Djet Triger Point Calibration

[knarf]

Greetings Forum Members,

After having run fine some months ago I began experiencing the car running progressively more poorly. The car is a 1973 450sl severely abused and butchered by the previous owner(s) . To cut to the chase, I narrowed the problem down to;
1. A short in the wiring of the trigger points themselves
2. A worn, stiff as plastic, distributor O ring letting oil up the distributor to coat the trigger points
3. Worn trigger point rubbing blocks.
The distributor O ring has been replaced and a new used set of trigger points checked for shorts and recalibrated. Attached are pictures of my Djet trigger point calibration set up using a spare distributor, 22 ga. female terminals, a picture of a round protractor, tooth pick, Scotch tape, mini alligator clip. 18 ga. wire and a multimeter set to beep upon continuity.
With the trigger points installed in the distributor, black ground lead from the multimeter attached to terminal 12 and the alligator clip (positive lead of the multimeter) inserted one terminal, 14, 24,22 or 13, at a time I slowly turned the distributor gear until the multimeter tone was heard and counted the total degrees until it stopped. The metal contact tabs that the rubbing block contacts touch were slightly bent to reduce the duration of degrees that the multimeter tone was heard for every 360 degree revolution of the distributor shaft at each terminal.
Researching the matter it seems that 110 degrees is the ideal reading. for the trigger points to be closed signaling the injectors to fire. I was not able to achieve that number due to the amount of wear on the rubbing blocks. The best I could do on one set of trigger point pairs was to bring them from 160 and 170 degrees to 135 and 140 degrees. You can only bend the tabs so far before you loose too much of the matting surfaces of the contact points. I hope someone can benefit from my experience as I have so many times from fellow members contributions to this forum.

Knarf

[Tony H]

You may be able to find ignition points from some other car that can be adapted for far less or rebuild your points from parts of inexpensive new points. Also I would highly recommend installing a Pertronix ignition. I don't think the timing of the actual event is that important but not sure of the optimum dwell time. Dirty/old trigger points will really affect operation-when I bought my car the PO had thrown a lot of money at it and cleaning the trigger points and installing a Pertronix cured 90% of the drivablilty problems.

[Graham]

Originally Posted by knarf

Greetings Forum Members,

After having run fine some months ago I began experiencing the car running progressively more poorly. The car is a 1973 450sl severely abused and butchered by the previous owner(s) . To cut to the chase, I narrowed the problem down to;
1. A short in the wiring of the trigger points themselves
2. A worn, stiff as plastic, distributor O ring letting oil up the distributor to coat the trigger points
3. Worn trigger point rubbing blocks.
The distributor O ring has been replaced and a new used set of trigger points checked for shorts and recalibrated. Attached are pictures of my Djet trigger point calibration set up using a spare distributor, 22 ga. female terminals, a picture of a round protractor, tooth pick, Scotch tape, mini alligator clip. 18 ga. wire and a multimeter set to beep upon continuity.
With the trigger points installed in the distributor, black ground lead from the multimeter attached to terminal 12 and the alligator clip (positive lead of the multimeter) inserted one terminal, 14, 24,22 or 13, at a time I slowly turned the distributor gear until the multimeter tone was heard and counted the total degrees until it stopped. The metal contact tabs that the rubbing block contacts touch were slightly bent to reduce the duration of degrees that the multimeter tone was heard for every 360 degree revolution of the distributor shaft at each terminal.
Researching the matter it seems that 110 degrees is the ideal reading. for the trigger points to be closed signaling the injectors to fire. I was not able to achieve that number due to the amount of wear on the rubbing blocks. The best I could do on one set of trigger point pairs was to bring them from 160 and 170 degrees to 135 and 140 degrees. You can only bend the tabs so far before you loose too much of the matting surfaces of the contact points. I hope someone can benefit from my experience as I have so many times from fellow members contributions to this forum.

Knarf

Good Job Knarf! I don't think the actual number of degrees is that important. But best that each set is about the same. It also seems that once the number gets high, problems seem to crop up. Some think it is because points start to bounce. Perhaps not helped by a certain amount of bearing wear. When the points close, they initiate an injection pulse. But if bouncing causes multiple opening and closing, who know what the ECU makes of that

By the way Tony - I don't think anyone has found "ignition" points that can be adapted. But I have read about trigger point parts from old VW and even BMW Djets being less expensive and adaptable. Bosch do now have a rebuild kit, but it is not cheap. Easier to find in Europe than here.

Finally, if you contact Norbert (Nordfisch), he has a simple but effective tool for adjusting trigger points. I have one. He will ship it to you from Germany for a very reasonable price.
Trigger Points adjustment gauge - Mercedes-Benz Forum

[knarf]

Thanks for the replies,

I have a post from June 2015 on the Pertronix 91885 conversion I did on this vehicle. I have since changed the wire set to Taylor Thunder Volt 8.5 MM low resistance wires and NGK BP5ES non resistor plugs. No worries about leaving the ignition on too long as with the Pertronix 1885.

[berfinroy]

The ignition points last a long time as the system is a rudimentary electronic system that uses very low voltage to the points themselves. Of course, the rubbing blocks are still subject to wear and hence periodic adjustment is still needed.
The biggest problem with the trigger points in these now old cars is oil contamination. And in my experience a new "O" ring is not enough. I fashioned an dense, flexible absorbent disc aproximately 1/16" thick with an OD equal to the inside diameter of the distributor below the trigger points (2.75"), and a center hole the same size as the distributor shaft below the trigger points (5/8"). I then cut through the disc at one point so I could fit the disc around the distributor shaft. My "oil barrier" disc solved the problem!

[Funkloch]

Hello Knarf,

here in Germany we build a tool to adjust the trigger points.

https://oldtimer.tips/de/forum2/jetronic/6-werkzeug-fuer-trigger-impulsgeber-gebiss

[Tomguy]

Remember, the O-ring only seals outside the distributor (between the housing & timing cover). The O-ring doesn't seal anything from going up the shaft & contaminating the trigger points. The only things you could do to reduce/eliminate oil contamination are:

• Rebuild the distributor shaft bearing,
• Fabricate a felt pad or other blocker below the points,
• Find a way to reduce crankcase blowby.

Crankcase blowby (higher pressure in the crank than the distributor) is the cause of fine oil vapor escaping out, which then condenses in the relatively cooler distributor (cooler than the crankcase). These engines don't have a PCV system, but I wonder if you adapted one to it, if it'd help.

[Graham]

Originally Posted by Tomguy

Crankcase blowby (higher pressure in the crank than the distributor) is the cause of fine oil vapor escaping out, which then condenses in the relatively cooler distributor (cooler than the crankcase). These engines don't have a PCV system, but I wonder if you adapted one to it, if it'd help.

I don't recall when, but according to my post in the thread linked below, you once told me there was a PCV And for OPs car, I think you were right! (although MB don't call it that)

Crankcase vent/starting valve - Mercedes-Benz Forum

[knarf]

Tomguy, I do see what you mean, thanks for the correction.
Berfinroy what material did you use to make your oil blocker.

[meltedpanda]

god to see some of us Djet folks are still around. I have been through much of what you have done, when I finnaly sourced a brand new set of trigger points, I still had some issues, but found that is was my dizzy shaft, worn and little wobble, petronix set it right

Good stuff and hey Graham, good to see you are still at it

[Graham]

Originally Posted by meltedpanda

Good stuff and hey Graham, good to see you are still at it

Hi Ron,

Yes, I am still at "it" Two years ago, I spent a LOT of time bringing my 300D back from the brink, then had a break!

Recently decided it was time for some tuning and upgrades on the 350SL.
- rebuilding injection harness
- checking injectors
- new plugs, rotor cap
then, in Spring
- repairing battery harness
- clean up and paint battery tray area
- check timing and centrifugal advance is still OK
- etc

My Pertronix 1885 has been in there since 2008 and still working well as points replacement with aftermarket Bosch wires. Have Flamethrower coil ready, but that will be another project.

All the best for the Holidays

Graham

[Tomguy]

Originally Posted by Graham

I don't recall when, but according to my post in the thread linked below, you once told me there was a PCV And for OPs car, I think you were right! (although MB don't call it that)

Crankcase vent/starting valve - Mercedes-Benz Forum

I forgot about that! Ooops. Well then, it needs to be more efficient

[berfinroy]

Berfinroy what material did you use to make your oil blocker?

knarf: I don't really know. I had 2 fiber discs from I know not where, and they were exactly the right dimensions, so I used them.
I have been to several hardware stores to try and identify what they were originally designed for, with no luck.