stripped spark plug threads

[OldRiverine]

My boat engine is a '63 Gale Sea King Model No. GG18805A and the first time I ran it, only one of the two pistons were firing. When I pulled the plugs, one had thread shavings which concerned me of course, and stripped when replacing it. I've used heli-coils successfully in the past on a car engine, but wondered if there would be any reason I shouldn't on this. I assume it's not an aluminum head being 43 yrs. old. Otherwise, I suppose I'll be on a quest for a replacement head.
As usual, thanks for your help!

 

[JB]

Re: stripped spark plug threads

Yes, it is an alloy head, and helicoils are not the best way to fix stripped plug holes.

The steel helicoils mess up the designed heat transfer rate from plug to head and the plugs do not work well.

There is a threaded insert sleeve called "Time-sert" that is aluminum and has very close to the stock heat transfer characteristics. To use it you drill out and thread the hole for a larger thread (like with the helicoil), then install the time-sert with a special tool (can be rented) that expands it to tightly fit.

Used to use them on stripped Corvair heads. Worked like a new head.