ESE's works engine tuner

[husaberg]

Its the old story of simply moving the weakest link from one area within an engine to another.
Basic bearing operation dictates that full compliment needles will handle a heap of load, but are ultimately limited, in that the rollers are all rubbing on each other
and this leads to failure.They also cannot handle ANY movement away from dead true in any plane, as they then skid even more rapidly.
Having the big end well open with alot of clearance around the rod and cage helps access by the oil film and makes this area pretty bullet proof. with no washers in the way.
But this then moves the point of most wear up to the location washers in the piston.
In a KT100 the versions with alloy washers in the small end will have wear marks on these washers in a very short time, the small end being caged makes it bullet proof,and
the open rod big end lasts well, until the cage wears on the rod bore.
In the end it is the rod big end cage wear that forms the limiting factor, and it has been found by thousands of engine rebuilds, that the silver coated big end cage and washers have about the same ( acceptable ) limiting
lifespan - the open, caged small end lasts forever in either case.
Simply removing the washers is plain dumb - I have seen a couple of new crank designs done this way just recently, both failed very badly with lube failure around the rod big end - IT DOES NOT WORK, reliably.
Thus having the washers down the bottom becomes a known factor - replace them when you replace the cage.
The rod and pin will usually take around 4 bearing replacements.
Iin fact if you could buy them, simply replacing the cage ( with the washers as well ) would mean you could keep the rollers - for the life of the rod.

I thought long and hard before i replied as i often agree with you (Because you are in fact far cleverer than I )
Yes it has to be engineered to have the thrust clearances maintained from the little end only.
But there a a few advantages one being the little end is easy to get to replace alter.
The other as you alluded to i guess is that stress are far less on the little end end.
Chasing the weakest link or limiting factor is I believe what any sort of engine development is about .
Yes The big end in most (if not all cases) can be made reliable for the stress buckets are under yes granted.
But the quality parts to accomplish this reliability are not always actually F4 and f5 class legal.
There are some parts that were used in road and non competition bikes or sold as size that will be legal but not in all sizes.
Just my opinion really not that it really maters because i still are procrastinating on my build and have ran in a bit of a problem.

[Yow Ling]

I thought long and hard before i replied as i often agree with you (Because you are in fact far cleverer than I )
Yes it has to be engineered to have the thrust clearances maintained from the little end only.
But there a a few advantages one being the little end is easy to get to replace alter.
The other as you alluded to i guess is that stress are far less on the little end end.
Chasing the weakest link or limiting factor is I believe what any sort of engine development is about .
Yes The big end in most (if not all cases) can be made reliable for the stress buckets are under yes granted.
But the quality parts to accomplish this reliability are not always actually F4 and f5 class legal.
There are some parts that were used in road and non competition bikes or sold as size that will be legal but not in all sizes.
Just my opinion really not that it really maters because i still are procrastinating on my build and have ran in a bit of a problem.

If you are going on about whether or not big end bearings are bucket legal then its probably a waste of breath.
When did a bucket ever get stripped to that level and who can tell if the bearings are legal or not.
When was the last time a bucket was pulled to bits for tech at all?

[husaberg]

If you are going on about whether or not big end bearings are bucket legal then its probably a waste of breath.
When did a bucket ever get stripped to that level and who can tell if the bearings are legal or not.
When was the last time a bucket was pulled to bits for tech at all?

Mike could tell and so could I. At least on a MB/H100. I also have a stack of Cr ones and it is easy to tell.

I've been looking for a good big end bearing for Gary's bike. Whilst at the kart shop I checked out a KT100 rod kit. Turns out the big end bearing is 26X20X13.8, EXACTLY the same as a MB100. Moral dilemna for a bit. They are a bit different to look at and I could spot one even if it was all assembled onto the crank/rod. Further research has come up with a same size bearing with a description that makes it similar design to the KT part. Moral dilemna over. It does mean if you wanted to build a cheater engine which handled 16,000rpm that the parts are available from your local kart shop.
Just in case anyone thinks I honestly thought for more than a second about using an illegal bearing, anyone is welcome to have a look inside my engine, or Gary's but you'd have to ask him about pulling his one apart.

True it would be real easy to cheat, but is i believe and so does Mike it is eminently more satisfying to remain legal. (I have always thought the bearing and rod rule to be rather silly myself though i should add)
What i was going to add to my post. i was rereading George Begg's Burt Munro book (for inspiration i guess)and was surprised how tiny his crank pin was before he finally got around to modifying it for positive lubrication. It was smaller than most buckets (admittedly very narrow as it had Knife and fork rods) yet took the force of at the time 90 odd horses with a hit and miss lubrication to boot. Yes i believe the rollers gave trouble more To do with heating due to lack of lube but it seems ,notehe also sweared by std genuine chamfered Indian rollers as well. not relevant but interesting

[wobbly]

Dont think it matters any more - a "suitable " legal rod can be found to work in just about any bucket application you would, or could,dream up.
Especially if you are prepared to modify the crank by spark eroding or eccentric bushes, or whatever.
And as there are several manufacturers that have a range of "off the shelf " silver plated big end cages ( generic types ) that are not specific
to any so called competition based engine, then I believe that this makes it impossible to enforce that long standing rule.

The KT100 has two types of rod location available, and the version with thrusts up the top has wear issues with these, maybe hard anodising ally washers would ameliorate this current problem.
But - the big end cage still ends up wearing out due to rubbing on the rod bore - despite the better access by the lube mist with no thrust washers.
Thus as I pointed out,the big end cage is the limiting factor to longevity, no matter what the mechanical setup is.
And as it has been proven in the field that the silver plated washers and the cage, have similar life span,then in my opinion there is no reason at all to not use this method.
The manufactures that dont are very much the odd people out now days amongst what we would call normal applications - there are a few other solutions used in small super high rpm race engines,
but these are overkill for anything only spinning to a paltry 14000.

[husaberg]

but these are overkill for anything only spinning to a paltry 14000.

i also read something interesting (1970's)which suggested a 2 vs four stroke comparison was approx
100cc vs 140-150cc using both volumetric and mechanical efficiency.
which suggests the MNZ rules are pretty close and a hell of a lot more equal than the AMA mandated rules of 144 vs 250 and 250 vs 450.

Also when is it worthwhile crossing to a twin cylinder. (I must admit it would be hard to match the simplicity and value money wise of a single though)
But what would be the ultimate cylinder size (within the rules for buckets) for ie where mechanical efficiency (for want of a better term) and volumetric efficiency meet.

I seem to remember Wob mentioning something about a 100cc twin would have to spin to something like 19000rpm to match the BMEP of a single 100cc pulling 14000rpm

The only way you would see any advantage running a twin is if you have the knowledge and wherewithall to build it properly.
This would mean running it to around 20,000 rpm to achieve a higher bmep than the single.
And as we already see in the 100 class, those engines dont rev as hard as the 125 GP single motors, when to see the advantage of a 50mm stroke the 100cc should be going to at least 14000 all day. - so basically, forget it.
A twin wont make as much "torque" but will make alot more "power" if done right.

But if its possible to build a 20 odd HP 50cc single that was only reving to 14000rpm why not a 40hp 100cc twin Is there a lot more losses somehow or is it all relative per cylinder?
I am certainly not doubting you wob, but only trying to get my head around it.

Getting 20 from a 50 is easy, its all in the numbers,but its certainly not cheap..
If you have all the components working together in synergy then the STAs tell us it can be done.
Note how well every variable is right on the money - and as long as you implement every mod remembering that we are dealing with a "on the limit" scenario,then the numbers do translate into reality.
I have a KTM50 cylinder on its way from England for a customer now, the pics look like its very very well made.

[rgvbaz]

Husaburg,

I cant see the pic properly at the bottom of your post, It looks like the TA screen from Dat2T.

In terms of TA the twin 100cc should be able to have more than the 100cc single as 40 x 40 bore stroke (50.3 cc) has 5026.5 mm^2 wall area X by 2 cylinders gives a total of 10053mm^2 for the twin

A 50mm x 50mm bore stroke (100cc) has 7854 mm^2 total wall area for the single. 10053/7854 = 1.28 so the twin 100cc has 28% more wall area for ports! so should be able to support more TA.

I'm sure there is probably more to it

Cheers

Dave

[rgvbaz]

Just had a quick look at power potential for a given port area for a twin and a single. I happened to have a file for a 50cc twin so I used this for the study. It is purley based on STA that DAT2T calculates as a potential that could be achieved from a port. All of the figures are in hp.

For both engines I kept the timings the same 190/130 duration, both are square with the same conrod/stroke ratio. I used 70% of the bore for the flow width of the exhaust port for each cylinder and 70% again for each transfer flow width, there are 2 transfer ports in each cylinder.

Here is a graph of the power potential of the transfers and the exhaust blowdown. As you can see, even at the lower rpm, 13000rpm, the twin has the advantage in TA.




Cheers

Dave

I should look at it again for different bore/stroke ratios.

[wobbly]

I wasnt saying at all that technically the 100cc twin was not capable.
What I am saying is that we have 100cc buckets making 30 Hp now, and they are only reving to 13,000 when in fact a 50mm stroke should be going to well over 14000 - thus making 40Hp a reality, if done " properly ".
Christ its taken 5 or more years for people to get that 30 Hp was easy - as I said to Nige and Mike so long ago.
Why would anything change when we go to a 40mm stroke with a twin, the chances of it being done " properly " are virtually nil, and where is the non competition close ratio box going to come from, let alone
cylinders that could be even remotely considered as being able to be modified to make decent power ( a fully modern KTM type 50cc cylinder with everything copied from Jan Thiel is needed to make 20 Hp ).
The twin will always be capable of alot more power - the know-how and mechanical/financial restraints have a much bigger part in this sports reality , than simply playing around in a simulator.

[husaberg]

I wasnt saying at all that technically the 100cc twin was not capable.
What I am saying is that we have 100cc buckets making 30 Hp now, and they are only reving to 13,000 when in fact a 50mm stroke should be going to well over 14000 - thus making 40Hp a reality, if done " properly ".
Christ its taken 5 or more years for people to get that 30 Hp was easy - as I said to Nige and Mike so long ago.
Why would anything change when we go to a 40mm stroke with a twin, the chances of it being done " properly " are virtually nil, and where is the non competition close ratio box going to come from, let alone
cylinders that could be even remotely considered as being able to be modified to make decent power ( a fully modern KTM type 50cc cylinder with everything copied from Jan Thiel is needed to make 20 Hp ).
The twin will always be capable of alot more power - the know-how and mechanical/financial restraints have a much bigger part in this sports reality , than simply playing around in a simulator.

Agreed while technically feasible it is cost prohibitive. The original question was more what is the optimal cylinder size for the bucket rules.
Although i was incredibly impressed when i picked up a complete KTM50 engine they are tiny and incredibly light (san gearbox admittedly) the pics are the old (beta Engine)New one is far sexier.

and bits for race 50's are incredibly cheap. but not my cup of tea with the extra complication of 2 of everything as well as twice the number of things to replace and modify build etc pay for etc.
But i did struggle to get my head around why the 100cc twin would have to rev to 20000rpm to do 40hp when the 50cc single was capable of 20 at 14000rpm?

Oh yeah Wob you mention eccentric bushes how are these made?
As it seems some engines have there mainshafts so close to the crankpins it makes the normal machining fraught.
I have also heard of the spark erosion (from you)I guess t is the same process used to remove studs or so forth?
With this method is it possible to for want of a better term drill the half offset hole without filling? is it cheaper than filling re drilling? w\
While on the subject is the filler material (used when the four stroke cranks are filled) stainless and why what sort of cost would be expected for each and pros and cons.Sorry long question lots of assumptions pos required as well so lets use this crank as an example.
It may look familar.
It caught me by surprise as i certainly wasn't expecting Honda to change the spine and the mainshaft diameter from the NS125 vs NSR125 as well as the diameter of the crankwheels is a bit larger than i expected as well.(I guess to allow for the NSR150) for reference the pin is 24mm dia.
The last 2 pics are the 50.6mm stroke cylinder reed NS125 pics for reference.Bloody honda why change the spines method when you are normally so lazy.

[2T Institute]

The MBA 125 twin was the bike that forced the single cylinder rule in 125cc GP. A RD125 with it's 43mm stroke and using 39.5mm pistons from a range of Euro 50cc bikes with custom triple exhaust port Nicasil sleeves would be an awesome little machine.

[wobbly]

The problem lies with the fact that you need super sex technology to get 20 Hp from a 50 at "only "14000.
Its the short stroke of the 50, or for that matter a 100 twin, that is its inherent advantage - as we all know Hp = T * RPM/5252.
Thus double the rpm and you double the power - as long as you can hold up the torque at the level.
Without very good cylinder geometry, along with a PV then the only way to get some power, is to rev the shit out of it.
Then the power band width becomes progressively narrower, needing more, closely spaced gears to make it work.
Without most of the help of plenty of technology,the 100 twin in a Bucket scenario just becomes a screamer with no real advantages - hamstrung by its weight and lack of a close ratio gearbox.
Of course I would love to have a go at one, I had a TA125 in a sprint kart back in the day, and just loved the howl of the thing spinning to 16000,with a genuine factory close gear set.
Even if my poxy red cylindered air cooled Honda CR125 was faster.

Need to look closely at the Honda setup for you but the best way I think is to fill the top of the big 24mm pin hole, and use a much smaller pin - offset down to get the stroke needed.
For example 125 ICC kart engines all use 20mm pins, and they are dead reliable to 15000 - of course we need to find a legal rod eh.

[husaberg]

..Without most of the help of plenty of technology,the 100 twin in a Bucket scenario just becomes a screamer with no real advantages - hamstrung by its weight and lack of a close ratio gearbox.
Of course I would love to have a go at one, I had a TA125 in a sprint kart back in the day, and just loved the howl of the thing spinning to 16000,with a genuine factory close gear set.
Even if my poxy red cylindered air cooled Honda CR125 was faster.

Need to look closely at the Honda setup for you but the best way I think is to fill the top of the big 24mm pin hole, and use a much smaller pin - offset down to get the stroke needed.
For example 125 ICC kart engines all use 20mm pins, and they are dead reliable to 15000 - of course we need to find a legal rod eh.

All revs no action 2x everything to fiddle with adjust make pay for wear out faster too.The thought of two carbs to tune as well

.,the 100 twin in a Bucket scenario just becomes a screamer with no real advantages -

there is a certain procreative advantage's to having a screamer, certainly to be preferred over the moaner i am saddled with anywayI know which one i prefer anyway.

The rod i think i have sussed. Name thy preferred length 104 or 105mm.
Whist on a net troll i came upon some some GP spec rods and i was surprised just how long the RSW and RSA Aprilia rods are.
I did notice however the Cagiva crankshaft is quite similar to the NSR125. Are those Europeans still copying the Japanese

[wobbly]

Was pissing down this morning so didnt make the trip to Taupo - went to Gingers place this arvo in Huntly to set up his new Ignitech on Bultaco 350.
Obviously will hear all about it here.

The Aprilias had around 2.2 rod/stroke ratio, with 50.6 stroke the closest rod would be around 110 long - still a little shorter ratio.

[twotempi]

Having a longer rod ratio - say the Aprilia at 2.2 - will decrease the difference of rotational speeds of the big-end bearing between TDC-Half Stroke-BTDC.

Example - If the rod was of infinite length the big-end bearing would constantly rotate at half crankshaft speed

So do longer rods have a significant benefit for the big-end bearing ??

[F5 Dave]

Was pissing down this morning so didnt make the trip to Taupo - went to Gingers place this arvo in Huntly to set up his new Ignitech on Bultaco 350.
Obviously will hear all about it here.. ..

Or over on the F4 picks thread. But suffice to say no one is blowing any trumpets of glory. It could have all gone so differently.