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i took the rotor off of my delco single point unit. then i just grabbed the weights and shaft as a unit and rotated it back and forth. this is not side play as in a bushing problem. what i noticed was about 5 distributor degrees of rotational play of the shaft [very similar to steering wheel play]. can this really be normal or do i have a problem. seems like way too much slop. any thoughts?????? i am tracking down a problem of "missing" at idle and am focusing on the distributor as the culprit.
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Re: distributor shaft question
Lightly grap the weights at their ends and pull them out. Can you feel spring tension? Now let them back. Do they pull back to the stop?
If the above tests are passed, the centrifugal advance is probably okay. Even if the centrifugal was malfuntioning, it would probably not cause misfiring.
One quick check you can do with a dwell meter is to free rev the engine close to the redline. If the dwell drops off more than about two- three degrees, there is likely excessive end play, side play, or the breaker plate is wobbly. If the dist. passes this test, it is probably okay. Run the test with the vacuum advance connected and not connected. You can also check the breaker plate for wobble by pressing it on the OD to see how much up and down play it has. It should be snug.
Check all primary connections including the firewall connector, and if you have a spare coil swap it in to see if the problem persists.
Check the cap and rotor for cracks and check all the secondary wiring. A "engine analyser" with a oscilloscope is best as it can be used to check both the primary and secondary wave form. Leakage from a bad coil cap, rotor, or wires will show up as an abnormal secondary wave form.
Duke -
Re: distributor shaft question
duke, thanks. how about the radial "play" in the shaft. even if i squeeze the weights against the cam, the shaft can be rotated back and forth about 5 distributor degrees. is this normal? seems like a lot of play to me.
wernerComment
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Re: distributor shaft question
I suggest you check if the timing swings at idle with the vacuum advance off for #6 & #1. Timing should be real close for both. If it swings or bounces around(assuming the timing chain is ok and there is not distributor gear ware)it’s time to have the distributor reworked.Comment
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Re: distributor shaft question
If the shaft has noticeable backlash, it's probably due to end play. The spec is two to seven thou. As built they are sixty thou or more.
DukeComment
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Re: distributor shaft question
i did not know that the correct term for my problem is backlash. to me, i can rock the shaft back and forth abaout 5 degrees. i did check end play and it is about .006 [using a feeler gauge]. i have added a .030 spacer below my distributor housing because my block has been decked, and i wanted to compensate for this, but i cannot see how that would affect backlash. any thoughts would be greatly appreciated as i am completely stumped. i guess the only thing to do is to rebuild the unit as carefullly as possible.
i will try the things that everyone has suggested before i do that, though.
thanks again everyone.
wernerComment
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Re: distributor shaft question
Depends on how much your block was decked, but it they just took a small cut to be sure they are level, it's usually only five to ten thou.
Never heard of putting a spacer in the dist. to compesate for decking the block. Take it out. That may not solve you problem, but it should reduce the backlash.
DukeComment
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Re: distributor shaft question
agree with duke; decking the block should not change the relationship of distributor to any reference point you choose pre and post decking. mikeComment
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Re: distributor shaft question
When the block is decked, it's just done on the surfaces where the bores are; the center "deck" where the front and rear of the intake manifold seat aren't touched. Adding spacers under the distributor will just reduce contact between the teeth of the distributor driven gear and the drive gear on the cam.Comment
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