I have a standard 2.1 motor and have managed to strip the 8mm thread in the engine block where the LH exhaust pipe bolts into it. The thread in question is the lower one.
I now have the option of drilling and tapping 10mm deeper into the block or increasing the size of the hole to accomodate a 10mm bolt.
I am concerned that either way I may hit a cooling or oil gallery.
Has anyone had the same problem or knows where the galleries are in this vacinity? Greg
Greg - are you talking about the cylinder head? If so, just use an 8mmx1.25 'helicoil' thread insert. You can purchase a recoil kit at any good engineering supplies shop that includes the appropriate drill bit, tap, installation tool, and about ten helicoils.
More helicoils can be bought cheaply if you ever need them.
Last time I bought a kit it cost around $125.
You will need to get the exhaust flange out of the way first.
The helicoils are easy to install by following the instructions. Just make sure you have the drill 'square' to the job, use low speed and gentle pressure, and the drill will follow the original hole. You will feel when it bottoms out.
There are no oil or water galleries to worry about.
I routinely insert helicoils into cylinder heads and generally use a stud instead of a bolt [as outlined in a recent post] as the bolts invite cross-threading. This makes it a bit harder to install the exhaust but saves the hassle of re-threading.
You will have to hacksaw a slot into the pushrod-tube protection tinware so that you can slip the bracket over the stud. You'll see what I mean when you try to refit the tin.
Use Loctite when installing the stud so that it doesn't unwind next time the nut is undone, and use copper-threaded or brass nuts so that they don't rust in place. These nuts are available at VW or muffler shops.
This job is easily within the scope of the average handyman.
Cheers, Roger [Beetle].
I'll have a look at an old head tomorrow to check it out,
Roger.
Hi Greg, I checked out a couple of old cylinder heads, and here's what I found -
The threaded hole for the lower exhaust bolt is 27mm deep on each side, but the useable thread depth is 22mm.
I experimented by drilling deeper and broke through into a water gallery after 5mm. [The same gallery exists on both sides, front and back].
I checked out a Spanish AMC head and they look identical.
So it looks like the idea of drilling a deeper hole doesn't hold water.
It might be possible to use a longer bolt to reach the undamaged portion of thread: If thread depth is 22mm, flange is 9.5 mm thick, and gasket crushes to 1 mm, that means you can use a 30mm bolt without bottoming out. Just make sure you clean out the hole and blast it with compressed air.
You might gain a bit more by running a 'finishing tap' to the bottom of the hole.
Finish off with a 2 part epoxy 'stripped thread repair kit' for the damaged section of thread. Buy one of the better brands that includes a 'release agent' so you can apply it and the epoxy to the appropriate section of the bolt, screw it in and let it set overnight before removing the bolt for final reassembly. That way you won't clog up the bottom of the hole with epoxy.
Alternatively, purchase a 10mm/8mm step stud and rethread the hole to 10mm.
I'd still go with the 8mm helicoil as it is a lot quicker and easier than any of the above, and stronger than the original thread.
best of luck, Roger.
No worries Greg. Installing a helicoil insert is not much harder than installing a dyna-bolt into a brick wall.
Just google 'helicoil installation video' to check it out.
Helicoil kits include the helicoil thread inserts, a drill bit, the tap for cutting an oversize thread, and an installation tool to screw the insert into the hole.
You may need to purchase a "tap handle" to suit the tap in the kit, if you don't already have one.
Go to Repco or an engineering supplies shop and ask for "an 8mm by 1.25 helicoil re-threading kit". There will be comprehensive illustrated instructions in the kit.
Don't forget your safety glasses! You'll need snug-fitting ones.
You will also need an electric drill with variable speed so you can drill out the existing hole. Use low speed and proceed slowly in short bursts until the drill bottoms out in the hole.
If you don't have access to compressed air, use a spray-can of carburettor cleaner to blow the metal particles out of the hole.
Then insert the helicoil as per instructions. Easy peasy.
Put it all back together and make a note in your diary that you owe me a beer around the campfire.
Cheers, Roger.