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Advance unit

Submitted by pete_sykes on Tue, 09/04/2024
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Heavy Twins

I'm looking into  the bad starting on my Dommie 99. 

  • Carb cleaned  in an ultrasonic bath, refurb kit fitted  ( needle jets ...) and the brass slide is a good fit in the body. 
  • Magnets points set and the magneto was refurbed 4 yrs and about 4k miles back
  • Timing checked ... and this is where I think I have the problem. 

When I set the timing, the auto-advance is wedged open. With no pressure on the taper, its free to move and moves well. The springs are new. When I tighten the taper, it gets very stiff and I suspect is stuck in whatever position  it was in when I did up that dual threaded bolt. 

The question is what do I need to tweak or replace, the auto advance, the bolt, the big aluminium washer behind it and the C shaped one or what?

 

Thanks

 

Pete Sykes

 

Submitted by howard_robinson on Tue, 09/04/2024

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Hello Pete - Is your auto advance unit the same as depicted in the Dominator Service Notes, Chapter 21 - Electrics, page 104 in the top right-and corner ?  You will find the DSN's on line in the Library section if you haven't got a hard copy yet.  I am struggling to see what you describe as the large aluminium washer behind the bolt.  Inboard from the head of the taper bolt is a "C" section steel washer then a large thin tin washer with two location holes that engage on the pegs on the unit's arms. Lucas part number for this tin washer is 48339.  It is necessary to wedge open the auto advance arms ( I use a thin nut) as you time the ignition at the full advance position and then tighten the taper bolt onto the rotor with the points just breaking.  When you remove the wedge the springs should pull the arms back to the retard position unless the points are on a cam of course. The advance units are extremely reliable but must be free to move on the rotor under the strength of the two springs.  Good luck, Howard 

I can see it here 

https://www.nortonownersclub.org/html/archive/rh/HTC_V1/36/index.html

and here

https://rgmnorton.co.uk/buy/magneto-automatic-advance-retard-assembly_4367.htm#!prettyPhoto

The two washers in the RGM webpage are the ones I'm referring too and it may be tin I thought it was quite light though.

However, as you note, if the points are on the cam, then resistance to moving will be higher.  I'll check next time I'm in the garage.

 

Thanks

Sorted, I'd taken some slack out the magneto drive chain ( Yes I do have a cutaway timing cover to hold the shafts) However, I'd done it with the double threaded bolt loose and the magneto drive not fixed on the taper. Then I'd not checked how tight with the bolt done up.  I think this is what software engineers (I was one)  call an  ID-ten-T * error  

 

*otherwise written ID10T

 


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