You may recall my post of about two weeks ago, seeking advice for my
1974 TR6. The problem I am having is that the car occasionally
misses at speed in 4th on the highway, typically between about 2700
and 3000 rpm. I first enter the highway after about 10-15 minutes
of driving, so the temp gauge indicates normal operating
temperature, although the entire engine, manifolds, etc., is
presumably not yet up to full operating temperature.
The first misses will occur after about 1 minute on the highway, and
only occur at speeds above 50mph. I typically get four or five
misses over a 2 minute period, and the problem is then gone. I have
not had any problems with misses in backroads driving.
Last week, I received a few suggestions, and ended up changing the
spark plugs, replacing the RN9YC plugs that had been in the car with
RN12YC plugs, noting that the rear three plugs had some carbon
buildup, and not changing anything else. This seemed to help
somewhat, but did not cure the problem.
Last night, I decided to go and purchase a timing light -- a
purchase I've managed to put off during ownership of my past N cars,
through borrowing a light from my father-in-law by doing timing
checks at his house. I decided it was probably time to have my own
timing light, and be able to check my time at my house,
rather than having to drive 100 miles to CT.
Having done so, I'm now confused about what I found, and am not sure
how to proceed. In specific, I'm having difficulty with determining
if every thing is working ok, or if the Bentley shop manual is not
entirely correct. (It would not be the first time; I'm starting to
become pretty disappointed with the Bentley manual...)
What did I find? Well, the timing for my '74 TR6 should be set
(according to TRF companion, and Bentley manual) at 10 degrees BTDC
when checked statically, and 4 degrees ATDC when checked
dynamically. I commenced by simply hooking up the timing light, and
checking to see if I could read the timing marks. The timing was
right on 4 degrees ATDC.
Well, I figured I may as well check the distributor, points, etc.,
and go through the timing procedures according to the manual. So, I
started by checking the contact gap. It was right at the .015 gap
setting, according to spec.
Proceeding onward with the Bentley manual, I checked the static
timing. It was off, I don't recall quite how much. In any case, I
set the static timing to where it was supposed to be, and rechecked
it to make sure it was set correctly. (BTW, is there an easy way to
rotate the TR-6 crankshaft for setting static timing or the point
gap? On past cars, I've always turned the crankshaft by turning on
the fan. The TR-6 fan, however, is too flimsy, and the engine is
difficult to turn by pulling on the belts...)
In any case, I went on to check the dynamic timing. According to
the Bentley manual, the first step in checking the dynamic timing is
to disconnect the vacuum from the vacuum retard unit on the
distributor. Well, when I do this, the engine speeds up from the
800/850 rpm idle to about 1150-1250. This is, I believe, to be
expected. (The shop manual says that this behavior verifies that
the vacuum retard is indeed doing something...) Yet, the rest of the
dynamic timing instructions proceed with the vacuum retard
disconnected, but indicate that the idle speed should be at the
800/850 range! But, since the vacuum unit is disconnected, engine
RPMs are now way up at 1150-1250!?!
Well, I decided that I really didn't know what to do. That is,
whether to set the timing at the 1150rpm idle with the vacuum retard
disconnected, or to use the 800/850rpm idle with the vacuum retard
connected, or whether I was supposed to reset the idle to give
800/850 with the vacuum retard disconnected, and then set the timing.
Rather than take a car which drives pretty well, and goof it all up,
I decided I'd note the timing figures, and send the results off to
this list for perusal. (And, of course, take a drive, and see if
the missing symptoms were improved at all...)
So, the timing figures:
I think the static timing is now correctly set at 10 degrees
BTDC.
With the vacuum retard connected, idle speed is 800/850rpm, and
timing is at 2 degrees ATDC.
With the vacuum retard disconnected, idle speed is about
1150rpm, and timing is at about 12 degrees BTDC.
To further muddy the picture, I still haven't done anything further
with the rear carb that may be running slightly rich, as indicated
by the carbonized rear three plugs. Plus, I drove the TR6 for a
quick ride last night after making the static timing change, and
this morning. On both rides, the missing was significantly
improved. I had only one tiny miss this morning on the ride in,
rather than the typical 5 or 6.
Suggestions? Help?
--ken
Kenneth B. Streeter | ARPA: streeter@sanders.com
Lockheed Sanders | UUCP: ...!uunet!sanders.com!streeter
PTP2-A001 |
65 River Road | Voice: (603) 885-9604
Hudson, NH 03051 | Fax: (603) 885-0631
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