Carb slide top nut loose

[pmtremblay]

Hey all - On my last ride, the carb slide top nut (the knurled round nut) on my R27 kept coming loose. I had to reach down at every stop and hand-tighten it back up, and eventually wrapped duct tape around it to keep it in place.

Is this common? If so, is there a simple fix? Will loctite on the threads do anything? I'm assuming this is a hand-tighten only nut. I'm ready to order a new nut, but want to rule out a simpler fix first. Any ideas?

Photo is with the nut removed, it never came fully off while riding.

[Micha]

The fine thread on the body of the carb is delicate and one only mount that cover when it is completely straight to the carbs body, or it may cause the threads to stirp. The alloy from which the body is made will not win the first prize either. I suggest that you carefully check, with a flashlight and if necessary with a magnifying glass, the condition of the thread in the body and the nut. Maybe even move the cover from the other side and see where the problem is, as the thread is not always stripped on both parts.

[Seek]

I don’t have the problem but heard that the version with the large O-ring doesn’t have this problem.

[vechorik1373]

Looking closely at your photo, the O ring does not appear to be round anymore, or maybe it is not the correct one.
Assuming the threads on both the carb body and the ring nut are in good/fair shape, you will find that a correct fitting O ring will go a long way in preventing the ring nut from unscrewing.

[schrader7032]

Is there an oring in the picture?

[pmtremblay]

There is no o ring. I don't think there is supposed to be one according to the parts diagram on Max BMW and the Bing book. It's a Bing 1/26/83, type 122.

If there's an o ring that'll fit it'd probably add enough tension to stop the loosening. Anyone have a parts number or source?

I have a new nut on order, and some anti-vibe thread tape.

[xackley]

A piece of string or small hair bungy if you want it fixed today.
I would not put any thread locker or anything with grit on those delicate threads.
Don

[vechorik1373]

All of the Bing carbs use this same O ring. Part number 13 11 0 042 149 When you get it, you will think that it is too small, but it is not. You have to stretch it over the lid and get it into the empty groove shown in your last photo.

[pmtremblay]

Thanks Vech! O ring is ordered and I should be back on the road shortly.

[pmtremblay]

To close this out:
Thanks to Vech my carb nut issue appears to be solved, the o-ring was the fix. I installed the o-ring, cleaned all the grimy threads really well, then coated them with a little grease as suggested by the Barrington book. No movement over a 25 mile test ride so I'm calling it fixed. I don't know why the o-ring isn't on the R27 carb diagram or fiche, but I know the knowledge on this forum is unmatched, literally better than the manual in this case.

I got a new knurled nut as well, but after inspecting the threads and test fitting against the original nut, I elected to stay with the old one. The new one doesn't feel as substantial as the old one, is shaped a little taller with shallower knurling, and is way too shiny.

Unrelated, but I checked my brake lights before heading out and discovered my rear switch had crumbled. That may have been the last of the original non-metal parts on the bike. New one on order.

Thanks again Vech!