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Cylinder Head Exhaust Stud Repair


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2:25 AM
Mar 20, 2011
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I'm running a set of 452 iron heads on my motor. Years ago, I removed the end exhaust studs on both heads (goes into coolant passages) for header clearance (big tube Hookers, which I no longer have) and used header bolts with RTV on the end stud (now bolt) holes on both heads....worked for years. Now, I've developed a small coolant leak on the passenger back header bolt. I've tried to re-seal it 3 times & no amount of RTV will seal it. I "think" the standard SAE threads in the cylinder head have worn & are "sloppy" (not yet stripped, but getting there).

How do I fix this short of removing the head?

I've considered draining half the coolant, unbolt & pull the passenger header back, scrape off all the old RTV, degrease/dry with carb cleaner & install a factory exhaust manifold stud in that hole with some epoxy? Does anyone have a better idea? My local exhaust shop won't touch it. THANK YOU!
Pipe thread sealant. Longer bolt.
If it is indeed rusted to the point of a wobbly faster, you may need to tap it one size larger. I would say helicoil it, but I don't know how that would hold up in a wet hole.
I would find the next larger size Metric thread size and re-tap the hole.
Try and match the pitch of the american thread to the metric thread. You
won't be going too deep, and you will clean up the hole nicely. No one
will know except you and me!
I have 3/8" coarse threaded inserts but you have to drill it out to and Tap it to 1/2". Not real easy to do in the car. I did buy a special bit to help drive them in and used loctite. These aren't like a helicoil..you have to tap the hole larger. Tapping can be a challenge. I had two go easy and one that stunk.

I may have to try pipe thread sealant first. The RTV worked for 20 yrs with the headers on/off a dozen times (fyi). I first thought about the metric drill/tap (no skin off my nose), but it’s the back stud on the passenger side, so I only have about 4”-5” clearance and I don’t own an angle drill….it would need a short bit too AND maybe have to drill out the hole in the header flange (probably have to take the header completely off). I already have one of those “big inserts” in one of the end exhaust studs….not sure which one of the four though. That would be the best fix, but I’d have to take the head off.

Any other ideas or just pipe sealant? And, is that pipe sealant on my header bolt in the loose hole? Or, on a stud that I install?

Also, what about using a stud now that the cast iron hole/threads are getting worn???
Well draining half the coolant is a good start regardless of what else you attempt!

Next I'd pull out the stud or bolt and see what it looks like. It would be odd for the threads in the head to rot and not the stud as well.

Next, get in there with the appropriate tap to clean out whatever crud is in there. A small wire bottle brush in the hole afterwards would really help - as well as compressed air and brake cleaner.

With a "supposedly" clean hole I'd screw in a CLEAN bolt to see how snug it fits - does it wobble, etc..

Unless its ridiculously loose I'd give it another chance with plenty of THREAD SEALANT this time. If you're using a stud, use one that has both coarse and fine threads and thread it in till it bottoms out - this pretty much ensures its sealing one side of the threaded surface and the thread sealant is filling the rest of the gaps.

ONLY if this fails would I then go to any trouble of drilling, installing inserts or any of that other stuff. Try the simplest stuff first !!
Going with the Metric tap, you won't need to drill it out. It's just a hair larger and with the threads being loose now
I think it would be the esiest.
I would try thread seal tape. Had a pesky one years ago and that fixed it.
I would clean it well, use a teflon paste sealer, install a stud, tighten and let sit for 3 days. Probably will not leak.
If you're ok with using a stud, I have a permanent fix. Which means the stud is in there for good.
Clean it good like stated. Run a correct tap to clean up existing threads. Permatex high temp thread sealant, the hole is next to the exhaust, liberally on a correct stud, and in the hole. Screw the stud in by finger till it bottoms out. Let it set for a few days. Torque the nuts when you reinstall the manifold. Try and do this right the first time. I had a leaker after drilling out a broken stud, went a tad off course when drilling out the stud, but barely. Hasn't leaked since.
Good luck
What Bird said. This stuff works. Had a leaker on my Bee, used this. Never leaked since in 15 years. I used a thread chaser instead of tap, no metal removal.

Permatex 59214 High Temperature Thread Sealant, 6 ml Tube, Pack of 1 https://a.co/d/3RnPPnK
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Napa sells a lead based pipe thread anti seize & sealant used for high temp / High pressure hydraulic applications.
Drain down the block under the hole level , clean the silicone out, dope up a stud with that napa sealer and assemble, let it set overnight before adding the coolant.
Going with the Metric tap, you won't need to drill it out. It's just a hair larger and with the threads being loose now
I think it would be the esiest.
I recently had two heads with worn and enlarged holes. I used inserts, but next time I think I would go the metric route.
This may sound strange but it has worked for me many times, and is easy ! Drain water down below hole ! Dry and clean it nicely! Run a tap in it to chase threads somewhat! Apply the long cure J & B adhesive to the clean dry chased threads, apply vasoline to the threads on the stud liberally! Let cure couple of days! Put headers back on ! You now have fresh threads in the head ! !
An M8 X 0.8 tap should do it!
An M8 x..8.... Don't know that I've ever seen one.... The normal M8 pitch is 1.25... The super fine M8 is 1.0....
Plus M8 is very close to 5/16 but being a 452 head I'm assuming this is a Big Block.... Exhaust bolt holes on Big Blocks are 3/8-16.... I thing the metric bolt of choice would be M10 x 1.25... It would work but the potential for a coolant leak would concern me... I think I'd be looking at a thread repair insert like the easy lock posted above...
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