Iam putting new points,plugs,cap,rotor and wires on my 450sel and I would like to know the proper way of setting the dwell. I have a dwell/tach meter but the last time I used it was on a 1969 Ford 302 and that cap had a window so I was able to set it while the engine was running. Thanks for any advice.

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You can tell a lot about a person by the way they take care of their ride.

I had a '67 Chevy Impala with a 283 for a few years, and I really liked being able to set dwell with the engine running. Ain't so with the German stuff I've messed with!

You need to use a feeler gauge to set the points gap to spec, then run the engine to see where dwell ends up. If it needs to be fine tuned you have to pull the cap off, make the adjustment, and then run it to check dwell again. Kind of a PITA.

If the dwell angle is low the points need to be closer. If dwell is high they need to be opened up some. To minimize the guessing game you could use feeler gauges that are a little thinner/thicker than spec for this fine tuning.

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- Greg -
1973 220D, The Prodigal Benz
1974 240D

On the M117 engine, I have never seen a spec for the points gap. Just for dwell. I have used 0.014" as a starting gap, and it almost always provided a dwell within spec. (30-34deg at idle. Otherwise, it is trial and error. Choose a gap, close everything up, check dwell with meter, take everything apart, adjust points gap, reassemble and so on.

I have installed a Pertronix 1885 (just as a points replacement) on my 4.5L M117. No more adjusting points! Been in service for years.

It's been a while for me, but are the points adjustments not opposite what is stated in above quote? Reduce points gap to increase dwell angle ; increase gap to lower dwell angle. In other words, "As you increase the gap,the dwell angle goes down and vice-versa)"

But really, for under $100, forget points and install a Pertronix. Later if the MB switchgear ever fails, the Pert can be rewired to replace that too. If you need wiring diagrams, see this link. Use model 1885 rather than 91885 because latter does not like copper core ignition wires.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

We're saying the same thing, but in a different way. If shooting for 30 degrees and you read 20, you'd need to reduce the points gap (If the dwell angle is low the points need to be closer = Reduce points gap to increase dwell angle). If you read 40 the gap would need to be increased (If dwell is high they need to be opened up some = increase gap to lower dwell angle). My language wasn't the best.

I too like Pertronix and used it all my old VWs with great success.

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- Greg -
1973 220D, The Prodigal Benz
1974 240D

You can adjust the dwell by cranking the engine and adjusting the points at the same time with the distributor cap removed. Tighten the points hold down screw after adjusting the dwell to the correct setting and check again.

I've done that in the past but removed the plugs. I take I don't have to do that step. Thanks

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You can tell a lot about a person by the way they take care of their ride.

Correct, there is no need to remove the spark plugs

Job is done thanks for the help. One note I set the gap to .04 with a feeler gauge cranked the engine and the dwell was 30 degrees. Put the cap on and ran the car the dwell was 32 degrees right where it should be.

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You can tell a lot about a person by the way they take care of their ride.