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Old 08-13-2019, 02:09 PM   #1
f balsiger
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Question model a engine jumps time

checked distributor drive gear....ok camshaft next?
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Old 08-13-2019, 02:21 PM   #2
1955cj5
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Default Re: model a engine jumps time

Make sure you have the washers under the cam screw....the cam may be moving on the shaft...


https://www.brattons.com/distributor...with-hole.html


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Old 08-13-2019, 02:44 PM   #3
Benson
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Default Re: model a engine jumps time

Please note that SOME repro screws are too long and the effect is same same missing a washer if used with original thin lock washer and original thin flat washer!

The screw bottoms out before the cam is tight.

The long REPRO screws come with an extra thick lock washer to correct this.

So if you use the long repro screw with original THIN lock washer and original thin flat washer the cam will slip.

Last edited by Benson; 08-13-2019 at 02:53 PM.
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Old 08-13-2019, 03:13 PM   #4
1955cj5
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Default Re: model a engine jumps time

Another thought...the cam itself has teeth on the bottom...perhaps yours is worn?


https://www.brattons.com/distributor-cam.html



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Old 08-13-2019, 03:36 PM   #5
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Default Re: model a engine jumps time

I had a Model A that jumped time every time I hit a bump or hit the brakes. I would then have to pull over and reset the timing again. I went over the distributor several times, switched to another distributor known to be good, but the problem persisted.

I later found that the spring inside the camshaft thrust plunger had broken due to rust. This allowed the camshaft to move back and forth resulting in variable ignition timing. When the timing was reset, the act of pulling back to take up slack on the distributor shaft moved the camshaft (and its drive gear) back to the correct position. After resetting the timing, the engine ran fine until I hit a bump, sneezed, scratched my bum, or had impure thoughts. Check that out as a possible cause.
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Old 08-13-2019, 05:32 PM   #6
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Default Re: model a engine jumps time

FWIW, A friend was describing to me just yesterday that his engine with a high pressure oiling system would change timing as the distributor drive that goes into the valve chamber would move upwards due to the high pressure. The distributor/oil pump drive is held in place only by a spring and the extra load on the skew gear was enough to cause it to rise, thus changing the timing and he'd lose oil pressure because the drive to the oil pump would come apart. Once the timing was off far enough, the motor would slow and things go back to their normal place and function. It took him quite a while to work it out.
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Old 08-15-2019, 06:07 AM   #7
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Default Re: model a engine jumps time

or had impure thoughts




unconfessed sin will get you every time!


lol
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Old 08-16-2019, 11:09 AM   #8
Jim Brierley
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Default Re: model a engine jumps time

I understand having impure thoughts, but it is unsafe to scratch your bum while driving!!! This from the CA DMV booklet. -
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Old 08-16-2019, 04:18 PM   #9
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Default Re: model a engine jumps time

Quote:
Originally Posted by Jim Brierley View Post
I understand having impure thoughts, but it is unsafe to scratch your bum while driving!!! This from the CA DMV booklet. -
And, DO NOT FORGET: "This action is known to the state of California to cause cancer, reproductive harm, warts and ingrown toenails." So stay out of California, and you'll be safe!
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