TR2/3/3A Point gap and dwell.....

[karls59tr]

Anyone know what the ideal "dwell" reading should be when a new set of points are installed and gapped correctly?

 

[Geo Hahn]

I believe it is 60° ±3°.

Of course, you can set gap or you can set dwell - as both use the same adjustment. There are possibly advantages to each method and for the insatiably curious it is interesting to know what each is.

 

[TR3driver]

I believe it is 60° ±3°.

Of course, you can set gap or you can set dwell - as both use the same adjustment. There are possibly advantages to each method and for the insatiably curious it is interesting to know what each is.

Then of course, when they don't match, you get to wonder if it is your instruments, or there is something wrong with the point cam

 

[Brinkerhoff]

If you had a small block Chevrolet ( like the 283 in my 57 pick up) its much easier to adjust the points through the small window in the distributor cap while the engine is running with a dwell meter than taking the cap off and literally laying on top of the engine to get to the points to adjust them with a feeler guage. You end up in the same place but half an hour earlier !

 

[TR3driver]

Indeed, that was a great innovation by GM/Delco. In case it's not clear to some, there was just a screw that you turned to change the point gap; none of this loosening, and prying, and tightening only to discover that the adjustment moved while you were tightening.

And measuring dwell angle was considered more accurate, which was especially important on V8s with single points.

PS, found a photo of sorts
https://books.google.com/books?id=D...H#v=onepage&q=gm adjust points window&f=false

 

[sp53]

I have some old Sun diagnostic stuff I bought years ago new. I use the dwell meter and was surprised how close the points are together to achieve 60 degrees. If you have a dwell meter, first set points with a feeler gauge @15 and start the motor with dwell meter hook up, and I bet the dwell is like 40. Next I bet you have to tighten up the point gap to @11 to get a 60 dwell. IMHO when the dwell meter is used the idle returns a little quicker and the pre- ignition is reduced. The dwell meter also shows distributor problems, like a floating dwell demonstrates the shaft is wobbling in the distributor. Most mechanics will say the dwell is not a big concern on a 4 cylinder, and yes sure, but I think it helps on the old British stuff.

 

[mgedit]

If you had a small block Chevrolet ( like the 283 in my 57 pick up) its much easier to adjust the points through the small window in the distributor cap while the engine is running with a dwell meter than taking the cap off and literally laying on top of the engine to get to the points to adjust them with a feeler guage. You end up in the same place but half an hour earlier !

Had a 66 Buick Lesabre with that type of distributor. Absolutely fantastic way to set points. Since I never throw out tools, I still have the special adjusting tool I bought back around 71 just for that job! Cheers, Mike

 

[CJD]

I have some old Sun diagnostic stuff I bought years ago new. I use the dwell meter and was surprised how close the points are together to achieve 60 degrees. If you have a dwell meter, first set points with a feeler gauge @15 and start the motor with dwell meter hook up, and I bet the dwell is like 40. Next I bet you have to tighten up the point gap to @11 to get a 60 dwell. IMHO when the dwell meter is used the idle returns a little quicker and the pre- ignition is reduced. The dwell meter also shows distributor problems, like a floating dwell demonstrates the shaft is wobbling in the distributor. Most mechanics will say the dwell is not a big concern on a 4 cylinder, and yes sure, but I think it helps on the old British stuff.

Since points tend to close up as the rubbing block wears, I prefer to set the gap on the high side instead of low. The reduced preignition with less gap is likely because, with a tighter gap, you are also retarding the timing...unless you readjust it after setting the dwell.

 

[John_Progess]

I just checked my dwell this weekend and it was 55. Is it worth going in and adjusting the gap to try to get closer to 60?

John

 

[Geo Hahn]

I don't think so but do you know what the gap is now? If it was last set to .015, how many miles ago was that?

Knowing what the gap is and what the dwell gives you a benchmark - then you can use your dwell meter to see if the gap later changes.

As noted above -- you set the timing after you first set the gap or dwell.

 

[dklawson]

My father had an Olds that had the Delco distributor with the points adjustment window. I loved how easy it was to tune that ignition. I wish Lucas (or Delco Europe) had offered that for the 4 and 6 cylinder distributors in British cars.

 

[bnw]

Correct me if I'm wrong. As I recall, the dwell reading is the number of degrees of rotation the points are closed allowing maximum coil saturation for a given application. 60 degrees for a 4 banger, 32 for a V8 and 45 I think for a 6. The point gap is secondary to that number. When I ran a Yamaha shop back in the 70s, timing of the Yamaha single 2 strokes was set by adjusting the point gap, not by moving an adjustable backing plate. The gap was acceptable somewhere between .013 and .018. Widen the gap, advance the timing.

 

[sp53]

That is one way to look at it, but the distributor cams can be different. On a high lift cam on a 4 cylinder the dwell is from 55 to 63 because the lob is almost pointed and the low lift cam the lob is more rounded with a dwell of 41 to 49. So I guess the points open and close slower on a low lift.