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Distributor Cap HT lead positions

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Brucey
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Distributor Cap HT lead positions

Post by Brucey » Mon Mar 14, 2016 12:02 am

I've been (unsuccessfully) trying to track down a slight misfire recently; thus it was with a dull sense of inevitability that I realised that I'd have to take the distributor cap off. It has been undisturbed for several thousand miles / about two years or so (following the infamous disintegration of my rotor arm), so overdue an inspection anyway.

On a fairly balmy spring morning, with tools to hand and in no special hurry, it is a vastly more pleasant job than by the side of the road in a chilly breeze. It is so much easier once the fan (and fan shroud) is off, I have decided to pack a 32mm wrench in the car tool kit, so that if I ever need to remove the distributor cap again, I'll be able to do it easily. The other trick is to remove the radiator top mounts (not all E24 versions) and this allows another few mm clearance because the radiator can swing forwards a little.

I found that the distributor cap was actually pretty good, just a bit dusty inside really. The rotor arm still looks like new more or less too. Both parts are pattern parts, not OEM ones. The cap was the same one as survived the exploding rotor arm, and is at least 15 years old.

I cleaned it up the distributor cap inside and to make a proper job of it, I thought I ought to clean the outside too. Once I got the leads off, I realised that, unlike an OEM Bosch part, this pattern part
didn't have the correct locations for the plug leads marked on it anywhere. D'oh! I remembered making a mental note, a long time ago, to mark the correct lead locations onto the inside of the black distributor cap cover, but then didn't do it because I didn't have my vibro-etch to hand, and wanted to make a neat job of it. This time I just had at it with a screwdriver.

For the reference of others, the six pins inside the cap at 1 o'clock, 3 o'clock, 5 o'clock, 7 o'clock, 9 o'clock, 11 o'clock are cylinder #s 3, 5, 1, 4, 2, 6.
Image00188.jpg
shiny happy distributor cap
Image00188.jpg (134.94 KiB) Viewed 1702 times
Similarly the connections left to right in the photo are 2,4,6,ZS,3,1,5 where ZS is the coil (king lead) connection.

I also cleaned my spare distributor cap; this OEM Bosch one was very manky indeed, but with application of much elbow grease and not a little solvol autosol polish, it came good too. I used cotton buds (Q-tips) to clean the inaccessible nooks and crannies. No single solvent would ever shift every kind of crud from the inside of a distributor cap, but the solvol autosol cleaned everything nicely. Small scuffs and scratches can be polished out using solvol too.

BTW the carbon brush ought to protrude about 5mm from the centre pillar. If the brush is a little worn, often the spring underneath can be reset slightly to allow the correct brush protrusion.
cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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slofut
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Re: Distributor Cap HT lead positions

Post by slofut » Mon Mar 14, 2016 1:18 am

Thanks Brucey, good sticky.
'87 635csi, 5sp man, dk blu on pearl beige
'88 635csi, auto, black on grey
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Brucey
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Re: Distributor Cap HT lead positions

Post by Brucey » Mon Mar 14, 2016 9:38 am

also, this is my freshly cleaned 'spare', shortly to be consigned to the boot (trunk) along with my other 'essential spares'.
Image00189.jpg
another shiny distributor cap
Image00189.jpg (152 KiB) Viewed 1676 times
There is a little wear on the six pins, but the distributor cap is free of cracks or tracking, which is the most important thing. I'm still amazed at how it cleaned up; it looked like it had been under the sea before!

BTW you can see my freshly applied markings inside the black cover, just in case....

cheers
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slofut
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Re: Distributor Cap HT lead positions

Post by slofut » Mon Mar 14, 2016 11:16 am

Good idea! I'll be marking mine just in case.
Btw, I broke the dang pulse generator wire on #6. Glued it back but need a new one. They look to be stupid pricey, any suggestions?
'87 635csi, 5sp man, dk blu on pearl beige
'88 635csi, auto, black on grey
'63 BMW Isetta
'75 XJ6C, 2dr, warm 350
'86 XJ6, th700r4
'75TR6
'64 Olds 88 conv
"68 T120 Bonneville

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sansouci
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Re: Distributor Cap HT lead positions

Post by sansouci » Mon Mar 14, 2016 2:26 pm

Brucey,
Love the matching orange cloth...
Sansouci
84 E24 633Csi Auto, Bronzit/PearlBeige 6997510
93 E32 740il M60 Auto, Alpenweis/Ultramarine
60 528i M30 5-speed Green/Beige (crushed)
71 240Z 4-speed White/Blue (rusty & sold)
65 396 Chevelle 4-speed, Marina Blue/Black (stolen)

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Re: Distributor Cap HT lead positions

Post by songzunhuang » Mon Mar 14, 2016 7:02 pm

I replaced my distributor cap with an aftermarket one when I had my rotor woes about 6 months ago. Neither my original Bosch or the aftermarket cap had the black cover. Is it just a heatshield or what? It doesn't seem like it would get that hot since it's in the path of the air (although I guess it's air passing through a possibly hot radiator).

Also without the black cover, I found that I could actually get the cap on and off without too much interference from the fan shroud. It was tight and I had to press on the shroud to get clearance, but it worked.

As for the wires, I used sharpie and marked the silicon boots (my were blue colored so black sharpie was legible). After installing the new cap and wires in the right place, I wiped off the sharpie marks. Not a permanent solution, but it worked for the intended purpose.

Ok, last question. What is the resistance supposed to be in the main wire from the coil to the center of the distributor cap? Mine seemed to be a bit high and I was wondering if I was looking at a bad wire.
-----
Song Huang
1984 633CSi
Last 7 of VIN: 6997383

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Brucey
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Re: Distributor Cap HT lead positions

Post by Brucey » Mon Mar 14, 2016 7:51 pm

OEM plug lead sets are normally marked 1-6, but if the distributor cap has no markings on you are a bit stuffed! Often you can slide the plug leads through the conduit a little and this way work out which is which, but it is easier if you don't have to.

IRRC OEM plug leads are a few Kohm each and the resistance is in the terminations, not the wires. I have found that the OEM leads contain enough suppression resistance that resistor spark plugs are not necessary with OEM leads. You can make up new leads by assembling the parts yourself. The typical arrangement is 1Kohm at each lead termination (except for the plug tops which are 5Kohm). The rotor arm also has 1Kohm in it.

I have seen plug lead sets sold for these cars (at vast expense....) that were made up using resistor wires and obviously the #1 lead has about 1/6th the resistance of the #6 lead.... :roll:

Re the cam sensor, I don't know for sure how this works (has anyone put a 'scope on one or dissected one...?) but I have always supposed that it would be something simple like a ferrite ring with a few turns around it to give an AC signal when the plug fires; similar arrangements are used for timing strobe lights where the sensor clips round the plug lead.

You can see the parts for post 6/87 builds here;
http://2009.bmwfans.info/parts/catalog/ ... distrib_c/

the other three setups used on M30 engined 635s are on adjacent pages to that.

The black cover is to prevent water, dirt etc from getting onto the distributor cap. Judging by how grubby the outside of the cover gets, I think it is best to have it there rather than not. I think it also helps to keep the cap warm and dry when the weather is very cold and damp. Remember that this was one of Bosch's first really high voltage ignition systems, so I get the impression that they were not in the mood to take chances with it.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Re: Distributor Cap HT lead positions

Post by plip1953 » Fri May 22, 2020 7:14 pm

Resurrecting Brucey's thread....

I'm in the process of renewing my distributor cap and rotor arm (both original from 1987) and wondered if I should also check the state of the HT leads. Visually they look just fine, but I also had in my mind that each lead would have (and need to be of) a specific resistance, but then it did occur to me that they are of different lengths so how would that factor into the equation.

Courtesy of Brucey, I now see that the resistance is in the terminations rather than the leads themselves, so does that mean the wires are effectively of zero resistance?

Anyway, I put a meter on each one end to end and they registered from around 1790 ohms to 1805 ohms. Does that seem about right, and is a bit of a difference ok, or should they all be of a very specific value?
Phil
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baders
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Re: Distributor Cap HT lead positions

Post by baders » Sat May 23, 2020 1:10 am

Those resistances look fine. Remember though that your ignition system is high voltage, so using a mere multi meter may not show up insulation breakdown. If in doubt, replace them.
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Re: Distributor Cap HT lead positions

Post by plip1953 » Sat May 23, 2020 8:51 am

baders wrote:
Sat May 23, 2020 1:10 am
Those resistances look fine. Remember though that your ignition system is high voltage, so using a mere multi meter may not show up insulation breakdown. If in doubt, replace them.
Thanks. I'm keen to retain the original leads if at all possible. If I ran the engine and observed the plug leads area in darkness would the presence (but hopefully absence) of and sparking be a good test of the insulation properties - or does that tell you something else?
Phil
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Re: Distributor Cap HT lead positions

Post by hornhospital » Sat May 23, 2020 8:22 pm

Good idea in observing the wires in the dark. You can also spritz them with water to see if it induces any missing. I don't mean water-hose them, just a mist from a hand pump spray bottle. If it passes that test, they are in excellent condition.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann";'87 325is "Odette"; '93 325is "Elvira"; '95 M3 "Ashlyn"; '95 318is "Bebe"

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Re: Distributor Cap HT lead positions

Post by plip1953 » Sat May 23, 2020 9:04 pm

hornhospital wrote:
Sat May 23, 2020 8:22 pm
Good idea in observing the wires in the dark. You can also spritz them with water to see if it induces any missing. I don't mean water-hose them, just a mist from a hand pump spray bottle. If it passes that test, they are in excellent condition.
Another great tip - thanks :-)
Phil
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