[TR] TR4 - Dwell v Points Gap

[Jeff Scarbrough]

At 11:56 AM 6/1/2008, Geo & Kathleen Hahn wrote:
>I believe the dwell for a correct TR4 distributor is usually quoted as 60* or
>else as a range centered on that such as 57* - 63*.  Points gap is either .015
>or a range of .014 - .016 depending on where one looks.

60 degrees sounds like a lot of dwell...are you sure about that?  I 
would guess 45 to 50 degrees would be more likely...


>I have always set the gap and thus ignored the dwell but recently I looked at
>both.
>
>I find that I cannot adjust to both specs.  A .015 gap yields a dwell of 48*
>--- a 60* dwell can only be achieved with a .008 gap.

I always set the gap, then fine-tune with a dwell meter.

>Either way, once I re-adjust the timing, the engine runs fine.  Maybe not
>exactly as well each way but any difference is beyond my notice.
>
>Soooo... which way do I set it?  Or do I split the difference?  Since the
>relationship between gap and dwell would seem to be purely mechanical based on
>the shape of that little cam in the dizzy it doesn't suggest to me that
>anything is really wrong.

The relation is purely mechanical as you suggest, but... there are 
many things that can affect the measurement...

Make sure the points are smooth - no pits, depositions, or wear of 
one contact into the other.  Any of these could affect the ability to 
get a feeler blade between them without changing the effective 
dwell.   Make sure the lobes on the distributor are smooth and 
unworn.  Are the points uncontaminated with the grease you put behind 
the rubbing block?

Make sure your dwell meter is operating correctly, possibly by 
testing it on another car.

>No I don't want a Pertronix, having so much fun with this set-up.

As long as you're having fun... <g>


Jeff Scarbrough      75 TR6 x 1, 76 1500 x 2, 78 1500 x 1, 80 1500 x 0.5
http://www.fishplate.org/vehicles/
Athens, Georgia         #354