Re: Rebuilding a Distributor

Posted by Joe on May 12, 1998 at 07:49:49

In Reply to: Re: Rebuilding a Distributor
posted by Bob Johnson on May 11, 1998 at 17:11:01

: Marco,
: What about the rotational play caused by the coupling at the joining of the upper and lower shafts. I have never seen and specs on how much if any play is acceptable. Since that joint is a simple "tounge and groove" type connection used as a simple universal joint there will be some rotational play. Do you have any idea what the limits would be ?
: Bob
Bob
When I took my original engine apart for rebuilding and compared the original distributer shaft to the new, I was surprised by the relative difference between the new precision parts and the old worn ones.Hard to imagine that the engine ran as well as it did with that much slop in the connections.
But, if you think about it, the action of the distributer is all in one direction.There is no real problem with slop (at least in first consideration) since any change in relative timing of the action of the distributer is made up in the position of the distributer cam.If we were to talk only about the points opening, any amount of slop should be o.k.
Actually, this is not true.What can happen if there is a lot of slop is that the motion of the point lever can tend to "pull" the distributer shaft around when the points are in their closing direction.You can get a sense of this action by taking the loose distributer in your hand and twiddling the shaft in your fingers: what you are feeling is the lumps (lobes) of the cam as they pass under the slider block.At four points in your twiddling, you'll feel the distributer shaft attempt to get ahead of your fingers.
The net effect of slop is to change not necessarily the timing but the dwell and other aspects of the ignition action.
The effect this kind of slop has on your engine is most pronounced at idle.My engine prior to rebuild ran well at speed but idled terribly.No matter how far retarded the spark, the engine rolled and shuddered at idle.New parts (and a rebuilt distributer) solved the problem.
Incidently, in another engine I rebuilt (which was the one which finally ended up in my truck) someone had stuffed a piece of leather into the worn distributer shaft ends to try to reduce the slop.I never saw this engine run but I presume the shadetree mechanic fix worked.The leather was nearly worn through on one side.
Hope this all helps,
Joe

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