Cracked Pistons

[g50nut]

All you engine build techs out there, I have a 1977 911S im bringing back to like, done full lines/brakes. Got to engine and turned by hand, seemed some resistance so removed spark plugs. Its on the side where some oil is leaking around exhaust manifold area, RH bank.
I found 2 cylinders with what seem to be cracked pistons, yes thats correct!. can you confirm what would cause this as im on borderline of pulling engine and replacing whole engine or doing a head/piston replacement on the two offending ones. Guidance is appreciated. image and video is down one of spark plug holes. See how piston wobbles in the Vimeo link.

[TibetanT]

What was in the oil when you drained it? Anything metal, shavings...etc., etc..
Just wondering.

Good luck

[stownsen914]

Its a little hard to tell what we're looking at there. It looks like an unusually large gap for a space where there isn't much extra space to have a wobble like that. Granted, not sure what else you'd find looking down the sparkplug hole ...

[thetorch]

the OP posted this on Rennlist and probably hasn't been back here yet. He determined it was not cracked pistons but a trick of the boroscope camera and the oil reflection.

https://rennlist.com/forums/911-forum/1311856-1977-2-7-cracked-pistons-help.html

[Speedy Squirrel]

That is bizarre. I have a similar low dollar boreoscope, but I have never screen anything like that. Had me fooled.

[stownsen914]

OK. That makes more sense.