valve recession

oldspert

oldspert

Senior Member
The engine block I bought has one intake valve that is recessed about .030 lower than all of the other valves. Need opinion on whether to replace the seat or just do the valve job and let it go. The block has already had babbit re-poured and is bored .080 with new pistons, counter balanced crank and is ready to assemble.
Ed
 
The bring a seat back to the correct width, cut the seat to 45 degrees. Then cut the bottom of the seat to 60 degrees and the top to 30. As you are cutting, check to make sure the width of the seat that is at 45 degrees is in the center of the valve face. Do a light lapping of the valve to the seat. Just to the point of having a uniform grey ring on the valve. Some mechanics will cut the seat to 46 degrees which provides a sharp edge at the top of the valve face and, it is thought, a better seal.
 
nkaminar said:
The bring a seat back to the correct width, cut the seat to 45 degrees. Then cut the bottom of the seat to 60 degrees and the top to 30. As you are cutting, check to make sure the width of the seat that is at 45 degrees is in the center of the valve face. Do a light lapping of the valve to the seat. Just to the point of having a uniform grey ring on the valve. Some mechanics will cut the seat to 46 degrees which provides a sharp edge at the top of the valve face and, it is thought, a better seal.
Click to expand...

Good info to give to my machinist. I always lap valves just enough to leave a grey ring on the valve face. An old timer told me once to take a lead pencil and mark the seat with it, if the valve removes the mark when you rotate the valve, the seal is good.
 
it depends on how recessed the other valves are and as has be mentioned- the form and width of the seats
I have seen them cut so deep that the mushroom on the valve stem was almost gone and the keeper resting on the tappet with the top cut to narrow it the seat
almost under the gasket.

Take some pictures.
 
Kurt in NJ said:
it depends on how recessed the other valves are and as has be mentioned- the form and width of the seats
I have seen them cut so deep that the mushroom on the valve stem was almost gone and the keeper resting on the tappet with the top cut to narrow it the seat
almost under the gasket.

Take some pictures.
Click to expand...

The valves are not stock. they have straight stems so shortening them is not a problem. Adjustable lifters too. All of the other valves are above the block surface.
 
Typically having a valve low will not cause too much trouble other than limiting port flow
It should be noted that removing material from the seat will never raise the valve up
Replacing seats is an option but there can be complications if not done properly
So, if you have late model valves already I would look for a larger valve to replace the offending one or two
This allows for the seat to be corrected and get the valve raised back up

John
 
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