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MG TD TF 1500 - Pertronix Puzzle

I have installed the pertronix Ignitor,set the timing at TDC as is usual. The engine fired right up and I took it out for a short test run. The motor had no power and after about 10 minutes, I had it back in the garage with the coolant boiling. I reset the timing to 10 degrees BTDC and the power was much improved and the coolant remained normal. QUESTION? How far can the timing be safely advanced without doing damage. I have searched the archives for some information on this subject but could not find the information I needed. I am tryng to understand why the different setting for the Pertronic system. Any thoughts or suggestions would be most welcome.
George Raham
TD 4224
G. L. Raham

George, Were you setting it statically (ie with motor off using test light) or with timing light with it running? George
George Butz

Hi George, WOW, thanks for your quick reply. I was setting it statically with a test light, and should have noted this in my thread. [motor not running]
George Raham
TD 4224
G. L. Raham

While I do not intend to install any Pertronix or similar, I fail to see why timing should be affected by that. Some degrees, say 5-10, before TDC at 700 rpm is adequate for the 97 octane fuel sold over here.

Denis, 1950 TD
Denis L. Baggi

George, positive ground or negative ground? Where did you connect the test lamp leads?
Bud Krueger

Hi Bud, I am neg. ground and the lamp was connected to the coil connection from the dizzy, and a ground on the block. George
G. L. Raham

I have just installed the Pertronix, or I should say one of our club memebers did it for me and no problems with anything. I like the thing, starts right up. Mine is Positive ground.
TRM Maine

I installed a pertronix (positive ground) and had quite a bit of trouble setting the timing. Reading various BBS postings I was not alone. It seems that for some reason static timing doesn't work accurately in all cases. When I did mine, it wouldn't run at all around TDC using static timing.

However, I moved the distributor until it started and then got an advance timing light and used that to time it. When I was done the distributor was turned quite a ways from the position that it was in when I timed it using points statically. I have heard of differences in the magnet placement in the ring, and other explainations, for this 'offset'.

But it sure was worth the effort ! The car has never run as well, idled as smoothly, and run as well at high RPM. I have read an article where an MGB was dyno tested with 5 more horsepower with the pertronix, and that feels about right.

Another thing that recently happened that improved the performance was the breaking of my throttle return spring. The car just took off, and reved much faster. Apparently the old spring had so much force that it inhibited me from depressing the pedal as fast as the engine would take it. I ordered a replacement spring from Moss, and I will see if how that behaves. Right now I have a wire onto the old spring, yielding less tension. It is a whole new car now, and much more like like a 'real' sports car.

Larry
Larry Ayres

George, I don't remember exactly how I timed mine initially. Believe it or not, I have always timed my TD by feel and ear. I gradually advance until it starts idling a touch rough (about the same time the idle speed stops increasing as you rotate the distributor), and then retard a bit, test-drive, and fine tune from there. Not scientific, but works for me. My idea about the Pertronix- I think it is a "Hall effect" pick-up which is triggered by a magnet in the sleeve. Thinking back to physics, a moving magnet induces a current in a conductor(that is how many electric motors/generators work). Perhaps when setting statically the magnet has to be right at the sensor to trigger, but with it moving, it would likley induce a current (ie trigger) at a different location? Or I could be totally wrong! see this article http://en.wikipedia.org/wiki/Hall_effect_sensor
George
George Butz

Hi George, Thanks for giving me your method of timing the Pertronix. It sounds like an interesting idea and I plan to give it a try if it ever stops raining. It makes sense to let the motor tell you when it is unhappy and when it is happy. When I find the happy spot, I'll mark the pulley so I have something to go by next time. Thanks also for the information on how the thing works but, my understanding of electronics is very weak. This is why I enjoy the MG so much and the Pertronix has been a problem for me. I do believe I am making headway thanks to MG enthusiasts like yourself who will give their time and experience to others. Thank you very much.
George Raham
TD 4224
G. L. Raham

It's been quite a while ago, but I seem to remember having to reverse the light on/off process. Instead of the test light comming on at TDC I had to set it when the light was just going off at TDC. I could be wrong (won't be the first time and certainly not the last) but I beleive it has to do with the way this is wired with our positive ground vehicles. What led me to this process was the fact that the light would stay lit on a large rotation of the distributor but dark on a very short section, leading me to believe that when it is dark it is acctually at the firing position on the distributor. Strobe timing light confirmed the setting when done.

LaVerne
LED DOWNEY

Hi LaVerne, When I did my initial timing, I set it statically with a test light. I had changed to a neg. grd. a number of years ago so when I set up the light, it came ON at TDC. When I checked the location
of the rotor, it was at the no. 1 spark plug wire.
I did notice that the test light had a very low glow, when the rotor was between plug wires and came on very bright when the plug should fire. I wonder if the ON/OFF difference was could be due to the difference in the pos./neg. grounding. I am sure that someone with more knowledge of these things, could comment on the possibility.
George Raham
TD 4224
G. L. Raham

George, the Hall effect sensor is triggered by the presence of the magnetic field, not by the change in field. It's not like a transformer. I've seen this same condition that you've described before, especially when one tries timing with a strobe light. The positive ground system is wired in a totally different manner, i.e., the Hall switch is between the coil and the power source, rather than between the coil and ground. I have a couple of suspicions that I'm going to check out on my TD to see if I can emulate the condition. I'll let you know what I find out.
Bud Krueger

Hi George, Well it finally stopped raining and the sun has returned to the mountains. I released the distributor and moved it back and foreward and got the effect you described. I found the "sweet spot" and locked it down. Took it out for a test run and was very pleased with the performance. The acceleration and torque both were much improved. When I got home, I got the test light out and found the timing was 13 degrees BTC. I have never set the timing so far advanced, but there was no pinging under load, so I expect that the advancement will be alright. Thanks once again for your advice.
George Raham
TD 4224
G. L. Raham

This thread was discussed between 21/05/2008 and 30/05/2008

MG TD TF 1500 index

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