Just for my personal education.......

[viclioce]

Attached are three photos of the .040 piston which came out of my CW cylinder. This was in my Wombat with a cracked top ring. However, I don't recall IF the crack in the ring lined up with the damage to the crown. I can only say it possibly did but I'm not 100% certain because it's been 2+ years since I pulled it apart.

Does this look like the kind of damage which would be caused by a cracked ring blow by, or, do you think it was caused by detonation, or something else?

As seen in the pictures, the damage would be to the right of the exhaust port.

I'm curious who has experienced this type of piston damage, and what the determined cause was. ; D Victor

[Bullfrog]

Appears to be erosion caused by detonation. Air leak, lean jetting, advanced timing, ethanol blend fuel (see lean jetting) are all potential contributors (could be many other contributors as well). Detonation effects are probably what caused the ring damage.
Ed

[viclioce]

OK, thanks Ed. I figured as much.

This was how it was when I got it. I know the bike came to NM from CA. So for the conditions here it was configured rich for lower elevation. But I suspect it wasn't run here at all given the condition it was in.

It's good to know what detonation damage can look like. Funny though, because it had a #40 pilot in her and a 190 main jet. So I'm guessing it was more the effects of dried out, hardened up seals.
Does anyone know if there are any 5 over CW pistons out there? ; D Victor

[Dale]

Just installed one. Check at Strictly Hodaka if you haven't already.

[Bill2001]

One problem with autopsying something dead after the fact is that you don't always know the entire history. Sure, the diagnosis is detonation, but we don't know what led up to the final damage and what was tried before it finally expired. Detonation from mixture, timing or lousy fuel is the likely culprit, but the rich jetting may hsve been something that was tried along the way with the motor in a death spiral.

Remember when my engine seized and I beat myself silly 'cause I checked everything out and it shouldn't have failed? My assumption was that the top end was brand new and the bottom end was a recent rebuild, and I didn't double check that. My suspicion was that the top end was actually old and has seized and freed up before, so it was another seizure wating to happen the first time I took it out on a 5-6 mile road run. I spent a lot of time trying to diagnose something that had moved on.

Best advice, is to trust your own work, and view anything else with suspicion. ;

[viclioce]

So true Bill! With the ability to wrench and discuss issues on this forum, there isn't ANY issue that good, hard work, and money, can't fix! ; D Victor

[Darrell]

I'm wondering...would there be any side, or adverse, effects from running a Wombat piston in a Combat Wombat (Victory-Ported) cylinder? With out the piston port where will the intake boost travel?

[viclioce]

No intake boost. It runs like a non ported cylinder.

I'm considering a change. But grandson hasn't ridden if much yet. He gets frustrated by the clutch and goves up too easily.

I also just bought a Model 03 motor which I plan to restore for it. Bringing it closer to original. But I need to finish the 2 Toads first. The Model 03 motor will likely be a Winter project. ; D Victor

[taber hodaka]

I had to let the grandson play with it on his own. Me standing over him was too much pressure. Yes the other kids were better teachers. Victor you are on a roll. -----Clarence

[viclioce]

Well, when I finish #4, I don't know what I'll do next.

But I've always wanted a Yamaha IT 200 or 360! There's a guy on the FB Vintage Enduros selling an IT 200 for $1200 or best offer. If I find one when I'm done, for the right price, I might just.........