ESE's works engine tuner

[Frits Overmars]

https://youtube.com/shorts/YVAGrbG3M...VUzrVRnbH3sraE
Powervalve operation, twin ports.
How far round should the transfers come?

They look fine to me, assuming they are aimed backward strongly enough.

[Flettner]

They look fine to me, assuming they are aimed backward strongly enough.

Seen here .........

[Frits Overmars]

...........

[Frits Overmars]

Aren't you guys getting tired of having to look at my thumb for over a week now? I know I am

[Wos]

Frits, your personal thump is such a beauty

Does your thump like to write? ��

So i tell you...rotax 124 had its rollout...had two eduro classic races...think its the strongest 124 rotax under the competitors ��

Inlet timing we achived a little to opening 145 closing to 85 and found litte improofment in rpm to 10300.

Pipes max is 8500/ 550 ms...

Think we have bonce back anyway, as we kept the 200 mm inlet tunnel...no way to adapt carb directly in enduro use.

Carb is very moody as you promised a year ago ... two jet sices between everything fine...and stuttering in higher revs / wont reve with 2 numbers richer main.

There is a tendency to enrich i think, cause of bonce back...

Nex we want to try closing 90 after tdc.

What do you think Frits?...step in right direction?
Step to small...to big?

Tell it all your fingers... special thanks to your thumps ��

Viele Grüße! ��

Wolfgang...nearby liedolsheim

[ApolloMotoMoto]

Aren't you guys getting tired of having to look at my thumb for over a week now? I know I am

Ah ha! We've caught you now...

Openly admitting he enjoys answering endless questions about our favorite little pandoras box?

Or at the very least open amaussment, maybe even some kind of schadenfreude as we all discover our own ignorances.

It's as if Frits has -as many before him had, and as I imagine he hopes continues into the future- bushwhacked a fairly clear path through some fairly dark forest, and is now waiting paitiently for others to discover this neatly cleared path, walk it's course, and choose to pick up the tools for themselves to continue even deeper within the mystery.

Let's not disappoint him!

[ApolloMotoMoto]

So... Next on my list of things to do for 9x identical race engines I am preparing for Octobers race event is preparing some cranks.

We have Italkit rod kits that we sourced directly from Italkit.

I'll be pressing apart the stock cranks and pressing them back together with all the Italkit parts, crankpin, rod and bearing.

The main reason being the stock bearing radial clearance is way too big.

Stock big end bearing radial clearance is in the range of 0.050mm - 0.070mm total radial clearance.

Cranakpin is 16mm, rod big end is 22mm.

After everything I have researched, I have come up with values for an "ideal" range at these diameters being more like 0.035 - 0.045mm allowable total radial clearance for brand new parts, with an absolute service limit of 0.06-0.08mm depending on the engine manufacturer (reviewing 80cc 2 stroke service manuals because the diameters are similar).


What are your thoughts for the ideal bearing radial clearance for the big end bearing, given my diameters?

Also, how "true" would you be trying to get your race cranks after pressing?

If anyone has any techniques, tips, or considerations to share on the general process of pressing 2 stroke single cranks, I would appreciate it.

Attached are some images of the crank press tool I just acquired, I have a fairly standard 20 ton hydraulic shop press to do the pressing.

Given the tools, does it look like I am setup for success or are there any pitfalls I am not accounting for that need to be addressed with this tooling setup?

What is your preferred method of checking runout?

Should I recut the "center" featueres on the shaft ends of each half when I have them apart so I can check runout between centers?

[Frits Overmars]

rotax 124 had its rollout....think its the strongest 124 rotax under the competitors.
Inlet timing we achieved a little to opening 145 closing to 85 and found little improvement in rpm to 10300.
Think we have bounce-back anyway, as we kept the 200 mm inlet tunnel...no way to adapt carb directly in enduro use.
Carb is very moody as you promised a year ago....There is a tendency to enrich i think, cause of bounce-back.
Next we want to try closing 90 after tdc. What do you think Frits?...step in right direction? Step too small, too big?

With that long inlet tract there is a very real chance of bounce-back. Closing the inlet disk 90° after TDC or even later could help. Alas, the fact that the inlet disk is hidden behind the clutch makes experimenting rather cumbersome.

For those who'd like to read a bit more about bounce-back here is a text that I wrote some time ago (and that you can also find at https://onedrive.live.com/?authkey=%...D58EFB966FB3DC )
=====================================
In all inlet systems the inlet flow accelerates as long as the pressure upstream of the inlet tract is higher than the downstream pressure.
When both pressures are equal the flow has reached its maximum velocity and because mixture keeps entering the crankcase, the crankcase pressure rises above the upstream pressure and this rising pressure gently slows the flow down to a standstill (or suddenly instead of gently if the inlet port closes too soon, which can happen in both piston port and rotary induction systems).
In any case, the pressure at the crankcase side of the inlet tract will then be higher than the pressure at the bell mouth, and mixture will start flowing back towards the free world. The extent of this back-flow may be so small that it is not noticeable at the bell mouth, but it is happening nevertheless. Reed valve systems do it just as much as other inlet control systems.

If the engine rpm does not suit the inlet timing, we can either experience blow-back if the inlet port closes too late, or bounce-back if the inlet port closes too early.

Blown-back mixture is mixture that initially entered the crankcase but then reversed its flow direction because of the rising crankcase pressure while the inlet was still open.
This rising crankcase pressure resulting in flow reversal has rather little to do with the piston moving down after TDC. It can even happen before TDC if the Helmholtz frequency of the inlet system is too high for the engine revs (low revs, big carb diameter, short inlet tract, small case volume).

Bounce-back occurs if the inlet is slammed shut while the mixture is still on its way to the crankcase. The mixture flow then collides with the inlet disk or the piston, causing a large local pressure rise at the free world side of the disk or piston. Bounce-back may be hardly noticeable, but on the other hand it can be much more vicious than blow-back.

As an experiment I once put a 200 mm elongation tube between the carb and the rotary inlet cover of a 125 cc Rotax.
It lowered the Helmholtz frequency of the inlet system so much that inlet flow velocity was still near its maximum when the inlet disk closed. Bounce-back was so severe that within seconds the dyno room was completely fogged up with mixture. It frightened me to death; a spark would have been enough to blow the roof off.

[Wos]

Thanks a lot Frits!!

Yes Frits...little nightmare to change disc...most work is to remove old dry silikon sealing of cover and case 😉

Now i am looking forward to do this work 😉 as we can expect some more progress.

Think 5 degree steps to recognice a diffrence will be practical steps in our konfig Frits !?

Thanks!

Grüße Wolfgang

[wobbly]

When the Rotax 256 was introduced it had 135/85. Going to 88* was a huge jump in peak and overev power.
Then going to 138 was an improvement, but any more and the mid range tuning became very difficult, with no more power to be had.
Going to 90* only gained about 0.75 Hp in the overev, but lost nearly 2 Hp at 10,000.
I believe going in 2* steps is plenty.

[husaberg]

As an experiment I once put a 200 mm elongation tube between the carb and the rotary inlet cover of a 125 cc Rotax.
It lowered the Helmholtz frequency of the inlet system so much that inlet flow velocity was still near its maximum when the inlet disk closed. Bounce-back was so severe that within seconds the dyno room was completely fogged up with mixture. It frightened me to death; a spark would have been enough to blow the roof off.

I can't remember the circumstances but Pops Yoshimura wore some pretty bad scars from dyno fire.

[F5 Dave]

I used to put the fire extinguisher by the door. My health and safety talk to participants went something along the lines of. Don't stand anywhere that a wayward bike that breaks loose will go and for godsake don't stand behind the spinning wheel or where you can touch the drum.
If there's a fire, don't stand between me and the exit. I will use you for traction.