Quote:
Originally Posted by Dave Page
There are some very intelligent articles on-line and some very misleading ones, the latter will have you buying stainless valve seats and etc.
The truth is the older engines that we run are - low-compression - so do not generate the pressures and heat that would cause valve problems in a high-compression engine. It wasn't that many years before our ww2-engined vehicles that cars were running on an alcohol and castor oil mix.
During the war both unleaded and leaded fuels were used by the military, the lead being added in very high doses to boost the octane of lower grade fuels to eliminate engine knock, this saved a lot of money and time over actually making high quality fuel for everything to run on.
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I've been reading up on the subject in the past and a good source, among others, is a chapter on the subject in Dr. Ulrich von Pidoll's book "Kaefer: Ein Auto schreibt Geschichte" (Hamburg: Nikol, 1996, ISBN 3-930656-36-1).
Indeed, lead was not added to car petrol until after WW-2. Also, during the war, when the race for higher power output from aircraft engines was in full swing, it was found that by adding lead to petrol the octane rating could be raised (i.e. petrol became more resistant to spontaneous combustion). Thus higher compression ratios and supercharging became possible.
After WW-2, increased power output for car engines was also solved by raising the compression and the revolutions per minute. Adding lead again solved the pre-detonation problem (although up until the 1960s other additives were also used for this purpose). The advantage of lead additives is that after being burned, they act like a solid lubricant on the exhaust valves and seats, and thus reduce the amount of wear over a given period. (The process is comparable to the use of white metal in engine bearings.)
Now that leaded petrol is banned (for our own health), what can we do?
1) fit induction hardened valve seats and valves when rebuilding the engine. This is recommended by the Dutch Federation of Historic Car Clubs, as the cost of hardened seats and valves is only slightly higher than non-hardened ones, and is simply the most durable solution.
But what if we have an engine which is not yet due for a rebuild?
2) Dr. Von Pidoll quotes a 1986 SAE technical paper. A number of SAE tests (incl. one on Army vehicles) proved that the wear on valve seats and valves with unleaded petrol is not noticeably higher (compared with leaded petrol) if the engine is operated under 3,000 rpm.
My own opinion is that the latter is a good tip, as 1940s and 1950s MV engines are rarely operated above 3,000 rpm. over long periods.
HTH,
Hanno