Head Gasket Change:

Hal the Elder

Local time
9:58 AM
Oct 20, 2008

I was given the instructions for removing the head with the engine in the bike.

OK, Fine.

I was then advised to "lap the head" before installing it over the new copper gasket.

Does this mean hand-surfacing the head on a sheet of Emery Cloth over a perfectly flat, hard surface?

I have a Lathe, Drill Press, Grinder, Band Saw, but I don't have a Mill!

Last edited:
Hi Hal, I use a peice of granite with a peice of #220 sandpaper to lap the head after I mill them to remove the tool marks. You can also use a good peice of glass for the straight surface.
Hope this helps,
Have fun,
You Mill Heads?

What's the most material can you remove to allow valve clearance and to limit high compression pressures before the lower end becomes stressed?

Also, what's the stock compression ratio...6:1?

Hi Hal, I have removed up to .095" on a few heads without any ill effects. Never worry about the "bottom end" of the Whizzer motor due to increased compression. Also never worry about the valves hitting the top of the head after it has been milled, because the valve pockets are DEEP. Your only concern is the tip of the long CE7 sparkplug hitting the exhaust valve on a milled head, solution is simply add one or two extra plug washers. I have seen a couple motors where the exhaust valve closed the gap a little.

I have some motors with over 165 pounds of compression, but you should expect to end up with somewhere between 110 and 120 pounds after milling the head [.060" to .070"].
Have fun,