Manifold washers

whitepunkonnitro said
I disagree on the washers being used to protect the castings rather than the bolts themselves.
Those conical washers only show up in two places...Slant Sixes (three positions) and the SB. In both cases the fasteners are only 5/16s.
Exhaust manifolds that use 3/8 bolts and studs use standard flat washers.
The conical washers are intended to expand and contract along with the undersize bolts.

Any washer would expand and contract, that's a physical property of any metal. A flat washer will expand and contract and so will a conical washer. The big difference is that the conical washer only makes contact on it's outer diameter thus putting the force of the torque (bolt head) on the outer edges of the washer. By putting all the force (torque) on the outer edge of the washer you don't put pressure on hole area. Since most manifold gaskets crush to some degree they allow the manifold ears to flex (bend) into the gasket where the bolt exerts pressure. We all know that cast iron will only bend so much before it breaks. So by distributing the load (torque) to the outer edge of the washer you don't press on the hole area and cause it to bend into the gasket. It's just like pushing a car....if you push a cart using a pointed ice pick you'll push a hole through the body before you actually make the car move. But if you you push with the force distributed over a large area (both hands) the car will roll without any damage to the body. In the same way the conical washer will press the whole manifold ear against the gasket, not just the hole area. Maybe the conical washers have a dual purpose. One may be to distribute the load more evenly and the other may be to decrease the surface area of contact to allow for expansion???? That would make sense because if the washer only touches the manifold on it's outer edges it can expand and contract more easily (less surface contact). I know one thing for sure...those ears will break, especially if you're using gaskets.

treblig