[sharpie]

When did Chevy start using hardend valve seats,I'v got a 68 327 havent checked the casting numbers. Just the motor casting number.

 

[32551]

you will need them. if they are 68's i think it is when unleaded gas was introduced

 

[SWHEATON]

No hardened ex valve seats for chevy in 68,i believe the hardened ex valve seats were intro'd for chevy in 73-74 timeframe.

Scott

 

[engineguy]

GM started using an "induction hardening" process for exhaust seats in all of their engines in 1973. Unleaded gasoline was made available to the public in 1974.

 

[Keith Tedford]

In 1971 GM dropped the compression on all engines to run on unleaded gas. I believe that they also started induction hardening the exhaust seats at the same time. Your old heads probably have enough carbon soaked into the seats that they will be ok.

 

[Schurkey]

I would have said the induction hardening started in '71.

The old, used seats will probably be fine--until you have a valve job done. No promises after that.

 

[animal69]

I believe it was 1971 with the low compression. My 1972 Monte took unleaded gas.

 

[sharpie]

So I can cross my fingers hope the heads have hardend seats,Motor was rebuilt by the previous owner. Thanks

 

[SWHEATON]

Rich,again,in 68 GM DID NOT HAVE HARDENED EXHAUST VALVE SEATS unless they were installed in prior rbld you spoke of.

But even if you dont have hardened seats i ran my 396 for 25+ yrs without hardened seats but did run the inexpensive valve/lead additive and the exhuast valves did not receede at all into the head when i tore it down for rbld in 2002.

Its when the motor is under heavy loads like towing or sustained high speed crusing without the hardened seats that makes the ex valve seats to start wearing away/receede into the head.

Since your in doubt just run the inexspensive lead substitute and dont worry about it. I used to get a bottle of lead additive that treated 320 gals for approx $10.00,cheap insurance.

Scott