logo How to make valve seats for small valves

by Glen Bond

Here I will attempt to describe how to make valve seats for the valves previously described. This idea for the seat is not mine but was suggested by Ron Colonna, who responded to a query I posted in the model engine club. He suggested making a valve seat and guide in one piece. Press fit it into the head. Then drill the ex/intake passages into it. I am going to detail how to make it before I ever make one (yeah, right!).

First determine the size of hole that you will be making in the head. I think it might be nice to go with a common drill size. I used 21/64.
Then ream or lap the hole to get a good smooth clean finish.
Then make a plug out of aluminum brass (I didn't have any aluminum brass, so I used yellow brass) that will press fit to the hole. Drill a 3/16 inch hole in the center. Use a reamer to make a nice smooth and precision hole. The valve stem should be slightly smaller than the hole. I didn't have a reamer so I managed to lap the hole until the valve stem fit.
Then drill out one end (the end that will have the valve seat) with a 3/8" drill to about 0.300" deep. This is where the intake/exaust passages will connect.
Next set the compound slide to 45 degrees and cut a seat. For the small valves that I am making I didn't even cut a seat. In order to keep the seat as small as possible, I just left the edges square and then lapped the valve into it. This made a really small seat. The seat should be as small as possible and still get a good seal.
Once you start making this part, don't take it out of the lathe chuck until it is complete. The seat and the valve stem alignment is critical.
Then part off the plug a little longer than you need so that you can face the end until it is the correct length.