Manifold 'fat' washers.

P

pbishop

Senior Member
I am about to remount my 'new' manifolds. The car has been apart and idle for months. Does the 'flat' side of the fat washer go toward the head, or does the 'domed' side go toward the head? I cannot remember, and it is not specified in the manual I have.

Thanks, Paul
 
it should be a concave side and a domed side. Some repros had a flat side. But the better ones are cupped on one side, and that faces the block.
 
pbishop said:
I am about to remount my 'new' manifolds. The car has been apart and idle for months. Does the 'flat' side of the fat washer go toward the head, or does the 'domed' side go toward the head? I cannot remember, and it is not specified in the manual I have.

Thanks, Paul
Click to expand...
Paul,
As Pat says...cupped side toward engine. Original 'fat' washers were cupped on one side! I believe that the original , installed correctly, had a 'spring' effect on the washer to keep in place..from working loose.
 
pbishop said:
I am about to remount my 'new' manifolds. The car has been apart and idle for months. Does the 'flat' side of the fat washer go toward the head, or does the 'domed' side go toward the head? I cannot remember, and it is not specified in the manual I have.

Thanks, Paul
Click to expand...

Important - If the domed side is installed toward the manifold there is a very high risk/likelihood that you will break one or more manifold ears. A "flat" side may do the same but at a much lesser risk. As mentioned the originals were concave so the perimeter was the point of contact/pressure.
 
Thanks, CarlG. When in doubt, follow the original engineering intent and published instructions.

The washer couldn't perform it's intended spring-action to hold the manifold in place if it were reversed (concave-side out).
 
My understanding is that the extra spring action supplied by the cupped washers is necessary due to the exceptional thermal expansion/contraction that occurs in that connection, which is why similar washers are not needed elsewhere.

If you try to tighten the nuts with the cupped, concave side out, the corners of the nut dig into it.

Steve
 
steve s said:
My understanding is that the extra spring action supplied by the cupped washers is necessary due to the exceptional thermal expansion/contraction that occurs in that connection, which is why similar washers are not needed elsewhere.

If you try to tighten the nuts with the cupped, concave side out, the corners of the nut dig into it.

Steve
Click to expand...

To be honest I doubt that has any bearing on it. The fact is the design of the mounting ears requires that they be bridged to place the pressure inboard of the tips. If the pressure at the tips of the ears were to exceed that of the inboard location it would be doomed to eventual failure.
 
My opinion is the spring action of the washers is to apply equal pressure to both the intake and exhaust manifolds from a single bolt. Not to mention as the exhaust heats it will expand more than the intake.
 
MrTube, your opinion is correct. The cupped washer is an ingenious, simple and cheap way of both applying equal calmp-up force to both manifolds and accommodating thermal expansion in the joint as steve s said.
 
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