Dwell changes depending on RPM

[miked_md]

I am trying to resolve some tuning issues with my 230sl.  I have the dwell set to 38 degrees at idle but noticed that it drops to 30 degrees when I rev the engine up to 2500-3000 rpm.  Is this due to distributor wear?  It is the 051 distributor.  The car had not run in five years and I had to take the distributor apart to free the centrifugal advance mechanism.  The advance works now as does the vacuum retard.

Can someone point me to a source for a rebuild kit?  I see that Buds will perform (out source?) the rebuild so parts must be available.

Thanks,

Mike

[Benz Dr.]

The bearing at the top of the shaft is often the first place I look and wear can also occur between the cam lobe shaft and the main shaft. The advance plate can also wear but that is a separate function because it's run by the vacuum retard system.
In all cases, this wear makes everything defect sideways which causes the points to close up as RPM increases. As long as the main shaft isn't worn at the top a new bushing can be installed and this will take up most of the play on the main shaft. The repairs to the advance plate and cam lobe shaft are proprietary and that requires a distributor tester to do properly.

I bought my tester 25 years ago so I would be able to set up dual point distributors such as 300SE, 6.3, 600, and 300SL. As good as Bosch single point units were when new, in comparison, the dual point systems were high tech in terms of build and design. Nothing comes close to a 300SL dual point/dual coil system.

I run all distributors that come into the shop and fix what I find wrong.

 

[miked_md]

Thanks for the reply.  I’ll do some more testing, and maybe get a better tach/dwell meter to see if the anomalous results persist.  The main thing I needed to know was that the dwell should be stable across the RPM range.

I’ll send you a direct message to see about having you checkout / rebuild the distributor.

Mike

[Benz Dr.]

Dwell should stay within 3 degrees over the whole range. I usually test up to about 5K RPM but a good unit will stay steady up to 6K RPM or more.

[Ed Riefstahl]

Hey Mike,
Many of us with Pagoda's have replaced the points and condenser with solid state, electronic pick-up inside the distributor, made by PerTronix. Or, a 123 complete distributor. I switched both of my vintage cars to PerTronix about 11 years ago, works like a charm, and it looks totally factory original without removing the distributor cap.

As for myself, I just got tired of always fussing with the points. I keep the original points in the trunk.

1966 230SL (Ms Magoo) Horizon Blue
1970 280S (Miss Daisy)
1999 BMW Z3 5 speed
1991 BMW 318I 5 Speed
1997 Toyota Paseo Convertible - One of 1000, (have you ever seen one?)
1997 Ford Ranger step side (Mater)
2023 Mazda CX 5

[miked_md]

Thanks for the suggestion on the electronics ignition.  I removed the distributor to check for worn bushings, I didn’t feel much play.  I did notice that the blue metal piece that holds the ball bearing against the breaker plate could be push down further.  I loosened the screw, pushed it down and tightened the screw while pushing.

Problem resolved.  The dwell is now steady across across the rpm range.