2003 Discovery II

Replacing the head bolts and all was going well until it came to replacing the exhaust manifold, passenger side.

It wouldn't quite line up and was a bear to shift into place even with a helper and one of the bolts was forced in at a slight angle and has stripped the top 3-4 threads in the head.

We immediately stopped once my mate told me it felt "tight" as it was being screwed in and close inspection shows the first few threads have gone.

Now the bolt will not go in straight at all and it looks like I will have to tap a new thread.

Anyone had a similar experience and can share the best way to fix this?

Ideally I'd rather not have to remove the head and bin the brand new gasket & head bolts but if I have to so be it.

Is it possible to tap the thread in the head as it sits?

Lastly, what thread pitch will I need.

Thank you!!!

 

A tap isint that bit, you can do it still on the truck.
But yeah, you are going to need to tap new threads.

 

you can try to tap new threads, but if they are buggered it's likely they won't match. I'd try a thread chaser before a tap and make sure it goes in straight.
I think there are chasers that are smaller than the needed diameter, you insert them, then expand them in to the threads, then back them out so they are starting in a good threaded section. I may be dreaming it, but I think I saw reference to them somewhere ages ago. A good machine shop should know if such a thing exists or not.

If you can't get them fixed, really your only alternative is a helicoil insert.
Amazon.com: Helicoil 5546-10 M10 x 1.5 Metric Coarse Thread Repair Kit: Automotive
I can't remember the size, if no one else responds soon I'll go check a head in the garage.

FWIW, I always use a thread chaser on things like that as part of the prep work.

 

Thanks for the replies.

My concerns with trying to re-thread the hole in situ is ensuring the tap / chaser goes in dead straight. Not easy when you are bending over, reaching and driving it sideways!

If I use a tap / chaser does anybody know the thread pitch of the bolts?

Thank you!

 

** Update **

I got in touch with Paul at PTSchram Land Rover. I bought the head Gasket Kit from them at a great price and he offered the following advice:

"Remove all of the exhaust manifold bolts from the head. Carefully remove any loose material from the messed up hole.

Using a 3/8-16 tap (ideally, it should be a re-thread tap) gently try to grab a good thread and try to restore the threads.

When we've got a good thread in the one that was messed up, run a lightly oiled bolt in the hole, but do not tighten. Insert the rest of the lightly lubricated bolts partway. When they are all inserted and the threads engaged, THEN begin torquing them down the rest of the way, paying particularly close attention to the one that you had the problem with."

I went to AutoZone & rented their thread restorer kit. Using the 3/8 as suggested by Paul with a ratcheting wrench on the end, I was able to apply thumb pressure to keep the tap square in the hole. The net result result was a nice newly threaded hole and a complete success.

On re-fitting however, I unbolted the exhaust manifolds from the exhaust pipe which made the whole re-assembly process a breeze.

Paul was also able to get me the two exhaust manifold to pipe gaskets I needed. Without his advice I would almost certainly have pulled the head and then had to buy another head gasket & head bolts. He actually talked me out of a sale! How's that for customer service?! Thanks again Paul!

Anyway, time to move on with the rest of the re-build but thanks to all who replied.

 

I'm glad I was able to talk you back from the ledge (I've been to the edge, stood and looked down, lost a lot of friends there baby, got no time to mess around).

I'm sure that at the time, it seemed as though there was no way out, but a deep breath and steady hand will get us through many of these situations.

I'll have your manifold gaskets in tomorrow's mail. I've been hittin' it HARD trying to get this engine done so the lady what owns it can get home tomorrow.