Low compression

[Malcolm Towrie]

There are 4 really bad exhaust valve seats in the block, corroded and pitted. My local machine shop agreed they should be replaced, but he couldn't do it because modern seat removal/replacement tooling is designed to hold cylinder heads, not a whole block.
I decided to use the welding technique to remove the bad seats because i could do that at home, and buy replacement seats, figuring i could make up the simple tooling required to install them. I hit some snags.

The seats came out no problem by fitting a slightly loose 1/8" thick washer inside the seat bore and MIG welding it to the seat. This shrinks the seat and loosens it in the block so I was able to tap the seat out using a brass punch on the underside of the washer. One photo below shows the block with the seats removed, and the other shows the removed seat.

The first snag was the seat counterbores in the block were 0.005" out of round, varying from 1.625 to 1.630". This seemed a bit much considering the press fit of the seat in the block is 0.005" interference. The other snag was the new seats were 0.010" over nominal size on the outside diameter, which I found out is normal. The supplier assumes you will be cutting the counterbores 0.010" oversize to clean them up. Another minor problem was the new seats are 1/4" thick, when nominal size is 7/32".

So now I need to find a machine shop who can bore out the counterbores in the block to 1.635" ID so that I get the right press fit for the 1.640" OD seats. Parry Automotive in Orillia may be able to do this.

Malcolm

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