The Ford Barn

JRrev · 01-08-2026, 11:37 AM

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.

alexiskai · 01-08-2026, 12:08 PM

Anyone know the spec thickness of those washers? I have a couple that are thicker than the rest.

JayJay · 01-08-2026, 12:57 PM

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 · 01-08-2026, 01:58 PM

Quote:

Originally Posted by alexiskai

Anyone know the spec thickness of those washers? I have a couple that are thicker than the rest.

I measured several originals:

.200 to .215

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

alexiskai · 01-08-2026, 08:12 PM

Quote:

Originally Posted by Benson

I measured several originals:

.200 to .215

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

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?

Bill G · 01-08-2026, 08:20 PM

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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.

Bruce of MN · 01-09-2026, 08:03 AM

Quote:

Originally Posted by alexiskai

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 measured a couple that I assume are original at .285".

Bob Bidonde · 01-09-2026, 09:15 AM

This slide shows how the concave washers are installed on the manifolds. I made this slide just for you all.

nkaminar · 01-09-2026, 10:13 AM

The concave washers also work as a bridge to even out slight differences in the thicknesses of the manifolds. The washers will cock slightly to accommodate the flanges being slightly out of plane.

katy · 01-09-2026, 10:27 AM

Quote:

Originally Posted by Bruce of MN

Our thick ones https://www.snydersantiqueauto.com/p...9407&cat=41733 are spring steel? I'm no expert, but they sure look like more ordinary steel.

Take a file to one and compare it to an regular flat washer.
Maybe check w/your supplier, see what they have to say about them.

JayJay · 01-09-2026, 10:48 AM

Quote:

Originally Posted by nkaminar

The concave washers also work as a bridge to even out slight differences in the thicknesses of the manifolds. The washers will cock slightly to accommodate the flanges being slightly out of plane.

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.

JayJay · 01-09-2026, 11:26 AM

Quote:

Originally Posted by nkaminar

The concave washers also work as a bridge to even out slight differences in the thicknesses of the manifolds. The washers will cock slightly to accommodate the flanges being slightly out of plane.

Deleted - duplicate

01-08-2026, 11:37 AM	#21
JRrev Senior Member Join Date: Jan 2018 Location: Frenchtown Township, MI Posts: 1,092	Re: 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.

01-08-2026, 12:08 PM	#22
alexiskai Senior Member Join Date: Apr 2018 Location: Mebane NC Posts: 3,176	Re: Manifold Replacement Anyone know the spec thickness of those washers? I have a couple that are thicker than the rest.

01-08-2026, 12:57 PM	#23
JayJay Senior Member Join Date: Jan 2020 Location: SF Bay Area Posts: 2,670	Re: Manifold Replacement 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. __________________ JayJay San Francisco Bay Area ------------------------ 1930 Murray Town Sedan (under reconstruction) 1931 Briggs S/W Town Sedan It isn't a defect, it's a feature!

01-08-2026, 08:20 PM	#26
Bill G Senior Member Join Date: Jun 2017 Location: Walla Walla, WA Posts: 1,072	Re: Manifold Replacement Sponsored Links (Register now to hide all advertisements) 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.

01-09-2026, 10:13 AM	#29
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 6,847	Re: Manifold Replacement The concave washers also work as a bridge to even out slight differences in the thicknesses of the manifolds. The washers will cock slightly to accommodate the flanges being slightly out of plane. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.