Field Coil Screws Of Evil

[GoldenFailure]

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.

[trevinoz]

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.

[beezermacc]

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.

[GoldenFailure]

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?)

[manosound]

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.

[beezermacc]

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.

[andy]

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 ??

[beezermacc]

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