exhaust manifold bolts

[Paul]

Why are exhaust manifold bolts hollow? Can they be replaced with solid bolts? Also, on '80's FSJs, why are the two front and two back bolts smaller in diameter than the two middle ones?

[joe]

Paul, just use solid bolts.

[Chrome]

If I'm not mistaken the bolts are hollow to allow for heat expansion. As far as the two center bolts being larger...well that goes back to when the AMC V8 was first designed and they ran out of manifold bolts so after a couple of hours of looking around Wilbur said to Bob "Here just make these work".

[Bob Barry]

They went to smaller bolts on the outer ports in '79. Why, I have no idea, but it's a PITA if you're not paying attention when swapping engines or heads.

[KYJ10]

I just got some grade 8 bolts from Home Depot. I had to grind them down some, but they work fine. Dennis

[ April 12, 2003, 10:41 AM: Message edited by: KYJ10 ]

[Joe Guilbeau]

Pull the exhaust manifolds off, and tap the offending threaded holes with a tap and die set.

We used stainless steel Hex Headed bolts, easier to torque, cleaner looking, and all of the holes are now the same size.

To some, this would not matter, for us, it bothered us, so before the engine went in, we tapped 'em.

Pretty simple, and easy to do.

[Joe Guilbeau]

Originally posted by Joe Guilbeau:
[QB]

We used stainless steel Hex Headed bolts...

QB]Doh...that should have been Allen Head SST bolts...

[Don in Missouri]

The smaller bolts would let the exhaust manifold lenghten with heat. I had one set of heads with the larger holes on all ports. I used solid grade 8 bolts. One of them spontaneously sheared off. I can only assume it happened because the manifold expanded.

Those remanufactured heads ended up pounding the valves right through the seats in 90,000 miles. I had my original heads redone and am back to the original small hollow bolts.

I have what sounds like an exhaust leak, but can't find it. I'm thinkng about getting some my manifolds planes. I'm wonders if I should get different manifolds. This is on my '86. I notice the manifolds on my '78 are shaped a little different shape and have donut gaskets where teh Y-pipe connects. My '86 just has a flange with no gasket. Would the style manifold be better? I'm nto runngin any emissions junk on mine.

[Antelope]

If you care i think i spent about $20 at the dealer buying those odd little hollow bolts!!!!!

[Cliff]

I always replace these with stainless steel. never had trouble getting them out. Grade 8 looks good too, and is stronger of course. I think SS is grade 5.

[mdill]

On the manifold you do not need GR8's, the heat will likely turn them
in to GR2's after a short while anyway. Do not crank down the outter
(small bolts) as that is just asking for a cracked manifold, the manifold
has to be able to move separate from the head between hot/cold cycles.
The center bolts can be snugged pretty tight with no worries as the
distance between them is pretty short, but the outter bolts should not be
over tightened as the this will try and keep the manifold from moving,
I say try because something is going to give it has to, the head when hot
runs at ~ coolent temp say 220 degrees, the manifold can be 900 degrees +,
so the manifold has to expand much further than the head when hot, and
somewhere something is going to have to give if the manifold and head are
pinned together.

Mike D.

[billyrb]

where the heat riser is, at the y-pipe uppers, there are flat gaskets....but what is used on the flanged side where the manifolds bolt into the y-pipes?

[Iron Horse]

Originally posted by Don in Missouri:
I have what sounds like an exhaust leak, but can't find it.I had a persistant leak after I replaced my manifold gaskets. It drove me crazy until one day I discovered I forgot to replace a washer on one of those small bolts....it was leaking around the bolt. :mad: Put a washer on it....no more leak.

[Zacko]

If you open up the end holes make sure to open up the manifold holes too. Mine where too small to fit the 3/8 bolt until I opened them up. And as far as using grade 8's goes. I worked in a muffler shop for a few years and it definitely makes a difference. If you use grade 5's you better be good at using an easy out because the next time you pull them out they WILL break. Also avoid the cad plated (silver) bolts and use the black oxide coated bolts (the black ones) Many auto parts stores (like Napa) carry bolts specifically designed as exhaust manifold bolts with the narrow shank and shoulder. There is a lot of relative movement between the head and the manifold. So you literally wear out manifold gaskets, thats why you shouldn't use header gaskets on manifolds. This is also why you need to have extra clearance for the bolts on manifolds.

[Don in Missouri]

Originally posted by billyrb:
where the heat riser is, at the y-pipe uppers, there are flat gaskets....but what is used on the flanged side where the manifolds bolt into the y-pipes?I'd also like to hear an answer on this. As far as I know there is no gasket. My Bronco has a 1/4'-1/2" slice if exhaust pipe inside the flange that goes up into the manifold. I might see if I can stick something similar in the Wagoneer joint.