Cylinder Head Helicoils

[1972_911T]

I have just spoke to my head guy and he has informed me my heads need three helicoils on the exhurst studs, will this cause me any issues I should be aware of I,e weekness of the studs? do I need special studs or will the standard studs fit the helicoils?

Thanks Steve

[ChrisBennet]

Standard studs will still work.
Maybe it's overkill, but I'd prefer Timeserts.
-Chris

[cgarr]

Dont they make oversize studs?

[sammyg2]

A better way to do it would be to use stepped studs i.e. standard size where the exhaust nuts go on, and the next size larger where they go into the heads. I can't tell you where to get them off the top of my head, but I know they are out there. Maybe some of our gurus like Tyson or Henry or JW or Grady can help.

Heli-coils are not as strong as solid inserts, but also don't require as much metal to be removed. They can also back out of the hole when the stud is removed.
I don't like heli-coils and only use them as a last resort.

[ChrisBennet]

I'd be surprised if stepped studs came in the correct exposed size. Heck it's hard to find normal studs in that size.
My "head guy" warned me about stud quality in this application. The studs he uses (which look like or are the Porsche ones) are a higher quality than some that are available. (He sent me some for free once.)
A Timesert is also smaller in diameter than then next stud size up i.e. it takes a <10mm tap AFIK
On an obsure note, he uses stainless Timeserts in heads.

-Chris

[DonE]

I used the stepped studs for about a year with no problem, then when I had the head ported, I had the machine shop install time certs.

On a not so obscure note, nearly all the studs (stock except for one) were not perpendicular to the exhaust port. The engine had 140,000 miles on it and the header was difficult intalling. Big difference now.

[cgarr]

someone should make a .25mm .010 over stud, they are made just for this reason, or cut some on a lathe.

[Henry Schmidt]

When studs are broken we do our best to remove them without the need for an insert. This is quite often possible when a mill is used to remove the stud. We have a special fixture just for exhaust studs. But when we are unlucky Time-Serts work well and offer little or no down side. We use them all the time and if for some reason you need to replace the stud you are removing a stud from an insert not bare aluminum. I believe that a Time-Sert is a far better solution than a step stud.

[john walker's workshop]

get one of quiet boom's custom drilling jigs. it allows you to drill out the stud dead center and then you can remove the threads with minor effort and have a standard size hole. timeserts rock if you have to use them.