Re: Unleaded Petrol

[Mike Wattam <MikeWattam@domain.elided>]

Hi Tim

What you have pulled out of the ROM agrees exactly with Tony Hart and the
TSR recommendation.

If running the Stag on unleaded (and the TR7 exhaust valves are not already
fitted) there is a fair possibility of trouble.  This may be mitigated by
using a 'lead replacement gasoline' or a lead substitute additive (these
are now in common use with reasonable results in many countries).  If the
engine is used gently, the valve/seat wear potential is greatly reduced
with unleaded, LRG or additives.

As you say, TR7 exhaust valves should give a permanent solution as the TR7
was designed to run on unleaded.  The standard Stag exhaust valve is
definitely softer than the TR7 version.  There is some evidence that later
Stag engines and cylinder heads supplied by Unipart have the TR7 valves
fitted and one of our members has confirmed this to me from his own engine
bought from Rover/Unipart about 12 years ago.  Also there is some
possibility these valves may have been fitted on production at Triumph for
cars destined for the north American market, but nobody positively knows.

Those who claim they can run their Stag on unleaded without any ill-effects
may be experiencing the 'memory' effect on valve seats due to the lead not
wearing off for a while - commonly 5,000 miles or more if used gently.

As regards timing, it is a question of assuming that the distributor
timing, advance curve and engine tune in general is not exact, therefore
some engines will be more prone to pre-ignition than others and action
should be taken to adjust to eliminate pre-ignition if it is present.

Mike Wattam
Chairman - Triumph Stag Register