Hello,
I have a 1978 Fiat Spider that I have been restoring for the last 18 months. I hit a significant setback today.... I have the engine back in and was installing the exhaust manifold. I have a refurbished head and installed brand new studs for the exhaust and intake manifolds. As I was torqueing the exhaust manifold to head nuts to 18 ft lbs, 3 torqued fine to 18 ft lbs and on the 4th one I realized one nut was starting to get looser. Sure enough, it pulled the threads right out of the head. I had torqued it to 10 ft lbs fine, was attempting 16 ft lbs when it stripped. What a let down, given all the time I took to install cam's, set valve gaps, install it on the engine, etc.
So first of all, is this typical of used heads? Is there anything to be done to prevent this from happening, or a way to check that a given head/thread will not strip?
Second, what to do? Can it be repaired, install helicoils or weld over and retap? Does head have to come off engine to do any of that? Should I just get a new head to the tune of ~$1K? Does anyone have a good refurbished head for sale? Trying to consider all my options for a robust solution that will not break the bank or my patience.
Thanks in advance for any advice or thoughts. Feel free to share any experiences as well as misery loves company.
Thanks,
David

Helicoil for shure

Upon further investigation, I found that the new studs I got for the intake and exhaust manifolds were short on the head side... the originals have 14-15 mm thread on the head side and the newer ones only 9-10 mm. I will get the appropriate studs for starters. Also, it appears time-serts are more robust than helicoils, so looking into that. Especially given that some of the EM/IM studs enter the valve shaft oil cavity, and so it will be important to minimize the path for oil leaks. Again, and advise or experience shared would be appreciated.

Dave, I would not be looking at a new or rebuilt cylinder head at this point, as these things can be fixed. Sometimes even with the head on the engine block, although some solutions might require removing the head. And yes, you are correct in that some of the studs go into oil galleys or the like, so you'd want to look into some sort of thread sealant when you get to that point. Not threadlocker, but something to block the oil from seeping past the threads.

Clean out the threaded holes as best you can, and you might even try a thread chaser or the like. You could use a thread tap, but I've heard that is meant for cutting new threads and can weaken existing threads which might make your problem worse. You could also try a stud with longer threads (in the head side), perhaps 17 or 18 mm. You could also just test a long bolt on those damaged thread holes to see if you can go deep enough to get enough "grip" to be able to torque to 18 or so ft lbs.

Bottom Line: These things do happen, and they're fixable. I've seen helicoil inserts or the like installed, although I have never had to use these myself. A good machine shop can give you advice, but make sure you find someone who has worked with aluminum heads.

Also, you mentioned 4 studs on the exhaust manifold, but there should be 5. That's what you have, right?

-Bryan

Can anyone identify which of the head bolts pass through into oil galleries on a 2L engine?

A Twin Cam cylinder head that doesn't have a few aluminum threads stripped and repaired with inserts has lived its life in a garage. The best exhaust manifold studs are the ones that came in the head from the factory. Perfect length and best metalurgy. They are routinely scavenged from scrap engines and reused. Ask around.

Thanks for all of the advice and encouragement that all is not lost. I have been distracting myself with other projects on the car for time to think and research. My research pointed me to Time-serts as more robust, though also more expensive. I have bought the kit, though have not yet tried to install. I have an extra head to learn on, then will install on head in the car.
As to prior posts... yes I have 5 studs on the EM, it was the 4th one I tried to torque that stripped. When I mentioned bolts through to oil passage, I was referring to the EM to head bolts, Not head to block bolts. The top 2 pass to cam shaft oil chamber. I’ll use some thread sealant as suggested, any suggestion on type? Silicone?
Other holes are just pocket holes. I bought longer threaded studs As well... 14mm Threads vs. 10mm. Extra threads are always better. I got 14mm deep serts, a little deeper than std 11.7 mm serts. Through holes are about 15 mm deep, and pocket holes are 22 mm deep. Hope to get a start on it this or next weekend. Thanks again!

DustyDave wrote: I’ll use some thread sealant as suggested, any suggestion on type? Silicone? !

Dave, I think something like this is what you want:
https://www.permatex.com/products/threa ... d-sealant/
They also make a "non high temperature version" which might work. But, given the proximity to the exhaust manifold, I'd use the high temp version.

Let us know how things progress.

-Bryan

Awesome, thanks Bryan!

I assume the sealant on both the Time-sert and stud?

DustyDave wrote:I assume the sealant on both the Time-sert and stud?

Having never done Time-sert (or Helicoil) myself, I can't offer any advice there.

Have you given up on "fixing" the problem with longer stud threads to provide more "meat" to grab into the head?

-Bryan

Bryan,
I have not given up on longer studs, I already received a full set them for the EM. However, at least the one hole has a full 10mm depth of threads that pulled out with the torquing down of the nut, so that hole will definitely need a Time-Sert. I will fully inspect all holes this weekend and determine if any others will need a Time-Sert as well. I’ll let you know how it goes...
Thanks,
David

Almost all of my exhaust studs were shot. Thanks, DPO.

I got fed up with it and tapped two of them to M10 and then used bolts with collars.

Yeah, yeah you get some tiny flakes of metal into the oil. Big whoop, it's not a Formula One engine. Based on the way the oil flows, it goes straight to the filter from there anyways. So use a vacuum cleaner while you are tapping, run the engine when you are done for two minutes and install a new filter. Problem solved.

If I recall correctly, NONE of the head bolts/studs enter OIL galleries,...I think that ALL of them enter engine coolant galleries.
I'm pretty sure of that,...
Hope that helps some of you!
Todd.