Hi Guys, I am dealing with a De-Smogged 76 that has some stripped threads in the holes in the heads. Two of the plugged holes are fine, but the other two slowly back/slide out, one of them pretty quickly. I was just wondering if I could re thread the holes just slightly larger. Two worries I have are... 1) would the larger diameter cause any problems with other parts of the head, and 2) would the little metal shavings that would come off into the head cause any possible problems or would they just eventually get blown out the exhaust?


Thanks,
Jim

Coast the tap with thick axle grease ... it will capture the shards.

I'm not sure of the thickness of the head in the air injection area, but cleaning the threads up or taping one size oversize shouldn't cause problems. I suppose you could also try JB weld on the threads and see if it would hold.

The refuse will all go out the exhaust as the hole is ion the exhaust port. Might be a good idea to have that particular exhaust balve in overlap when you drill. If you make the hole oversize, what are you gonna put in there. Assuming it's gonna remain "de-smogged", you still have to find a plug that'll go down into the hole.

The Cap'n

If you were going to put a plug in it you might consider a pipe tap as these form threaded holes that taper in at her bottom. This tends to wedge the plug in tighter as it goes in. If you want to use a conventional tap you'll like need to put a short bolt in the hole so the bottom of the bolt head can wedge against the hole. If you just screw a headless allen set screw into a straight tapped hole it will likely loosen up from the repeated heat cycles and if this happens exhaust may blow by the threads eroding things faster thus making the plug even looser.

Thanks for the reply's. I am considering using a M11 bolt with a standard thread, but I like the idea of using a tapered thread to wedge a headless bolt into the hole. Would make any future removal of the engine tin a little easier.

I will oil the tap, but I will be especially sure to check the valve position before I start.


Jim

Pipe thread cut with thick grease and valve closed, backing it out and cleaning the threads every few rotations. Then drill a hole in the head of the bolt and safty wire it to the other bolt head.

It wouldn't be a big deal if the crap gets into the port, but why trouble trouble?