Paul:

I guess you could say it has a design flaw. In the later distributor the rubbing block on the points moves in an arc, the early ones rotate about the CL of the shaft.  As I stated above, apparently point construction also makes a difference.  The "cheap" points mentioned above had a plastic rubbing block, maybe the location of the block on the point arm was different.  The straight and curved arm vacuum units do not interchange.  I feel that with a quality set of points, the later type dist would have minimal change in dwell, but I think you could still measure it.  I have seen wear in the pivot pin and hole, which would be a no-no.

John - "The Hoosier Hurricane"

Thanks John "H": So, the 60 & later distributors in effect have a design flaw? I didn't make a note of mines #s but I think it's a 1960. I'll pull it to check that & the vertical shaft slack, mentioned by Old Car Mark, as it appears when checked with the timing lite, that there is some unsteadyness in the timing. Could a worn timing chain also contribute to that problem? Anyway, I went to Mummert's distributer listings & noted that the later ones also came with a vacuum advance with a curved arm. The original 57-59s had a straight arm vacuum advance. Do they interchange & would it make any difference to dwell readings if it's wrong? According to the instruction booklet with my Dwell meter, low dwell can cause misfiring under heavy load..

Paul

Paul: 

Your distrubutor is probably not a '57, since it is a rebuilt by Cardone.  The '57 used a ball bearing point plate that rotated about the centerline of the shaft.  Those plates, made by one of the bearing companies became unavailable long ago, so Ford quit using that type plate.  The pivot type points plate is the later type, which your distributor probably has.  The problem with the later type is that the pivot point is an inch or so away from the shaft CL, and the vacuum advance pulls its end of the plate straight back and forth.  Since the pivot point is off center, as the plate pivots, the rubbing block changes its position in relation to the shaft, so the dwell changes.  We once had a customer with that problem so bad that engine performance noticeably changed.  He had put a set of cheap points in it, and we changed them to Echliin and the running problem went away, but the dwell still changed a little.

John - "The Hoosier Hurricane"

No It was from Cardone.Everything else was fine.New points mounting plate and the vacuum advance was adjustable no problem.The only problem I hadwas the timing marks  would "float"and never return to the same setting after revving it up.Spent some time trying to figure out why.Got my shop manual out and did some reading.When I saw the spec for shaft endplay i thought it was something to check and sure enough it was twice the maximum specification.When I got the shim kit I was able to get it just slightly more than minimum.Fixed my problem.

  

Mark: a side question. Was your defective rebuilt distributor done by Autoline? That was the case with the 1st one I had the problem with. Wasn't right from day one, but I didn't discover it until the return period was gone..

Paul

I believe it would Paul.

  

Mark: You're referring to timing, correct? I'll have to check it, but I don't think there is varience at idle. I had the initial at about 8 degrees, it seemed steady. It's just the dwell above idle. However, there did seem to be quite a lot of slack vertically in the shaft, but I didn't give it much thought. I was interested in side play. I assume as the shaft moves up & down, it's changing position at the cam gear. Would that change the dwell readings also?.. Thanks

Paul

Paul-How much vertical freeplay is there in the shaft?There is a spec for maximum play and I believe its .030-.050.I was having trouble with the exchange dist. I purchased where the timing would not stay stable at a fixed RPM.Turned out there was .100 freeplay allowing the shaft to move enough vertically to change timing.There is a shim kit available from Mr.Gasket with 4 different thickness' of shims to go between the collar and main body of the dist.You can measure it using feeler gauge between the collar and body, obviously the dist. has to be out of motor.

  

My 57's stk distributor would not adjust to correct or hold dwell readings. There was a problem with the advance plate pivot & it was touching against the vacuum advance arm. Obtained another unit, which was readily available, and had a friend clean it up & set it up on his Sun machine, with new points, condenser & vacuum advance unit. It reads about 28 degrees at idle, which is spec, but when the engine is accelerated drops back to about 21 degrees, which is well below spec. So, I thought about it & disconnected the vacuum advance. It then holds, only varying about 1 degree. This seems to indicate some wear in the bearing setup of the advance plate, or what is likely the trouble? Are parts available? Thanks..

Paul