Re: Puch Moped Head on HT 67cc motor- thanks Foureasy!
I've said it before, and I'll say it AGAIN. Lap BOTH mating surfaces with 600+ grit sandpaper on a piece of plate glass.
Dry fit your top end together, and check your squish clearance with a piece of rosin core, lead based solder. Squish should be No Greater than .030" Measure with accurate calipers/micrometer.
Shim up or down squish clearance with thicker/thinner base gaskets.
Clean all mating surfaces with alcohol or brake cleaner, and assemble head to Cylinder with a VERY light coat of Ultra Grey silicone. You're going to argue that it says right on the tube not to do this. That's so morons don't do it. If you're Smart, you'll realize that lapping the cylinder and head Flat is what's doing most of the sealing. The silicone is mostly there to adhere the head to the cylinder, and provide extra sealing.
Torque it all down and let sit overnight. Check torque before riding. You shouldn't need much more than premium gas for this head IF squish clearances have been set properly.
The head has much better cooling than the stock heads, and the Squish design retards the tendency for end gases to detonate, even under the additional compression.
Expect to see an increase in Low to midrange power. It's also possible that overall power will go up drastically, as the combustion chamber shape is idealized, and promotes a total burn much more quickly than the stock chamber. This essentially 'Builds In' Ignition advance without the negatives associated with advancing the ignition.
DON'T FORGET TO RE-JET.