Anyone know what the threads are in the head for the intake/exhaust bolts? I have a broken one and I know they break easily anyway... I want to upgrade to to some grade 8 or something....

 

Pull one out and bring to the store. Also using Permatex Anti-sieze will help in the future with repairs. I buy the big bottle at the parts store. About half gone now. Almost everything gets a coating of anti-sieze for me. Within reason of course.

 

3/8-16x1.25", 11 pieces. There are also three studs with nuts on them that hold the corners of the manifolds but they're a different thread pitch than the rest of the bolts, but I don't know what they are.

The stock torque spec for these bolts is 30 ft. lbs., which is in line with a grade 5 (mine had grade 8s on it when I got it but they were all loose).

If you keep it grade 5 I would skip the anti-sieze and torque them in dry so they don't over-stretch due to lube on the threads. If you go to grade 8 then go with anti-sieze and torque to 30 ft. lbs.

BTW, if your Jeep still has them, keep the little cup-shaped washers that are already on the bolts. Don't switch to new flat washers. The cup washers let the manifolds expand and contract without over-loading the bolts.

 

Thanks Blasto!

I could have figured it out like Diskman had suggested but I didnt want to pull one out then drive to the hardware store. It's my DD.

My front one broke, I think it's a stud but I dunno

 

1) 3/8"-16x1-1/4" should be what you want.

2) Do not use SAE8 - use SAE5. SAE5 will retain strength longer than SAE8 (verified experimentally when I was in school and had access to heat-treat ovens. SAE8 will anneal much more rapidly to a "soft" condition than SAE5.)

3) If possible, get brass or bronze screws. Copper and its alloys respond to heat-cycling opposite iron and its alloys - it will get incrementally stronger instead. Look for a local Fastenal.

4) Make sure you reuse those bowl-shaped washers under the OEM heads, or replace them with actual Belleville spring washer (also available from Fastenal.)

5) Use LocTite #271 (formulated to resist exhaust heat - or was that #277? I'd have to check) or don't bother - no other grade will hold up.

6) If you use never-seez, torque to 9-10 pound-feet instead of 19-21 pound-feet. This is to accommodate the lubricity of the never-seez, and should get you roughly the same installed tensile preload (which is important, in this case!)

 

Wow, Thanks 5-90 That's the exact info I was looking for!