Another Pro Mag Issue

Running a KB Olds, AJ Chevy Heads and a big cap Pro Mag 44 out front on a RCD reverse rotation 90 degree mag drive so it converts the Chevy to a Hemi rotation. Ran it for several years starting on the crank trigger with a 12v block mounted "Chinese Chrome" starter. Could start on the mag or crank trigger and I could set the timing the same on both so if I wanted I could switch back and forth if needed and not move anything. Always ran on the crank trigger though and never had an issue starting.

At a race about two years ago we broke a belt and a between round thrash resulted in getting the hex drive for the pump extension one flat off. To compensate, we moved the plug wires a couple of cylinders and adjusted the mag body to get it to fire. Since that time, we have not been able to get the engine to fire correctly on the crank trigger. Tried moving the hex back and forth, moved plug wires and tried different phasing's on the mag body and nothing will let us fire correctly on the crank trigger. Sent the mag back to Leahy and it's got a clean bill of health and puts out 50 amps. Tried several crank trigger pickups with no change. Runs fine and dandy on the mag. We switched to 24v starting and will start on the crank trigger but only when the timing is set to 36.5 degrees or above on the trigger. We run normally at 35 so this won't work for the combination. When running on 12v start, it would start only with 39 or above degrees on the trigger.

I talked to Dave, called MSD several times, talked to BR Motorsports and everyone says just drop it in and it'll go. I'm pretty sure it's a phasing type issue but can't seem to nail it down.

 

You have the mag at 36?

 

Start the engine and set the mag at 35. Look at the rotor phase and it's right on. Will start on crank trigger after that if it's at 36.5 or above but will not if set to 35.

 

Are you actually running 35 degrees or changing it electronically?

 

Checking the mag with a MSD battery powered timing light. Set the mag at 35 on the pointer. The pointer was checked and adjusted relative to #1 piston at TDC. Move the trigger pickup to 36.5 or above and will start. Taking timing with light and say it's 36.5, shut off engine and move pickup 1.5 degrees (by referencing the RCD degree ring) to 35 degrees and the engine will not start. No other changes. Move the pickup back to 36.5 or above and it will start right up. Pickup gap is at .045. Have used both MSD and Leahy pickups with the same result.

 

Check the rotor phasing when cranking, to see if its at the same place that when running.Is there a timing adjust box on this?

 

I have the big MSD test cap with eight holes in it for checking rotor phasing so I can see exactly where the rotor is in relation to the terminal. This problem was there with a MSD Grid and the current Davis Profiler I use. If the timing is below 36.5 degrees, the timing light will not flash so I can't get a reading and it will not start. If the timing light flashes, it will start.

 

Tom I'm guessing you are just on the edge of firing and had the perfect combination of luck and magic to make the system work before.
I measured the output of a bunch of triggers and the lahey put out the most volts. The 3/8 threaded Msd starts the best though. We unhooked our trigger changeover circuit this year and knock on wood have started fine at 4 races.

 

I hear ya Mike. I have schooled a lot of people on how to set up a mag including all the phasing details and it's all worked for them. I thought I knew what I was doing but this one has just bit me in the butt and I can't find a solution. Running on the mag seems to work fine but the RacePak graph is very noisy over running on a crank trigger. I suppose I should just go to a Hemi and get rid of this issue and tackle all the problems you have encountered, lol. I'm convinced it's something in the phasing and the way the mag drive operates I'm using but I just can't figure it out.

 

If the the wrong rotation mag is installed will it even run?

-Dale

 

The firing order would be backwards. I don't think the engine would run like that. In my case it runs fine on the mag but not the crank trigger. One thing I did is borrow a friends mag with a small cap and it started right up on the crank trigger and I could time it correctly. It may not be the small cap but may be something weird with the mag I have. I'm getting to a point where I'm out of ideas.

 

did you check the the wiring in your mag plugs? sounds like 2 wires could be switched. compare it to the mag you borrowed.

 

For any given angle, the small cap will have less linear distance from the rotor tab to the plug wire post in the cap. Way back at the beginning of the thread, you said you moved plug wires around to correct for the hex drive. Could it be possible the mag is firing 'backwards' to the plug behind the rotation? That could explain why moving away from 35 to 36.5 or higher is working.

Chris Saulnier - Team Tigges
Mechanic Falls, Maine

 

Pretty sure I did that before but I'll double check it this weekend. Thanks for the reminder.

 

I would think that would cause an issue if I didn't look but I have the big MSD phasing cap that has eight big holes in it to make sure the rotor is pointing at the correct plug wire. It is and I have adjusted to right on and also to lead to compensate for pulling timing and still have the same issue.