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B21A Carby Engine and Premium Unlead Use vs Valve Seat Recession 200 1981

posted by  someone claiming to be Rhys on  Thu Apr 28 17:16 CST 2005 [RELATED]

Canada has had unleaded fuel since 1986. The generally accepted fact is that aluminum heads with hard steel inserts do not experience valve seat recession. Only cast iron heads with intergral seats which are not locally induction hardened have recession, and then only under certain operating conditions of very high constant load or high RPM. Pleasure boats and hard working trucks are about the only applications that have a problem. I have rebuilt lots of B21 and B23 heads, mostly because of blown head gaskets or excessive guide wear. I have never seen recession on any of them. Some B20's have recession, and some don't, probably because of the engine seeing lots of high RPM service. I rebuilt a B20E head two weeks ago that had recessed exhaust valve seats, but that was the result of a customer that drove across North America with a non-working overdrive, averaging 4000-4500 RPM all the way. The valves were fine - I re-used them, but the seats were down over .080 inch.
I would not worry about recession on the OHC engines at all.






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