Distributor shaft backlash

M

M2116x6

Junior Member
How much backlash should a distributor shaft have on an A? Our 1928 was running fair after coming out of hibernation. I went through the tune up procedures setting plug gaps, rotor and point gaps, timing, etc. Afterward, the car would not start. Long story short, I found that it preferred the point gap to be around .010" to run again. At this tight setting it will run fair and only on full retard. Any movement on the advance lever down will stall it. I suspect timing problems because I have about a half inch movement back and forth on the rotor which must be throwing off the timing.

Any thoughts?

Thanks,
Jim
 
There will be some backlash from the joint between the upper and lower shafts, the lower shaft and the drive gear, and the drive gear and the camshaft. My car has new shafts and a new drive gear, and I see about 1/8" to 3/16" of backlash at tip of the rotor arm. The amount of backlash would depend on how well the tongue-and-groove joints of the shafts and drive gear fit together. You should have a look at the ends of the shafts and see if the joints are mangled or worn out.

A worn out upper shaft and/or worn-out bushings in the distributor body are probably the things most likely to cause irregular timing. But there is NO distributor easier to rebuild than an A distributor! Good replacement parts are easy to get, and there is no centrifugal advance to get out of calibration.

Doug
 
If I grab the top of the distributor shaft and wiggle it side to side, there is hardly any movement. That seems fine. My guess is that with the excess backlash, I'm not getting the timing right.
 
Ours has around 1/4" or so worth of backlash but it does not seem to matter.

I set the timing against the backlash, with .020 for point gap. I don't see how the point gap should be effected by backlash? The only thing that would effect your point gap is wear in the distributor bushing and the distributor cam unless I am mistaken? There should be essentially NO movement in the distributor side to side "horizontally"

backlash is play\movement in the gears. It sounds like your distributor shaft is moving in the bushing or the breaker plate is not moving correctly.
 
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I did try the points at .020 but the car would not start. Prior to gapping them I noticed that they had previously been about .010 so I went back to that setting and it fired up and will run only on full retard.

On the timing, I did set it against the backlash. The timing must be off. Last night the car was running a bit hot and also backfired.
 
To properly set the timing "against" the backlash, rotate the cam CLOCKWISE until the points have just closed, which is the equivelant of turning it CCW until they just open, but you have now accounted for the backlash.
Use the proper .020" setting.
It should also run correctly with a proper "throw" of the spark advance lever using this technique.
 
your setting the gap at the highest point on the cam I assume?

Also do the points close completely? They should close and open without any resistance. Also make sure the contacts are very clean. Also make sure you have a decent consistency between the 4 lobes on the cam. I would assume a badly worn cam or block could cause an issue where you cannot get a wide enough gap.

Check for side to side movement in the shaft, check for your .020 gap on multiple cylinders.

Keep in mind, the main goal of those points is to close and charge the coil and then open and discharge it. You need them to close and produce a near perfect connection and then break that connection to fire the plug. If they do not do those 2 primary things at high speed again and again with near perfection you will have problems.

i'm sure other more experienced people here can help you better. But I figured i'd do what I could.
 
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The backlash will vary, depending on the wear of the oil pump and distributor drive gear and the teeth on the center cam bearing. A half inch backlash is probably about average for an 82 year old engine unless the cam and drive gear has been replaced.

It sounds like the backlash is causing problems with the way you are setting the timing. It can be difficult but this is the way that I set the timing. First set the points at .022 . Turn the engine over until the timing pin drops in to the indentation of the cam gear. I then adjust the dist. cam so that the trailing edge of the rotor aligns with the number one plug wire contact in the dist. cap body with NO clockwise back lash. The backlash all needs to be in the counter clockwise direction so that it doesn't effect the timing. The important thing about setting the timing is where the rotor points with NO clockwise backlash. Set the points first and it doesn't matter about where the spark lever is. I think that a lot of people are trying to watch when the points are about to open and get things ALL messed up. If the distributor cam is correctly manufactured, the points will be in the correct place when the trailing edge of the rotor aligns with the number one contact in the dist. body with no clockwise backlash. If you don't believe what I am saying go ahead and try it just for the hell of it. What have you got to lose? If it continues to quit running when you move the spark lever check the wire between the dist. plates or the connection of the wire to the points. There could be a short to ground or a loose connection.
 
1/2" backlash isn't too bad.. They'll run with far more than that.. That lash comes from slack in the distributor drive shafts and the drive gear,, so,, there is a lot of room for slack even with decent shafts and gear.. New re-pro shafts and gear are readily available,,but,, I think you have something else wrong.. I don't intend to be a wise-a$$,but, are you setting the timing correctly?? Marco's site has the quickest and easiest way of doing this.. Also make sure the points contact surface is very clean after they have been set.. Rubbing alcohol on the stiff clean rag works well for this..
 
Patrick L. said:
Rubbing alcohol on the stiff clean rag works well for this..
Click to expand...

Just make sure you let it dry before starting the engine :)

We knew a guy that essentially soaked his points in alcohol, tossed the cap on and started the car. It was quite amusing for everyone but the owner of the car :)
 
OUCH !
I meant, POINTS SHOULD JUST CLOSE completely when spinning the cam to the right instead of to the left as standard if you are taking up backlash.
 
Bruce Adams said:
OUCH !
I meant, POINTS SHOULD JUST CLOSE completely when spinning the cam to the right instead of to the left as standard if you are taking up backlash.
Click to expand...

Bruce you confused me on this one. As far as I know you should turn the distributor clockwise until it stops (against the gear), but don't put too much pressure . This is where you set your timing. And the points should JUST be ready to break on cyl #1 with the timing pin in. Any movement of the timing lever should break the points.

Distributor rotation is counter clockwise. So turning it clockwise should be against the backlash, and where the gear normally rides.

At least this is how I did it and it works good.
 
Your problem appears to be incorrect timing. See Marco's web site for directions: http://www.abarnyard.com/workshop/timing.htm. You can check your timing by retarding the spark lever, remove the distributor cap and body, turn on the ignition key (make sure your car is in neutral with E-Brake on). Press on the timing pin and slowly crank the engine until the pin sets into the timing gear recess. Do this while watching the points. At the exact moment the timing pin falls into the timing gear recess the points should spark. If not your timing is off.
 
LOL ! Mr Tube.. Talk about a flash in the pan !.. And here I thought rubbing alcohol evaporated pretty quickly..
 
Thanks guys for the replies!

I took another look at it today after work. Starting with the points, I reset them to .020". With all of my vehicles running points, including my daily driver, I am very well acclimated with setting them. After the points were set we located TDC. I then rechecked the timing as per Purdy Swoft's post at 1:11pm today. It was right on from where I set it last night after reading the A Barnyard site. With the points opened up, it runs better and we do have the ability to advance the timing once it starts. It does run decent with the lever around the 9 o'clock position.

It is good to know that the backlash we have is not a major issue.

Jim
 
DistShaft.jpg


It doesn't take long to remove the distributor to check it and the lower shaft for wear. The last couple of shafts I installed needed to have the tab or slot filed a couple strokes to have a snug, but free moving joint.

If you need to remove a head nut to remove the distributor cable, then be sure to drain the coolant, so it doesn't get into the oil if the head gasket would leak near that head nut.
 
Thats a nice looking picture of the shaft.. It almost looks like it was made like that.. The teeth on the gear a little 'pointy' too ??
 
Patrick L. said:
Thats a nice looking picture of the shaft.. It almost looks like it was made like that.. The teeth on the gear a little 'pointy' too ??
Click to expand...

I don't recall the teeth, but I do remember the cam gear had lots of slop and the rods had lots of play, like at least .010", and the previous owner said it was a good running engine.

NEVER trust a used car salesman!!! :(
 
Hi, Mr Tube,
My point is that normally you spin the cam ccw with the points JUST OPENING when setting them. If you, at #1 TDC turn it CW, the lash is taken up. Then you set it when the points JUST CLOSE, CW, which is the SAME as just opening, CCW, but the lash is eaten up.
Is it still muddy?
 
I purchased a new point setting tool from either bratton's or snyder's, believe it was nu-rex. It fits onto cam, loosen cam screw, with dist cap body on, rotate tool 2 turns CW until tool hits #4 cyl post on body. Tighten screw, points should just be opening. Removes the slop we're talking about in previous posts. just my 2 cents.
Paul in CT
 
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