Triumph Repair: Fuel and oil viscosity, triumph spitfire 1500, richard ferris

Question
Jim,
I own a 1973 Triumph Spitfire 1500.
I have 2 questions.  What viscosity oil would you recommend?  And also would you recommend unleaded
Reg. or Premium fuel, and should a leaded substitute be added to the fuel?
Cheers
Richard Ferris  

Answer
Richard,

Both questions tie into what kind of shape your engine is in.

First off, I tend to run 20W50 in my english engines.  This is mostly because they are all built with slightly looser tolerances than we're used to today, and all of the engines are between 25 and 40 years old!

Especially here in the Dallas area where cold weather driving is not an issue.  The thicker oil does rob some engine hp to pump... but I prefer to see the oil pressure guage to register real pressure when I'm driving in the summer!

So, if you have an original unmolested 1973 Spitfire 1500.. it may be worn.. just a bit.  :-)

And if it's a truly original '73 engine, it should have the dished 7.5:1 compression pistons.  Assuming that the carburetor mixture is correct and the timing is set correctly and the distributor advance is working correctly (I'm an engineer, I need to leave myself these "outs" :-) then regular octane gasoline should be ok.

If the engine hasn't been rebuilt then you're running a cylinder head without hardened valve inserts.  The factory did do a "flame" hardening of the exhaust seat area and if the engine hasn't been badly abused then this is usually sufficient.  

As to lead substitutes...  on the one hand I think they're like snake oil....  sold to the gullible public....

but I do use it regularily in my Mini Cooper... so I guess I'm part of that gullible public!

Cheers,

Jim