ESE's works engine tuner

[husaberg]

Hi Wobbly, I have arrived at the stage of destroking the engine from 125cc to 110. Using an oversized big end pin (24mm dia) where previously a 22mm dia. The machinist is going to offset bore it to fit the new big end pin to achieve the required stroke. Can you please tell me, how much of an interference fit does the big end pin to the new crank web hole is acceptable? 2 -3 thou? Thanks in advance.

Have you considered inserting sleeves into the 22mm bore and doing an offset bore to destroke using a 18mm or 20mm pin.

24mm pin is pretty big for 110cc
You can key the sleeve but i doubt it's required.

the opposite of this powroll


The other other option just use a shorter stroke crank.
or get the crowd that built the pin for Speedpro to do you an offset pin.

My crankpin was made by heat treatments. machined, heat treated, and ground. Hasn't let go yet but still early days. 20mm ends with a 22mm centre, offset .75mm. Very helpful guys.

https://www.kiwibiker.co.nz/forums/s...post1130471126

[porttiming124]

The groove will indeed constitute a bypass. Whether it will actually serve as a bypass, depends on the exhaust and transfer pressures.
As you say, the effect may be small. Just try it; you've got nothing to lose.

ok thanks i will try it

[porttiming124]

Over herein Oz around a century ago, there was an engine used in karting for little kids, it was called the Comer S80 or SW80.
It had a chrome bore and a 2 ring piston. The tuning trick of the day was to reduce friction from the second ring. The rules stated that both rings must be in place.
What the "gun" tuners did was to reshape the second ring such that it was tensioned into the ring groove, ie making no contact with the bore, but still there to prevent short circuiting and also satisfy the rules.
To achieve this, the ring was squeezed into an "undersize" ring, such that the ends must have overlapped, ie forming a helix. Then it was heated, presumably to some annealing temperature, maybe 800 - 900 C for cast iron, less for steel.

Then it was fitted to the groove such that it was tight to the bottom of the ring groove. Clever ??

So, if you have old rings to play with, maybe this is the go.

No guarantees though.

I will try to remove a ring and leave the groove open and if I see that I have a loss I will try that. thank you

[porttiming124]

I tried what Woobly and Frits have already discussed. Retaining the flow of the reed box which does not only want to come out in front but also in the side. I gained 2 hp on an 800cc 3 cylinder engine that makes 210hp.
thank you

[vro46i]

Have you considered inserting sleeves into the 22mm bore and doing an offset bore to destroke using a 18mm or 20mm pin.

24mm pin is pretty big for 110cc
You can key the sleeve but i doubt it's required.

the opposite of this powroll


The other other option just use a shorter stroke crank.
or get the crowd that built the pin for Speedpro to do you an offset pin.


https://www.kiwibiker.co.nz/forums/s...post1130471126

I have another RG bottom end to build up as the spare engine, so that will be the one to try other forms of destroking the engine. I think the cleanest but most expensive way is to machine up a shorter stroke crank.
Thanks for your advice and recommendation, lots to think about now....

[wobbly]

I have found the cheapest way to do restroking is to bore the hole offset and oversize.This makes the hole size irrelevant.
Then insert a sleeve that is size for size to this hole , and has the interference fit for the pin on its ID.
That way welding isnt needed , and as long as the two holes are bored exactly on the same centerline , its easy to align the assembly with no runout.

[Condyn]

I have a question about the exhaust port floor. I found this drawing, which appears to be from Frits. It shows a very high floor compared to what I am used to seeing. On our snowmobile engines with auxiliary exhaust ports we typically run 81° ATDC exhaust open timing and 115° transfer open timing, which equals 34° BD.

The exhaust port floors I see almost always are at the same level as the transfer port floors. Since we already do all kinds of welding on these cylinders before resleeving with aluminum sleeves, would it be wise to raise the floors like the drawing?

If anyone has any insight on this subject I would love to hear it.

[porttiming124]

I have a question about the exhaust port floor. I found this drawing, which appears to be from Frits. It shows a very high floor compared to what I am used to seeing. On our snowmobile engines with auxiliary exhaust ports we typically run 81° ATDC exhaust open timing and 115° transfer open timing, which equals 34° BD.

The exhaust port floors I see almost always are at the same level as the transfer port floors. Since we already do all kinds of welding on these cylinders before resleeving with aluminum sleeves, would it be wise to raise the floors like the drawing?

If anyone has any insight on this subject I would love to hear it.

I believe from the drawing that frits shows us it is to show the height of the blowdown.

[wobbly]

Lifting the Ex duct floor is only effective when the Blowdown STA has been fully optimized.
In a single Ex port scenario this is rarely achievable.
I have not seen any direct dyno data to prove how effective this technique is in a conventional 2T layout apart from Jans final experiment at Aprilia where it was lifted 3mm on a 54.5 stroke , so you are in unknown territory above that level.
But hey its easy enough to lift it higher and then drop it incrementally to find the optimum , apart from exposing the ring to alloy when re chamfering and probably ultimately needing a replate.
What is fully proven and documented is reducing the duct exit area to 75% effective ( chordal area x cosine of the down angle ) in a 3 port , and 90% in a single port.
Filling in the port bottom corners with large radi below TPO also is common proven SOTA technology to help reduce short circuiting from the A port front wall.

[Condyn]

I have used the “ wobbly duct “ with success. Surprised? No, but still not sure I understand the why.

Is the 75% number in itself a rule unbreakable, or is the associated Mach value the focal point?

The reason I ask is because if we find the exhaust port floor is too low ( on the dyno ) with optimized blowdown do we then have to shrink the duct exit even more because of the smaller port or do we target a specific mach number?

I realize this is somewhat speculation on my end and there might not be available answers. Just thinking out loud.

[wobbly]

The answer is all down to achieving Mach 0.8 at the duct exit before the tapered transition into the header.
Less than this always looses power , and after doing a huge number of projects with this number being used , I did an analysis of the results gained and that is where the " 0.75 area rule of thumb " came from.
Frits has always said I should be relating the Blowdown area with a factor for the duct exit , and I agree with him , but the current guideline works so well I honestly cant be bothered.
This is alot more relevant to single Ex port race engines , where getting anything like 0.8 would seem impossible as the gas flow regime is so low in comparison to a 3 port - but I hardly
even see single port engines these days , so again I cant be bothered putting in any unnecessary effort - especially as I make a living doing way more interesting stuff.

[Condyn]

Fair enough. I have seen the duct work first hand so thats proof enough for me.

[Muhr]

Hello finally done with the clutch! Then there is "rubber" left, did some simulations and 50 shore seems to be a good starting point for a small engine like this.

[TZ350]

Because Team ESE use the Suzuki RG50 and GP125 engines from the late 70's and early 80's I found the early racing R&D development years and comments from the original 60's development race team very interesting. A bit of bike action too.

[TZ350]

Hello finally done with the clutch!

Beautiful work. ...