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Andy's Austin Seven Page - Unleaded Petrol

WARNING. When I started putting information together on unleaded petrol I thought I knew a bit about the subject. I now realise that I know very little and suspect that many others know less than they should. There are arguments for and against unleaded petrol and lots of opinions on what to do with older engines. I cannot be held responsible for any damage to health, motor cars or the environment as a result of anything you may read on this web site. Where I refer to 'information' this is not an endorsement or an indication of accuracy. The opinions expressed are probably held in good faith but many are conflicting. You are on your own chum, good luck.

I don't really know much about unleaded conversions but I do know that various organisations - universities etc have researched this and published their findings. Unfortunately I don't have any of this material, all I have is verbal accounts from friends who have read articles in historic car magazines which in turn are loosely based (one hopes) on the original scientific study. The concensus of half a dozen English Austin Seven owners on an evening in December 1997 in a saloon bar of a pub in the London suburbs was as follows: The main problem relates to exhaust valve recession caused by overheating of the contact surfaces of the valve and seat. Lead tetra-ethyl fuel additive provides a transient coating on these surfaces which acts like a lubricant and prevents erosion of the critical surfaces. Lead-free and 'low lead' fuel does not have this effect. Modern engines which are designed for unleaded petrol have hardened valves and seat inserts and sometimes valve guides of a type of metal which will conduct heat away quickly. A low power, slow revving engine will produce less heat and have the valve and seat in contact for a greater time which will conduct more of the heat away from the valve. Such an engine may be safe with unleaded petrol. Medium to high performance engines designed for leaded petrol may need to have special exhaust valves (stellite? high chromium content?) and special valve seat inserts fitted to prevent seat recession. They may also need to have the ignition retarded to prevent pre-ignition.
The Austin Seven community does not seem over concerned with this issue, apart from a few people who have been using unleaded for a while with no apparent ill effects there is no experience on which to draw. I intend to get the valves and seats of my Austin Seven into good order together with new valve guides and then run with unleaded fuel, checking valve clearances and cylinder compressions periodically.

See Roy Berry's article on Unleaded petrol on page 51 of the March 1988 edition of The Automobile magazine.

See articles in Practical Classics (UK) DEC 89 and JAN 1990 about Carbonflo and Broquet

The Federation of British Historic Vehicle Clubs (FBHVC) has given me permission to reproduce these articles from their News Sheets.

There is a booklet 'Valve seat recession and the use of unleaded gasoline in older engines' which was published on behalf of the VSCC and is now available from the Federation of British Historic Vehicle Clubs (FBHVC)PO box 2506, Henfield, West Sussex, BN5 9QW price �5.50 plus p&p

Personal experiences

  • California has not had lead in gasoline for some years and before that it was very low, phased out over a number of years. I restored an MGA in about 1987 and installed hardened seats and bronze guides as a precaution. It performs just fine with not a hint of valve recession. I have driven it on some long trips at 3500-4000 rpm for long periods in hot weather, ie desert, with no problems. I have since since restored a MG Midget and a MGB without changing from the stock heads. Both have shown some valve recession, but not a serious amount. What I mean is that every 5,000-10,000 miles I check the valves and some times I have found the exhausts a little tight so I readjust. Last time I checked the MGB it's valves were just right. I gave the Midget to my daughter when she graduated from college and she or her boyfriend didn't adjust for a long time and a slight miss developed at idle. I found the exhaust valves to be tight and set them to nominal and it runs fine. None of these cars get the work out pulling a trailer could give, so if I were rebuilding an engine I'd install hardened seats and bronze guides as a safe solution. The guides should have about 0.001in more clearance than stock or the valves tend to stick. I think this was discussed in some postings in the last 6 months or so.
    Regards,
    Jack (California U.S.A.) March 1998

  • Ruairidh Dunford of Glasgow has written a letter in the 1998B edition of the Austin Seven Clubs' Association about his experience of driving 97,500 miles in several Austin Sevens using unleaded petrol with no ill effects.

    WWW resources

    I searched the www for references to 'unleaded petrol' and unleaded conversion' and found lots of references but nothing with any great authority, you might be luckier. I did find a few engine reconditioners in the UK who have done several conversions, there are links to some below.

    There are some web sites with technical information about the use of unleaded petrol:

    http://www.kipping.co.uk/info/unleaded-article.html

    http://www.rroc.org.au/info/unleaded.html

    http://www.faqs.org/faqs/autos/gasoline-faq/

    There is some official information

    http://www.erin.gov.au/portfolio/epg/fact_sheets/leadswitch.html

    UK Department of transport

    And some unofficial information

    http://www.altnews.com.au/nexus/ulp1.html

    http://www.altnews.com.au/nexus/ulp2.html

    http://www.altnews.com.au/nexus/ulp3.html

    http://www.strathcona.vic.edu.au/~jtaylor/petrol.htm

    There are additives and catalysts available:

    Broquet

    comments about catalysts Consumers' Institute of New Zealand

    and a complaint about advertising of catalysts Advertising standards authority

    There are engineering companies who do unleaded conversions:

    Ferriday - engine reconditioners an unleaded conversions

    http://www.pjcleigh.demon.co.uk/Engine.htm

    http://www.jandm-machine.com/

    Beckett & Garner Ltd of Hodgson Street, Sheffield, South Yorkshire (tel 0114 272 5074)

    Footnote

    The organisation mentioned above "half a dozen English Austin Seven owners on an evening in December 1997 in a saloon bar of a pub in the London suburbs" is not an official UK government body nor does it pretend to be such.

    Do you have experience of conversion to unleaded fuel? If so I should be very interested to hear from you What did you do? What did it cost? How many miles have you done since? There seems to be a dearth of this information and the Austin Seven community does not seem keen to be at the forefront of this issue. Please say if I may publish your message and if I may attribute it to you and include your email address or not.


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