heavily pitted combustion chamber...how to fix?

[jonaswintermans]

hi all,

Rebuilding my 1973,5 911 2.4 CIS, (using wayne's book) i ren into serious pitting in the combustion chamber of one of the heads...such a set back, i wonder if it's too much to ignore, and if so, how to fix it or deal with it....any help is much appreciated. I am rebuilding to a high standard so temporary fixing with pastes like JD weld is not really an option i guess. Note that valve stems and seatings have not been replaced but will be in any case, makes more sense to do that after fixing pits. (i used light glass bead blasting, i suppose the material where pitting came up was very weak). just for the fun of it a also attach the "before" picture of this head, shocking...

questions i have: 1)if i sand/polish/mill it away, do i affect compression ratio or geometry too much? 2)if i can find a welder, do i risk warping the heads? 3)if i buy a replacement head, i risk having a rebuilt one, i have one shallower head than the others so cam tower/chain housing will not fit.


thanks, jonas

PS the root cause of this i don;t know (maybe not important), can be either 30 years of grease soaking into the aluminium, or oil i used for rusty nuts that i applied for a week or 2 that turned out too agressive...

[Henry Schmidt]

There are ceramic coatings that are applied to the chamber to control thermal dynamics. Techline can do it for you.
https://techlinecoatings.com/

If that isn't your preference, we have a few sets of the 2.4 CIS heads on the shelf. We don't use them so they're not very expensive.
You can buy one or a complete matched set. We can also sell you a completely restored set. New valves, guides, studs, set spring height, etc.

[aturboman]

Hi Jonas that head is junk. You should be able to buy a single good used head pretty easily if the rest are not corroded and damaged like this one.

If the rest have similar damage then a replacement set as Henry mentioned is the way to go.

Long term improper storage coupled with moisture is not a good friend to these engines.

[racing97]

As long as you can have the heads surfaced with a reasonable amount of material removed and the deck cleans up and the valve seats can have the angle generated
once again with out burying the seat into the head, you are good to go.
All the heads will need to be surfaced as a typical valve job would be done as well.
Carbon will fill the chamber and the engine will never have the chamber under performing.
Cause was water sitting in chamber
regards

[911pcars]

Originally Posted by racing97

As long as you can have the heads surfaced with a reasonable amount of material removed and the deck cleans up and the valve seats can have the angle generated
once again with out burying the seat into the head, you are good to go.
All the heads will need to be surfaced as a typical valve job would be done as well.
Carbon will fill the chamber and the engine will never have the chamber under performing.
Cause was water sitting in chamber
regards

Agree. You can resurface the combustion chambers, even polish them to reduce carbon buildup (do it evenly to all), then machine the sealing surface as suggested. It'll also increase/restore the compression ratio.

Sherwood