MASCOT November - December 1998

Unleaded here I come

Bill Haverly

NOTE: This article was written in 1998 before the demise of leaded 4 star and before anyone had much experience of additives. Nevertheless it contains helpful information (webmaster)

The one thing historic car owners will certainly not be celebrating at the Millennium, is the loss of leaded petrol; the fuel that has kept their engines running sweetly for over 60 years. Far from any celebrations I predict that most of their time will be spent chasing around for a suitable replacement for the dreaded lead, now banished from the pumps after many years of successfully helping to control knock and valve seat recession. An alarmist view perhaps, all the more so because at the beginning of this season I felt confident that some inspired boffin with commercial backup would develop a lead substitute that, would make him a small fortune and the old car movement happy to go along for the ride. Now, in the middle of November, I'm not so sure. Here we are, only six months or so away from a point where leaded petrol starts being withdrawn from the tanks, and there is still no lead substitute on the UK market that has been scientifically proven as a satisfactory substitute! The good news, as I write, is the FBHVC investigating the merits of available lead substitutes, and hopefully in a few months time they will be able to recommend something that will do the business.

In the midst of all this inactivity, my 4AB Roadster, back on the road after a two year lay up, decided mid-season to develop `water in the oil' symptoms and it was weird, for once to have a rising level on the dipstick.

With bad starting accompanied by droplets of water in number two cylinder, the probability was a weepage from one of the water passages. So the head was removed, and with some bowing evident, was given minimal skimming by local engine specialists in Kingston. But while this work was underway I began to think more about the uncertainties surrounding the long-term future of lead substitutes and lead replacement petrol, and decided to take this opportunity and have it converted for unleaded, side-stepping the leaded issue once and for all.

Talking to the engine re-conditioners about converting heads to unleaded petrol, it became clear that there is much difference of opinion here as on the lead replacement issue, but I accepted their standard treatment of fitting hardened steel exhaust seat inserts only, used in this case with the existing XB rated valves. The cost of fitting these inserts was just over £100. An alternative view suggested an expensive combination of bronze valve guides, stainless exhaust valves and hardened exhausts seats were the way to do it, whilst the opinion of another engineer spoke of bronze valve seats and stainless valves necessary to deal with the problem.

All very confusing to the Singer layman, who would welcome some no-nonsense technical advice to put him straight on the matter. One thing is sure, however - the Singer .9 Roadster/Ten head can be converted, for there is enough support metal beneath the valve seat to accept an insert. One thing not so sure is whether the 1500cc head used on SM1500's, 4AD Roadsters and Hunters can be successfully converted to unleaded. With an undercut area directly below the valve seat, my engineers doubted is there was enough base metal to take an insert satisfactorily.
But all is not lost, for without a trail attempt, theirs is just another opinion open to challenge, and at the bottom line, there is still an optimistic choice for the 4AD owner of lead replacement petrol or efficient lead substitutes - when they eventually arrive.