Of Unleaded Fuel and Burned Valves R. Kwas revised 1/03
Lead is dead... as a gasoline additive anyway. This is of interest (or should be) to us owners of ancient Volvos since the use of unleaded fuel in these cars without the proper provisions can and will lead to problems. If this sounds like a case of Ron relates another lesson learned, your right. I certainly consider it extraordinary when less then a decade goes by and the cylinder head of my car needs to actually be removed for serious service!
Some background: The addition of lead to gasoline (in the form of lead tetra-ethylene) it was found many years ago increased the octane rating (essentially the ability to avoid pre or self-ignition in an internal combustion engine). Further, the combustion by-products of the lead padded the incessant closing (or should one say hammering) of the exhaust valve onto its seat.
In recent times, research has shown that lead or its compounds is not exactly the best thing for you or your catalytic converter to be inhaling. In the case of the human body, especially small ones such as children, it can cause a number of serious health problems none the least of which is brain damage and god knows there's already enough of that to go around! In the case of your car's cat, it will neuter the chemical reactions within to say nothing of clogging the fine passages with those same combustion by-products. So there it is, lead is history, but when your 122S was engineered in the 50's and 60's all of this wonderful information was probably confined to some S.A.E. research paper. Now, here we are in the 90's and these venerable Amazons still refuse to die with merely the application of some good maintenance and perhaps occasionally a bit of T.L.C. or a rebuild every decade or so. Except for that thing with the unleaded fuel...it seems that without the softened closure eventually those valve seats, which were cast into the (soft) head and precision machined later get eroded away (enter valve seat recession, not to be confused with any automotive sales trends).
I cannot over-emphasize the importance of using a lead substitute (generally a sulfur based compound) on a regular basis when fueling up. Don't let the lack of instant result or gratification lull you into a false sense of security. The results and benefits are long term. I speak from (a bad) experience in the form of a burned #4 exhaust valve and others that were badly receding and I hope others will benefit from this pass on knowledge. In my case the long term repair meant installing hardened valve seats into machined recesses in the head to accept these. The original ATE valves are of excellent quality and may be cleaned up per specs and reused.
Would you like a picture?
Here's the head just before putting it back on the engine:
While were on the subject of valves, specifically adjusting them, please look at the valve clearance adjustment hint on the Service Notes page.
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