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MG TD TF 1500 - TD Distributor Drive Dog

The distributor that I just removed from the TD is off a TC (dated 9/47) & was in the car when I bought it in 1969. I intend to use this as a backup to my 123 EI. No problem there however there is about an 1/8" of play between the dog & the body. Best practice suggests this needs to be almost entirely eliminated leaving just a few thou to ensure adequate clearance.

If I put a stainless shim/washer between the dog & the body this effectively lowers the centre shaft so that the points "arm" bears on the shaft at the top of the bearing area. If I push the dog & shaft all the way up to the body the arm then makes contact in the centre of the shaft bearing area, which seems more ideal.

Obviously a high shaft will raise the rotor button, a low shaft will lower it, effectively altering the plane in which the button spins & its relationship with the posts inside the cap. Is one of these positions more desirable from both a quality spark/operational point of view & also to ensure solid engagement with the dog & cam gear?

I'm wondering if I should pull the dizzy apart & see if I can place a washer inside to raise the shaft so that the arm bears in the centre of the shaft bearing face, which I assume is how Cecil intended. Also there has to be an optimum point to ensure the dog engages fully with the gear on the cam. This distance is determined by the shoulder of the distributor seating on the block & the relative position of the dog.

My question is, where should the "arm" bear on the shaft? Cheers

Peter TD 5801
P Hehir

Had a reply off line suggesting there should be a wave washer between the dog & the body. The various parts diagrams do show a shim/washer of some sort. Anybody confirm if this is indeed a wave washer? Cheers
Peter TD 5801
P Hehir

Hello Peter. There is a washer inside, I believe that it was made from a phenolic. No one lists them in any of the suppliers. I make them out of impregnated delrin when I am repairing the units. For the lower washer I make a brass washer that fits with .002 clearance. That is the clearance that is given in the Lucas manual.

Butch
R Taras

G'day Butch. I've been informed that the washer shown in the parts drawing between the drive gear & the body is & should be a spring steel wave washer but is missing from my dizzy (& a great many others it seems). It's been suggested that these washers can & do deform over time & end up appearing to be simple shims. I also now understand the difference between a dizzy dog & the spiral cut drive gear as fitted to the TC, TD & TF. Apologies to any of you who were miffed at my use of the incorrect terminology.

I had another couple of emails off line (Thanks Tom, Peter & Fletcher) & I accept the desirability of raising the button. I'm also sure now about the top bush wear being the cause of my problem. The solution is therefore to replace the bushes. This will raise the rotor button in relation to the distributor cap & also allow the points "arm" to bear more centrally on the shaft bearing surface. If I can then find a spring steel wave washer thin enough to deal with the resultant gap between the drive gear & the body, that should see the problem solved. Cheers
Peter TD 5801
P Hehir

Peter - be VERY careful if you chose to replace the bushing yourself, to properly support the dizzie body when you press a bushing in/out. The distributor tube VERY easily loosens from the Mazak dizzie body, and sometimes cannot be repaired at all.

I knew what you meant when you spoke of the dog, but was too polite to say anything...

LOL Tom
t lange

Noted. PS. You're a gentleman Tom.
P Hehir

Peter - another thing to look for when using a TC distributer in a TD (unless it is an early TD) is where the drive gear rides on the cam. - Bob Grunau has a great write-up on the various distributors here - http://www.mg-tabc.org/library/distributor.htm
Gene Gillam

Thanks Gene. A very useful post & link which I'm sure others will also appreciate. I intended to note the degree of engagement of the TC dizzy drive gear with the gear on the new cam, by peering up from below & rotating the engine by hand, once both are installed. Cheers
Peter TD 5801
P Hehir

This thread was discussed between 04/07/2014 and 05/07/2014

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