TD New Guy
Join Date: Jul 2015
Location: Ontario, Canada
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Dropped Valve Seat
I have a ported big valve G head with a dropped valve seat. There is very little material left between seats so boring for an oversize seat would result in overlapping the intake/exhaust valve seats.
I came across this on Mini-Mopar:
Avoid "siamese" valve seats, where the intake and exhaust seats are touching. This design does not allow for proper heat expansion and the exhaust seat will transfer heat to the softer intake seat, and the shape of the seat can become distorted. The valve will not sit properly and low compression and severe valve wear can result.
I don't have a shop nearby that specializes in head repair. Actually, I didn't get a good vibe from the only local machine shop, either. So I'm hoping that the knowledgeable members here can help me out.
From my research, I have a few options:
1) Weld and re-bore - I'd have to find a good shop. One source I came across suggested that all seats and guides would need to be removed to preserve their interference fit due to the heat/expansion involved. I don't know if this is true.
2) Stake the seat - I don't like this idea. The seat had dropped before, was peened and eventually dropped again.
3) Overlap/Siamese the valve seats - See above but I don't know if this applies with these seats (why would they use different material?). I think this would be the easiest to have done, at least semi-locally. Unless...
4) Could I go with a taller (deeper bore) seat to restore the interference fit? From cross-cut pictures of the head it looks like there is room above the seat to work with but I don't know if taller seats are available.
Thanks in advance for any input.