>> is, set the timing at 4 ATDC like the book says. Needless to say, the
>The timing of 4ATDC isn't as absurd as it seems, because when you touch the
>throttle to accelerate and the manifold vacuum plummets, the retard backs
What happens is practice isn't this. Assuming a "normal" well worn TR6
with dwell and timing adjusted per the manual with the retard "on", i.e
4 ATDC.
>off and you get back into "normal" range.
NOPE, you're wrong. On a new car maybe, but not any I've seen...
There are various stages of each of the following:
1. vacuum units leaks etc. and doesn't work correctly
2. pivot plate is worn so the movement of the rod "torques" the plate
(you can see this if the upper plate will "rock" on the lower)
ANYONE HAVE A WAY TO FIX THIS, I used to buy new plates for $10
but haven't seen them for sell in years, rebuilt dist's though,
so I suspect they exist, likely more profit at $250 vs. $10?
3. cam wear, it would appear the metal cam wears, hard to believe,
but the scoring I've seen came from somewhere. This means that
as the shaft raises, leans, or the pivot plate moves, the profile
changes. I've seen 1/4" vertical movement of these shafts.
4. bushings, these allow the shaft to "lean", you'll note as much as
1/8" on some. This sideways movement effects the dwell which effects
the timing. 1/8" is 0.125, with points gap at 0.015, seems we've
got the ability to toggle the ignition off/on.
The net result being a perfect example of a variable mechanical circuit
providing a variety of dwell/timing combinations based on engine speed,
vacuum and the "height" and "lean" of the cam. You end up with an
engine that is "only" in tune at the time you set it. I've seen +/-
4 degrees of dwell and +/- 2 degrees of timing with this setup.
I plug the retard line at the carb with a 1" hose and a 1" rod/bolt the
size of the carb fitting, i.e.
dist line -> elbow -> rod -> 1" hose -> carb fitting
This seals the carb, maintains the appearance and eliminates this weak
attempt by Triumph to spoof the idle emissions laws at the time.
This elminates 1 and 2 and seems to limit 3 and 4.
Oh, this is NOT just an idle thing, though that's what it was for
initially, it also works every time you let off the gas and or change
gears, i.e. built in hesitation at best, variable dwell/timing and
a burst of unburnt fuel as the engine coughs between gears at the worst.
An electronic ignition conversion will give you a hotter spark with
the stock coil and avoid the rest of the above problems. A vast improvement.
You can see this on some cars as a 1 degree "blur" with the timing light.
(after electronic conversion, this becomes a razor sharp, bright beam)
WHAT COULD HAPPEN YOU ASK?...
You'll also note that no dist shaft is worn past the 1/8" movement.
Triumph designed in a self correcting feature here, pretty slick
I'd say. Just past 1/8" lean, the weights will catch on the distributor
body preventing the shaft from turning... well, the shaft is connected
to the cam, the cam to the crankshaft..., crankshaft to the rear tires
and the car is still rolling..., hummmm.
Now for the fun part, first you hear the metal to metal of the weights
hitting the dist body (your left leg starts for the clutch pedal).
Next you hear a loud chicken tortured as the distributor body rotates
about 200 times. There is the additional sound of torn metal as the
dual vacuum units (it would have to be the rare dist!) are ripped off,
not being able to pass the head as they rotate (your left leg is now
on the clutch pedal). Finally, there is complete silence as the
ignition wires are converted into a 6 strand twisted wiring harness.
This is about the point that the cluch is disengaged and a lovely
Monday morning drive to work is destroyed by the failure to fix $1
worth of bushings. Our hero now is fully awake and madly attempting
to find the right lane, avoid being rear-ended and quickly searching
for cops and/or lawyers which might be interested in the many pieces
of the early model TR6 distributor which are now bouncing down the
freeway.
Thanks to previous experience, our hero grabs the previously made
out check from the glovebox to Chotes Wrecker Company ($45 from anywhere
to anywhere in the city limits on a flatbed), nails autodail #1 on
the cell phone and has the wrecker on the way before the car stops.
Thumb out, pausing slightly to avoid the folks that picked up the
larger bouncing pieces in their grills, our hero makes it to work on time.
NEXT TIME...
redline tire detonation at 75 mph in 104 degree heat
OR frame off restoration vs. flying steel belts
OR new record set for unmounting tire on moving car
--
Roger G. Bolick, rgb@exact.com 512-794-9567, FAX 345-2879
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