Bosch Distributor Rebuild

Hello Gentlemen,

I have a '73 2.4S motor built to 2.7RS specs. I have been having a problem with my idle hanging up in the 2,000 rpm range, after driving at higher revs (either spirited driving or just normal street driving).

I diagnosed the problem as a sticking ignition advance by lightly tapping the distributor with a screwdriver handle to get the idle to come back down.

My distributor is Bosch part number 0231169010 JFUD6. It currently has a 7,100 rpm rev limiter rotor in it, which I believe is the rotor for the "E" model, right?

I just pulled the distributor out of the engine and proceeded to disassemble it and I have the following questions:

1) One of the tabs that is part of the points plate and attaches the plate to the distributor housing is sheered off. Does this mean that I need a new points plate and is that part readily available? When cleaning the points plate, do the two plates slide on each other at all or are they fixed together?

2) My initial quest was to get to the mechanical advance mechanism and disassemble, clean, re-lube and reassemble.
Upon initial inspection, the springs on the mechanical advance mechanism appear to be intact, which may mean the mechanism is just gummed up and in need of cleaning and re-lubing. It also occurred to me however, that my hanging idle problem may be related to the vacuum advance/retard mechanism. Do those parts fail periodically and if so are they readily available? Does it sound like that unit may be the source of my hanging idle problem or is it more likely to be in the mechanical advance mechanism?

3) Do I need to pull the shaft to access (clean and re-lube) the mechanical advance mechanism? If so, can I re-use the shaft pin or do I need a new one? Should I use loc-tite when I reinstall the pin?

4) Lastly, do I have the wrong distributor part number for my motor? If so, would locating the "proper" one make any difference? At a minimum I should probably go ahead with the 7,300 rpm rev limiter "S" rotor, but since I do bump into the existing 7,100 limit on a regular basis, should I just keep it as an added level of protection?

Thanks as always for any advice you may have.

JA

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John
70/73 RS Spec Coupe

John,

That p.n. is a '73 'S' distributor, same as mine, but it doesn't matter ... all of the "T.' 'E,' 'S' distributors had the same advance curve ... only the rev-limiting rotors were different! You need a 1.234.332.206 7300-rpm rotor!

Disassembly of the distributor is best done indoors on a clean table covered with newspapers, and care should be taken not to lose flying identified objects, such as C-clips or springs!

The two-piece point plate is a pivoting assembly, with the lower part fixed to the housing with two screws, opposed 180 degrees apart across the housing ... your broken tab could be repaired by MIG welding a newly fabricated tab, but the alignment would have to be precise. The two plates are lubricated with Bosch grease from the factory, and could be stuck together by congealed grease. A ball bearing and spring-loaded assembly tensions the upper plate to the lower plate. The vaccuum-retard mechanism rotates the point plate. I seriously doubt if many of the distributor internal parts are still available.

No, you don't have to take the cross-pin and gear off the shaft to service the centrifugal-advance assembly. Remove the felt plug beneath the rotor. Take out the C-clip with a spring pick/dental tool, and the cam assembly is free to come off after removal of the spring ends from the posts on the lower shaft assembly. Spray brake cleaner/degreaser will remove old grease/oil/gunk from the mechanism. Pelican has tubes of the Bosch grease to relube with, or you could use engine oil.

I can't really tell you what is causing the idle problem, but a 'stuck' centrifugal advance mecanism will definitely cause an 'odd' running engine! The vaccuum-retard can be disconnected with no ill effects, but one that is malfunctioning could be troublesome, as it has a range of motion of 10 crankshaft degrees (5 distributor degrees) that is supposed to only be active at idle, but could conceivably mess up your idle if sticky and intermittent!

I have B & W photos of the point plate from 1982 when a broken ground wire disabled the engine. I replaced the ground wire and took some close-up pics of the process and finished product. Email me if you want digital copies.

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Warren Hall
1973 911S Targa

That's the distributor side of things, but it could also be worth checking the throttle body part of the vacuum advance: There are small holes on the bodies (no's 1 & 4 cylinders) that the hoses are connected to (assuming you have MFI), and these have a tendency to clog. Remove the pipes and squirt seme chem tool down the holes & loosen with a suitable probe. Holes should be completely clear. My No.1 hole was completely blocked; the distributor was receiving only 50% of the vacuum it needed. Apparently these systems 'struggle' to get the required vaccuum even when healthy and new. Best make sure everything is working as well as you can get it!

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'72 911 TE

Good info, Matt.

In fact, I do have MFI and was looking in that location yesterday as I am planning to re-do all of my vacuum lines.

One question, though. Per Warren's post, it appears that the only function vacuum serves in the distributor is for smog purposes. Warren, am I right? If that is the case, it seems those could be clogged and it would not impact running.

Am I off base with my understanding of the vacuum mechanism?

Thanks,

JA

Hello


0231 169 010 indicates an early mY 1972 Distributor. They changed to 184 xxx within 1973. Sorry not sure about the numbers but as I remember the Carrera had 169 009
Later units where 184 003. 169 010 seems to be an uS version and not sure about the specs.

1.) As you descripe it the plate seems not to "float" and you need an new one. But try to relube it, One missing tab ? Well if it is the one with the rollerball then you will have problems. The plates are fixed together by an slight rollbeding in the inner diameter.
If you need a new plate then look for period and earlier distributors from Mercedes 6 Cyl. Also several other Bosch units are usable even slightly different in design.
Just visit your local Bosch service to have a look in the parts reference list.

2.) After removing from the sliding point carrier plate you will see the fullcrum wights and can clean rebuild them.
AFIR you can pull the upper shaft to relube, just look if there is a screw in the middle of the shaft.

The vacuumsystem can be ckecked by messuring the movment relatet to vacuum.

Normaly they get shot over the years.

Your hanging at 200 can also be supportet by the MFI. However first to do is the ignition.

3.) AFIR No. Shaft pin can get bend then renew but mostly not. Remember any mistake there and your brass wormdrive will spool up and you have to split the case.

4.) The 2,4 S and the 2,7 have very close specs and early 169 009 are similar.

You can reset the original Fullcrum wights to RS specs.

My advice would be to try to fix as much as possible and if you have no succes or find to much wear then let it redo proffesional to RS specs. You need an distributor bench to redo it proper you might also ask for a more aggresive curve if you have higher octane fuel and higher compression then the stock euro setup.

Grüsse

Just a note about removing that advance plate:

It does come out easily... but you must twist the plate clockwise or anticlockwise(forget which direction sorry!) before it will come out. If you look carefully you will see what needs to be done. Just remember, TWIST BEFORE ATTEMPTING TO REMOVE.

That pin is a pain to remove. I ended up drilling after most other things failed. The only reason you need to get it out is if the endfloat is out of spec on the shaft, as was my problem. I ended up removing it and machining up a spacer to get the endfloat right. Warren knows the spec, but it's basically fairly small, ie, you shouldn't be able to slop it up and down.
I replaced the pin with an engineers rollpin (choosing the very tightest I could) and pressing this in place after loctiting. I too had doubts about the pin, but this method has so far proved 100% reliable. I'm in the habit of checking it periodically, but have to say that it seems to be the soloution.

Using Mercedes parts is a great idea. I'm not sure what the value is of old Mercs in your respective countries, but over here they're dirt cheap. Most of the Bosch stuff is very familiar to Porsche owners, distributors being a great example. Check it out!

On a vaguely unconnected note, I just bought a VW Golf as a city beater and was quoted $10 for a CV boot kit that needed replacing. I had forgotten how easy and reasonable it is to get parts for normal cars. How nice!
Bores the hell out of me compared to the P though

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'72 911 TE

John,

Just sent you the pics.

Yes, you have to rotate the point plate about 1/2" to get the notch past the feedthrough connector for the points lead.

And, a rollpin will replace the pin holding the gear on the shaft just fine, should you need to replace bushings or shim the end play. My original '73 (worn) distributor still measures 0.001" end play and my new, spare RS 2.7 distributor measures 0.0025" and neither have any play at the cam end of the shaft.

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Warren Hall
1973 911S Targa