Valve Seat inserts

On original engines that have had many valve jobs and rebuilds, cylinder block material was removed with each valve job and rebuild, and the valve seats have become recessed below the upper surface of the cylinder block. To compensate for this, the valves need to be shorter, and 3-angle valve seats are required to keep the seat narrow and centered on the valve face. To restore a cylinder block and replace the material removed and return the valves to seat at the top of the cylinder block, rebuilders can install valve seats or install larger valves. There is a risk of getting a press fit with the valve seats, especially if there are cracks, so many rebuilders prefer to use larger valves.
 
As Terry mentioned by the time a model A block needs rebuilding it may have had many valve jobs. Thus sinking the valve into the block. This shrouds the valve and affects performance. It is best if the valve sits up high on the block. For me it just made more sense to install 8 seats and surface the block.010 or .015. the seats could then be ground to a proper width and the valves would sit proud of the block. The exhaust seats were stellite and the intakes were cast iron. The standard press fit for seats was .0045 and I can tell you that is a tight press and they will not come out. I can't answer the O.P.s question on who makes seats now but stellite was the material.
 
8EL said:
Forgot to mention I used to use liquid Nitrogen (boils of at -320 DegF at sea level) to chill the inserts and they would drop in mostly on their own. Liquid carbon dioxide would probably work and is not as cold about -80 DegF so is a little safer to handle.....But either one will immediately cause frost bite or freeze your eyeball....wear a face shield Bubba.....
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We had a dairy farm and my dad did artificial insemination and we had a tank of liquid nitrogen, my brother and I would put different things in it to see the results . Rubber hoses after being dipped would be like ice in seconds and shatter when struck on the floor. I just watched a bus/motorhome video where the mechanic was using it to install bearing races in rear hubs on a large provost. He had a what looked like a baking pan placed in closed cell foam and would pour the liquid over the large race and it would boil, when it stopped boiling the race would free fall into its seat and as it warmed up was solid tight. Really cool stuff.

Forgot to add,,,, he would pour the stuff back into the storage bottle and reuse until it wouldn’t work anymore. I can’t remember the shelf life of the stuff or if I ever knew it.
 
Richard Knight said:
As Terry mentioned by the time a model A block needs rebuilding it may have had many valve jobs. Thus sinking the valve into the block. This shrouds the valve and affects performance. It is best if the valve sits up high on the block. For me it just made more sense to install 8 seats and surface the block.010 or .015. the seats could then be ground to a proper width and the valves would sit proud of the block. The exhaust seats were stellite and the intakes were cast iron. The standard press fit for seats was .0045 and I can tell you that is a tight press and they will not come out. I can't answer the O.P.s question on who makes seats now but stellite was the material.
Click to expand...

Hello Richard: You did perfect explanation of the valve seat process and why it's needed.

In asking what is the perfect valve seat,?
There are variables of what is needed depending on what has been done to the block.
Has it had prior valve seat installation? is valve seat cracked? how deep did they machine existing iron of block?
I have mentioned 3 examples and there are more.
https://www.facebook.com/270076059772640/videos/1081231091990462
https://www.facebook.com/270076059772640/videos/1076202209160017
https://www.jandm-machine.com/valve_guide.html
 
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