<< ...not convinced 40795A would be original on your engine (TR4A). My
information is that the 4A high compression engine used dist number 40798. >>
Wiard and Randall,
I believe there is a mistake somewhere.
MOST documentation says TR4A distributors should be Lucas #40795.
Supporting publications include;
FACTORY TR4/4A Workshop Manual,
LUCAS EQUIPMENT SPEC SHEET,
MICHELL MANUAL from local library and,
SURVEY I did of many TR4A owners a few years back.
Note: I did find a typo once in a Lucas publication in the past,
but all other info I have, including OTHER Lucas pubs, state that for
normal TR4A motors (which are high compression) 40795 is the ONLY
distributor,
with Vacuum Advance unit marked: 2-6-3 (the larger-sized numbers stamped on
neck).
Agreed that Lucas distributors can be reconfigured to different factory
curves, you'll need the correct vacuum unit (very un-common), correct weights
(common), correct advance arm 'limiter' (several common choices: 10,12,15
degree),
and correct weight springs (5 common choices).
I easily converted a good MGB 40897E distributor to TR4A specs by installing
two new 40795 spec'd springs and a 2-6-3 vacuum unit. That's all it took.
Wiard, I would recommend trying for the factory TR4A curve.
Many Lucas distributors are identical except for; the 2 weight springs, the
advance limiter arm (under the cam plate), and the vacuum unit.
Weight springs are easy - brand new 40795 pairs at Moss for about $9. Advance
limiter arm with 10 degrees stamped on it is a very common number - maybe
yours is already marked that way. The 2-6-3 vacuum units are harder to find.
But
if you can at least find a rebuildable 2-6-3 unit they can be restored. It's
the spring inside that differs - many vacuum units otherwise, exactly alike.
Or you could buy the new Mallory distributor if you can't find good used
Lucas distributors/parts but they can't read vacuum and are a bit pricey.
If you need the Official TR4A Factory Manual SPECS for a TR4/4A Distributor
and Vacuum unit - I can copy and mail it.
Regards,
Carl
'63 TR4 since '74
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