Dwell readings changing?

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71FourDoor

71FourDoor

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After replacing the points, getting it in the ballpark with the feeler gauge, then checking with my dwell meter, I'm puzzled by readings that vary wildly. Looking for 30-34, but I'll see a 5, then it'll jump to 20, then 24, then 40. What gives?

I was able to set my timing and the engine is running okay. Bad dwell meter? Or is this a sign my distributor is worn? Time to switch to electronic ignition?
 
Sounds like a sloppy distributor shaft or a worn eccentric.
 
On a small block, there's a bushing in the block that wears out and causes dist. wobble. It's cheap, but can be a pain to change. Look down in the dist. hole an see if it looks out of round.
 
Has anyone ever replaced this bushing? How big a nightmare is it? Assuming it's a sloppy distributor shaft, I wonder if an electrical ignition conversion would negate the issue.
 
skykeith said:
On a small block, there's a bushing in the block that wears out and causes dist. wobble. It's cheap, but can be a pain to change. Look down in the dist. hole an see if it looks out of round.
Click to expand...

The bushing in the block supports the oil pump drive shaft. If it's worn you will get excessive wear of the drive gear and cam gear. I could see it causing timing variations but not dwell.

I vote for slop in the distributor shaft. You can check by grabing the rotor and try to move it side to side. If you feel play it's time for a new distributor.
 
Replacing the bushing in the block requires 2 special tools - one for removal, the other for installation. The installer actually does 2 jobs - it installs and burnishes the bushing to the proper size and finish. I would strongly recommend renting/borrowing the proper tool if you are going to replace this bushing. Chrysler tool numbers - C-3052 for removal; C-3053 for installing.
 
Thanks for all the information and suggestions. The timing stays dead on, so maybe the bushings aren't the culprit. Moving the rotor clockwise, there's some play in the direction of travel (about 1/4") and side to side, there's a very slight wobble. I'm a firm believer in "when in doubt, swap it out," especially on a middle aged vehicle, so I'll probably just get a new distributor. And I might just kill two birds with one stone and go for the upgrade.

Any thoughts on this one?
http://www.summitracing.com/parts/DCC-3690426/
 
If the timing stays dead on then the dwell can't be changing. The dwell is the amount of time in degrees the points are closed. If it is changing as much as you stated in the first post then the timing would have to be changing also.

I would take a close look at your dwell meter. But in the mean time if you gapped the points to spec and the timing is steady I wouldn't worry about it.
 
A worn out distributer can cause poor performance and constatly changing performance. A reman'd distributer can be like dipping one of these old cars in the fountain of youth.
If you can rotate the lobe to the high spot and push the rotor button left and right changing the point gap, replace the distributer. Check them at the parts counter the same way. I have made Autozone bring in 3 before I got one acceptable.
 
Redfish, he says his timing is staying steady so the dwell can not be changing in the distributor. I suspect he has a bad dwell meter and not a worn distributor.
 
Initially I thought it might be my new timing light/dwell meter malfunctioning ( equus 5568 ), because the readings were so strange. It claims to be a "professional" timing light, so it's got to be good, right? ;) I'll either get a NOS distributor (if I can find one) or shell out the big bucks for an upgrade. Life's too short to mess around with questionable "remanufactured" junk from the chain stores. I've been down that road before.... I'll report back once I've done the transplant. Thanks again for all the advice.
 
I'm thinking you have a bed dwell meter or bad ground to it or something to that effect. Try it on another car with points to find out. Even with a worn distributor it should not fluctuate wildly.
 
Perhaps points are bouncing on closure, this could lead to incorrect dwell. Since timing is when the points open, it is correct.
 
He has points and the dwell is jumping around but the timing is steady. He is getting bad dwell readings and very likely does not have an issue with his distributor.

BTW, mopar solved the too much dwell at low rpms by using a ballast resistor. By definition a ballast resistor varies it's resistance with temperature. At low rpms the current flows for enough time for the ballast to get hot increasing it's resistance and reducing current flow through the coil and keeping it from over heating. At higher rpms the current flows for less time so there is not as much heat build up in the ballast so the resistance is lower and more current flows resulting more coil output.
 
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