Combustion Chamber Pitting
 

I pulled the head looking for the source of a large cloud of steam on my '29 pickup. I found a crack in the head, so nice to have some resolution there. But that's not what I'm asking about. While the head was off I noticed lots of pitting in the combustion chamber of #4. There is some pitting in #2, and very little in #1/#3. The current pistons have no damage. See picture at the bottom of this post (pitting to the left of the hand)

I assume what caused this pitting is engine knock (detonation) at some point in the past? If that's the case, why is one cylinder so much worse than the others? I would think if you had something that made one cylinder knock (too much compression, wacky timing) they'd all knock and so you'd expect similar damage in all cylinders?

https://i.imgur.com/YC6FtN8l.jpeg

Re: Combustion Chamber Pitting
 

A block I have that looks like that had cracks in the valve seats near the cylinder bore , long term slight coolant leakage, sitting without spark plugs can also cause rust pitting

Re: Combustion Chamber Pitting
 

To back up what Kurt said, a friend of mine asked me to help when he bought a Model A that had been parked for many years. The compressions weren't good and we decided it was the valves. He took the opportunity to replace the original style valves with modern ones and the cam followers etc at the same time. We left the engine in the car and removed the head. I noticed pitting just like that in number 3. I pulled the cam out, replaced the followers and guides, ground the valves and reassembled. When we started it, it ran well enough but he noticed a day or two later that the coolant level was down and there was water in the oil. Long story short, we found that the head was cracked (uncommon in a Model A_) at number 3. Clearly, it had been wet in there for the time it was parked (probably why it was parked), slowly rusting away. I had a spare head which I had checked for flat, we fitted it and away he goes - pitting and all.

Re: Combustion Chamber Pitting
 

Re: Combustion Chamber Pitting
 

That picture shows the block had been sitting with water in it for very long period of time prior to being put back together.

Re: Combustion Chamber Pitting
 

No, the head is cracked between 2 & 3. This was covered in a healthy layer of carbon when I pulled the head so I assume this happened sometime in the distant past.

Okay, thanks! Does the pitting you get from detonation look different than this corrosion pitting? Or does it rarely get that far because you really need a lot of knock to actually start doing damage?

Re: Combustion Chamber Pitting
 

[QUOTE=Ian Curtis;Okay, thanks! Does the pitting you get from detonation look different than this corrosion pitting? Or does it rarely get that far because you really need a lot of knock to actually start doing damage?[/QUOTE]

Detonation will attack the aluminum pistons long before you will see evidence of it on the cast iron surfaces of the block or head.

As stated by others, it appears that the pitting is due to water in the combustion chamber, possibly from a prior leaking head gasket.

My opinion,

Chris W.

Re: Combustion Chamber Pitting
 

I don't think detonation would affect the iron head or block. I would suggest that engine sat for a very long time in a damp environment with the exhaust valve open. Evrytime I see that kind of corrosion I think water us involved either due to a crack or poor storage.

Re: Combustion Chamber Pitting
 

Agree with you for sure!!