>
>In article <01HWRWKBHBJ2000459@holly.nene.ac.uk>,
>"Richard Jackson -Network Technician ext. 2570" >
<RICHARD.JACKSON@nene.ac.uk> wrote:
>>
>> I have been using a mix of unleaded with the occassional dose of lead for
>> nearly two years and 40,000 miles, when I did the clutch the other
>> week I noticed how easy it was to turn the flywheel by hand, so
>> hopefully in the near future I'll whip the head off and check the
>> state of things in there, I don't think it rings causing the lack of
>> compression as itdoesn't burn any oil, but it's a Triumph, so who knows.
>
>After approx. the same mileage on very low lead and lead-ersatz petrol,
>the exhaust valve seats on my 150bhp 2.5 PI were pretty well burnt, to
>the extent that one exhaust valve har a crack in it. The inlets were
>still perfect.
>
Perhaps; however burnt exhaust valves are most often caused by setting the
exhaust valve clearance too tight or by too lean a fuel mixture. Tighter
clearance will make the engine less noisy but allows the exhaust valve
less seat time in the head and, therefore, less time to loose heat to
the mass of the head.
A lean a fuel mixture may give good fuel economy but too lean a mixture
allows a lot of supper heated Oxygen to flow past a hot exhaust valve
burning the valve. It is better to have the mixture a bit rich,
especially if you are accelerating hard (read driving hard). Remember,
your Triumph probably doesn't have a modern fuel system with an oxygen
sensor and computer to automatically increase the fuel to oxygen mixture
by sensing too much oxygen in the exhaust gas.
Please be sure to check these two things first and frequently - the new no
lead valves will not help much if either the valves are set too tight of
the fuel mixture is to lean.
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