I'm doing some major winter projects on my '63 Coupe de Ville and one of them is to pull the motor to fix the rear main seal leak. While the motor is out, I'm thinking about pulling the heads and having hardened valve seats installed. I've had the car for a couple of years and I've put about 8,000 miles on it. I add the Motor Medic lead substitute with every fill up but that's getting expensive and I'm not quite sure how good of a job it's doing. Plus, I don't know if the previous owner used any lead substitute so I don't know the condition of the valves/seats. When I install a vacuum gauge, it fluctuates quite a bit so I believe I already have some leaking valves. I plan to do a compression test soon.

Has anyone had hardened valve seats installed in their heads? If so, I'm anxious to hear how you made out.

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I would perform a cylinder leak down test, that will tell you which  valves are leaking by listening @ the tail pipe for exhaust valves & the carb for intake valves, also the oil fill tube for rings leaking. I have used hardened valve seats on Pontiacs , and will be on my 429 Cadillac  rebuild, they work fine.Given your cars age it could need valves, seats, and bronze wall guides and valve springs.

Thanks, Chris for the good information. I'll definitely perform a leakdown test once I find the low compression cylinder (if I find a low cylinder) but whether I find low compression or not, I still want to install hardened valve seats for any potential future issues. I 'm looking forward to someone on here chiming in regarding their experience with installing hardened valve seats on their Caddy project. 

For those who came across this thread wondering about hardened valve seats, in a nutshell, here's the deal: When our wonderful cars were built, gas was way different. It was relatively cheap, it was higher octane and it included tetraethyl lead (lead). The addition of lead helped increase the octane but, more importantly, it helped "cushion" the valves each time they slammed closed on the valve seats. Unfortunately, lead was found to be bad for the environment so it was removed and we now only have unleaded fuel. Now, without the lead to cushion the valves, the valves can get hammered into the seats which can damage the valve and the seat. This damage will stop sealing the air/gas mixture in the cylinders and cause an inefficient burn. This can lead to poor performance, a "miss", poor fuel economy and other issues.

There is a lot more to it but this is the gist of it. And, this is why I'm anxious to hear about other Caddy owners installing hardened valve seats.


I agree with what you wrote, but a petroleum engineer once told me (and I've read the same, over the years) that lead does not increase octane. It reduces the potential for detonation. And also provides a cushion for the valve seats, as you said.  

Bring back lead!




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