Death Of A Classic Part II

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Furthermore, independent laboratories are currently developing lubricative additives to replace the dwindling tetraethyl lead. One such firm, the Lubrizol Corporation, has researched and is in the process of marketing a sodiumbased additive-PowerShield-for leaded or unleaded fuel. Though their ultimate goal is to supply bulk quantities to refiners and blenders (pending approval by the EPA), packaged retail allotments are already available under a number of different brand names.

If you're committed to a mechanical solution, probably the simplest is to swap heads from a similar later-model engine designed for unleaded fuel operation. Most every autosalvage yard has a copy of Hollander's Interchange Manual, which is something of a bible to those searching for used parts. (In a pinch, you can match up a head gasket from your engine to see if the newer part would fit.) Besides solving your valve-recession problems, use of a latermodel head will lower your engine's octane requirements, since its combustion chambers have most likely been relieved to lower the compression ratio.

Slightly more involved, but equally effective (especially for engines which don't have an updated, no-lead counterpart), is the use of hard stellite inserts on the valve seats. This is strictly a machine-shop proposition, and its success is dependent upon the thickness of the head casting; some manufacturers use a thin-casting technique in their foundry operations, which precludes the use of inserts. In these cases, induction or inlay welding of a hard material such as nickel into the seatsimilar to the process used at the factoryyields a surface about .060 " thick that can withstand high temperatures and erosion far better than iron can.

While the cylinder head is off, other factors to consider are the use of sodium-filled or stellite-faced valves, hardened steel or bronze valve guides (to check progressive lateral stem movement), and maximum-rate valve springs. Too, the quality of valve seat grinding is critical; the seats must be perfectly aligned with the valve guides, and the valves shouldn't protrude excessively into the combustion chamber. To encourage positive valve transfer cooling, the seat should be fairly wide and be ground to the same angle as the valve face to make a consistent match. Finally, any deposits in the water jacket should be removed, since a buildup of scale or alkaline deposits can greatly influence heat dissipation within the cylinder head.

However, even after you've faced the prospect of valve recession, you can't ignore the possibility of destructive detonation within the combustion chamber. Again, under normal conditions, severe knock probably won't be a problem . . . and occasional "pinging" can be controlled by easing up on the throttle when the ping is audible. But that clatter spells calamity for the pistons and bearing surfaces . . . and can mean meltdown in minutes if allowed to continue.

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