Cylinder head crack repair

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Created: 2023 October 25

Updated: 2023 October 25

Thanks to Jim Pissot for sharing his experience with me. In Jim's own words and photos:

I decided to cut a small groove in the hairline crack between the spark plug hole and exhaust seat. Then a local shop welded it up and I ground off the excess, cleaned up the threads and polished the combustion chamber. The weld looked solid and there is a lot of casting between the combustion chamber and outer atmosphere. As I said, I am familiar with these repairs on thin sections with cracks into water jackets. So I am confident the repair will hold.

I had planned to stake the exhaust seat since it had endured focused welding heat at one narrow location. And, as you said, it would be a bummer to invest all that work and money only to have a seat come loose... When I replaced seats in aluminum heads back at Beck Company, we always staked the valve seats. Usually just 6 or 8 punches; or we used a special beveled chisel that staked a line just outside the circumference of the seat.

Some replacement seats had a beveled outside diameter top edge; so the staking/peening actually forms an over-lapping ridge to really secure the seat. But I went crazy with the punch because I wanted to be VERY sure; and I am the machinist AND the customer, after all... Secured the intake seat as well.

Anyway, staking or peening a valve seat is a common practice when servicing aluminum heads.

I lapped both the valves (new exhaust valves) and the seat contact is excellent. Again, I was worried about the potential hot spot where the welding was focused.

I used a 5/16 stud, a rubber coupling and a drill to speed up the lapping process. All good. Happy it's only a 2-valve head...