I'm temped, as a challenge to a problem that raised when getting ready to assemble my engine, to modify the pistons skirts since one of the pistons got a crack in the skirt, under the pin side. I see racing people do this on their engines, and obviously engine lifespan is not a problem for them. So my question is: would modifying my pistons this way would reduce their lifespan? Or would they last as if they were in their original shape?

First pic shows where the crack is, second pic is a very rough idea of where I can cut it.

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  • I think the biggest problem you'd have here is balancing the pistons (getting them all (nearly) exactly the same). An imbalance in your rotating assembly will cause you issues. Second thought is, this skirt area is there to add strength to the overall structure. Removing it is going to really reduce its overall strength. If you aren't spinning this thing to the moon, you can probably get away with it. Still a big gamble to my way of thinking. Commented May 12, 2017 at 11:46
  • So it would be better to run the piston with that dent, than modify them all? Commented May 12, 2017 at 16:22
  • my personal take is that if your careful you can get away with trimming and balancing with proper tools, including a mill and a scale. mill to be sure you removed the same material from each side of the same piston, and a scale to be sure all Pistons are the same in the end. and that I believe is close enough. not that a piston can't be strong workout a skirt there are many without, but this one was designed with it so... too many unknowns here. that said I'd do it if I had good reason I might be successful.
    – axa
    Commented May 13, 2017 at 9:26
  • Notice that a piston failure is unlikely to only affect the piston. Your engine may suffer in various places if your modified piston disintegrates at some point. Get a new replacement piston for the broken one.
    – JimmyB
    Commented May 13, 2017 at 11:07
  • and obviously engine lifespan is not a problem for them... That's because they replace or rebuild their engines pretty frequently. The goal in the case of a race car is to reduce rotating mass, which can have a significant impact on performance. I'd just replace the piston in your case.
    – 3Dave
    Commented Jul 16, 2018 at 16:19


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