After paintgate, I have tonight been given a bosch vac advance dizzy. As they can be better than my powerspark, how do I tell if it is a good un? What to look for in it?
Check for wobble in the base plate and shaft/bearings. Blow down the inlet to the vacuum advance diaphragm and make sure the base plate turns (advances the points)correspondingly. But best of all stick it on, set up, and check the total advance you get with and without the vac line attached at 3500rpm (32 and 28 degrees from memory but check Bentley or Haynes). Then fit accupark or equivalent and it all over again. Then, for peace of mind and minimal maintenance, fit a 123 Ignition dizzy. Well, that's my story anyway!
The way the rotor arm feels when you waggle it with the distributor in the engine is another sign. The springs in the centrifugal advance should prevent a rattly backlash and so there should be smooth progressive resistance to turning the rotor one way and fairly solid resistance the other way. If it slops around without resistance it could just need the advance mechanism weights lubricating. If it doesnt give much then you may have the advance mechanism seized. Oil on the felt bit under the rotor and more waggling may free the concentric shaft. The drive dog on the base should have a squarish profile to the ridge that engages with the drive gear. Not triangular.
