distributor cap oring p/n?

E28 technical advice asked and given! Troubleshooting, modifications and more.
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bk_856er
Posts: 111
Joined: Dec 08, 2012 8:30 PM

distributor cap oring p/n?

Post by bk_856er »

Anyone know the p/n for the large diameter oring for the plastic shield behind the rotor and cap?

I don't see it in realoem and keyword searching only brings up M flavors, which are presumably different.

I seem to get a film of what looks like condensation on the insides of caps/rotors that I remove my from my '85 6er. Probably not a good thing. Oring is there, but maybe it's taken a set and doesn't seal so well anymore.

BK
Owndapwn
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Location: Kansas City, MO

Re: distributor cap oring p/n?

Post by Owndapwn »

12111288167 for the cover. My replacement distributor cap came with an O ring.
bk_856er
Posts: 111
Joined: Dec 08, 2012 8:30 PM

Re: distributor cap oring p/n?

Post by bk_856er »

I see - so the plastic piece comes together with the oring and the oring doesn't have a pn. Meh, not sure it's worth $25 to me.

I've bought plenty of Bosch and Bremi distributor caps and I don't remember one ever coming with an oring! Is it a dealer thing?

BK
Owndapwn
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Location: Kansas City, MO

Re: distributor cap oring p/n?

Post by Owndapwn »

Nope. Just a Bosch cap from Autohaus. Is that not normal? Should I be making sure I didn't get a refurb or something?
If worst comes to worst, try a dealership. I'm sure they used the O ring on multiple cars, especially since the M30 was in so many models for so many years.
tn535i
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Location: Middle Tennessee

Re: distributor cap oring p/n?

Post by tn535i »

The film is probably from ionization of whatever is in there. Heat and cool cycles will move air out the back by the camshaft and some fresh air in regardless. I doubt the o-ring plays a role in that and probably there more for splash/wash protection on the front side.
bk_856er
Posts: 111
Joined: Dec 08, 2012 8:30 PM

Re: distributor cap oring p/n?

Post by bk_856er »

I think you're probably right. There are weep passages on the underside anyway.

My dealer parts guy couldn't find the separate oring.

Maybe I'll just plan to clean things out once a year or so.

BK
Owndapwn
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Location: Kansas City, MO

Re: distributor cap oring p/n?

Post by Owndapwn »

It looks pretty standard. Have you tried the local hardware store? Probably wouldn't hold up like OEM, but it'd be better than nothing, I'd imagine. It's a pretty big groove it looks like.
Blue Shadow
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Re: distributor cap oring p/n?

Post by Blue Shadow »

maybe some kind soul will measure accurately the one they have on a motor sitting around for a rebuild of something and you can get that o-ring from a company that supplies o-rings. Unfortunately, those companies like to have minimum orders. So order a few sets of alpina wheel o-rings, too and sell em here. Make enough money to cover the cost of your o-ring, about $1.30 or less.
bk_856er
Posts: 111
Joined: Dec 08, 2012 8:30 PM

Re: distributor cap oring p/n?

Post by bk_856er »

My oring is intact, but I suspect that it has taken a set with all the time/heat and doesn't seal as well as it could/did. No longer a round profile. I started to remove it and stopped because it's a bit hard and I didn't want to break it and be left without one. Surely it is a standard oring number available from McMaster or similar, probably Viton since it's held up this far and buna would not, but tricky to get accurate sizing with the squished shape. With all the M30 motors out there it's weird this info is so hard to come by (for the non-M motors).

BK
tn535i
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Location: Middle Tennessee

Re: distributor cap oring p/n?

Post by tn535i »

I think it's the same o-ring on all these M30, M20, S14 and S38 motors. The plastic back shield is different due to the cam adapters being different though. I had a broken shield due to a failed rotor on the S38 and the shield I had was wrong but was for an M20 maybe M30 motor so I had to order one specific for the S38. But I want to say the o-ring will be identical just like the dist cap is identical regardless of the back shield shape. If you are saying you can find an S38 o-ring easily enough go for that.
bk_856er
Posts: 111
Joined: Dec 08, 2012 8:30 PM

Re: distributor cap oring p/n?

Post by bk_856er »

In that case it's 60x3mm BMW pn 12111252257 or McMaster pn 9263K746 in Viton.

Weird that no vendors or ebay sellers indicate non-M fitment. Error in some database that gets perpetuated?

BK

**edit** I just thought to measure a spare upper timing cover in the garage and the ID where the distributor cap mounts and the oring seals is more like 113mm, so the dimensions and pn above can't be right.
bk_856er
Posts: 111
Joined: Dec 08, 2012 8:30 PM

Re: distributor cap oring p/n?

Post by bk_856er »

I recently bought the shield and removed the o-ring for measurements.

The actual o-ring dimensions are 3.4mm width and 115mm OD.

The plastic shield ID for the o-ring is ~108mm.

This might cross with a #244 o-ring in dash sizing, but could also be a custom size.

I have a spare distributor cap and upper timing chain cover to test fit and everything looks good/correct. By design, the o-ring does not actually fit into the ID of the aluminum timing chain cover as I initially assumed, but compresses against the top lip when the rotor is bolted on.

Note that the o-ring does not "seal" the internal rotor area from the outside world because the distributor cap has two sets of 3 grooves on the lower part to allow drainage, breathing, etc.

BK
BRRV
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Re: distributor cap oring p/n?

Post by BRRV »

I just did the upper timing case cover gaskets and removed the dust shield after the cap and rotor; no o-ring. Since I seem to recall my BMW parts guy saying that it was no mo available and mine didn't have one anyway (and the dust shield on mine didn't seem to have any real provision for it) I reassembled same as before with no issues (and there were no leaks so far as I know). I seem to recall the dust shield that is OE on my car had, for lack of a better descriptive term, an integrated design that seals the cam cover without a separate o-ring, upon examination, because I expected to find one, too. My car is a 10/85 build DC74 M30B34.

EDIT: You know, its possible that the dust shield had the o-ring on it and it had sealed so well against the shield that it appeared to be inseparable and one piece; I sure couldn't see any way to separate the two, even if I knew it was there..
Last edited by BRRV on Nov 06, 2016 9:44 PM, edited 1 time in total.
bk_856er
Posts: 111
Joined: Dec 08, 2012 8:30 PM

Re: distributor cap oring p/n?

Post by bk_856er »

Sorry, I mis-typed above and meant to write:

"...but compresses against the top lip when the distributor cap is bolted on."

BTW, today I thought I would try to just replace the old hard o-ring on the existing shield to save myself the trouble of removing the rotor adapter and maybe needing to then use a new cam seal. The old plastic shield cracked when I pried on it just a little bit to lever the o-ring out. I probably should have cut it off instead. Beware of brittle parts....

I suspect the o-ring actually does very little, unless you try to pressure-wash your motor. I think the annual oil film/condensation on the interior of my cap is probably due to minute leakage from the cam seal.

BK
shipsareneat
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Joined: Sep 04, 2015 1:02 AM
Location: San Diego

Re: distributor cap oring p/n?

Post by shipsareneat »

Resurrecting this thread to share a recent revelation I had: an oil filter housing o-ring is a good replacement for the dried, cracked, NLA one commonly found on the distributor cap.

While replacing the ignition cap coincidentally around the same time as an oil change, I noticed that the cap diameter was pretty similar to the oil filter housing. Sure enough, the the filter o-ring was a damn near perfect fit on the dust cover. Better than nothing, and easier than running all over town to find an exact fit.
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