Author Topic: Field Coil Screws Of Evil  (Read 2078 times)

Offline GoldenFailure

  • A's Best Friend
  • ***
  • Join Date: Dec 2011
  • Posts: 33
  • Karma: 0
  • Wales
Field Coil Screws Of Evil
« on: 19.01. 2012 21:28 »
Any suggestions for getting the field screws out of the dynamo? I haven't got a blowtorch, heat gun or replacement screws, Ive tried an impact driver and wd40.
1955 Plunger Golden Flash (doesn't work)
1967-2005  Enfield Bullet bitsa (evil)
Absence of common sense or car to go with it.

Offline trevinoz

  • Newcastle, N.S.W. Australia.
  • Wise & Enlightened
  • *
  • Join Date: Jul 2006
  • Posts: 2903
  • Karma: 67
Re: Field Coil Screws Of Evil
« Reply #1 on: 19.01. 2012 21:36 »
When all else fails. centre pop the screw and drill out in stages.
Eventually the counter sunk head will come off and the assembly will fall out.
Occasionally the stub will screw out of the shoe easily but if not it will have to be drilled out.
Thread is 5/16" BSF.

  Trev.

Online beezermacc

  • Resident Legend
  • *****
  • Join Date: Dec 2011
  • Posts: 994
  • Karma: 39
  • Not for the purist!
    • Priory Magnetos Ltd.
Re: Field Coil Screws Of Evil
« Reply #2 on: 19.01. 2012 23:02 »
Strangely and coincidentally I am currently making a tool to do this as my original tool is now knacke...d! Lucas originally recommended a 'wheel operated screwdriver' which is a brace which wraps around the dynamo enabling a srewdriver tip to be screwed down onto the screw head then using a wheel or T bar the screws can be unscrewed. The problem with using an impact driver is that so much force is needed it is possible to knock the dynamo casing (referred to as the 'yoke' in Lucas literature) out of round unless the pole shoe is supported very solidly internally. By knocking the yoke out of round it is possible that the armature will come into contact with either the pole shoe or the yoke so it's best to avoid whacking the screws. If the screws are particularly stubborn I would be inclined to drill them out, as per tevinoz's suggestion, and replace them. Similarly, when rebuilding the unit it is crucial to avoid any airgap between the pole shoe and the inside of the yoke. Make sure the countersunk heads are a good fit in the yoke before commencing the rebuild and employ a pole shoe expander (small scissor jack like thing) to squeeze the pole shoe against the yoke. Ideally, use a wheel operated screwdriver to refit the screws.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline GoldenFailure

  • A's Best Friend
  • ***
  • Join Date: Dec 2011
  • Posts: 33
  • Karma: 0
  • Wales
Re: Field Coil Screws Of Evil
« Reply #3 on: 20.01. 2012 13:23 »
Cheers guys, will get the drill out... :( 

Do you think a couple of nuts, bolts and short metal tubes would work to jack the shoe up? (Nut screwed halfway down the bolt, then tube over the bolt resting against the nut, other end of tube against the shoe, bolt head against inside of dynamo body, then spannering the nut upwards towards the shoe?)
1955 Plunger Golden Flash (doesn't work)
1967-2005  Enfield Bullet bitsa (evil)
Absence of common sense or car to go with it.

Online RichardL

  • Outside Chicago, IL
  • Wise & Enlightened
  • *
  • Join Date: Nov 2007
  • Posts: 5062
  • Karma: 48
Re: Field Coil Screws Of Evil
« Reply #4 on: 20.01. 2012 15:03 »
Regarding the 5/16ths,  don't forget that that is not the inside diameter you are going to drill, that' the O. D of the screw.  Be very carefule to center punch right on center.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online beezermacc

  • Resident Legend
  • *****
  • Join Date: Dec 2011
  • Posts: 994
  • Karma: 39
  • Not for the purist!
    • Priory Magnetos Ltd.
Re: Field Coil Screws Of Evil
« Reply #5 on: 20.01. 2012 21:45 »
What you are suggesting is worth a try in the absence of a purpose built tool. However the pole shoe is curved to match the curvature of the armature so I would cut a v-slot in the top of the tube you are thinking of, then use the V-slot to trap a horizontal round bar between the top of the tube and the pole shoe. (Does that make sense!? ;). Use the thickest bolt and tube you can lay your hands on.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline andy

  • A's Best Friend
  • ***
  • Join Date: Apr 2011
  • Posts: 66
  • Karma: 1
  • and so the fun begins !!
Re: Field Coil Screws Of Evil
« Reply #6 on: 21.01. 2012 07:02 »
what about a piece of scaffolding tube cut lenthways then using two "long nuts"(about 3/4" long) and bolts to use as spreaders think that might work ?? *dunno*
only 2 things needed in life wd40 and duck tape....if it moves and shouldn`t use tape if it don`t move and should use wd40.

Online beezermacc

  • Resident Legend
  • *****
  • Join Date: Dec 2011
  • Posts: 994
  • Karma: 39
  • Not for the purist!
    • Priory Magnetos Ltd.
Re: Field Coil Screws Of Evil
« Reply #7 on: 21.01. 2012 07:53 »
Worth a try. The important thing is that the pole shoe is held tightly against the inside of the body to avoid any airgap after the screws are tightened
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline rowan.bradley

  • A's Best Friend
  • ***
  • Join Date: Aug 2016
  • Posts: 101
  • Karma: 0
Re: Field Coil Screws Of Evil
« Reply #8 on: 30.08. 2016 19:13 »
What about turning up a couple of conical wedges out of mild steel or aluminium, or even hardwood, and then fitting a large bolt and nut through a hole in the middle. I would have thought that that would have held the pole shoes firmly against the yoke while one did up the screws (using the mythical Wheel Operated Screwdriver).

Rowan


Current bike: 1958 A10 Super Rocket (in bits), purchased in 1967.
Previous bikes: M21

Online BSA_54A10

  • Wise & Enlightened
  • *
  • Join Date: May 2008
  • Posts: 2018
  • Karma: 32
    • BSA National
Re: Field Coil Screws Of Evil
« Reply #9 on: 31.08. 2016 10:05 »
One and only time I did it I used an impact head in a ring spanner held down using a G clamp.
You don't need to push down all that hard, just enough to stop the tip popping out of the screw slots.
Bike Beesa
Trevor

Offline trevinoz

  • Newcastle, N.S.W. Australia.
  • Wise & Enlightened
  • *
  • Join Date: Jul 2006
  • Posts: 2903
  • Karma: 67
Re: Field Coil Screws Of Evil
« Reply #10 on: 31.08. 2016 22:12 »
You can also use a drill press for this job.
I always remove them with an impact driver or a drill bit.
I have never had any issues with body distortion after using the impact driver.
I mostly replace the slotted head screws with Allen head screws.