distributor shaft play

does anyone know the amount of shaft play i should have in my 3874598 distributor? apparently there is what looks to be about an 8th of an inch of up and down play. that seems excessive to me. i guess i should also describe why we are looking at the distributor. we have been experiencing a detonation at a certain rpm...no amount of retarding the distributor seems to correct it. we are running the highest station octane we can get, and it's without the vacuum advance on. i know i need to get a tach and be able to give an rpm amount, but without it i can say it's at the same rpm range, and it isn't a stomp on the pedal test, it's a gradual increase in speed when test driving. this is on a 66 225, the distributor is from a 76 225.

Read the shop manual. Checking distributor play is in there, section 8, electrical. You can download many years, free, at MyMopar

I would be checking your TDC mark (use a piston stop) and actually CHECK as to how much advance you are getting.

"Smog" distributors, IE starting in CA in 66 and Federally in 68, and getting worse "by the year" typically have very long, very slow advance curves.

Such things as burning oil aggravates perceived detonation.

Page 8-38 of the 72 Plymouth manual, picked at random

fonzy is talking up and down play, 1/8" is kinda mucho, but typical. I think u can remove a roll pin and add a shim on the lower area of the shaft, but I don't think the play is causing your problem. 67dart is talking sideways play, probably not causing pinging. when no amount of retarding cures the noise, I question that is detonating. what is your compression ratio and octane?

Be very sure that you are finding that play in the right place. Typically you can lift up and drop the dizzy cam a fair amount and that matters not a bit. The part to be concerned with, is the shaft itself, underneath of that cam.Also note that the play may be different between on the bench and installed. Again the installed play is what you are interested in.
I seem to remember tho, that on slantys, when the shaft climbs up the camgear, it goes into retard. Am I wrong?

Detonation avoidance is not limited to timing controls. It is often/usually caused by too much heat in the chamber. Lean running, excessive EGR (not an issue in 65 I know),and carbon buildup in the chambers, are all suspect. As well can be, to a lesser degree,a plugged exhaust, and excessive coolant or intake air temps.

You can "see" the actual shaft vertical play by looking at the bottom where the gear/ spacer / etc is. It all moves up and down against the bottom of the distributor. That is not nearly as important as side play

If there is any question, I'd just tear it down and inspect the parts.

Be careful how you check the end play of the shaft; you can't check this from the top by pulling on the rotor or top shaft, because you are pulling on the mechanical advance plate and upper shaft, not on the main shaft. This needs to be checked from the bottom with the distributor out. With all new bushings and such, the main shaft will have an end play of the main shaft on the lower end of the distributor in the .007-.010" range.

Pinging is more likely what you are hearing; it is very high pitched like tapping a very tiny hammer lightly on a hard surface and is erratic. Detonation usually is much harsher and with a deeper tone.

Is the carb from the '76 also? If so, it might be from a Dart Lite or Feather Duster, and the carb was calibrated very lean; my '76 Dart Lite pinged normally under certain moderate throttle positions at lower RPM's just like you are describing.

The '76 distributor for these particular models had a different advance curve too. Is the vacuum advance connected to the ported vacuum on the carb? And are there 1 or 2 vacuum ports on the distributor's vacuum advance dashpot?

But I am more suspecting that that the carb is just leaning out, since the timing is not effecting it. I would troubleshoot that by putting a vacuum gauge on the manifold runner to cylinder 6, and look at the vaccum at which this pinging starts as you add more throttle and when it ends as you add even more throttle. The vacuum readings where it starts and stops should say what carb circuit is being activated when the pinging starts and you can investigate that. Feel free to report what you find for vacuum levels.

67Dart273 said:

You can "see" the actual shaft vertical play by looking at the bottom where the gear/ spacer / etc is. It all moves up and down against the bottom of the distributor. That is not nearly as important as side play

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Remember that this is a geared distributor with a very small diameter gear, so end play translates into timing changes, unlike the small block distributors.

But, the symptoms, with timing changes not effecting the pinging/knocking, don't point to distributor timing variations as the likely problem.

nm9stheham said:

Remember that this is a geared distributor with a very small diameter gear, so end play translates into timing changes, unlike the small block distributors.

But, the symptoms, with timing changes not effecting the pinging/knocking, don't point to distributor timing variations as the likely problem.

Click to expand...

That's true but because it's a helical gear, it should be "driven" against the thrust. In normal running it should be fairly stable.

for the lower shaft axial play: drive out the pin/remove the slip on collar and add flat washers to reduce the end play to .005" . Speedway mtrs has a kit of washers of diff thicknesses for this for cheap or source your own just make sure they are flat with no "edge" on the one side of the ID/OD like most are when "stamped" & if so (barely) chamfer it off & the OD of your selections can be quite a bit larger than the plastic collar as there is plenty of room in that area, nothing to interfere. EDIT the shaft is 1/2" OD

ok, decided to try a new distributor...no more ping, not certain if the springs were worn, or the shaft play had anything to do with it..but it's gone after being replaced. timing has been adjusted and now we are just driving it to get a gauge on fuel usage...woot!:blob:

Stay away from Proform. Excessive shat play and the collers come apart. Made in China

67Dart273 said:

That's true but because it's a helical gear, it should be "driven" against the thrust. In normal running it should be fairly stable.

Click to expand...

If the timing chain has any slack, I doubt that the drive to the distributor gear will be steady.