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Garage => Mechanicals => Topic started by: raueda1 on 06 September 2018, 01:46 PM

Title: 6.9 distributor fixes
Post by: raueda1 on 06 September 2018, 01:46 PM
Background:
I've long suspected that my 6.9 wasn't performing quite as well as it should be.  Last week I had the good fortune to attend the Fall "Lodefest" in Oregon.  Lodefest is an event organized by the M100 group which covers the 300sel 6.3, the massive 600 and the 6.9.  There I had the chance to swap 6.9's with somebody so we could compare notes.  This confirmed my suspicions - my euro 6.9 was certainly no quicker than the other guy's USA version, and possibly even a bit slower (subjective judgement based on seat-of-the-pants driving on various mountain roads). 

Fortunately Mike Morris of Morris Motors https://www.morrismotorsusa.com/ (https://www.morrismotorsusa.com/), regarded by many as a demi-god (or more!) in the world of old Benzes, was in attendance so we were able to discuss the issue.  Mike was adamant that something was going on with the distributor/timing and to do nothing else until that was sorted out 10000%.  I looks like he was 10000% correct.  My timing was kind of right, in a ballpark kind of way, but still funny.  Sometimes the idle would spontaneously change a little.  Sometimes idle speed would hold steady when AC was switched on, other times it would drop.  Sometimes the vacuum advance at high rpms would move around.  So, I decided to take the step of taking the whole damn distributor apart and looking for problems.  And I found some!  Going through the process would have been a lot easier if I had "how to rebuild your distributor" guide, so I figured it might be helpful to document it all.  What follows is a guide to dismantling the distributor and what I found when I did.  Here goes.

The Process:
Step 1:  Remove the distributor, duh.  When you take the cap off be certain to mark the position of the rotor so you're in the right place when you put it back together.  Otherwise you may go nuts, either from trial and error or trying to crank the engine to find the TDC reference.  Plate 1:  distributor as removed from car.  These distributors have 2 compartments.  The upper contains the ignition mechanism communicating with the coil (stator magnet and rotor) and the vacuum advance/retard mechanism. The lower compartment contains the centrifugal advance mechanism. 

Step 2:  Remove vacuum advance pod and cable connector.  For the vacuum pod remove the screws and carefully disengage the arm from its pin inside the distributor.  The pin faces down, so gently wiggle the arm off in a downwards direction.  Note that the vacuum pod has 2 small plastic parts on either side of the shaft (Plate 2).  These are fragile but can be wiggled out.  Don't try to force!  The cable pulls straight of the distributor body.

Step 3:  Now let’s examine what we’ve got and how it’s assembled.  The components are labeled in Plate 3.  The base plate is fixed to the distributor body by 3 hex screws (3mm heads).  The coil is fixed to the base plate from underneath.  The stator (magnet) rotates about 30deg on the central shaft. In my case the stator rotation was impossibly stiff and didn't rotate freely at all.  On the bottom side of the stator is the pin connecting to the vacuum advance pod.  this pin limits the rotation of the stator magnet.  The rotor is held on the shaft with a c-clip and index pin (see plate 4).

Step 4:  To disassemble first remove the c-clip and spring washer on the shaft.  You can then remove the rotor, though it may take some effort.  Note that there's a miniscule alignment pin that locates the rotor on the shaft.  Don't lose it!  Next remove the entire base/coil/stator assembly.  First remove the c-clip and washer so the assembly id free to slide off the shaft.  Then remove the hex screws fixing the base plate to the distributor body.  It’s fiddley but can be done (see plate 5).  Set the assembly aside and have a look at the now exposed centrifugal advance components (see plate 7).

Step 5:  Yikes!  All the centrifugal  elements were gunked up!  The brown is gum and varnish and maybe a tiny bit of rust.  The action was sticky and sluggish.  The parts are shown in Plate 7 as they were found, not a pretty sight.  Removal of the weights, springs etc is straightforward.  They are shown in Plate 8.  I blasted everything clean using ground coconut shell as the blast medium followed by air blasting and solvent wash.  Plate 9 shows everything cleaned up.  Pretty nice, eh?  The action was then perfectly smooth and immediate.  It's worth noting that when you lubricate the wick under the distributor rotor, this is where that oil ends up.  It's not surprising that it turns to gum over the decades and literally gums up the works.  I'd hazard a guess that many, or most, of these older cars have something similar lurking in the same place.

Step 6:  Now let’s return to the upper section.  The coil needs to be freed from the bottom plate to remove the stator magnet.  This is accomplished by removing the 3 flat head screws on the underside of the bottom plate (see Plate 6).  These screws are extremely tight!  I had to use very strong downward pressure to not strip the screw heads (which were perfect beforehand and are now a bit scarred).  The stator coil and magnet can then be removed.  Plate 10 shows the bottom plate separated from the stator magnet. Note that the magnet plate needs to be able to move freely on the bearing on the bottom plate.  Mine did not, it too was gunked up.  After cleaning it up the stator magnet rotated freely.  For the vacuum advance to work right the stator magnet must be able to rotate freely.

Step 7:  Reassemble.  A couple tips:
   1.  Keep the distributor in an upright position (like in a vise) and do not pull up on the central shaft
        until everything is put back together.  Doing so may unseat the springs.
   2.  The stator/bottom plate/coil assembly can be reassembled and installed as a unit.  Dropping the
        hex screws into the hole in the bottom plate before installation makes this easier.

Step 8: check and set timing.  This has been discussed in depth elsewhere so I won't repeat it.

The results:

Next?
My timing setting above was really a first approximation - somewhere within spec, but the specs are a range and I didn't pay too much attention to exactly where.  Since there's no knocking I'll see if I can squeeze out a little more by a hair more advance.  What needs to be stressed here, I think, is that there really is such a thing as "close," and just close isn't good enough.  In addition, the problems were totally invisible until the distributor was taken apart. 

In closing, this project brought major performance gains at no cost and with no parts.  If you've got any symptoms that this might explain then go for it!  There's nothing to lose, much to gain.  Happy motoring and cheers,
Title: Re: 6.9 distributor fixes
Post by: daantjie on 06 September 2018, 02:30 PM
Wow Dave what a monster post, nice work!
A bit off topic and not sure if it has any bearing, but are you running the rev - limiting rotor on your 6.9?  I think it has the rpm cut - out setting printed on the rotor somewhere, might be like 5 300 rpm or thereabouts from memory.  or maybe 6 300.. ::)
Title: Re: 6.9 distributor fixes
Post by: rumb on 06 September 2018, 02:32 PM
Wow!..  I see my disti being pulled in the future and cleaned up.

Thanks for the how to.
Title: Re: 6.9 distributor fixes
Post by: raueda1 on 07 September 2018, 09:34 AM
Happy distributor cleaning, gentlemen!  As for rev-limiting, I didn't notice any indications on any of the parts but I wasn't looking either.  One thing I didn't mention is that the WOT shifts are noticeably later than previously and significantly closer to the speedo dots. 
Title: Re: 6.9 distributor fixes
Post by: TJ 450 on 07 September 2018, 09:10 PM
Fantastic thread! This is something that’s been on my to-do list for years now. My 6.9’s never been quite right and the only thing that hasn’t been touched is the distributor, although I did swap it with another, probably equally as tired.

Tim
Title: Re: 6.9 distributor fixes
Post by: irvine on 08 September 2018, 10:07 PM
Great idea for a proper distributor clean up. Giving the prices for new points etc I’m liking the idea of a big clean and refresh before I spent a few $100 on points.
What sort of time scale did it take to carry out I’d love to get stuck in on my next weekend off.

Neil.
Title: Re: 6.9 distributor fixes
Post by: raueda1 on 09 September 2018, 08:10 AM
Great idea for a proper distributor clean up. Giving the prices for new points etc I’m liking the idea of a big clean and refresh before I spent a few $100 on points.
What sort of time scale did it take to carry out I’d love to get stuck in on my next weekend off.

Neil.
It was maybe a couple hours going very slowly and some interruptions.  I stupidly forgot to mark the rotor position when I took it out so I had to rotate the crank to get back to TDC and then all was well.  But rotating the crank was damned hard! 
Title: Re: 6.9 distributor fixes
Post by: john erbe on 03 January 2019, 06:10 PM
Raueda1. After not checking the 116 website in some time, saw your post and thought I mention that you might want to check the part number on your distributor. Your photo caught my attention showing that black wire, as it's consistent with the domestic model. On the Euro distributor it typically is green.
Title: Re: 6.9 distributor fixes
Post by: slfan on 30 January 2019, 08:19 PM

1. Great post!

2. Curiosity: Is the 6.9 distributor unique to 6.9 or will a "regular" 450 SEL distributor also work on the 6.9?

Thank you and regards
Title: Re: 6.9 distributor fixes
Post by: raueda1 on 31 January 2019, 04:44 PM

1. Great post!

2. Curiosity: Is the 6.9 distributor unique to 6.9 or will a "regular" 450 SEL distributor also work on the 6.9?

Thank you and regards
1.  Thanks!  I'll add more in due course as I get it tweaked better.
2.  I don't know, but I doubt it.  Per post above even euro and USA 6.9 distributors aren't the same.  My guess would be that it will physically fit but that timing curve is different.  But like i said - just a guess.  Someone else may know better.
Title: Re: 6.9 distributor fixes
Post by: raueda1 on 31 January 2019, 04:47 PM
Raueda1. After not checking the 116 website in some time, saw your post and thought I mention that you might want to check the part number on your distributor. Your photo caught my attention showing that black wire, as it's consistent with the domestic model. On the Euro distributor it typically is green.
thanks for that John.  Actually mine is green.  It didn't photograph well and the insulation was discolored blacker closer to the distributor itself.  As PVC ages is almost always discolors towards black or brown.
Title: Re: 6.9 distributor fixes
Post by: slfan on 03 February 2019, 03:30 PM
Dave,

Thanks for the information.  After seeing your post, I now have a new project.

Regards
Title: Re: 6.9 distributor fixes
Post by: irvine on 11 February 2019, 01:21 AM
Any updates to how the dizzy is running after getting some miles on it?
Thinking about doing this in the next few weeks.

Thanks,
Neil.
Title: Re: 6.9 distributor fixes
Post by: raueda1 on 13 February 2019, 01:15 PM
Any updates to how the dizzy is running after getting some miles on it?
Thinking about doing this in the next few weeks.

Thanks,
Neil.
Not yet.  Car has been in winter hibernation.  But do the project anyway.  You can't go wrong.
Title: Re: 6.9 distributor fixes
Post by: irvine on 10 May 2019, 02:16 AM
guys, I'm trying to do this clean up but I'm stuck trying to remove the first section under the dizzy cap, the one that has the injector contact and condenser screwed to it.

it looks to be heled in by 3 little indents in the distributor body, it looks like its simply twists round to align the indents with 3 gaps and off the plate should come. I've tried this but nothing budges, am I missing something??????

neil
Title: Re: 6.9 distributor fixes
Post by: raueda1 on 10 May 2019, 06:48 AM
guys, I'm trying to do this clean up but I'm stuck trying to remove the first section under the dizzy cap, the one that has the injector contact and condenser screwed to it.

it looks to be heled in by 3 little indents in the distributor body, it looks like its simply twists round to align the indents with 3 gaps and off the plate should come. I've tried this but nothing budges, am I missing something??????

neil
Can't follow the question.  What's the injector contact and condenser?  Aussie nomenclature perhaps?  Maybe describe the picture(s) corresponding to what you're talking about.
Title: Re: 6.9 distributor fixes
Post by: daantjie on 10 May 2019, 08:54 AM
Been tempted to do this too, but I have nightmare visions of me cocking something up, and this jobby turning into a nightmare.  My forays into the electrical "never never" have almost always led to pain and suffering :o
Title: Re: 6.9 distributor fixes
Post by: irvine on 10 May 2019, 05:32 PM
When I take off the distributor cap the inside compartment holds the rotor arm, this sits on a plate which has the injector contact screwed to it. Also the arm from the retard diaphragm is fixed to the plate. Hope this helps.
 I’m out at the minute and on my phone I’ll post a pic once I get home.

Thanks,
Neil.
Title: Re: 6.9 distributor fixes
Post by: irvine on 10 May 2019, 06:37 PM
Here's the pics,

Plate with everything attached:
(https://live.staticflickr.com/65535/46905402615_653bb8952b_z.jpg) (https://flic.kr/p/2esSs3c)W116 (https://flic.kr/p/2esSs3c) by Neil Irvine (https://www.flickr.com/photos/113709696@N07/), on Flickr

And now with the bits removed:
(https://live.staticflickr.com/65535/46905402395_717815a56c_z.jpg) (https://flic.kr/p/2esSrYp)W116 (https://flic.kr/p/2esSrYp) by Neil Irvine (https://www.flickr.com/photos/113709696@N07/), on Flickr

I've no idea how I'm supposed to remove the plate, I've tried twisting it, carefully prying it up, it wont budge.

Thanks,
Neil.
Title: Re: 6.9 distributor fixes
Post by: raueda1 on 11 May 2019, 02:24 PM
Here's the pics,

Plate with everything attached:
(https://live.staticflickr.com/65535/46905402615_653bb8952b_z.jpg) (https://flic.kr/p/2esSs3c)W116 (https://flic.kr/p/2esSs3c) by Neil Irvine (https://www.flickr.com/photos/113709696@N07/), on Flickr

And now with the bits removed:
(https://live.staticflickr.com/65535/46905402395_717815a56c_z.jpg) (https://flic.kr/p/2esSrYp)W116 (https://flic.kr/p/2esSrYp) by Neil Irvine (https://www.flickr.com/photos/113709696@N07/), on Flickr

I've no idea how I'm supposed to remove the plate, I've tried twisting it, carefully prying it up, it wont budge.

Thanks,
Neil.
Your pictures explain why I'm unable to offer much help.  You've got a totally different distributor than the one in my write-up.  Compare respective pix carefully.  Is yours actually from a 6.9?
Title: Re: 6.9 distributor fixes
Post by: irvine on 11 May 2019, 05:04 PM
No it’s a 280 6 cylinder d-jet, I’ve searched loads on google and yours is the closest description I could get.

I ended up cleaning a mountain of gunk from inside the distributor, put it back together and it’s like driving a new car.

I recommend this overhaul highly

Neil.
Title: Re: 6.9 distributor fixes
Post by: daantjie on 11 May 2019, 11:16 PM
This brings to mind another question...Does anybody know for sure the right part# for the 6.9 distributor?  I have checked mine and it is stamped with Bosch number 0237405002, but when I Google it it shows it to be a 450SL version ????
Title: Re: 6.9 distributor fixes
Post by: Alec300SD on 12 May 2019, 12:18 AM
The plate may be sealed in place wih some adhesive.
Try prying it out as demonstrated in the link.
https://www.howacarworks.com/illustrations/dismantling-a-bosch-distributor--6
Title: Re: 6.9 distributor fixes
Post by: TJ 450 on 12 May 2019, 03:19 AM
Hi Daniel, yes I've been wondering this myself. I have a feeling that mine is an M117 part as well. It is also 0 237 405 002.

The engine still pings at 3.4k+ under load, despite having a rebuilt WUR and is running great otherwise.

Tim
Title: Re: 6.9 distributor fixes
Post by: daantjie on 12 May 2019, 09:49 AM
Hi Daniel, yes I've been wondering this myself. I have a feeling that mine is an M117 part as well. It is also 0 237 405 002.

The engine still pings at 3.4k+ under load, despite having a rebuilt WUR and is running great otherwise.

Tim

Tim looks like the "right" number is 0237404007. Will this make a big difference in performance?
Title: Re: 6.9 distributor fixes
Post by: daantjie on 12 May 2019, 02:15 PM
Correction, looks like the 0237405002 is the correct distributor for the US spec 1977 - 1980.  I did some sleuthing and the boys @ the (now dormant, maybe dead(?)) M100 board corroborate this. Also confirmed in the service manual. Euro has part number ending in 004 and 007.
Title: Re: 6.9 distributor fixes
Post by: TJ 450 on 12 May 2019, 08:37 PM
I see, okay that’s good to hear. I’ve started tearing down my spare one of the same part number, so will hopefully get some results.

There is a new M100 board currently being set up.

Tim
Title: Re: 6.9 distributor fixes
Post by: slfan on 01 June 2019, 12:37 AM
Hello Administrators,

This post is great and has extremely helpful information.  Any chance it can be fixed at the Top of the Mechanical section? Just a suggestion.

Best regards,

Angel
Title: Re: 6.9 distributor fixes
Post by: daantjie on 05 June 2019, 08:40 AM
Quick question on this very informative post.
What do you guys think the function is for the little cover plate/plug in the bottom section of the housing?  Is it perhaps to clean/lube the mechanism?  I guess you can blast this spot with some carb cleaner to de - gunk the works if you are not keen to pull the whole thing apart, though that of course would be the best way to do it.
Title: Re: 6.9 distributor fixes
Post by: TJ 450 on 06 June 2019, 05:58 AM
I had mine apart the other week, all cleaned and lubricated although the car feels different, I have not experienced any miracles yet.

I will be rebuilding the cast iron fuel distributor next.

That plate, yes I was thinking the same. It must be for servicing.

Tim