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MG TD TF 1500 - Pertronix

Here's an interesting observation which may be of use to some considering installing pertronix ignition in their vehicles.

Following considerable work on an XK 120's engine,
( yes, I know) I decided to upgrade to a P. ign. system. After fitting it, the engine started well and I hopped in and drove it for about 2 miles until it suddenly started to backfire and then stopped completely. Upon inspection I discovered that the rotor had so little clearance between it and the part of the new distributor cap which holds the carbon spring loaded brush, that the two parts had been rubbing sufficiently hard to wear a mark on the brass metal of the rotor and to cause the brush to get worn down rapidly and to loose contact by getting jammed inside its receptacle, resulting in engine failure. The brush had left a film of carbon dust inside the dist. cap which undoubtedly aided the misfiring.

P. had never heard of this problem before. I solved it by using a Dremel to cut away about two millimeters off the dist. caps brush compartment and about 4 mms off the base of the rotor enabling it to be pressed further down the rotating shaft.. This allowed there to be a few mms clearance and the problem was solved.

Hope this jem might be of use to someone in the future.
Geoff Love

Geoff, I've seen similar effects when folks don't press the Pertronix magnet collar all the way down over the distributor cam.
Bud Krueger

Yes, that would do it. I had made absolutely sure that the collar was pressed all the way down to the shoulder on the cam, before completing the rebuild. The collar required a lot of force to get it to move all the way down, and I was concerned that it might fracture before I got it there.

I think it was a surprise that, despite getting the collar firmly seated, there was still not enough clearance to allow the brush to do its job properly. It took only a millimeter to bring the whole car to a standstill. The dist. cap was new, as was the rotor. Poor quality control?

The only good thing was that I had my cell phone with me and it wasn't pouring with rain!
Geoff Love

This thread was discussed between 06/09/2007 and 07/09/2007

MG TD TF 1500 index

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