TR2/3/3A idle wandering TR3a

[Jim Lee]

I was kind of right. But nothing as dramatic as a break. The male part at the bottom of the distrib shaft (distrib drive dog?) had jumped the shark as in it was not engaging in the female
part that it is supposed to. I was able to get it back in and hook that up but I am still baffled at how it jumped and also why it would jump after
xx number of years. First thought was the the distrib assembly was not fastened tightly with the two bolts that attaches it to the platform.
They were tight as I assume they have always been. I do not remember ever taking the distrib out before. The next thought was that perhaps
the extra washers on the right side bolt that were beneath the assembly was keep it too high. But if it was too high, and have never removed the
distrib, and the nuts were not loose, and there was definitely no play in that two nut connection. Then what did it all of a sudden decide to jump up
and out of the slot now? That pin is pretty thick. Definitely not less thick than a washer or two.

I am in process of putting the distrib back in with the dog engaged so that the rotor can do its thing and if it stays in there forever that would be fine with
me but I am still going to be curious as to what happened in the midde my testing yesterday. I was actually looking at the timing mark with a strobe and driving
around the neighborhood minutes before this occurred.

Any ideas on apparent mystery?

Thanks,
Jim Lee

 

[TR3driver]

This picture still isn't making any sense to me. The distributor shaft has to turn at not only exactly the right speed, but at very close to the right phase relationship to the camshaft & crankshaft; or the engine will not run at all. If the dog did somehow manage to jump out of the slot, the engine would stop running until the gear made a full turn (two crankshaft revolutions) and the dog fell back into the slot.

The gear rides on a brass bushing that is pressed into the cylinder block below the pedestal. If that bushing was somehow broken, it might let the gear fall low enough for the dog to slip out. At the top of the pedestal, there is a sheet metal bracket (the thing that carries the horizontal pinch bolt) which is supposed to clamp onto the distributor body. If that pinch joint was loose, or the ridge on the body was broken, then the distributor could move upwards enough for the dog to slip out. Try grabbing the distributor and pulling upwards; if the pinch joint is the problem then it will come off in your hands.

Overtightening the pinch bolt is how the distributor body gets broken. You can try building it back up with JB Weld or whatever, but usually it means a new body. Fortunately the same body was used on basically all 4-cylinder British cars of the period, so they are frequently available cheap (in rebuildable condition).

The washers underneath the pedestal sound troubling, though. Sometimes it is necessary to add as much as .030" to that joint, to set the appropriate end float for the gear, but it shouldn't be any more than that. Most engines are worn enough by now to not need shims at all. If someone has mistakenly spaced the pedestal up in the air by 1/8" or more, then there might be enough slop to both cause your idle problems and occasionally let the dog slip out. Might even be that the gear bouncing up and down has now broken the bushing? At any rate, I would want to double-check the end float of the gear, since it seems something is not right.

PS, do you have a DM2 or 25D distributor? The Jaguar club article that Ken linked to above shows the 25D mechanism. The DM2 differs somewhat in the details (and has extra pieces), but still uses the stop to set maximum advance.

 

[CJD]

Are you sure one of the lower shaft sides is not broken?

 

[Jim Lee]

Fellow colleagues in the art of the TR3,

Had a couple of hours to play/fight with the TR today.
One thing I should make clear(er?). After I discovered
the rotor floating around the car never started. I might
have given the impression that I was driving around with
the distrib shaft disengaged. My path to the rotor was
when I was trying to start and it was doing absolutely nothing.
I picked up my strobe light and could see that there was no
spark. That is what led me to the distrib and thus the rotor
and thus the getting intimately acquianted with my Lucas
distributon this afternoon.

I think the root of my problem might be a beat up clamp.
I was able to get it together so that the rotor is
firmly engaged. Have not tried to start it yet because
I am tired. I probably put took the distrib in and out
7 times. Various problems with 54 year old nuts and bolts.
I put the distrib in once and noticed a gap of exactly
3 washers between the clamp and what it bolts on to.
Initially I put 3 washers in there to make sure I did
not bend up the clamp. When I did that I could feel
that the shaft was just barely touching whatever it
needs to touch. Touching so that the rotor was essentially
floatinig around as before. Put it on again and all of a sudden
no gap. Now it feels firmly engaged. I am hoping that tomorrow
I can twist and shout at the distrib and check the timing out

A question. Does an engine that is more retarded (special needs)
make for a harder to start engine? I did have a glimpse
of the timing once before the distrb adventure and it looked
to be about 10 degrees or more retarded.

Thanks very much and thanks for all the help.

Jim Lee

 

[TR3driver]

After I discovered
the rotor floating around the car never started.

Oh, OK, that makes a lot more sense. And it sounds like you are on the right track now.

10 degrees retarded would make it take more throttle to keep running, so might make it hard to start if it didn't have enough throttle (no choke or fast idle cam not working).