If we all lived in an ideal world (which sadly I've not yet found) your TR6
would be very happy on 101 RM octane leaded. That was what it was designed
for and it led a happy and healthy life on such a diet. However, some
listers will have noticed from posts submitted by me over the last few
months on this subject, that the UK is going into headless chicken country
because leaded is being phased out here by Jan 1 2000.
Within the Triumph 2000 2500 2.5 Register, we've been addressing octane as a
whole over the last few months and many of our members are worried about the
effects of unleaded in fuel injected engines. The big Triumph sedan had both
the GT6 carb and the larger injected TR6 power unit derated to about 132hp.
This latter unit is of particular interest to me because I've got one
myself - but I'll deal firstly with the carb 1998 and 2498 power units.
It seems many North American users have had little or no trouble running
soft valved cars on unleaded, though I'm not too sure whether they use
self-administered additives in the tank at fill-up. Recent tests in the UK
suggest that additives having a potassium or phosphorous base compound are
best suited to soft valved engines and Triumphs in particular. We use 95
octane RM unleaded here and in unadulterated form (without an additive) the
six cylinder Triumph should be OK providing revs are kept to say 4000rpm max
and there is no load in the form of trailer or caravan. It seems to me that
octane values in the States are lower because the RM grading is not used and
our 95 level roughly equates to 88 or 91 in NA. That should be OK.
What does interest me is I want to hear from any owner of an injected TR6
that has snuck in to the States over the years. Particularly, I want to know
how the unmodified metering unit and pump are standing up to this different
type of fuel. Modified (unleaded suitable) MU's are now on sale in the UK.
On the valve seat issue, one lister said his local shop told him there
wasn;t enough room in the head to insert hardened seats. It may be that his
head has had work done to it at an earlier stage and an excess of cast iron
has been machined out of the head precluding further work. Normally,
hardened seats will go in - and easily. Chris Witor, our big six engine guru
recommends a complete change of valves and guides - and I must say I agree
with him. If you're going to re-work the head, go the whole hog and don't
just frig around with the exhaust in isolation.
This is what I'm doing with my PI head.
First task is to change the inlet and exhaust guides. Copper bronze alloy
units are going in for the inlet and exhaust as bronze has better lubricity
properties and they've got closer running clearances as well which helps to
reduce pick up wear. The inlet guides have top seals to them to reduce oil
consumption and inlet valve head contamination. Once the guides are fitted
they're being honed to 7.92mm and this should result in a clearance of about
.0006in on the inlet and .0012 on the exhaust. Standard iron guides run
looser at .0018 inlet and .0024 exhaust. Fitted bore size of an original
guide is around 7.94mm. Sure, all this work is costly and I'm budgeting
around 500 quid ($825 approx) for this work. Apart from bankrupting myself
for life in this initiative (the unleaded metering unit adds a further 300
quid ($500) to the bottom line) - I'll end up with a head that will probably
still be A1 perfect when they carry me out in a box forty odd years from now
at four score years and ten!
John Mac
Book 1: http://www.toolbox.ndirect.co.uk/triumphbook
Book 2: http://www.toolbox.ndirect.co.uk/crocus
Triumph Over Triumph magazine: http://www.cyberware.co.uk/~chips11
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