Hard seats yes or no? I've went with idea that if it's not a high GVW or tow vehicle they are not needed.
Lots of threads about it. General consensus seems to be only if you run the engine hard. If not, then don't worry too much about it, like say if you have a stock engine and you cruise around. Of course, if you're rebuilding an engine to put in your "HOT ROD", you're gonna run it hard, right? Have them put in.
Seems like if you're going to the trouble & expense of replacing valve seats, why not use the best? Once & done!
I know a guy who's put over 100,000 miles on a 302 Jimmy without hard seats, running on unleaded gas. He adds a bit of two stroke oil to each tank of gas, has never had valve problems.
Cumulative effects. Besides, isn't it the standard to install hardened seats now whenever you have machine work done on heads?
It's a good idea to do the seats while the heads are being done, but I would just put a tip here having done a bunch of these type resto's in the past! In the beginning we had special seats made up for the SBC heads to our own specs which included a different radius on the outer corners of the inserts. We made them with an .093" instead of the usual radius. This helps avoid cutting into the water jackets at the seat corners. We made the cutters match the radius for installing the seats. We also use .218" on the depth as opposed to the more conventional .250" deep, again, it's just that much safer! One thing I would mention, never try to put o'size valves PLUS the seat inserts, most times it will not go. If it had a 1.500" valve stay with that size! Most of these jobs can be done safely but the inserts have to be configured for the job. Early Pontiac's are another head that have "thinner" material at the exhaust valves. Thanks, Gary in N.Y. P.S. Today we machine the conventional seats in-house using our own blades instead of doing any "special-orders". Saves time on the jobs. In the photo you can see the larger radius and the blade used to machine them.
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