In the latest issue of ``The Courier'' (the monthly magazine of the
Triumph Sports Six Club) there is a report on a presentation given
at the the Federation of British Historic Vehicle Clubs meeting on October
28 1989. Part of that report is a summary of a presentation given by
one Dr. Vincent on the subject of unleaded fuel in older cars. Dr. Vincent
is a specialist in fuel technology and also a vintage Alvis owner.
This presentation appeared to be the result of a series of
properly conducted bench tests on various engines and is of great interest
as most of the information on the subject seems to be of the `I've used
unleaded and my engine hasn't blown yet' variety.
The report is rather long so I won't re-print it here but the most interesting
points given were:
1. All engines with cast iron heads and no special hardening of the
exhaust valve seats will suffer SOME damage running on unleaded.
2. The extent of the damage depends on the engine and on the engine revs.
On tested engines the seat recession was found to double in some cases
as engine revs increased from 3800 to 4400.
3. No tested petrol additives prevented valve seat recession completely.
Some were better than others but NONE were able to replace the action
of the lead.
4. The minimum critical level of lead in the fuel is about 0.07 gPb/l .
Current levels in UK leaded fuel were 0.15 gPb/l and so mixing alternate
tanks of leaded and unleaded was likely to be successful.
5. It is impossible to predict wear rates accurately and often wear
shows up predominantly in only one cylinder.
6. Fitting hardened valve seats or performing induction hardening on the
valve seats was found to be effective in engines where either of these
processes could be done.
Also recent tests done by Rover and reported in the classic car press appear
to back up the theory that although unleaded petrol does damage all iron heads,
the less spirited driver will not notice problems until a high mileage has been
covered on entirely lead-free fuel.
Finally, tests performed by Rover have shown that the tin-alloy fuel additive
marketed as ``Carbonflo'' in the UK, does not work at all !!
So, it looks like when unprotected engines are bench-tested on unleaded fuel
and then stripped down, damage will always be evident. However, drivers seldom
complain of trouble running on unleaded---perhaps because they are not reving
the engine or are not covering high mileages.
I should also say that Bill Sohl may be partially correct about Triumphs as
many of the later models shipped to the US were fitted with stellite valve
seats. However, the Triumphs in the rest of the world, as well as older models
certainly can not be run on unleaded.
David Boreham, INMOS Limited | mail(uk): davidb@inmos.co.uk or ukc!inmos!davidb
Bristol, England | (us): uunet!inmos.com!davidb
+44 454 616616 ex 547 | Internet: davidb@inmos.com
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