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MG MGB Technical - stripped threads in Aluminum head

Looking from the drivers side 9of the car, second bolt in that holds exhaust and intake is stripped. This is an aluminum head. I am hoping I can repair this my self with out the removal of the head from the engine. Any tips or helpful hints?
Peter Murray

Peter,
No problem - just use Helicoil inserts. Either buy a kit and do it yourself (it's simple) or take it to a shop.

You could tap them out to a larger size, but the Helicoil route keeps everything standard.
David
David Overington

The repair is going to involve aluminium chips. Whether you have paid your gravity bill or not, some of those are going to wind up inside the cylinder, although heavy grease on the cutting tap will help along with cutting a few turns, removing the swarf, applying fresh grease and repeat. Safer to remove the head, but much easier not. Yes, helicoils are one of the greatest inventions of the 20th century.
David "helicoils; collect them all!" Lieb
David Lieb

Pete, David is right about the chips, but you can reduce the problem of getting anything in the engine if you turn the engine over until both valves adjoining the bolt are closed and then just before you start drilling or taping shoot some aerosol shaving cream into the ports. This will prevent the chips from getting in to far and is easily removed with a shop vac when you're done. Works great in water passages in a block surface if you're working on a head stud as well.
Bill Young

"David "helicoils; collect them all!" Lieb" LOL I love the way you always think of new quotes to put in your name! They always give me a chuckle.

Have you considered using araldite to hold in a new stud? I dont know whether that would work or not but I thought it was worth mentioning.
Ross Kelly

Hi Peter
Use helicoils mate it's the only way to go and you end up with a steel thread instead of aluminium and the outside of the helicoil is a size bigger in diameter than the original stud size giving it a better grip in the alloy. When you refit the stud in the helicoil put a smear of grease on the thread of the stud'this will stop it winding the helicoil out of the head if you ever have to remove the stud. Also an easy way to stop getting any rubbish in the ports etc while you are doing your doctoring is to simply tape up the face of the head with masking tape and cut a little hole where you're working. Blow the shavings etc away when finished then remove the tape. Hope this helps Gary
Gary

I recommend removing the head and helicoiling ALL threaded holes; it is standard practice on things like aircraft, for ALL threaded holes in alloy parts, for good reason.

If you screw up the helicoil installation, you will be in a pickle. It is FAR easier to remove the head so that the drill/tap/install can be done on a proper drill press or mill, than it is to destroy the head by drilling cockeyed or through the casting in unapproved directions. Even if you get the insert installed OK, it is most disconcerting to find that the studs are no longer square to the face, and the mating parts won't fit over them, and the stud is pulled cattywhompus by the nut.

Correctly drilling threaded holes oversize is not easy; the drill bit will grab and suck itself into the part in very uncontrolled ways. I always use made for purpose guide blocks and specially ground drills for this kind of operation, if I cannot set the part up in a machine.

Correctly installed helicoils will not back out with the stud, the threads are hardened stainless and will not seize or otherwise cause grief. You do not need to use LocTite or anything else in the hole before inserting the helicoil.

My baseline here is that if you were competent to do this, you would not be asking the question - that is no putdown, but my best shot at saving you a very expensive and frustrating lesson!

FRM
FR Millmore

I agree with Fletcher. While Helicoils are basically easy to install, they are even easier to screw up on the first couple of tries and that would really ruin your day on an expensive alloy head. As many helicoils as I have installed (and I consider myself pretty good at installing them and I have done my share that are at an angle or slightly off center), this is one I would probably turn over to a professional. Besides having someone who is much less likely to turn a high priced alloy head into junk, you have some recourse if he/she does. Cheers - Dave
David DuBois

Peter,

there is nothing wrong with Helicoils when a thread has to be renewed, but considre of UNC threads as the normal UNF are only O.K. for iron or steel.
You should also follow David's adwise and replace all threads on your head, otherwise you will be welcome by your machine shop soon again.

Ralph
Ralph

Thank you all for the replies....While removing the intake and exhaust headers i came across oil coming from a bolt hole, fourth one in from the front. Responses?
Peter Murray

Peter,

dont't worry aboit this, it is normal on most carst iron heads for this engine.

Ralph
Ralph

This thread was discussed between 08/04/2008 and 09/04/2008

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