Valve cover bolt thread stripped

A helicoil tap is going to be bigger than the bolt hole in the valve cover. You could maybe get away with it by drilling the valve cover hole to that size first but I do hate bodges. For instance a 6mm helicoil tap is 7.3mm diameter and an 8mm tap is 9.7mm diameter. The hole in the cover is only going to be a gnat's willy bigger than the nominal bolt size. Maybe 6.5mm for a 6mm bolt and 8.6mm for an 8mm one.

IME a stripped thread in ally, can usually be tapped to receive a Helicoil without drilling. Easier if it is pre drilled, but if drilling is difficult for some reason, one can be fitted without. I've done it many times.

I'd love it if it could be done in situ, but don't

Quite easily in fact. That is if you don't mind having a very slightly modified valve cover.

Assuming the valve cover is ally, you tap both the cover and the head with the Helicoil tap. The Helicoil insert is then screwed through the cover and into the head. Providing it finishes up entirely below the surface of the head, all you're left with is possibly a shallow thread in the clearance hole in the cover, which wont cause a problem, but is it that inconvenient to remove the cover?

And FWIW if you want the best, use genuine Helicoil inserts. They are much stronger and better than, Recoil, V-Coil, or any of the other look-alikes. Mike.

So do I, but if the valve cover was particularly time consuming to remove, it wouldn't worry me too much to bung the tap through the clearance hole in the cover into the head, 'without' drilling the cover to clear the o/d of the tap. Not a real bodge IMO. Having a shallow thread in a clearance hole in the cover wouldn't affect the integrity of the cover, or interfere with any future work on the engine.

Having said that the last head I did that had a stripped cover thread, I not only Helicoiled the stripped hole While I was at it, I helicoiled the lot. Even the ones that were OK. A job well jobbed IMO.:-) Mike.

I'd say so. But into ally you can often get away with simply tapping the new thread for the helicoil without drilling - which can be handy where space is limited.

I doubt the clearance hole in the cover would be large enough for the helicoil.

If you leave the valve cover on how do you get rid of the swarf from drilling/tapping, or is alloy soft enough to not damage anything in the engine?

Ah yes, the good old Bavarian Tractor Works.

It should all end up on the outisde. (If it's a spark plug you put the piston just below TDC, pack a lot of grease down the hole & when you've finished taping turn the engine so the grease pushes it out. Assuming you're bodging old vauxhaul engines whilst you wait for the camshaft to break)

If the cover is still on there'll be no route into the engine. The threads will almost certainly be 'blind'. But the normal way is to grease the tap - the swarf will then stick to it. Remove, clean and re-grease a couple of times while tapping.

It is after the tap has been through it and into the head. Mike.