Who can guess what's wrong with this engine?

Find and install forged pistons, job is done!

thomas rubino wrote:Find and install forged pistons, job is done!

I agree with Mr. Daley & Rubino

Anything more than that would involve total tear down, a year of microscopy, metallurgy, various laser micrometers and an x-ray machine resulting in the blueprint for a new 2025 Straight 6.with a lifetime warranty.

Hmmm, then the molds and casts,... and the mills ...well... maybe the 2027-8 model?

I'm a physics nerd with a 1 time rebuild of a 350 in a '74 Camaro @ 23yrs old. I have an inherent overthinking curse that things should be better, faster, stronger and last forever.

If only I could build them myself.

Now I'm wondering what the stroke count is over 100,000mls of a typical gasoline engine.

I never should have looked at this thread....

I wish you another 100k

I have wondered about forged pistons. I'm certainly no expert, but it looks to me like forged pistons are really meant for extreme performance engines, which this certainly is not. Forged pistons are stronger, but they have more thermal expansion than the hypereutectic cast pistons. To compensate, they have to be smaller at low temps to allow for the extra expansion. They also need more ring gap. This engine rarely passes 2000rpms, and the pistons would likely be running a bit on the small side most of the time. They say they can be small enough to get piston slap at startup, and possibly even damage in cold weather. While less likely to fail, they tend to have shorter lives. I noticed people online saying they have trouble even finding any standard sized ones for this engine, which I noticed myself. That may be a sign. The consensus I seem to be seeing the most is that they are not needed or recommended for a stock engine like this one. The cast pistons available now it seems even sometimes come with a paper explaining that the skirts have been redesigned to not fail like the originals. And the forged ones I have seen look like they cost about 600% more? I'll see what I can find locally this afternoon and go from there.

I'm not impressed with the design of the originals. The entire area that broke away is only about 1\8" thick. It looks to me like the redesign to improve fuel economy\emissions by making pistons lighter with less bearing surface is likely a main factor in the failures.