My C heads were "bracket ported" by Joe Mondello in 1996, since then they have had a few valve jobs. The valves look be sunken to the point that the low lift flow must be significantly effected (about (0.060"). My valve sizes are: Intake 2.072, Exhaust 1.710. What are the correct valve seats (manufacturer and P/N) that I should get for my machinist (when I find a good one)? Can my chambers, seats, and bowls be returned to their correct shapes after the seats are installed? I did a lot of searching and could not find the information. I did learn that you are screwed if you try to install the wrong ones or if someone that does not know what they are doing tries to install them.

Maybe I am wrong and the valve seats are normally that much higher than the surface of the combustion chamber. If someone has some good clear high resolution pictures that clearly shows how the valve seats should be relative to the combustion chamber surface on a C head, I would love to see them. If my valve seats are not as bad as I think, I will then know why the C heads have such poor low lift flow!!

If anyone can point me to a qualified machine shop that has Oldsmobile deck plates anywhere near central Maine, I would much appreciate it.



Thank you!!

 

Doug,

Put the valves in and measure the valve stem height above the spring seat. The spec is 1.876 - 1.906 That will give you some idea as to how far the valves are sunk.

As far as getting seats I would leave that up to your machine shop. There are only a couple of good manufacturers and everyone has their preferred ones to use. The ones listed in the catalog would probably not be my choice because of the porting. I would want to see your heads and measure them before ordering seats. Saves a lot of grinding to finish matching them. Let your machine shop do the job.

 

Thanks Bill. I remember hearing that there were only a few good seats, that is why I am asking. I'm afraid that their preferred seats might be the bad ones! I measured my valve stem heights. From the nominal height of 1.891", my valves have been sunk in the range of 0.050" to 0.074" Since my post yesterday, I found the Martin Wells website. They show part numbers and cross reference part numbers for over a dozen other manufacturers. I also found some information on wildaboutcarsonline.com that said "If an exhaust seat is thicker than 0.215” it is likely that it will pierce the water jacket in the cylinder head" The P/N W-730 that Martin Wells shows for their exhaust valve seat is 0.218!" I wish I had a machine shop. Hope someone out there can direct me to a good one.

 

Any aftermarket seat they use will be better than the factory head material. I use Jloy seats from SBI and the ones they show for the 2.072 valves are 3/16 deep. Thats only .187 deep. The ones for the exhaust are .218 I have always had good luck with the seats they recommend as far as depth and od.

Like I said you really need to measure what is there before deciding what seat to use. Especially when the valves have been sunk like that. You simply cannot go by what the book says will work.

Also the hgt from the spring pad is sort of ballpark on Oldsmobiles. You really need to have the correct tool to measure the hgt referenced off the valve cover rail and rocker arm pads.

Here is a drawing of the measurements I took from the factory GM tool that I have.

 

Where are you in Maine ?

 

Thanks Bill. That is great information! Mondello has that tool. I will get one.

 

a
The Mondello tool is not correct. At least the one that I bought wasnt

These guys have a good reputation but I don't know how far they are from you. They have helped me out a few times over the phone. They are AERA members also.
https://www.rlengines.com/Index.html

 

I am in western central Maine. Kingfield Maine.

 

It turns out that my heads will not take seats. Sad to have to trash them!

 

How did you determine that ? Just curious.

 

Bill. I brought them to Leo at R&L Engines in Dover New Hampshire. He cleaned them up, and after assessing them determined that there just wasn't enough material left to safely install seats. I think the extensive porting on the short side radii was the problem. What do you think about that?

 

I've heard very good things about these guys as well. They helped a friend of mine with the heads on his flathead Ford.

 

Very possible. I was just curious. Was he more concerned with the intakes or the exhaust ? You could probably get away with a pretty shallow seat on the intake, especially since the valves are sunk in as far as they are but the exhaust needs something pretty substantial. Hard to say without looking at them. Did you ever get a valve stem hgt measurement to see how sunk in they really are ?

 

Bill. Leo didn't say if intake seats could have been replaced. I did not get valve stem height measurements. I'll ask him those questions when I talk to him. Thanks.