The Ford Barn

Richard Knight · 02-09-2025, 08:39 PM

A few things I would like to mention. At the professional shop level you learn very quickly every single part you buy to be used in a rebuilt engine needs to proven as a good part for the engine at hand. Having refaced probably thousands of NEW valves I can assure you the few that I found that where bent, not concentric, oval shaped would have caused untold problems if not found before installation. Model A valves are no exception. Lapping the valves is also mandatory as it is the only way to prove the contact area. 1/16 to 3/32 is the generally accepted width for most engines. We had a kwikway valve grinder with a six ball chuck that established the valve center line period. I had both grinding equipment and neway cutters. As far as the interference fit this is more appropriate for modern engines with hydraulic lash adjusters. With 46-45 degree difference the valve seat gets wider over time and the valve moves into the seat over time. Model A engines where built with non adjustable lifters but now most use adjustable lifters but remember they are solid and NOT self adjusting. Lapping the valves, getting a good seat will insure when you adjust your valves they will maintain that clearance over the life of the engine similar to Ford's lifters and valves that where ground for clearance. Ford's exhaust valves have been stainless since day one. As the blocks wear and get rebuilt the valve seat gets ground and the valves drop down into the block and become somewhat shrouded. One of the secrets of model A engine rebuilding is having the valves sit proud on the deck surface for good breathing. No shop worth there salt would install a soft iron seat in the exhaust. Stellite is the go to material. Installing eight seats and decking the block corrects many issues. As far as heat transfer it has been mentioned the heat from the valve head is transferred to the block when the valve is closed the addition of seats may impead some of this heat but I think this is a non issue. Part of the reason for this is the extreme press fit of valve seats is generally in the .004 to .005 range.

02-09-2025, 08:39 PM	#21
Richard Knight Senior Member Join Date: Mar 2021 Posts: 312	Re: For those who have ordered stainless steel valves... A few things I would like to mention. At the professional shop level you learn very quickly every single part you buy to be used in a rebuilt engine needs to proven as a good part for the engine at hand. Having refaced probably thousands of NEW valves I can assure you the few that I found that where bent, not concentric, oval shaped would have caused untold problems if not found before installation. Model A valves are no exception. Lapping the valves is also mandatory as it is the only way to prove the contact area. 1/16 to 3/32 is the generally accepted width for most engines. We had a kwikway valve grinder with a six ball chuck that established the valve center line period. I had both grinding equipment and neway cutters. As far as the interference fit this is more appropriate for modern engines with hydraulic lash adjusters. With 46-45 degree difference the valve seat gets wider over time and the valve moves into the seat over time. Model A engines where built with non adjustable lifters but now most use adjustable lifters but remember they are solid and NOT self adjusting. Lapping the valves, getting a good seat will insure when you adjust your valves they will maintain that clearance over the life of the engine similar to Ford's lifters and valves that where ground for clearance. Ford's exhaust valves have been stainless since day one. As the blocks wear and get rebuilt the valve seat gets ground and the valves drop down into the block and become somewhat shrouded. One of the secrets of model A engine rebuilding is having the valves sit proud on the deck surface for good breathing. No shop worth there salt would install a soft iron seat in the exhaust. Stellite is the go to material. Installing eight seats and decking the block corrects many issues. As far as heat transfer it has been mentioned the heat from the valve head is transferred to the block when the valve is closed the addition of seats may impead some of this heat but I think this is a non issue. Part of the reason for this is the extreme press fit of valve seats is generally in the .004 to .005 range.