets because they are largely built from bits found in that bucket of shit that accumulates under the bench.

[layton]

.
I could not find a dished Kawasaki KX125 piston, only this empty box.

345491

The "5650" in the part number means 56mm piston 0.5mm oversize and CW16 means 16mm piston pin clips.

345492 The box's and pistons are probably mixed up.

This is a collection of different 56mm Yamaha YZ125 pistons. Flat top and shallow dome, 16mm pin.

I understand that Buckets is called Buckets because they are largely built from bits found in that bucket of shit that accumulates under the bench.
Ah nice, I re measured the bore and it's something around 56.04 hard to get an accurate measurement without a micrometer, so it looks like with a rebore I will.be either .25 or .5 over guess is depends on if I hone it or get it bored. The way my finances are at the minute it will probably be honed out to the next size, depends what piston pops up I guess. It also looks like there is bugger all difference between a RGV rod and the TS except with the RGv rod I will have to get the correct size B.E pin like $15 ish between them will wait to see what is around locally, not too keen to order stuff from overseas this carona virus will delay shipping considerably. I have been getting parcels from 3 months ago

[speedpro]

... i do want to get rid of the offset plug and o-ring the head but only because i am in this far already.

On my sleeved RGV cylinder motor I had the plug hole on the stock RGV head welded and a new plug hole placed vertically in the centre. RGV heads are pretty ugly to start with. I made a real effort to keep squish & compression exactly the same. The motor gained something like 1.5-2hp. The improvement was all over.

[speedpro]

If you end up making a spacer to go under the cylinder, get a pile of different thickness pieces of alloy, including paper thin if you can. Bolt them into a stack with the thinnest on the inside. Cut out the shape and you end up with a pile of shims and spacers to adjust the height of the cylinder. Really useful just for adjusting port heights and particularly if you change pistons or rods and need to adjust the cylinder height.

[F5 Dave]

This, but bolt the barrel down when taking measurements. Adjust the transfers to where you want and grind everything else . TF exhaust you can be brutal with like no other bike as it's meant for farmers. It is stupidly low. But I always try to engineer parts to handle as many revs as possible then decide on where peak power should be after that is known.

[layton]

On my sleeved RGV cylinder motor I had the plug hole on the stock RGV head welded and a new plug hole placed vertically in the centre. RGV heads are pretty ugly to start with. I made a real effort to keep squish & compression exactly the same. The motor gained something like 1.5-2hp. The improvement was all over.

Is there any reason people dont make an insert for the head and make the insert a spigot fit into the bore? Well, the same as some water cooled 2 smokes, why not with a air cooled motor?

Thanks to both dave and you for the info about the base space, I would of gone with one big piece of alloy

Seen this while looking around different forums, pretty simple and effective way to water cool a air cooled motor, form some sheet metal around the cooling fins and add an inlet and outlet so it's a water jacket. Not applicable to my application but cool anyway.345540

[F5 Dave]

Made more than a few watercooled barrels for my 50s and 100s.

1 piece spacer can work fine with 3Bond or Loctite master gasket to seal it, but working out how much you need is easier with gaskets added, you can make something later if there's too many for reliable sealing. Degreewheel with pointer plasticine stuck to case can work well. I use a thin feeler gauge and when the piston bends it the port is closed. Measure thrice, cut once.

People do spigot heads but is better done on plated barrels rather than ones that may need to be bored later.

[layton]

People do spigot heads but is better done on plated barrels rather than ones that may need to be bored later.

Ah, ofcourse makes sense.

[speedpro]

My scooter cylinder

[speedpro]

Up tp about 20hp you don't really need to worry about watercooling. My old TS was fine even on Manfeild or big Ohakea GP tracks or a couple of road circuits. My 22hp MB was OK even at Pukekohe

[layton]

Just a quick question, if i put a 110 mm conrod in this means the displacement is now over 130.5 CC i put a 110 mm conrod with a .5mm oversize piston the displacement is now 137.8 right? so i really need a 105mm rod max with a .5 mm overbore even then its 131.5 CC? how anal should i be on following these rules?

i have been trying to sort parts but at the moment its near impossible to get anything so may have to wait a few weeks then source what i need.

[husaberg]

Just a quick question, if i put a 110 mm conrod in this means the displacement is now over 130.5 CC i put a 110 mm conrod with a .5mm oversize piston the displacement is now 137.8 right? so i really need a 105mm rod max with a .5 mm overbore even then its 131.5 CC? how anal should i be on following these rules?

i have been trying to sort parts but at the moment its near impossible to get anything so may have to wait a few weeks then source what i need.

conrod length doesnt effect stroke, only the crankpin offset does.
With a longer rod, the piston goes up higher at both BDC and TDC.

[layton]

Alright, Thanks for clarifying that![emoji4]

Now I think about it, that makes sense...[emoji854]
Sent from my SM-G950F using Tapatalk

[mr bucketracer]

How's the build going

[layton]

Have bearings for the frame on order, everything is seriously slow at the minute, should get it rolling next week if I get the parts. I am waiting for level 2 so I can go into the shop and order a conrod and piston I want to make sure they get the right year parts.

Have the stearing head bearings here waiting on swing arm bearings, and fork seals

I am looking at a ts185 conrod and yz125 piston I forget the year. Seems to be the newest piston that fits the bore and in a range of sizes

Sent from my SM-G950F using Tapatalk

[layton]

Progress all be it slow, fork seals done, swing arm bearings replaced ( stupid bloody things), headstock.bearings done, frame and stuff painted. Made a hot dip tank out of a slow cooker so have been working on a nasty soup, works a treat.. been really busy at work hopefully I will get on to the engine shituation next week.

Also got a 3D printer so made some fork caps!! Cool toy.

[mr bucketracer]

I would cut that subframe off and have a light weight bolt on one

[layton]

That's a good idea, maybe after I do a few circles. Dont want to create more work at the moment I have other things that need attention

Sent from my SM-G950F using Tapatalk

[F5 Dave]

Good plan. Prioritise getting out.

[layton]

mmmm.... so i have been in to order the parts and they can't find any aftermarket pistons available in that size range! only the wiseco TF piston... that kinda sucks. seems that the stock is all but dried up! anybody have suggestions? i have asked a few different places with a similar answer..

i dont really want to build an engine that i cant get more pistons for as i am bound to cook a few.

i am okay with using the STD piston but was looking forward to building a frankenstein

[husaberg]

mmmm.... so i have been in to order the parts and they can't find any aftermarket pistons available in that size range! only the wiseco TF piston... that kinda sucks. seems that the stock is all but dried up! anybody have suggestions? i have asked a few different places with a similar answer..

i dont really want to build an engine that i cant get more pistons for as i am bound to cook a few.

i am okay with using the STD piston but was looking forward to building a frankenstein
Have you tried Mikita and Pro X TKRJ

I thought Rob (TZ350)) offered you some earlier
Failing that Ebay NOS

[TZ350]

346370 16mm pin.

I have had a lot of luck buying pistons off Ebay. What size piston pin are you looking for? We used different rods mainly to get extra crankcase volume and 16mm piston pins as there are more 56mm+ pistons available with 16 mm piston pins than there is for 14mm pins.

[layton]

16mm pin would be ideal due to there being more sizes available, i had looked on ebay and on the net there is a few around but i wanted something in the country like have my hands on it next week sort of thing.. ya know, wanted it yesterday and all that.

by the way you can get stepped pins from PROX.

[husaberg]

plenty others on site
https://454.co.nz/product/10351/
https://454.co.nz/product/22667/

[layton]

plenty others on site
https://454.co.nz/product/10351/
https://454.co.nz/product/22667/

Can I use a KX piston even though the bore on the tf isnt nikasil

I was told that KX rings wont work in the steel sleeve?

Are those CR motors piston port?

[husaberg]

Can I use a KX piston even though the bore on the tf isnt nikasil

I was told that KX rings wont work in the steel sleeve?

Are those CR motors piston port?

buggar you are right the latter 80-84 are CR cylinder reed rather than case reed.
ones prior to about 78 are piston port that will be okay.
but the os ones for 87 on are crankcase reed.

the 2mm oversize etc big bore pistons are made genarally for steel sleeves
hve a look through the list
personally i would try and find ones for a steel sleeve with oversizes the ones for plated cylinders only have std plus big bore.
shame strike dont do 56mm bores
WHat bore do you actually have?

[layton]

Pretty much bang on 56mm. I have been told conflicting information re the plated bores and using there pistons on steel sleeves. Seems there are a few KX options might be able to get my hands on a 90s yz piston, just need to double check with there supplier on the size ranges.

If all else fails I can go piston port and use the CR pistons and block the reed off.

I will find something!

Sent from my SM-G950F using Tapatalk

[TZ350]

Can I use a KX piston even though the bore on the TF is not Nikasil. I was told that KX rings wont work in the steel sleeve?

We ran Kawasaki KX 125 pistons and rings in our steel sleeved Suzuki GP125's for years with no problems. The GP cylinder is identical construction as the Suzuki TF TS cylinders. In fact we have run all sorts of makes of pistons and all sorts of ring material without problems other than the self inflicted wounds of poor tuning. The only real no no is a chrome ring in a chrome bore. Not may chrome bores now days, mostly they are Nikasil and you can run chrome rings in them.

[husaberg]

Pretty much bang on 56mm. I have been told conflicting information re the plated bores and using there pistons on steel sleeves. Seems there are a few KX options might be able to get my hands on a 90s yz piston, just need to double check with there supplier on the size ranges.

If all else fails I can go piston port and use the CR pistons and block the reed off.

I will find something!

Sent from my SM-G950F using Tapatalk

Early suzuki case reeds pretty much run piston port pistons
watch out for windows in yamaha pistons.


i have some new old stock CR125 Elsinore pistons here if you want try them
$50 each i guess i would have to check the sizes but pretty sure i have std as well os .25.
they have wide rings but should be good for a start.

But newer piston are better.

if you went 16mm pin you can go for TZR250 piston with are available in heaps of oversizes out to 2mm
http://tkrj.co.jp/goods/m-AY0930X-2YK.php

or RG in 14mm
http://tkrj.co.jp/goods/m-AS8040X-21A05-21A15.php

this might be a typo but RS125 pistons out to 2mm
http://tkrj.co.jp/goods/m-AHR010X-.php

[layton]

damn you are the man at finding this stuff, my brain melts when i look at parts catalogs for too long. i really like the TZR option, they should be in decent supply and have a good overbore size range, up to 58.90.

i am really leaning on you guys for experience, thanks for being patient!

will try and track some TZR pistons down.

[Brett S]

buggar you are right the latter 80-84 are CR cylinder reed rather than case reed.
ones prior to about 78 are piston port that will be okay.
but the os ones for 87 on are crankcase reed.

the 2mm oversize etc big bore pistons are made genarally for steel sleeves
hve a look through the list
personally i would try and find ones for a steel sleeve with oversizes the ones for plated cylinders only have std plus big bore.
shame strike dont do 56mm bores
WHat bore do you actually have?


We can do any size you want up to around 56.5mm using the KT100S casting, but piston weight at 56mm is going to be up around 160gm.
56x1x2.25mm rings are common from the old 54mm +2mm mx engines.
What compression height and piston length do you need?

[husaberg]

We can do any size you want up to around 56.5mm using the KT100S casting, but piston weight at 56mm is going to be up around 160gm.
56x1x2.25mm rings are common from the old 54mm +2mm mx engines.
What compression height and piston length do you need?

Not sure if it needs to be quite these dimensions but this is STD i believe
346375

ps cool
i think i need some soon on about 56mm too........

[Brett S]

The KT100S pistons are 56mm long and 23mm compression height.
It doesnt look like it would fit without machining a fair bit off the bottom of the cylinder and if piston ported may be too short?

[husaberg]

The KT100S pistons are 56mm long and 23mm compression height.
It doesnt look like it would fit without machining a fair bit off the bottom of the cylinder and if piston ported may be too short?

How big do the KT100J ones go to?

[Brett S]

How big do the KT100J ones go to?

The KT100J's are made for a bore of Ø50.0mm and would be very heavy at 56mm, the biggest i recall making was around Ø54.5mm for some agricultural/lawnmower situation.
Dimensionally they would suit better. 60mm length 33mm compression height.
You would have to spend alot of time lightening them.
They use the same outer die set as the KT100S which is roughly 58mm cast, but would also only clean up at around 56.5mm max.
Their gudgeon pin boss is thinner than the KT100S.

[husaberg]

The KT100J's are made for a bore of Ø50.0mm and would be very heavy at 56mm, the biggest i recall making was around Ø54.5mm for some agricultural/lawnmower situation.
Dimensionally they would suit better. 60mm length 33mm compression height.
You would have to spend alot of time lightening them.
They use the same outer die set as the KT100S which is roughly 58mm cast, but would also only clean up at around 56.5mm max.
Their gudgeon pin boss is thinner than the KT100S.

Cheers i remember seeing one it looked like a Villiers.
https://cdn.shopify.com/s/files/1/0015/9845/5861/products/DSCN7003_480x480.JPG

[F5 Dave]

Yeah i remember getting all excited about the Js for 100cc -until I saw one:sick:

[husaberg]

Yeah i remember getting all excited about the Js for 100cc -until I saw one:sick:

Yeah its a lot of space above the pin
here is Yows attempt
The pictures speak for themselves
No wonde everyone destroked.
Tis a shame as the KT100S pistons are just what the class needed only just a little too big in the bore.
346378346379

if only there was a Strike KT100S piston on 50mm and above sizes.
Plus a strike KT100s up to 58mm

[F5 Dave]

Pity Euro didn't make an AM8 engine. 100cc version of the AM5 or 6 but 99cc.

Hell I'll take it as a scaled down RSA but with crude restrictions to make it a roadbike while I'm dreaming.

Then we can spend our time tuning it to a standstill.

[Brett S]

Yeah its a lot of space above the pin
here is Yows attempt
The pictures speak for themselves
No wonde everyone destroked.
Tis a shame as the KT100S pistons are just what the class needed only just a little too big in the bore.
346378346379

if only there was a Strike KT100S piston on 50mm and above sizes.
Plus a strike KT100s up to 58mm

For destroking have you seen the eccentric big end pins:
https://www.sip-scootershop.com/en/products/crankshaft+pin+drt+eccentric_4043ad178
These can be used either for stroking or destroking or even illegally changing ignition timing on very controlled classes as someone got caught out for years ago.