How much smaller is the block machined than the OD of a replacement valve seat?
I run a small head shop, so I could probably answer your question, but I'm not sure just exactly what it is that you're asking...?
Are you wanting hard steel seats put in your Model T engine? If so, this is a fairly straight forward operation. The seats are approximately 1/8" larger than the valve head diameter.
I believe Jim is asking how much interference fit should he have when installing a valve seat.
Yes, Seth; I think you're right. I wasn't thinking along those lines...
Jim, the hole is machined about 0.003 smaller than the seat. They need to be driven in, preferably in one heavy tap rather than several small taps. Also, the seat is installed a couple thousandths below the top of the block, and is 'pinched' in by tapping a chisel-looking device around the new seat, something not unlike making a pie crust.
I hope this answered your question.
Thanks Jeffrey. That was my question.