Freeway did her in

[m in sc]

man that plug is oily.

It looks like the head gasket may have started to leak out the front side. How much run time since it was bored? Could it be that side was just a touch too tight? Is that a forged piston?

looks like it may have had a slight leak, under gasket,  at arrows. decel may have sucked air in and bam.  whgat does underside of gasket look like and cyl?

[Striker1423]

Here's the underside of the gasket and the cylinder.





I did use 3 coats per side of copper spray a gasket.

[Arrow]

This dark area, perhaps?

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[Striker1423]

Possibly. I don't really know what to think. Maybe the bore wasn't actually correct.

[Arrow]

These are simple bikes, but things seem to get more complicated some 1/2  Century after they were made. Thankfully/hopefully, they can still live.

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[Alain2]

Piston top and plug show the tune is too rich in general. Oil pump appears to be working. No sign of detonation.

I Also suspect the Piston/bore clearance was too small for the forged Wiseco. It didn't fail earlier because the tune was so rich that it prevented complete piston expansion, until the freeway did it.

Does the other piston show sign of wear on 4 corners?

[Striker1423]

Piston top and plug show the tune is too rich in general. Oil pump appears to be working. No sign of detonation.

I Also suspect the Piston/bore clearance was too small for the forged Wiseco. It didn't fail earlier because the tune was so rich that it prevented complete piston expansion, until the freeway did it.

Does the other piston show sign of wear on 4 corners?

No. The other side was fine.

[automan]

Been there-done that.
Cold siezure on a new build.

Minor, and fired back up. to limp it home. All 3 jugs/pistons were still perfect!?!

Hi guys! Newbie here.


cliff

[teazer]

Standard mode of failure on a 2 stroke.  Forget the piston wash interpretation for a moment because it ran home after the meltdown so we can't really tell too much.  Typically, a lot of carbon on the head or piston indicates a lean mixture and a clean surface with more washed than carbon tends to indicate rich, but we can't say too much because we have no idea if that carbon was built up when it was run hard or tootling along.

What we can tell for sure is that the piston expanded to the point that it had minimal to negative clearance and that's why it had a 4 corners seizure.  There's no obvious signs of detonation or oil film breakdown except on those 4 corners.

The causes are usually too little clearance or more likely, it's lean on the needle jet.  Most of us know how to check main jet color on a plug and for slow speed running but if it's lean on the needle, all we do is open the throttle a little more.  And that kills a two stroke cruising down the highway at steady throttle/rpm/speed.  Motor gets hotter and hotter and it either starts to detonate or it nips up like that one.

We had a TD3 that did that too many times at Daytona at full tilt and it turned out to be a minor air leak in an inlet manifold.

Do a leakdown test and see if there's a slight leak anywhere.  Follow that with checking piston to bore clearance or go slightly loose next time and if all that looks good raise the needle one step.

[Striker1423]

Good things to note Teazer. She's currently in boxes and a thousand pieces. If I'm overhauling it again I'm doing it up real pretty like.

[edgefinder]

Striker, I wish I was nearby and could measure the pistons and cylinders. Regardless of what really killed them the measured clearance is good data points for RD riders. If its closer to .002" than .003" then I would say it didn't leave a safety margin and part of the problem. You could clean the aluminum from cylinders with acid and hone a couple tenths more, fit new pistons and have that part fixed. If it didn't scatter aluminum into the crank I would run it if all else looks good