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  #1  
Old 05-16-2011, 11:30 PM
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Trouble setting dwell on 1971 W115

I have been trying to set the dwell on my 1971 MB 220 (W115) gas engine for the last week. I bought a new set of points and condenser before I started. Using my dwell meter I having a terrible time getting the value to 52 degrees. My current setting is around 73 with a gap of .093. With this gap the points just barely close. Any ideas?

Thanks in advance,
Bob

1971 Mercedes 220

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  #2  
Old 05-17-2011, 11:00 AM
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With the cap off and the ignition and dwellmeter on try adjusting the points as a helper turns the engine over--you should get a decent approximation of what the dwell will be when the engine is actually running.

Make sure the points have enough of a "heel" to open the contacts as the cam on the distributor shaft rotates--good luck



Tim Kraakevik
kraakevik@voyager.net
Four 114's, Four M110's
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  #3  
Old 05-17-2011, 12:29 PM
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try rotating the engine by hand until the points open and the rubbing block on the points is sitting on the highest part of the cam lobe. Open the points until you have a gap of about .014 and then try running the engine. You should have a dwell reading somewhere around 50 degress. If it's a bit more than that you can try closing or opening a bit until you reach the 50 degrees area + or - 2 degrees.
Check the shaft for wear by pusing sideways on it. Any play in the bearings or cam lobe shaft to main shaft will affect dwell angle at higher RPM's.
I recently rebuilt a distributor for a guy and the main shaft was actually bent causing three cylinders to fire properly but the other three were about 10 degrees out. If number one was in time ( the one you use to set timing ) four, five and six wouldn't be and would very likely ping on those three cylinders. I've rebult over a hundred distributors but this is the first one with a bent shaft. I have no idea how this could of been bent as the shaft is very hard metal.
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  #4  
Old 05-17-2011, 02:50 PM
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why not put in optical points, did this on my 72SL and no more worries ... works great
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Ron
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace
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  #5  
Old 05-17-2011, 05:50 PM
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Is that 0.014 inches? How much do optical points cost? Does it affect performance?

Thanks.
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  #6  
Old 05-17-2011, 09:52 PM
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they were less than $70 for my SL, more expensive than points /condenser but no headaches either, if by performance you mean enhanced - no , but they work fine
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Ron
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace
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  #7  
Old 05-18-2011, 12:29 AM
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Yeah, .014'' should be OK. Learn how to install points and save your money.
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  #8  
Old 05-18-2011, 12:31 AM
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Do you have a transistorized switching ignition unit?

I have a '73 220 that has this. It is located under the battery and is hard to see as it is toward the front. If so, then you cannot get a proper reading of dwell from the coil, but must clip the positive side of the dwell meter to the terminal on the transistor switching unit.

The green wire from the points coming out of the side of the distributor will go to the transistor switching unit, and the output of the switching unit (also a green wire) will go to the primary coil winding.

Try following the green wire from the distributor and see if it goes under the battery. If so, then you've got it, and the correct terminal should have a terminal sticking upwards that has a hole for banana plug. It's hard to see with the battery in and you'll need a light & a mirror.
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Old 05-18-2011, 10:37 AM
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I have that box under the battery with a green wire running to it from the distributor. Additionally, when I was removing the old condenser and points I noticed the wire from the condenser to the points was cut, but when I installed the new condenser and points I made sure that wire was connected.

Is there are reason why they cut the condenser wire?

Should I be connecting my dwell meter to the same terminal on the transistor switching unit as the green wire going to the distributor?

How is that different than connecting it to the coil?

Questions, questions, questions.

Thanks.
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  #10  
Old 05-18-2011, 11:19 AM
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It's entirely possible that the electronic ignition no longer works--five out of six of mine have given up the ghost after twenty years or so.

The coil can be replaced with a 12V version with an internal resistor--and the points with conventional VW Type II points and condenser. These cars run fine with conventional points and coils.


Tim Kraakevik
kraakevik@voyager.net
Four 114's, Four M110's
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  #11  
Old 05-18-2011, 03:08 PM
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How would I test if the electronic ignition is still functioning? The car starts and runs, but with a misfire.
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  #12  
Old 05-18-2011, 03:34 PM
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Mine typically just went dead. The M110 engine manual has considerable verbiage on how to test for dwell with the electronic ignition. The black box itself is full of condensers, resistors and contacts--which is why it was a $300 item nearly 40 years ago.

A misfire sounds like faulty plugs, wires, or corrosion on the rotor tip or inside the distributor cap.

Substituting a normal 12V coil and bypassing the box temporarily would determine whether it's the box or some other component


Tim Kraakevik
kraakevik@voyager.net
630 474-9164
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  #13  
Old 05-18-2011, 10:08 PM
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Connect to the same terminal as the green wire

Since your green wire from the points is going down to the transistor switching unit, that unit is obviously working or the car would not start.

Regarding setting the dwell, yes I think your connection point on the transistor unit IS the same terminal as the wire from the points (the green wire) goes to. As I said before, there should be a metal terminal for a banana plug to connect to that is sticking upwards. That is if someone hasn't removed it.

If you look under the battery with a light & mirror you can see the terminal. Once you know it is there, then you can reach in and feel it. This is the usual way to connect the banana plug into it. The other side of the dwell meter goes to engine ground as usual.
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  #14  
Old 05-18-2011, 11:55 PM
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Great job everyone. I plugged the dwell wire on my timing light onto the green wire coming off the points and the dwell was 23 degrees. I ended up setting it at 0.33mm as suggested and it was at 52 degrees. Now I need to get the idle and misfire taken care of.

I switched distributor caps after noticing a black dot on the top of the rotor. I am guessing it was arcing between the rotor and the cap. That helped, but I pulled the plugs and they were charcoal black, so I am going to soak them in carburetor cleaner over night.

Bob
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  #15  
Old 05-19-2011, 12:43 AM
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You may have problem w/ Stromberg starting enrichment

I assume you've still got the Stromberg on there.

There are some tiny parts underneath the dome on the side with the two coolant hoses.

There is also a pull-up diaphragm under the triangular plate facing upwards that interacts with these little parts in the start-up enrichment circuit. I seem to recall that these little parts can get a bit sticky in there and that this can result in an extremely rich mixture persisting.

There is a kind of ring gasket for the dome, but you may be able to access the starting circuit parts without removing the dome by removing the three screws that hold the dome and another piece on the starting circuit, but access to the screws might not be very good. You'll probably want to remove the cooling lines to the dome.

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