ESE's works engine tuner

[cotswold]

Saw this picture of a flat top piston running in a RS125R

[speedpro]

Are you certain the head and cylinder were clamped up tight rather than the nuts being bottomed out? I ask because I had a similar issue lately and that's what it was. It's a pretty big blowout as well covering quite a bit of the bore circumference.

[TZ350]

Are you certain the head and cylinder were clamped up tight rather than the nuts being bottomed out?

Different head and head bolts so quite possible ....

[twotempi]

I run "Viton" o-ring setup on an air-cooled twin for several seasons and never had a problem.

Checking that the threads are not bottoming is a good thing to check as I don't think the problem is the o-ring. Also check that the tube bolts nuts not bottoming on the cylinder counter bores as this will seem if all is OK but the head won't be clamped down tight. Easy to fix - shorten the tube nuts a few mm's

[TZ350]

Checking that the threads are not bottoming is a good thing to check as I don't think the problem is the o-ring. Also check that the tube bolts nuts not bottoming on the cylinder counter bores as this will seem if all is OK but the head won't be clamped down tight. Easy to fix - shorten the tube nuts a few mm's

Yes the O ring has been reliable, its the composite head gaskets that failed and took the O ring with it. I think you may be right about the tube head bolts, I will have a good look tomorrow.

[Flettner]

Nothing wrong with an o ring head seal on air cooled two stroke.

[F5 Dave]

Bit silicone there

[TZ350]

Are you certain the head and cylinder were clamped up tight rather than the nuts being bottomed out?

Yep your on the money. Rogue extra long cylinder head bolt got mixed in with the modified ones.



I was concerned that the piston skirt was not completely covering the exhaust port at TDC.



I scribed a mark on the piston skirt and it looks like I would be lucky to have 2mm coverage so I may yet have to build the floor up a bit.

[speedpro]

I'm sure it's been done already but raising the floor of the ex port would be an interesting experiment. Flow could be improved at part open but that would be offset by a restriction towards BDC. There could also be some advantage as the port closes with a better port shape directing the return pulse from the pipe more into the open port rather than it mainly just bumping up against the side of the piston. With the right pipe, say one with a milder rear cone it could result in less of a powerband. With the better port for the return pulse the pulse could have lower amplitude and still be as effective so the rear cones won't need to be so steep.

[2T Institute]

A "restriction" at BDC is exactly what you want in the exhaust duct.

[TZ350]

Neil turned up today with the two bikes he has fuel injected, we gave them a bit of a trot on the dyno and they went really well.



Neil also brought these parts with him, that he had made for me. A generator to power the Ignitec and EFI, and the Ball Valve with TPS.

I was going to run the Ball Valve inside a plenum but now I am going to try it with a 24mm venture insert behind it and see how that goes first.

[Flettner]

TZ, Thank you for all your time and patience today. We are happy with the results and very much appreciate your expertise with the dyno, I am at your service.

[Sketchy_Racer]

Looks like a interesting day on the dyno, are you going to thrill us with some numbers of the EFI dirt bikes?

[RomeuPT]

Saw this picture of a flat top piston running in a RS125R

A bit rich? Strange wrong scavenging sign maybe?

[TZ350]

Looks like a interesting day on the dyno, are you going to thrill us with some numbers of the EFI dirt bikes?

EFI YZ250, (the graph is in mph because I could not easily get an ignition timing signal for rpm, next time).



EFI Kawasaki F86M 350 Big Horn from the 70's.



Yamaha blue line, Kawasaki red.