Manifold Replacement

I have used 35 pound torque for over fifty years with no problems. While i keep the plane across both manifolds evenly, I torque the inner two first then the outer two and in steps to 35 pounds. I think many torque to 55 pounds because they are the same size as head bolts/nuts. But you are not clamping a head against compression.
 
Back to the muffler-manifold seal: I use a thin bead of Permatex 80355 Muffler and Tailpipe Sealer. It goes on like toothpaste and dries sort of like cement. Each time you remove and reinstall you need to clean both surfaces thoroughly, I chip away what I can and use sandpaper to smooth out the little bits I can't chip away. On the clamps: I wire brush the interior surfaces of the clamps and then sand to get them as smooth as I can so they will slip over the manifold and tailpipe during tightening. I also use a spot of copper anti-seize on the clamp bolts.

I loosely install the tailpipe in the rear clamp, then lift the muffler with a floor jack and gently rock it into position dry. Once in position I drop it slightly, wet the muffler and the manifold sealing surfaces, apply the goop to the muffler, gently lift and squeeze the joint, wipe the excess and apply the clamp. Tighten and pin the rear clamp and it's ready to run.
 
Benson said:
I measured several originals:

.200 to .215

some old rusty repros have slightly larger OD and .185 thick.
Click to expand...

OK, if we are measuring at the edge of the washer, out of 10 manifold washers that looked potentially original, I had one that was .215" and every other one was thicker than that. Most were around .250 and the thickest was .289.

Anyone else want to take a sample?
 
I used to have a 1978 Ford F250 with a six cylinder which also had the cupped washers on the manifold. I think they were maybe a little smaller, but I don't have the P/U anymore to check.
 
alexiskai said:
OK, if we are measuring at the edge of the washer, out of 10 manifold washers that looked potentially original, I had one that was .215" and every other one was thicker than that. Most were around .250 and the thickest was .289.

Anyone else want to take a sample?
Click to expand...

I measured a couple that I assume are original at .285".
 
This slide shows how the concave washers are installed on the manifolds. I made this slide just for you all.
 

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The concave washers also work as a bridge to even out slight differences in the thicknesses of the manifolds. The washers will **** slightly to accommodate the flanges being slightly out of plane.
 
nkaminar said:
The concave washers also work as a bridge to even out slight differences in the thicknesses of the manifolds. The washers will **** slightly to accommodate the flanges being slightly out of plane.
Click to expand...
I think this function is more significant than any “spring” they may add to the connection. If “spring” was the desired effect we would use cut lock washers. And note that it’s the backs of the flanges that NK is talking about, these will not compensate for the front (sealing surface) being out of plane since the two manifolds are a bolted assembly.
 
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