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MG MG Y Type - dwell angle

I just treated myself to an used dwell-angle meter because I know that with it, you can check the contact-point-gap better than with feeler gauges.

Now for the embarrasing part: can somebody please explain where I connect the red and the black wires (positive earth), and which dwell-angle a standard YA should it have...?

I searched on the attic for the textbook I should have about the theory behind dwell-angles but I couldn't find it. Can any of the "old hand electrical ingnition wizards" enjoy us with an in depth clarification?

Thanks,

Willem
Willem van der Veer

Willem - The red (pos) wire should go to ground or the most positive side of the circuit, with the black (neg) wire going to the most negative portion of the circuit or to a 12 volt source. If the dwell meter is just a two wire unit, it would be hooked up with the red lead to the connection between the coil and the points in the distributor (to the primary connection on the side of the distributor). The black lead will go to the other side of the coil (the primary connection marked - or SW (ignition switch).

Regarding the dwell angle, all I have is for the TD and it depends on which type of cam is inside the distributor to open and close the points. For the TD the values are:
Symetric cam 45° + or - 4°
Asymetric cam 49° + or - 4°
High lift cam 60° + or - 3°

If I had to guess which type of cam is in the distributor for the YA, I would guess either the symetric or asymetric. I have some pictures somewhere that shows the difference in the cam profiles that I will send to you when I can find them.
Good luck - Dave
David DuBois

Willem - I think that I may have given you the wrong connections in my last post (I use a later, 3 wire dwell meter and am not certain of the 2 wire unit's connections). It would make more sense that the 2 wires be connected, with the black wire going to the primary terminal on the side of the distributor and the red wire going to ground. This makes more sense when one considers that a dwell meter is reading the amount of time the points are closed verses the amount of time they are open. Cheers - Dave
David DuBois

Would it hurt the meter to connect it backwards? I have a two-wire meter as well (same meter as the RPM meter discussed in another thread) and I was thinking of trying it out for setting points.
Steve Simmons

Steve - I don't know if it would hurt the meter to hook it up backward or not. It might cause the needle to deflect downward, which in itself won't hurt the meter. All you can do is give it a try and watch which way the meter deflects. If it goes up regardles of which way you have it, then look at the angle it is reading and see if it is close to what you expect. I suspect that hooked the way I originally told Willem, the meter will give the complement of the angle you expect (a 3 wire dwell meter does that when connected to a positive ground vehicle - in fact the Gunson meter gives a conversion chart for use on 6 cylinder engines, 8 cylinder engines and for positive ground vehicles). Having never used a 2 wire dwell meter, I am not sure what you will see.
Cheers - Dave
David DuBois

Dave, thank you very much for your info, it is exactly what I hoped for! By the way, I have a two wire dwell-angle/RPM meter (made in Taiwan....)
Willem van der Veer

FWIW I use a dwell meter on my MGA (+ve earth) and connect it with red to ground and black to battery. The remaining connections as per the instructions. No problems so far.
Dan Smithers

Dan, that would be black to battery negative, correct?
Steve Simmons

Being of a grumpy old disposition, I still use an old bit of wire with a 12v bulb. Until it wears out I will forgo a dwell meter.

Neil.
Neil Cairns

Grumpy, how do measure the contactpoint-gap with a piece of wire and a 12V bulb, please "enlighten" me?
Of course I only bought the dwell meter at a car-boot sale to be able to say I have one! But as the weather forecast is good this weekend I'm going to try anyway.
Willem van der Veer

Steve, that's right. It won't hurt anything if you connect it to positive, but the meter won't work.
Dan Smithers

It might if you connect the negative wire to the positve terminal and vice versa!

Good luck,

P
Paul Barrow

Dwell is nothing more than a different way to measure points gap. The person who is good with a feeler gauge can be every bit as accurate setting the points that way as can be obtained with a dwell meter. My method, since I'm not overly profficient with the feeler gauge, use it to rough in the points so the engine will run and then refine it with a dwell meter.

Neil - I guess that I worked to many years in the world of electronics. I feel like the job is unfinished if I haven't seen a meter needle swing back and forth a couple of times. Cheers - Dave
David DuBois

S'wot I do too - I'm with Dave on this one.

Paul
Paul Barrow

This thread was discussed between 02/03/2004 and 27/03/2004

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