So, I replaced the chain on dad's 92 300D 2.5 a few months ago. Had a heck of a time getting the new tensioner to seal and threads in the head looked questionable. The motor looks like someone has had the head off at some point and galled up the threads.

However I got the tensioner moving in and out smoothly, no binding. New aluminum seal, and got it sealed up.

Motor developed a manifold leak, I guess I had never noticed but 3 exhaust studs were snapped off in the head. Unfortunately I had to remove the tensioner to get tools in to extract the first broken stud.

Since then I cannot get the tensioner to seal again. It appears the tensioner is going in fractionally crooked because the seal doesn't visibly deform on the section where it leaks. Tried a brand new oem seal ring and it still leaked.

I've cleaned all the oil off of everything and made sure nothing is in the threads (what is left of them) and have one genuine seal left (they are $.80 I can get a bunch more if need be) but I didn't know if anyone else had had issues with damaged threads or a non-sealing tensioner.

The tensioner will thread in and out by hand which is a decent sign.

Unfortunately I am left to deal with whatever went down when the head was off XX years ago and there is no good way to repair the threads if that needed to go down. There is an oil passage in the threads to supply the tensioner so a heli-coil isn't a good option really, and even if it was, it would have to be done with the head off, because if your insert was crooked the seal would not crush evenly.

I think I can work with whatever threads are left, but I'm looking for any tips or insights to sealing a questionable tensioner.

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