TF100 issues

[Bert]

Having made a start to my return to bucket racing over the weekend at manfeild, i ran into a couple of issues (as normal). One I am seeking some advice on from you lot.

I'm having issues with a slipping clutch, it revs nicely into band (quite a high reving monster being short stroked and over square) and then starts slipping. once it get really hot it seems to go away (well sort of) though i was pissing around with the cable adjusters during the rides as well.

I've put a new basket (well second-hand but near new) when i rebuilt the motor before taupo; and newish plates and fibres etc. but this seems to have made no real difference, (it was happening before hand, but it was the less of my issues at that time). the basket i took out had about 10 degree movement (read: slop on drive gear) were as the newer one felt a lot firmer (I'm assuming they have some form of spring loading??)

I'm running good oil (name I can't remember).

looking into it more I was wandering if the clutch springs are to soft ? or do i need to look into different plates?? I also had a though about oil density maybe to heavy?? the cable seems to be moving well enough as well.
I haven't really been able to find much about these clutches other than the vintage MX (but they are slightly different.

So any ideas, insight, knowledge or experiences that could be imparted on this issue?

(and no I'm not getting a four stroke)
(the other issue is that i just need to man up!!! aye Rich)

[speedpro]

You can screw the springs in a bit more. Do them one at a time and make sure you don't screw them in so far that they stick out the back of the clutch and snag on things. A good idea is to make or buy a hook to pull the springs out when you are putting the little pins back in. I only ever had a 125 bottom end and didn't have problems with a 19.9hp engine so I wonder if the 125 has an extra pair of plates. Could be worth checking out.

[F5 Dave]

Mike is right, just wind them in. A spring puller can be made from a spoke & 3" sawn from the end of the broom. Drill a hole & thread the needle through with the nipple. Sharpen the spoke end so it is a hook to pull with, but they are titchy little buggers so you will need some pliers to unhook & some safety glasses & some rude words.

The freeplay is common but not nice. Can be ground/drilled apart & some spacer, nylon or whatever to pack the rubber shock absorbers in back of clutch drive. then has to be riveted back together. On the 50 I used ht bolts & threaded the basket. Not sure how keen on a bigger bike.

[Bert]

Great, thanks Mike and Dave; had a funny feeling that one of you would have some solutions on this one.

I think I am running a 125 bottom end (internals), but the donner clutch might not be; so I will be checking that firstly.

as for the springs, cheers I didn't know that they could be wound in for more tension; so that's a great starting point as well.
when attempting this should one check for linear loading weight (tension) across all springs, I assume that if they aren't equal things might misbehave ???

and as for the spring pins; yes safety glasses are the go. Along with a clean work area to find them again...

Thanks Guys

[ajturbo]

or just use.."clutch saver" oil
Spectro i think

[Bert]

Hi all.

well the clutch suggestions nearly worked, only slipped a little bit. so one down, Thank you all for the input.

So here another one.

After a goodish weekend in Wellington, I started to pull down my engine to replace the broken casing (engine mount broke with some casing as well) which requires a near complete strip down.

anyway, attached are a couple of photos of the piston with funny burn marks (matching the exhaust port shape) and the exhaust side. (plus the first ~inch of the exhaust was a "not so nice" grey colour as well).

now it was suggested that maybe I had my exhaust lengths incorrect? and maybe this is so given the piston marks and grey header.

Any thoughts on the cause of the marks? or if it is a major issue or not?

This piston has only done about 2 hours (Taupo GP, Manfield and Wellington); not a pretty sight :shit:

[Ivan]

just get a four stroke

[Bren_chch]

What is that single ring piston from?

[quallman1234]

just get a four stroke

Just get a bucket.

[NOID]

iv got a rope,

well tie ur engine to the end of it :innocent: then

ill have an anchor for my dinny :yes:

man you pull that engine to bits alot, get a four stroke iv poked mine with stick once

unproductive i know

[Bert]

What is that single ring piston from?

KT100, with a shorter stroke longer rod. I would not suggest this mod to anyone. though the pistons are cheap the rest is well lets say not.


just get a four stroke
now where's the fun in that.


iv got a rope, well tie ur engine to the end of it :innocent: then ill have an anchor for my dinny :yes:

man you pull that engine to bits alot, get a four stroke iv poked mine with stick once

unproductive i know

hahaha, its only got to last a few more meetings. then the old girl will be relegated to under the bench.

Anyway, no one yet has provided some insight.

[Ivan]

haha its coming

[speedpro]

My MB runs KT pistons and the stroke has been reduced so I know your pain regarding reducing the stroke.

If I had to guess, I'd say you were getting blowby, typically from a well used piston and saggy old ring. Good thing with KT pistons is you give it a hone to straighten the bore and squeeze in the next size piston. Question: what piston clearance do you run when you first assemble it with a new piston?

Short stroking a piston port engine would have been some fun with the intake versus exhaust port timing

[Bert]

If I had to guess, I'd say you were getting blowby, typically from a well used piston and saggy old ring. Good thing with KT pistons is you give it a hone to straighten the bore and squeeze in the next size piston. Question: what piston clearance do you run when you first assemble it with a new piston?

Short stroking a piston port engine would have been some fun with the intake versus exhaust port timing

Hi SpeedPro.

Well; with this piston, I had the kart shop do the hone and piston/ring fitting, so not sure what the final clearance ended up being (I know it had to go out to the next size piston to actually get the bore shape right). but i wouldn't have though they would stuff it up to much (given the length of time I've known them)... but given the slop that is now there, I think you might be right;
I just found it interesting that i had a near perfect image of my exhaust port on the piston face, and did wander if something might be up with the exhaust lengths.

port timing, ummm yip, lets say I've made a few errors with this and learnt a lot regarding what doesn't work...
Biggest lesson was that I should have had it re-sleeved at the start and carried on running the RG400 pistons rather than heading down this route (and years of frustration).

[bucketracer]

as for the springs, cheers I didn't know that they could be wound in for more tension; so that's a great starting point as well.
when attempting this should one check for linear loading weight (tension) across all springs, I assume that if they aren't equal things might misbehave ???


I know that Dad does a quick check of valve springs by sitting one on top of another, then squeezing them up in a vice, a week spring will noticeably collapse more than the other, I expect clutch springs could be checked this way too.

[bucketracer]

I was wandering if the clutch springs are to soft ? or do i need to look into different plates??

The Team ESE clutch plates sometimes become hard and glazed and slip after a bit of a caning.

After a bit of a scuff up on CRC whetted 180 grit wet and dry and a glass plate to remove the glazed surface the clutch's work OK again.

[SS90]

Hi all.

well the clutch suggestions nearly worked, only slipped a little bit. so one down, Thank you all for the input.

So here another one.

After a goodish weekend in Wellington, I started to pull down my engine to replace the broken casing (engine mount broke with some casing as well) which requires a near complete strip down.

anyway, attached are a couple of photos of the piston with funny burn marks (matching the exhaust port shape) and the exhaust side. (plus the first ~inch of the exhaust was a "not so nice" grey colour as well).

now it was suggested that maybe I had my exhaust lengths incorrect? and maybe this is so given the piston marks and grey header.

Any thoughts on the cause of the marks? or if it is a major issue or not?

This piston has only done about 2 hours (Taupo GP, Manfield and Wellington); not a pretty sight :shit:

I have never actually seen that sort of marking on a piston before Bert, But I notice that there are "streaks" coming up from the ring land to the crown of the piston, and this normally indicates that your chamfering of your exhaust port is incorrect, (and/or) your exhaust port is very very wide (perhaps "on the limit")...is it possible your could post a port map?

If that theory is correct (and the shape/size/design) of your exhaust port is causing premature ring wear (as has been suggested) you can check the ring wear theory very easily, simply by putting the ring into the cylinder, about half way down, and measure the ring gap with a feeler gauge.

A good rule of thumb for an air cooled engine is 3 thou per inch of bore.

If you find that your gap is much more than this, this could well be the problem.

How many hours have you run on that piston/ring combo?

For example, if the ring is shown to be worn, and you have only run 5 or 6 hours, then I would suspect something else causing the ring wear (exhaust port size/shape is the biggest culprit here, and is easy to prove or disprove if this is the culprit), whereas, if you have run in excess of 20 hours on a KT100 piston and ring, then a knackered ring is acceptable.

On a Kt100, I am pretty sure you run a ring for about 7 hours before replacement, but they do rev to something like 15,000, and if your TS is doing that, you need a medal!

I think 10 or 12 hours on a ring would be acceptable in your application.

Perhaps if Speedpro could let us know how many hours he gets from a piston/ring combo, you could use that has a yard stick.

[gav]

This piston has only done about 2 hours (Taupo GP, Manfield and Wellington); not a pretty sight
You not read this bit SS ?

[Bert]

I have never actually seen that sort of marking on a piston before Bert, But I notice that there are "streaks" coming up from the ring land to the crown of the piston, and this normally indicates that your chamfering of your exhaust port is incorrect, (and/or) your exhaust port is very very wide (perhaps "on the limit")...is it possible your could post a port map?

If that theory is correct (and the shape/size/design) of your exhaust port is causing premature ring wear (as has been suggested) you can check the ring wear theory very easily, simply by putting the ring into the cylinder, about half way down, and measure the ring gap with a feeler gauge.

A good rule of thumb for an air cooled engine is 3 thou per inch of bore.

If you find that your gap is much more than this, this could well be the problem.

How many hours have you run on that piston/ring combo?

For example, if the ring is shown to be worn, and you have only run 5 or 6 hours, then I would suspect something else causing the ring wear (exhaust port size/shape is the biggest culprit here, and is easy to prove or disprove if this is the culprit), whereas, if you have run in excess of 20 hours on a KT100 piston and ring, then a knackered ring is acceptable.

On a Kt100, I am pretty sure you run a ring for about 7 hours before replacement, but they do rev to something like 15,000, and if your TS is doing that, you need a medal!

I think 10 or 12 hours on a ring would be acceptable in your application.

Perhaps if Speedpro could let us know how many hours he gets from a piston/ring combo, you could use that has a yard stick.

The ring wear is interesting (I was intending on putting a new one in anyway). The exhaust port is very wide, attached is a port scan. Also of note (which i forgot to provide) last year she seized, (on the exhaust face as normal), but there was considerable piston damage in the same places.

as for run time: must only be around the 2 hour mark. give or take a bit.
about a 20min run in, and a few laps at the pre-mentioned meetings. (hardly finished at any of those) :blink:

and o'yea she revs mate, not to 15k but well higher than what mister Suzuki made it too do.

[SS90]

This piston has only done about 2 hours (Taupo GP, Manfield and Wellington); not a pretty sight
You not read this bit SS ?

Clearly not.

I would (with-out seeing it) suspect that after 2 hours use and seeing the sort of blow by and scuffing that the picture has, that there is something not correct with either the ring gap from new, or, like has been suggested, premature ring wear due to either excessive port width (or even inlet port as well), or perhaps unchamfered ports.

[SS90]

The ring wear is interesting (I was intending on putting a new one in anyway). The exhaust port is very wide, attached is a port scan. Also of note (which i forgot to provide) last year she seized, (on the exhaust face as normal), but there was considerable piston damage in the same places.

as for run time: must only be around the 2 hour mark. give or take a bit.
about a 20min run in, and a few laps at the pre-mentioned meetings. (hardly finished at any of those) :blink:

and o'yea she revs mate, not to 15k but well higher than what mister Suzuki made it too do.

Thanks Bert,

How wide is that exhaust port? (in mm, or perhaps do you know as a percentage of bore diameter measured across the chord?)

[Bert]

Thanks Bert,

How wide is that exhaust port? (in mm, or perhaps do you know as a percentage of bore diameter measured across the chord?)

bore = 52
exhaust port top = 39.5
exhaust port bottom = 34.6

approximately. and all the ports are chamfered and have clean radius/arced tops to re-seat the rings, well at lease attempted anyway.

[SS90]

bore = 52
exhaust port top = 39.5
exhaust port bottom = 34.6

approximately. and all the ports are chamfered and have clean radius/arced tops to re-seat the rings, well at lease attempted anyway.

Hi Bert, I think that you will find that your exhaust port is too wide.

39.5 is over 75% of the bore width, and if you calculate that against the chord, it is even higher......

I think it is a true testiment to the strength of tha Yamaha piston and rings to be still running!

[SS90]

If you need to calculate your chord Bert, follow this link, you can download a trial.

http://www.machinist-calculator.com/Chords.html

You only need 2 values, and it will do the rest...ideally, you are looking for a chord length of LESS that 70%.

[Bert]

Cheers for that. I've just about finished building a excel workbook with all porting calculations (I will share once finished).

Yes well, I had a quick look at a couple of other barrels sitting in the shed. all ported by the same man (not me) and they are all rather large and similar shape in the exhaust port...

Basically similar to Bells earlier two stroke tuning book covering the RM125m (i think) the porting matches other than the bridge.

o'well, I'll slap another piston/ring in it and she if she will survive another few meetings.

I still am interested in the burn pattern & grey exhaust header, in relation to the potential exhaust length issues???.

[SS90]

I still am interested in the burn pattern & grey exhaust header, in relation to the potential exhaust length issues???.

I think the burn pattern is caused by the ring poking too far into the exhaust port and exhaust gasses leaking past the ring when the port opens.

Remember something like 80% of the exhaust gasses burst out the exhaust port the moment it cracks open, if that ring can't do it's job at this high stress moment....... That's my play on things anyway!

Like I say, I have never seen a piston look like that!

[F5 Dave]

I think SS is on the money here, but again I haven't seen one with quite such a pattern. Exhaust design a red herring I'm sure. (lets start talking when you have weird in-transfer patterns).

[Bert]

I knew you would be around somewhere Dave.

Sitting back a reading this again, I happy with SS conclusions. bugger it all. the problem is now what to do about it for a short term solution... (one meeting)

Me thinks a resurrection of another barrel and new piston to get me through the start of the session. with the hope that I can mod the exhaust to suit. all in a week... :shit:

and a standard crank and rod....

I'm glad I'm on my 2 week christmas holiday.

[F5 Dave]

Well measure the std barrel & see if it is worn & if the ring is worn. If just the ring then replace that, after all you are just trying to keep it going until the new engine is in place. If the bore is worn then you will need to attend to that. 2thou clearance in an aircooled engine with a steel bore should be safe. Run lots of oil, 40:1 of decent oil should be ok but keep adding more as the revs go beyond 10/11,000.

However; Look at the chamfering. you want to present a surface to the ring which is symmetrical & gentle. If the port roof is flat, or worse square edged, that doesn't mean the chamfer needs to look like that to the ring (even if the gas flow via the piston shape sees it differently). Super big eyebrow to the corner & one either side will make the ring look like it has a round port to ease it back in & out of support without 'seeing' the corners.

[Bert]

Cheers Dave & SS for your help.
I'll measure it all up and work on the best course of action.
At first glance today the bore looks quite good (still has the cross hatch visible all the way around) and the piston, outside of the burn marks still has most of its detail; so lets hope its just in need of a ring!!

I'll give the ports a check over as well.
The exhaust port roof is slightly higher in the middle / rounded shape; the corners are quite radius, not fully sure what you mean by eyebrow sorry.
I assume that you mean this?

Shed time.

some progress. went down and talked to my man at the shop. the bore isn't round anymore. new larger ring and lots of oil. and laugher lots of laugher.,...

quite a lot of measuring, turns out that the barrel above the exhaust port is slightly dished, suggesting that this is going to be an issue of a good seal.. but he suggest (like all go salesman) that if i keep chucking rings into it then it should last.
The underside of the piston was a nice brown colour (and in o.k condition), but has been very hot at some stage (little goldy flecks); at manfeild I dropped my magneto coils (advancing the timing) so this might explain things....

Better photos cn be found: http://www.kiwibiker.co.nz/forums/album.php?albumid=2701

as for the burn marks on the piston; he did suggest that the exhaust length maybe to short (and it did show signs of burning in the transfers). and I didn't prompt this conversation either.

anyway, its going back together as is (with new ring) and we'll see how long it will last for.

On the side note, we had a coffee and a chat/photographs about the racing over Easter, along with some discussion regarding the track up here and the issues of old.
Maybe just maybe if a presentation was done to the Palmerston North Kart club regarding the new requirements adopted in Wellington (nylon crash protection etc). and some feedback from the Wellington kart club on behaviour/track damage etc; we might have a outside chance. but it would require considerable groundwork and would have to run under MNZ.

Back to the shed.

[speedpro]

That porting, except for the inlet, looks very much like my old TS motor. The exhaust port shape is quite distinct. i see on the piston below the ring on the exhaust side that it has picked up a little bit. I can't see it but I bet there is a little bit of smeared alloy above the ring on the exhaust side. The smear will be up making a little lip on the edge of the piston crown. The little bit of staining above the ring is similar to what I used to get.
RG pistons in TF motors crack regularly once you open the ports up enough to make some power and rev them. I think the KT conversion is a good idea. The TS combustion chamber shape is not flash but can be machined to correct without the need for welding.
In my experience kart shops have some "distinct" ideas about the finish required on the bores which is at odds with regular motorcycle theory. I had my MB/KT bored and honed to 1.5-2 thou and then ran a whole tank of gas through it to run it in. My piston & ring has done lots of hours. I'm gonna run it up on the dyno and get some numbers and then fit a new ring. I'm not convinced about the need for new rings every few hours.

[F5 Dave]

. . . I'm not convinced about the need for new rings every few hours.
Yes but your ports will have been chamfered properly. Sharp port edges will accelerate wear. Some ring materials wear quickly but lots of revs & minimal oil are not good. Thinner rings are good for revs but I would venture wear the circumference quicker in extreme conditions. Measurement of the gap will answer the question pretty quickly. Good point about the ring land smear.