How many angels DO fit on the head of a pin?

 

Translation: I imagine that the surface variation of ANYTHING that you attach to the surfacing surface will have a greater variation than the surface's flatness spec. The particles on the emery cloth, not to mention the backing itself, almost certainly has a greater variation.

 

As someone said, the lapping process should tend to even things out anyways...

It is true we're not building a lense for a telescope. I'm just talking about a glob or a hump that you could do without. Now if you had a ridge across the middle of the stone, over lapping sandpaper or a line of glue, you never would get the head flat.

You could roll any sheet of most anything flat to the stone/glass with a roller like making a countertop.

Just a late note to this thread, watch the surface finish, you don’t want a polished surface on a cylinder head (or any other surface that holds a gasket), you need a little roughness to hold the gasket. Emulating OEM should work fine.

 

BTW, this idea isn’t really “backyard”, lapping parts for fit or finish is standard procedure in any machine shop. I personally have been using the “glass plate” surface plate as long as I’ve been working on stuff, I learned it from my daddy.

 

And to take it a step further, I regularly use a hard rubber sanding block or long board (bodyshop type) to clean, prep and flatten surfaces that I can’t take to the surface plate.

 

Gary

Good info for those that didn't already know this stuff. How about adding the highlights of this thread to the Ultimate Repair Manual?

The method with plate glass on heads works well.

I use the Norton oxide paper (just one sheet, per head) in my ghetto yard

 

Stage1 shows how bad the surface variations were between the chambers:

(plate glass also shown, but 1/4" is minimum you want to go, and must check glass for flatness before proceeding)

 

Stage 2 shows most of the imperfections gone:

 

Stage 3 and 4 came afterwards...