cparker688

Question,

I'm having to replace one of the mounting studs for the manifold as it broke off during removal. I've looked at other posts that said it's a 3/8-16 but the kit available online for replacement parts lists the stud as a 3/8-24. When I enlarged the picture of the kit it looked like the two ends of the stud had different thread sizes. The nut I have that came off the stud as well as the part of the stud that was broken off is definitely a fine thread. Is it possible that the end of the stud that sticks in the block is a 3/8-16? From the kit picture it looks like the fine threads would go into the block as it has a square boss on that end of the stud. (I'm trying to get the right tap and am stuck).

http://www.rockauto.com/catalog/moreinfo.php?pk=1027940

jeep3200

I have not had to remove the exhaust manifold on my jeep yet. So I do not have an exact answer.

Based on the picture of the kit you attached and your description of the broken parts. The coarse thread is what is in the head and the fine thread is what the nuts go on. The torx end of the stud is what you install the stud into the head with. So my best guess is that you need the 3/8-16 tap.

5-90

3/8"-16 into the head, 3/8"-24 under the nut.

There are good engineering reasons for doing so, but there's not enough strain to apply in this case. Replace with 3/8"-16 full length, and call it good. That's what I do when I have to replace a stud - usually cut a 2" or so length of 3/8"-16 brass rod and LocTite (#242) the thing in place Replace the nut with a 3/8"-16 UNC piece, and reuse the dished washer (it's important.)

viperjmb

I am trying to find the full specs on these bolts also, so i can order some higher quality fasteners for my header install. Can someone tell me (or point me in the right direction) the length and thread of the bolts and length and thread of the studs (both in the head and out) as well as any other info.

5-90

Ref post #3 - everything you need is in there.

viperjmb

Everything except lengths.....good info though.

5-90

You sure about that? I just checked - I mentioned how long to cut the threaded rod...

hankthetank

http://www.stage8.com/amc.html

Sorry don't know how to hyperlink from my phone. This kit retails here for $43 can. I've already ordered one...

hankthetank

Oh it worked...cool.

viperjmb

Yes. You mentioned overall length. I was looking for bolt length (under head length) and threaded length in the head on the stud.




those are perfect. Anyone install these? Have reviews or comments? Nice find!

5-90

If you're cutting your own, OAL is all you need. The reason I don't give the "in-head" length or anything like that is quite simple - it's really not necessary. I have yet to find pre-made studs in brass or bronze to be readily available to me locally, so I cut my own. The thumb rule for thread engagement into a casting is 1x to 1.5x nominal OD of the thread - for a 3/8" thread, that means 3/8" to [3/8 = 6/16, 6/16x1.5=9/16] 9/16" of thread engagement into the casting (more is just "along for the ride," less is weaker and should be avoided.)

The screws for the manifold are, I believe, 3/8"-16x1.25" hex head capscrews. SAE5 is preferred over SAE8, and brass or bronze (I use silicon bronze) is preferred over carbon steel (I've gone into the reasons for this preference before, so it's out there.)

Be sure to retain the little dish-shaped washers under the screw heads, or replace them with actual Belleville spring washers. They're there for a reason! (And a very good one...)

There is a version of LocTite formulated for use with exhaust heat - it's either #271 or #277. Use that - or nothing. Standard LocTite will break down inside of a week and do you no good whatsoever, and using Never-Seez is really not preferred here (since it's already a good idea to check torque on manifold screws annually, there's no reason to make it easier for them to move!) Torque to 19-21 pound-feet for all fasteners - stud nuts and screws. I also like to apply a thin layer of RTV copper on both sides of the manifold gasket before it goes in - this helps prevent gasket burn-through as the screws work loose (I find that three or four screws at the back are invariably loose after a year's service.)

viperjmb

^^^^^ excellent info. Thanks.