Don Terrill’s Speed-Talk

what is your assessment of this piston. Looks to me they got to close to the ring land with the valve relief. There is 2 others that broke the top of the piston off in the same spot. this one was on the verge of breaking.

Gas ported top ring! That hole looks like it was there out of the box. If that's what it is, there won't be any questions about warranty.

I am on my phone and didn't see anything that resemble a hole?

I zoomed and rotated the picture

Looks like the piston has been subjected to way too much heat, which has actually melted the top of the piston adjacent to the valve relief. Look for detonation and preignition.

I've seen valve relief pockets in a much more precarious position live perfectly fine with a good tune

I suggest some careful measurements to determine the proximity of the valve relief to the ring groove. Looks too close to me.

Tune up.

I would also look for symptoms of the top ring butting.(shiny ends, etc.) If the rings are butting then the weakest part of the piston will break first.

Allan.

Mark O'Neal wrote: ↑Mon Nov 04, 2019 11:51 pm Tune up.

Yup. Looks to me like some preignition was going on, followed by some detonation. Too hot a plug or some funky fuel.

Mark O'Neal wrote: ↑Mon Nov 04, 2019 11:51 pm Tune up.

X2
They do not stand up well when the tune is off. Yes they are close but when running correctly with a really good tune
they will live a long and happy life. Step over that edge and poof burnt piston.

While all pistons are not created equal those look like a common power pack piston. I have seen import guys have
the same issue and moving the top ring down will give a bit more area to dissipate heat but again if the tune is off
Poof

Where the crack is. To me, it looks like the pressure from the burning A/F has pushed against the wall of the valve relief, where the metal is thin, & this has caused the crack.

Until 0'Neal gets around to making investment cast steel pistons you can simply consider aluminum pistons are just a reciprocating fuse.

engineguyBill wrote: ↑Mon Nov 04, 2019 9:30 pm Looks like the piston has been subjected to way too much heat, which has actually melted the top of the piston adjacent to the valve relief. Look for detonation and preignition.

I'm familar with pre ignition damage on air cooled bike engines...it usual occurs in the center of the piston, very suddenly,like just a few cycles...But on that piston, the off center area that is damaged may be the weak point....
This is typical pre ignition damage...

Long term detonation . If the ring gaps are all lined up, it has run for a while with light detonation.