For those who have replaced the valve seats on a M20, what shrink fit are you using? I was thinking .003" would be OK?

I have replaced valve seats on various bikes but not on a M20 yet and the M20 runs really hot at the exhaust port so .005" may be better?

I have a M20 cylinder that needs new seats and will be doing it on a Bridgeport mill.

0.003” should be fine. Don’t go any tighter or the seat could close in on itself. With an iron head/barrel the seat should grow with the head at a similar rate. Just make sure you have a very clean finish on the bore for the seat.
What seats are you planning on using? The AE 6000 series are supposed to be good. Fondera sell the Martin Wells seats, but they can be tough to cut. They did say the last time I visited that they also have a range of seats better suited to cutting rather than grinding.

Mark

email (option): pes.sales@btconnect.com

I was thinking of using powered metal seats from Kibblewhite here in the USA. I normally use nickle chrome seats and have heard the powered metal seats can't be cut and need to be ground. I have also been told you can cut them so I don't know who to trust. Luckily I have a seat grinder if they can't be cut.