scarred

[HarnessThis]

Question. If the top of my piston is scarred/gashed from a valve breaking and falling into the cylinder, can I just grind down the piston to smooth it out? Or do I have to replace the piston? Thanks for your help in advance.

 

[adsm08]

Is this in the middle of the face, or at the edge? If it is in the middle of the face there is no real reason it needs to be perfectly smooth, and grinding it down will just create a larger weakened area. If it is at the edge, near the cylinder wall I would 100% replace.

 

[RonD]

Yes, +1 ^^^, no to grinding

There is also the possibility that piston has cracked where it connects to connecting rod, so all things considered I would replace it just on spec.
Piston clearance to head is very small in some places, if part of a valve ended up there just one time piston would break/crack or connecting rod would bend.
You can test for bent connecting rod by testing piston's height at TDC compared adjacent piston heights at TDC
It would be a shame to have to pull the head again if piston fails, but your call

 

[HarnessThis]

The gauge if you will is in the center of the piston, and I know the crank is fine, seeing how I can turn it fairly easy with a breaker bar. There is zero damage to the cylinder walls. I do not want to do that much work on this thing for I don't plan on keeping it once I can get it running. FML.

 

[RonD]

If there are no spark plugs in the engine you shouldn't need a "breaker bar" to turn it, should spin very easily

Put a straight edge across another cylinder and rotate engine until its piston is at it's TDC, top dead center
See what clearance there is then do the same for damaged piston

Unfortunately what you want and what engine might need are often not the same
Hate to see you waste time and money on top end fix and then end up with an engine that starts and runs for 5 minutes then breaks again, and you have to do the whole thing again, plus bottom end