TR2/3/3A Distributer defective?

When I rebuilt the motor in my TR3A I reused the old distributer. Put new points, condenser, cap and wires. Timed it up and it fired on the first try. Great.
I had noticed the distributer had some play in the main shaft so I got a new distributer from one of the big 3. The old distributer is a DM2 with side exit plug wires. The new one is a 25D with top exit plug wires.
I put the new distributer in the car but left the cap in place as I did not have the push in wires the new cap takes. No start. Check the timing still no start. If I pull the coil wire off the cap and flick the points I get a great spark but putting a plug on a wire touching the head I get no spark.
Checked all the dimensions I can think of in the caps and the height of the rotors and they are all the same.
I am not sure if I have swapped the rotors when I swapped the distributors.
Putting the old distributer back it starts right up.

Any thoughts.

David

David,
check the two units to be sure that they are both set up the same. Namely that the offset at the bottom of the units allow the rotors to point to the same place or plug. I had a distributor that was 180 degrees off. You can still use such a unit but you will need to change the locations of the plug wires on your cap. Distributors for the MG ( that use the different caps) are 180 degrees different from the TR's.

Hello Charley

Thank you.

I will check that in the morning. I think they are the same but I will double check it.

David

180 degrees wouldn't stop the spark; just keep the engine from starting. But a smaller angle error might keep the spark from jumping the gap from rotor tip to cap.

My first suspect would be the rotor, there were some bad rotors made some years ago.

Been a lot of years ago; but the NAPA store in Breckenridge CO had the parts to convert the wires for a top entry cap. All you need are the boots and the brass contacts. Slide the boot on, strip the last 3/8" or so of each wire, fold the center conductor over and install the contact.

You said you could manually open the points and get a spark there. That suggests all the wiring is OK. However, double check that the points are open about 0.015" when the heel on the moving arm of the points is resting on a "corner" of the 4-lobe cam that sits below the rotor.

In addition to Randall's comments about bad rotors being on the market, make sure the carbon brush button is still in place on your new cap.

I cannot address the availability and quality of distributor caps. However, when I last bought new ones you could still get the "right angle" caps for the 23D4 and 25D4. They have small openings so I believe they are limited to 7mm wires.

David, from your description it has to be something in the rotor/cap relationship. Either a bad part or an alignment issue. Alignment could include the key on the cam shaft.

Just checked the caps and they match so I swapped the distributer again noting where the rotor was pointing. It was hard to get it to engage in the drive, took a bit of pushing to get it to engage. So the problem may have been I did not have it fully engaged in the drive.

Started right up.

David

Isn't it great when you can get it to work and it did not cost you another arm and a leg.