951 Head Exhaust Surface Flatness

[dean thompson]

I am working on a 951 head to prepare it for a rebuild. As a part of the process I am flat sanding (sandpaper over plywood sanding block) the head surfaces and then checking with a straight edge to verify flatness.

Everything is going fine with the exception of one surface. The exhaust manifold surface is 0.004" out across it's length. Most of the other surfaces I can get to 0.002 with a feeler. This just so happens to be a previously leaking joint.

How good is good enough? The gaskets are quite thick.

Help?

[Bill O'Neal]

The idea is to get it flat, so keep sanding. When we do superstocker motors, we often remove material from these surfaces to shorten the runner length, so don't worry about taking too much. Get it flat so it won't leak and hydro lock the motor.

[chris w]

I would question the flatness of plywood. If you can get a nice flat piece of marble that would be preferred. Sand in a "figure 8" pattern.

[Bill O'Neal]

Glass, marble or a gound metal surface table with a piece of sandpaper stuck to it is the best way, other than the more popular, but not always available method of using a mill. We often just use the rotational method over a flat surface with sand paper stuck to it to get flat surfaces flat again.

[ February 21, 2003, 09:45 AM: Message edited by: Bill O'Neal ]