I am rebuilding an 8BA flathead and the guy doing my machining has never worked on one before. I have ordered new valves and seats from Speedway and the machinist is worried that when he press fits the seats in he might crack the thin piece of the block between the inlet and exhaust valve seats. Can any body tell me: 1 - how much undersize should the valve seat bore in the block be? 2 - is there any special method of fitting the seats to avoid damaging the block? 3 - should a glue or adhesive be used? I hope someone out there can help because there are not to many flathead experts here in Botswana! Posted from the TJJ App for iPhone & iPad
I don't know the answer in actual interference fit in thousandths of an inch, much less in mm, but when I saw it done in the old days, it was a hammer fit with the seat frozen in dry ice! Hopefully this somewhat vague answer will at least get you back to page one where someone with more knowledge on this can see your post and help. When I used and was around flatheads was over 50 years ago. In those days the people who knew such info kept it to themselves as much as possible, now it is available online and in books. Good Luck!!!!!
Coupla things... 1. Are you sure you don't already have hard seats?? The new engines from 1949 started production with 16 hard seats, later some passenger car engines went to 8 and then none, using valve rotators in the seatless engines. Trucks got 16 hard seats like earlier engines all the way through. If you have seats, most will reface nicely with only a light cut, and they can be replaced with Ford ones in original size or in a slight oversize...dry ice fit. 2. If no seats in there...are you sure you need seats?? The bit about leadless gas destroying cast iron seats is largely bull, applicable only to heavily loaded engines run mostly at full throttle. If seats are very badly eroded, consider simply going to the 1.6" valves to get out to good metal.
Thanks for the feed back - My engine has 8 seats that look like they're factory fitted, I bought the new valves and seats because of the unleaded thing but the car is only going to get weekend use so maybe I can keep the original seats. Can I use a 60 thou over stainless valve with the original seats? Posted from the TJJ App for iPhone & iPad
Stock valves are 1.5, 1.6 is an easy step up, both sizes readily available here as Chevy exhaust valves. The soft intake seats can easily go out that much and then be blended down into port via multiple stone cut angles and some grinding, original hard seats generally clean right up for 1.5, can be ground out a bit for 1.6 or lesser undersizes. Lead is not a big issue...lead came and went, the old engines kept right on. The studies of seat failure that were once a source of panic were actually based on small industrial and generator type motors that spent their lives at sustained full throttle. Best Botswanan car humor in a movie: The Landrover and the little 3 wheel motorized wheelbarrow in "The Gods must be crazy"
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