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mahle piston failure

General engine tech -- Drag Racing to Circle Track

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sccagt1racer
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mahle piston failure

Post by sccagt1racer » Mon Nov 04, 2019 7:16 pm

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.
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Re: mahle piston failure

Post by gruntguru » Mon Nov 04, 2019 8:03 pm

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.

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Re: mahle piston failure

Post by BLOCKMAN » Mon Nov 04, 2019 9:02 pm

When I see a piston that clean usually there is a lot of timing plus the edge of the piston looks melted. A lot of unwanted heat. JMHO

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Re: mahle piston failure

Post by af2 » Mon Nov 04, 2019 9:10 pm

I am on my phone and didn't see anything that resemble a hole?
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Re: mahle piston failure

Post by sccagt1racer » Mon Nov 04, 2019 9:26 pm

I zoomed and rotated the picture
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Re: mahle piston failure

Post by engineguyBill » 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.
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Re: mahle piston failure

Post by digger » Mon Nov 04, 2019 9:48 pm

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

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Re: mahle piston failure

Post by gruntguru » Mon Nov 04, 2019 11:29 pm

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

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Re: mahle piston failure

Post by Mark O'Neal » Mon Nov 04, 2019 11:51 pm

Tune up.

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Re: mahle piston failure

Post by superpursuit » Mon Nov 04, 2019 11:54 pm

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.

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Re: mahle piston failure

Post by Tuner » Tue Nov 05, 2019 12:23 am

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.

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Re: mahle piston failure

Post by ProPower engines » Tue Nov 05, 2019 1:20 am

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
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Re: mahle piston failure

Post by Geoff2 » Tue Nov 05, 2019 3:24 am

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.

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Re: mahle piston failure

Post by Tuner » Tue Nov 05, 2019 3:51 am

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

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Re: mahle piston failure

Post by Truckedup » Tue Nov 05, 2019 9:03 am

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...
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