Trigger Points Cleanup & Adjustment - Mercedes-Benz Forum
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post #1 of 31 (permalink) Old 11-25-2018, 11:15 AM Thread Starter
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Trigger Points Cleanup & Adjustment

Over the last 6 weeks or so, I have had a rough running when cold problem. I did not bother with my breakout box / multimeter / oscilloscope thinking it was a sticking AAV. The symptom persisted with a rebuilt AAV so I had to dig further. In retrospect, one clue to the problem was a worsening symptom - car would not run well after it warmed up.

I pulled my distributor and found a badly soaked pulse generator (trigger points). The lower pair was so oil soaked, I could see a liquid film when I manually opened the contacts. I installed a working spare, installed the distributor, reset the timing and the problem is gone. I think the lower distributor bearing is worn to a point where oil is weeping into the cavity where the trigger points live. It could also be that I did not use the right kind of grease on the cam pads. I need to find a better product for this.

A little research on https://oldtimer.tips/en/d-jetronic/tc tells me these trigger points are the latest in the production series and include plastic shields to protect the contacts. I had never disassembled these before so I thought I'd give it a try and document what I learned. Disassembly is necessary in order to clean the lower pair of contacts.

First step is to de-solder the wires from the connector; necessary to remove the connector and gain access to the two Phillips head screws that hold the trigger mount plate to the body of the assembly.

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-1-.jpg

I had to walk the connector body out of the slot prying at both sides

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-4-.jpg

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-5-.jpg

Next, remove the screws and carefully lift the plate from the body. If you hold the assembly with your fingers around the leaf springs, it is easy to wiggle it up and off the body. The wires from the lower pair are routed through the large hole in the plate.

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-6-.jpg

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-7-.jpg

At this point, use a pick to remove the circlip and fiber washer that holds down each rubbing block and plastic cover. I had to use the pick to lift the plastic cover off the adjustment tabs because they fit pretty tight - easy to break these if you don't lift them straight up from both ends.

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-10-.jpg

Right lower side clean, left lower side next . . .

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-11-.jpg

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-12-.jpg

I used Norbert's adjustment tool to set the gap at .5mm or .02". I experimented doing this with and without the plastic covers in place. There is a little play in the plate mount. Research taught me to push the plate as far towards the curved piece then tighten the screws. Any gap adjustment done before mounting will require readjustment after mounting so might as well assemble everything then make gap adjustments at the end. I used a small bent needle nose pliers pushed up against the plastic cover - careful not to break what you just cleaned.

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-15-.jpg

Finally, slide the connector back into place and solder the wires. Be careful not to let the solder iron touch the connector body like I did (upper right). I will look for a product to replace the rectangular seal on these trigger points

Trigger Points Cleanup & Adjustment-pg-cleanup-adjustment-16-.jpg

If this symptom repeats, I will look for oil on the replacement trigger points installed in my car, install this set in a spare distributor and send the leaking distributor out for a rebuild by Cardone.

Brad Cushman
73 450 SL
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post #2 of 31 (permalink) Old 11-25-2018, 11:45 AM
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post #3 of 31 (permalink) Old 11-25-2018, 05:40 PM
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Good work Brad. It's impossible to clean those plastic covered points. But then, I guess it should not be necessary!

I had a brand new set of trigger points. I think they have the plastic covers too. Before I installed them, I once checked them with Norbert's tool and found that the gap was not same as that in Norbert's instructions. I told him about it, but I think he decided to stay with his number? For life of me, I can't find the numbers or the correspondence with Norbert. It may not make any difference anyway.

There is a spiral on distributor shaft appears to be there to catch oil leaking into the lower bearing and then push it back down into the crankcase. There are two bearings/bushes in the distributor - an upper and a lower with a gap between them. can't recall, but you would think there should be an oil seal somewhere.


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1972 350SL 4.5L, E320, 300D, Outback 2.5 - near Kingston, Ontario
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post #4 of 31 (permalink) Old 11-26-2018, 07:02 AM Thread Starter
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Graham,

I forgot about that spiral oil bleed - maybe the contamination came from using the wrong grease. Oldtimers talks about using a high temp grease. I went to Autozone yesterday and was not sold on any of their products. I'll figure this out and post what I learn.

I had a look at some oscilloscope readings I took on a set of trigger points 5 years ago. The scope I used has a statistics feature that might give me some duty cycle info I can convert to duration in terms of degrees. I want to make a comparison of the installed triggers against these I just cleaned and adjusted. This graphic on Oldtimers provides an outline to channel assign the output.
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post #5 of 31 (permalink) Old 11-26-2018, 09:24 AM Thread Starter
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The Service Manual specifies Bosch FT1V4 grease for distributor cams (specifically at the rubbing block of the ignition contact points). Can not find a different specification for the trigger points but the idea is the same. This Bosch product appears to be NLA in North America. D-Jet enthusiasts at TheSamba.com recommend SuperLube as a substitute:

https://www.napaonline.com/en/p/NCB21030

I will give it a try.

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73 450 SL
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post #6 of 31 (permalink) Old 11-28-2018, 03:04 PM
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Quote:
Originally Posted by cushjbc View Post
The Service Manual specifies Bosch FT1V4 grease for distributor cams (specifically at the rubbing block of the ignition contact points). Can not find a different specification for the trigger points but the idea is the same. This Bosch product appears to be NLA in North America. D-Jet enthusiasts at TheSamba.com recommend SuperLube as a substitute:

https://www.napaonline.com/en/p/NCB21030

I will give it a try.
That grease contains PTFE (Teflon). Not good for conductivity if it gets on points. But then, I am not sure the silicone greases are either?

This looks like another option - Those British car guys should know

https://www.bpnorthwest.com/points-lube.html

https://www.summitracing.com/int/par...-sl2/overview/

Look at price in Canada! (but good picture to read label) https://www.amazon.ca/Standard-Motor.../dp/B000JKDAR6

I haven't lubed those points very often. I just checked my spare distributor. Cams are coated with grease What I noticed, was that the felt pads that are supposed to spread the grease and perhaps prevent it getting thrown off are impossible to inspect without totally dismantling the distributor, They are opposite the opening where the trigger points are inserted. Maybe a dentists mirror would help.


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Last edited by MBGraham; 11-28-2018 at 03:13 PM.
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post #7 of 31 (permalink) Old 11-28-2018, 03:24 PM Thread Starter
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I bought and used the product referenced in post #5. I applied it directly to the lower distributor shaft where the trigger points ride, to the corners below the rubbing blocks and to the felts on the trigger points. I did reach back to feel the felts were intact behind the distributor shaft but as you said, very difficult to access.

The trigger points pictured above are back in service; inspected 4 other spares and 5 spare distributors. I noticed it is easy to convert between the two types of distributor caps on these distributors. All my spares have a larger vacuum element with a single port. I'm guessing the weights on the mechanical advance are different, possibly the springs that govern them.

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post #8 of 31 (permalink) Old 02-02-2019, 03:19 PM
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Hi Brad, Hi Graham

I just noticed your postings here.

Maybe I can answer some questions...

The grease Bosch FT1V4 is the same used for greasing ignition points. Therefore you can use ignition points grease. Take care the grease you use doesn't absorb any oil, doesn't contain copper or graphite components. Just tough high-temperature grease.

Graham, I don't remember what you found out / told me about the gap you measured at the new unit.
But: Even new units have quite often not been ajusted very exactly. In most cases you will do the job much better than the factory did...

Using my tool, the points will work at a gap between 0.004 in <less = points opening no longer> and 0.04 in <more = points closing no longer>.
The gap of 0.5 mm (0.02 in) is the median and allows the highest tolerance the unit in positioning or the distributor-camshaft could have.

The pic shows the point in the fully opened position at operation when having been adjusted to 0.04 in.

Graham, please check your tool. You got one of the first I shipped overseas - maybe it has a diameter of 24 mm. I revised this after having 'discovered' the points units with the plastic hoods I hadn't seen before. If so, please tell me...

Regards
Norbert
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post #9 of 31 (permalink) Old 02-02-2019, 04:24 PM
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Hi Norbert. I am about 1500km from home at present and not back until April. So cant measure tool until then.

I did use your tool to adjust my two sets of old trigger points and they worked.

Eventually, I installed my new set, just because I had them!

As we have discussed, the exact setting is not so important. Seems that if the points stay closed for an arc of say 110 to 140deg, then the points work fine. But when adjusting, adjust to the low number to allow for future wear of rubbing blocks.

When that arc gets higher (over 150deg?) on one or all pairs of points, some owners (including me!) have had over-rich problems. Hard to explain, but perhaps points start to bounce causing incorrect firing of injectors? Or maybe ecu receives incorrect engine rpms (that also come from same points). Adjusting back to 110-120deg usually eliminated the problem.

Regardless of reasons, it makes sense to adjust points with your tool to your gap and/or the arc we sometimes use for checking wear. Then the points should be good for a while.

It is hard to do the adjustment without your tool! I always recommend it! Maybe post your contact info again so others can get one.


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post #10 of 31 (permalink) Old 02-04-2019, 01:25 PM
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Hi Graham,
I wish you have a good time...

It would be interesting to connect an oscilloscope to trigger points with a very high arc.
I think this is when the gap is around zero, the points will flutter because the distributor-camshaft does some fluttering, too. This will cause extra pulses when the corresponding opposite side flutters, too - because then the ECU-internal flip-flop is being resetted and the extra pulses can occur. This can't happen when only one point is near zero - the flip-flop-reset is needed to generate the next pulse.
Same can occur when the gap is too high...

One more: Volker <oldtimer.tips> as I by myself had trigger units for service (even with the original repair set installed by a professional) with the upper points-carrying-sheet not installed correctly or with the bolts underneath the soldering points not having been tightened enough.
When the upper sheet can move, the whole unit cannot work correctly because the points-unit-adjustment is realized by the fingers at the bottom of the main corpus.
Check this out!
You have to unsolder the leads to tighten the bolts correctly.

Regarding my tool: I am a hobbyist, it's not my professional business to sell the tool. Users can contact me by PM. I will send them a figure they can produce the tools using a lathe and the instruction - or I send them the ready-produced tool after I have received a payment of 20.00 US$$ via PayPal. Contact me by PM...

Regards
Norbert
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