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TR2/3/3A Dwell setting

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Chuck Murphy

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On a 1957 TR3 I know the distributor point gap should be 0.015. But I have trouble geting this set properly - poor eyesight or old age?? Does anyone know what the Dwell Reading should be - so I can check with my Dwell meter to see is I have the point gap correct.
Chuck Murphy
 
Believe it's around 35, but maybe someone else will chime in.

However, I'm not sure dwell angle determines point gap. As I understand it, dwell is the amount of time points remain open or closed. Again, someone with a bit more knowledge will be along.

Mickey
 
Typical 4 cylinder would be about 50 degrees. I've not seen one for the TR3 specifically. Tom
 
I know of no other reliable way to set the points gap than by twisting the screwdriver and checking with a gauge.

My garage 'tools' include an assortment of reading glasses, magnifying lenses and several jewelers' loupes. For close work like setting the points, soldering small connections, etc. I often use some visual aids.
 
I think the early distributors are 60 degrees, but I usually settle for 55. I set and re-check with the dwell until I get what I want.
 
All, back in the '70's when I got my first Dwell indicator, the MG's and Triumph's were 30-32 and they all ran great. The dwell would jump around if there was wear on the cam. That was mainly what I used them for, but it did relate to the correct setting of the points.

Wayne
 
The spec in the workshop manual for both TR3 and TR4 is 60 degrees, plus or minus 3 degrees. I've no idea what drugs the Rimmer Brothers are taking, but 32-38 is more appropriate for an 8 cylinder (Stag with dual point distributor is given as 34-38 in the Stag workshop manual).

Gap and dwell are directly related, you change the dwell by changing the point gap. The relationship is set by the shape of the point cam. Either method of measuring should be good enough; but at least in theory the dwell is the more important measurement.

My problem with setting point gap is always that it changes as the locking screw is tightened. If I get the gap perfect with the screw loosened just a bit, so I can barely move the point arm, it will still move during the final tightening. Measuring dwell instead of gap doesn't help with this problem. But usually, by using two screwdrivers at the same time (one to hold the point arm, the other to tighten the screw), I can get it pretty close after 2 or 3 tries.

Unless you are running really high rpm, dwell angle isn't all that critical for a 4 cylinder anyway. It's more so for 6 cylinder and even more than that for 8 (because as you add cylinders running from the same coil, the available dwell time per cylinder goes down).
 
My experience has been to get close to the 60 degree mark requires the points to get closer to being closed, and that requires some visual aid. When I look at a set of points that have a 60 degree dwell, they are closer to closed than if I set them with a feeler gauge. This is a problem if they start to pit because they can close up. I have found that if the points are set around a 55 to 60 dwell the idle comes down maybe 2 hundred, but I do not think there is any difference in performance. (Those old Chev points with the trap door and the Allen wrench were nice)
 
sp53 said:
.... (Those old Chev points with the trap door and the Allen wrench were nice)
Click to expand...

It wasn't just the Chevy, it was spread across all of the GM lines. I have long viewed that little door on the distributor cap so you could set dwell with the engine running as perhaps the most "user friendly" thing that GM ever did. It's shame that others didn't pick up on that even if it would have meant paying some sort of royalty during any time period that it might have been covered under patent protection.
 
Tybalt said:
It wasn't just the Chevy, it was spread across all of the GM lines. I have long viewed that little door on the distributor cap so you could set dwell with the engine running as perhaps the most "user friendly" thing that GM ever did.
Click to expand...
Wasn't that only on 8 cylinder engines, though? My 62 Chevy 6 banger didn't have it; although the 65 Olds V8 did.
 
TR3driver said:
Wasn't that only on 8 cylinder engines, though? My 62 Chevy 6 banger didn't have it; although the 65 Olds V8 did.
Click to expand...

Correct, but that feature was still spread across all GM lines as all had at least one V8 engine in their line up. Since the dwell settings were more critical on the V8 engines, it was probably deemed not worth fiddling with adding it for the four and six engines in GM's line up as they were much more tolerant with respect to dwell settings. Then again, all of this started going away once GM introduced the HEI system. I seem to recall that some CA spec cars got HEI before the rest and use of HEI was greatly expanded for the 1974 cars, but they didn't go across the board with it until the 1975 cars (captive imports excluded of course). My, how time flies when you're having fun......
 
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