Helicoil for Thermostat cover

[Whee]

Hello all,

Lots of familiar faces here.

I have 2 bolts of the three that hold the thermostat cover onto the head that won't tighten. I tried new bolts, so the head threads themselves must be stripped.

I assume the right approach is to helicoil? Never having done that before, any tips or tricks? What size do I need? Will any brand do, or do you have recommendations?

P.S:  Why stripped? I'm betting it's to do with the engine steady bar that connects to them.

Thanks in advance!

[MiniDave]

Helicoil is fairly easy to do, the size you need is to match the stud or bolt that's in there now, or you could go up a size to get more strength.

The kits usually come with the drill bit you need, or they'll say what size and you can buy one where you get the kit. I think there's enough meat on the thermostat housing and in the head that you could go up to 5/16 from the current 1/4".

The procedure is you drill the hole slightly oversize to clean out all the old threads, then tap the hole to fit the outside diameter of the helicoil insert (the tap comes with the kit, as it's a unique design), then you thread the insert into the hole, that gives you a threaded hole back to the original size, and the SS threads on the insert are much stronger than the original material.

[MiniDave]

If you have a scrap piece of aluminum, UHMW or even hardwood, you can practice a few times first before you try it on the engine. On your practice tries, just don't break the tang off at the bottom of the insert, just thread it on thru and reuse it for the next practice. Once you get the hang of it, then do the cylinder head.

The only thing even a little bit tricky is to make sure you're drilling the hole straight, other than that it's a doddle once you've done one.

[John Gervais]

Dave, have you ever had the screw hit the broken off tang stub and then the screw tries to drag the insert through?

[MiniDave]

No, the tang is scored to break off such that it should not be possible to catch the end of the insert with the head of the screw/bolt, unless when they break it off they bend the end of the thread inward. Break the tang off with either an upward and/or downward motion, don't twist it.

[MiniDave]

Helicoils come in different lengths, just get one that's the appropriate length for the hole you're working with, and insert it till it's flush or just below the surface.

If the only one you can get is too long, you can take an angle grinder and grind off the part sticking up, just be careful not to nick the mating surface.