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MG MGA - DM2 distributor position

Was previously running a non-vacuum advance Lucas distributor which I believe is a 45D but not sure of the model because there are no numbers on it. Have acquired a rebuilt DM2 and am having trouble setting the static timing. Isn't the position of the vacuum advance unit supposed to be more or less vertical? When I did get the engine to start (only for a few seconds), the vacuum advance unit was angled toward the rear of the engine and hitting the oil hose and the spring clip that holds the distributor cap was jammed against the top of the starter! Also, the starter barely turned the engine over. I had no. 1 piston at about 7 BTDC.

Thanks for any help!
Tom
Tom Custer

Vac unit should be near vertical. See here: http://mgaguru.com/mgtech/ignition/ig103.htm
Hard cranking was likely a result of still too much spark advance.
Barney Gaylord

Tom -
The vacuum unit should be vertical so the tube goes straight up and then around to the rear carb. Easy enough to turn the dizzy 90 degrees and then rearrange your spark plug wires.
I static timed my 1500 to 7 degrees BTDC and then used a light (with vacuum advance disconnected) and with the light it came out about 20 degrees BTDC. Still not sure why the difference, but I adjusted to go with the dynamic timing. Need to go for a test run (but I still have the GT needles so it will probably still be rough!)
Steve

Tom

I hope your DM2 was rebuilt better than mine. The wrong advance lobe was fitted in mine.

My 1800 engine should have about 32 degrees mechanical advance at 3000RPM. With a static advance listed for my late 18V listed as 7 degrees BTDC, this should have required a lobe of 32-7 / 2 = 13 degrees. The lobe fitted was 7 degrees.

If I set the dynamic timing right, I found that I could not turn the engine on the starter (ignition too far advanced). If I set the static timing right I found that the engine started running flat above 2500 RPM approx.

See here for some of the info: http://www.jcna.com/library/tech/tech0015.html

Steve
Steve Gyles

It sounds like the distributor drive gear is misfitted. You can remove it and refit it with the engine still in the car but plan on getting a skinned knuckle or two getting the distributor off the engine. Check out Barney Gaylord's web site (first response to your post). I am on vacation and do not have access to my workshop manual so I cannot give you the procedure for fitting the drive gear until I get home next week. In the interim you can rotate the distributor 90 degrees to the right to solve the clearance issues with the oil pipe. You will have to rearrange the spark plug wires to account for the new distributor orientation. While the distributor is out, go ahead and get the points' opening spot on (it so much easier with the unit off the engine.)

Good luck. I'll check back when I get home to see if this helped.

Don Carlberg
D. R. Carlberg

Thanks for your suggestions gents. I solved the problem but not quite sure if it's correct. To make a long story of trial and error a short one, here's the scoop. With the 45D everything works properly with the distributor drive gear at the approximate 2:00 position (larger segment uppermost). However, for the DM2 I had to set the drive gear at the approximate 11:00 position (7 BTDC with no. 1 on compression stroke). Oddly enough, one of my service manuals (Clymer MGA/MGB) states "...on MGA's, the slot in the spindle should point approximately to 11 o'clock... and "On MGB's, the slot should point approximately to 2 o'clock..."

This trial and error engineering was about to drive me mad. After I changed to the 11:00 position and the car started right up, with vacuum advance unit in the near vertical position, I declared victory and went in the house and had a Guinnes!

Thanks again for your help,
Tom
Tom Custer

This thread was discussed between 21/02/2007 and 24/02/2007

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