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Distributor Gear Clearance

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Bandana View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bandana Quote  Post ReplyReply Direct Link To This Post Topic: Distributor Gear Clearance
    Posted: May/20/2018 at 4:24pm
Is there any accepted rule of thumb for the gap between the top of distributor gear once pinned and the bottom of the distributor itself. Was putting on my new gear and with the two spacers that were already on the shaft (0.092”) I still have around 0.032” gap - or play. Is this good, to little, too much??

There were two spacers that came with the gear set for two different size shafts. Both have a raised collar in the hole - I guess for spacing?? Not sure i’d Use them ..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/20/2018 at 8:43pm
Rule of thumb is 0.010" to 0.015". 
That stated you should be looking at the distributor housing wear area and place shims top, bottom or both to keep the gear as centered to the cam gear as possible.
The bottom of the distributor housing wears during deceleration and the top while cruising.
A standard transmission and driver tending to gear down will wear the bottom more then the top.
At 0.032" I'd place a 0.020" shim on the bottom unless the top shows signs of more wear - just easier. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bandana Quote  Post ReplyReply Direct Link To This Post Posted: May/20/2018 at 9:34pm
Shouldn't be a factor I think but the distributor is an MSD Billet. Probably around 1500 miles on it and no signs of case wear. I'll have to order a shim pack (just did a Summit order a few days ago and didn't think of shims). There were two "shims" - I guess they are, that came with the gear set but they are pretty weird and i don't think I want to use them. Ever seen anything like these (the two black ones in photo.? Thought maybe they were intended to be bushings that fit up between the shaft and the case but they don't fit  - at least on this distributor.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/20/2018 at 10:48pm
The black ones may be poly like:
https://www.igus.com/iglidur/plain-bearing
So they could be very good! Industrial grade, no lubrication required, better then most any plain bearing material, run dry, oil or even water.
If they are what they look to be, check with the supplier, don't be afraid to use them.
Just make sure everything is clean before installing. The only thing that kills this stuff is abrasives, like aluminum oxide and oil from the distributor housing that was never cleaned.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bandana Quote  Post ReplyReply Direct Link To This Post Posted: May/21/2018 at 9:03am
They are steel not poly. When I checked the thickness at the raised lip it varied by a good .005-6". Thats not goo for a shim, plus having all the load on the thin lip... I don't know but I think I'll get some good shims..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_P Quote  Post ReplyReply Direct Link To This Post Posted: May/21/2018 at 10:19am
there have been a lot of threads on this lately for some reason. The problem with a narrow gap like .010 is that you are limiting the shaft travel and the gears may not be "happy" together in the narrow range you are now forcing it to be in. With a larger gap the gear can move to where it wants to be.

The factory point distributor shaft endplays I've seen are huge, .06"+, I assume for allowing gear meshing, and IIRC there is no spec for this in the service manual. I would not set it tight, you are asking for trouble IMO.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bandana Quote  Post ReplyReply Direct Link To This Post Posted: May/21/2018 at 5:20pm
I have 0.032” now with the gear on and pinned to my MSD distributor. Are you thinking that’s good? I’ve noticed a fair amount of play in different distributor shafts over the years but never measured any to get a feel for what is “ normal”. - or correct.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smills61074 Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2018 at 11:37am
Does anyone have any pictures showing distributor gears shimmed for correct mesh?  A visual would be worth a thousand words.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2018 at 12:42pm
The distributor gear and cam gear intersect at 90 degrees. The mesh of the gears, the center lines of the shafts and the cut of the teeth providing the design clearance.
Shimming just moves the distributor gear up or down to align the distributor gear to the center of the cam gear and ensures there is clearance between the top of the oil pump shaft and the distributor shaft. It also ensures timing does not float excessively between acceleration and deceleration.
MSD states 0.010" to 0.015", GM HEI state 0.010" to 0.015", Delco has some 0.015" to 0.020", and Ford has some 0.025" to 0.035". This seems to be specific to the distributor or the manufacturer.
AMC does not provide a specification that I have found but with so many putting on the MSD's why not go for the tighter tolerance. 
If the gears "bind" then the timing cover is wrong, not doweled correctly or the gears are not matched. Shimming has nothing to do with binding gears when shafts intersect at 90 degrees.
Should add that these are not like ring and pinion gears in a differential were shimming is critical to gear mesh. 




Edited by Trader - May/22/2018 at 1:00pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 67 Marlin Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2018 at 1:06pm
Just had my dizzy rebuilt by a carb and dizzy wiz. End play, with the dizzy out, was .047 measured with a dial indicator. He recommended against anything tighter. Didn't say it was bad to go tighter, but that mine isn't sloppy for a Delco and advised a little loose is better than a little tight.
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