Hey guys-

anyone know off hand what size the exhaust manifold bolts are? (where the manifold mates to the block)

I was missing one when I got the truck, and I managed to lose another while it was apart so I need to get a couple somewhere.

 

go to an out parts store and ask them they can look it up there like 30 cents or something like that.

 

take a bolt to napa and tell them that is what you need.

 

thanks guys, but it's looking like I may have a bigger issue at hand here. The missing bolt that was gone when I got the truck is the one closest to the firewall, and from what my research on NAXJA suggests it used to be a stud. A stud that commonly snaps off...


I put a piece of wire in the hole where it goes to feel around and it only went in about 1/2 inch- thinking there maybe a snapped off stud in there. Has anyone else had this issue?

 

to my knowlege older heads dont have studs because when I done the head swap on my old 98 i used a older model head and it didnt have studs.

 

yeah alot.I used to live in Portage,Ind(rust belt)I took a short bolt, same size thread,and drilled it down the center on my drill press.screwed it in as far as I could,took my drill and let the bolt I installed guide my bit.A little heat and they usually come right out with a easyout(screw extractor).The bigger the hole you drill in the broke off stud the better chance you have of it coming out.Some times the bit will jam and I'll reverse it and the broke stud will come out with it.
Good luck,It sucks.

 

There are thirteen fasteners that retain the manifolds to the head - two (both extreme ends) or three (extreme ends and top centre) may be studs.

All holes in the head are threaded 3/8"-16 - at least, for RENIX. Later years are probably the same, just check the heads. If you see SAE "hash marks," they're 3/8"-16 (1-1/4" long, I think,) and if you see something like "9.8" or "10.9," they're metric and probably M8-1.25 (may be M10-1.5, you'd have to pull one and check.)

Yes, losing the studs is common. And, they're a beast to drill out! Get a left-hand-twist drill bit when you get your screw extractor - the drill bit may grab it (and you'll probably have to remove the head, unless you have a right-angle drill and a decent amount of patience.) You'll have to remove the manifolds anyhow - five gets you ten the gasket has "burned through" back there and can't be saved by retorquing.

Suggest you replace all of the manifold attaching hardware. Use brass or bronze if you can get it - use SAE5 carbon steel if you cannot. The OEM studs are threaded 3/8"-16 on the head end and 3/8"-24 on the nut end (yes, there is a reason. No, it doesn't apply here...) and they can be replaced with studs cut from 3/8"-16 threaded rod (I use brass, but you can also use common threaded rod, which is usually H&T to SAE5 spec.) If you use carbon steel threaded rod, be sure to coat the cut ends so it won't rust from the inside out.

When you reinstall the manifolds, apply a light coat of RTV copper over both sides of the gasket - it will help when the screws come loose. Be sure to retain and reuse the little bowl-shaped washers as well - they're actually there for a reason. If you must replace them, either use Belleville spring washers (large side toward the manifold flanges,) or use a flat washer and stack three or four "wave spring" washers between the flat washer and the screw head. Treat this point as important.

Check torque annually - loosening manifold screws is a known quirk of side-draught inline six engines.

Thread compounds - use LocTite #272 (or equivalent) or nothing. No other grade of threadlocker will hold up to the operating heat, and you don't really need never-seez there anyhow (if you absolutely must use never-seez, torque to only 10 pound-feet!)