List----While the subject is fresh in my head, I'd like to pass on to
those interested some relative information. I always believed there was
conflicting info on how to set the timing on those engines that still
have the vacuum retard in operation, and also some disconnected!
In the Bentley Repair Manual 86.35.15 on p. 521 instructions are given
for "dynamic timing". Using the strobe light is by far easier and
probably more accurate than static timing, so I use the dynamic, or
engine idling method.
Anyway, here Bentley instruction 14--17 says to "pull off the vacuum
connections" and then refer to the data on 85.35.00. Here, it says the
timing at idle for all TR6s' to be at 4 ATDC. One problem if done that
way, when and if you reconnect the retard line, the timing would then go
to as much as 20 ATDC. I don't know of many of our engines that would be
happy idling with timing set so far retarded.
If set that way and you don't reconnect the retard vacuum, this would
mean that the total advance at max. engine speed would still only be
around 16 BTDC. (4 ATDC + 20 BTDC= 16 total BTDC) Still too far
retarded. (Other data shows it should be around 28 crankshaft deg.) I
know these Bentley instructions has confounded some of you.
My suggestion is to set the dynamic timing between 10 or 12 deg. BTDC,
depending on model year. (Possibly less, if you are running with a high
CR.) If you want to then reconnect the vacuum retard, you can expect
the timing to revert back to the 4 ATDC that the original specs call
for. If your timing does not retard that far, it's no big deal. Rather
to get it correct without vacuum input.
As always, I welcome others to offer their findings for discussion.
The part that the thermostatic vacuum switch plays in all of this is
still being investigated.
Dick
'73 CF11143
L.A.
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