piston damage (new problem)
 

While doing valve job on my 51 8ba I discovered this damage to #6 piston. It was not there 10 months ago when I had the head off. Never heard anything and the compression was good when checked before I took head off. Looks like a small piece broke off piston top edge and bounced around before being ejected. See attached picture. Not looking forward to dropping pan and removing piston to examin. Any ideas?

Re: piston damage
 

Broken top ring

Re: piston damage
 

Plus top ring groove will be totally eaten out by the pieces of broken ring. (One of which finally ate its way to the top of the piston.)

Re: piston damage
 

like the others, my guess is a broken top ring, I wouldn't run the engine any more till its fixed

Re: piston damage
 

A ring? Shouldn't be.We shall soon see. Lets see the head.

R

Re: piston damage
 

What does the wall look like?? That does not look exactly like the broken ring problems I have seen over the years. I wonder if something came from a valve or port or through a valve and port? I guess anything is possible so it is good that you have the engine apart and can get it reviewed.

Re: piston damage
 

Sure looks like the the mark on top of the piston was made by whatever was (forced ?) out of the hole on the opposite side. It's a mystery.

Re: piston damage
 

picture of cylinder head--cylinder wall looks clean with a couple of very slight vertical scratches on the bottom side where it corresponds to the piston damage. this does not show up in a picture.

Re: piston damage
 

Cylinder head looks as one would expect it to look considering what happened, but no matter how one tries to get around it, the engine should be dismantled to properly check and correct the problem.
If left as is, there is the possibility you could loose the whole engine.

Re: piston damage
 

looks like damage done by the ground electrode that has broken off a spark plug. Marlon

Re: piston damage
 

This is a classic long term broken ring result. When the piston is pulled the ring groove will be well hammered as previously stated , by other people.

Re: piston damage
 

Had that happen to me back in 1964, when I drained the oil I found broken rings in the pan.

Re: piston damage
 

Thanks for all the advice, I will drop pan and remove piston next week and report back to you with the results and pictures. In reinstalling the valves I'm having a problem pulling the intake valve guides down to install the horseshoe clip. The rubber seal around the guide is the problem, even with the proper pry bar they won't budge, any tricks I could try. Maybe i'll start a new thread.

Re: piston damage
 

I don't think you will find a broken ring that caused the damage.the more it is looked at it looks like foreign object damage (fod)

R

Re: piston damage
 

You can try a little lube on them, or just use rtv instead of the seals.

Re: piston damage (new pictures)
 

I like the idea of the RTV is that an acceptable substitute for the rubber seal.

Re: piston damage
 

RTV will work just fine. I think if you had a broken ring, the bore would be pretty well scratched up

Re: piston damage
 

I tend to agree. #6 is right under the carb, any chance a washer or screw went missing?

Re: piston damage
 

Only on the intakes, I think the exhaust would get too hot.
I just pulled apart a 350 I did ten years ago, had rtv on the intake manifold ends instead of gaskets. Was still holding just fine with no leaks.

Re: piston damage
 

Recently had a top ring break. Heading for a car show when all of the sudden I got a rattle sound from the engine. Shut it down, had AAA carry the truck home. Same damage as you showed on top of #5 piston. Pulled the piston and found the broken ring, Just went ahead and replaced all the pistons while I had it opened up.
Good news, no cylinder damage. Sad news is that when I had my machinist do some work for me 5500 miles ago he said that the piston were "about" ready to need replacing. Well no $ put that on hold...Guess what now I have new pistons, rings, gaskets and a "woulda, coulda, shoulda" moment to add to the list.
Those horseshoe clips are a "learning experience". get the claw on your bar to catch the lower portion of the valve guide. Push up on the bar just enough to expose the clip groove and get the clip started in the groove enough to get the valve guide to remain visible. Then gently tap the tab on the clip with a small hammer. It should slip into place and seat in the recess. Because my hands are size 90 and the space size 10 I use a long pair of needle nose pliers to initially maneuver the clip into the slot. You'll get it.