which way is up for floats?

[Bruce Frey]

Interestingly, there seem to be several different R12 ignition timing numbers floating about:

English Handbuch Illustration: 1/4" - 19/64" (±6-8mm)

English Handbuch text: 8-9mm

German Handbuch Illustration: 5-6mm

German Handbuch text: 7-8mm

R12 Data Sheet: 42 degrees, 12mm (I checked this mathematically and 42 degrees does work out to be ±12mm)

I THINK all the numbers are in the same context.

Cheers,

Bruce

[Barry Robin]

thanks for the offer, guys! feel free to just click on the email logo below my post to get a hold of me. if that isn't working, my address is: barryrobin@aol.com

the thing is with my timing problem, is that as the timing was set only about 500 miles ago-when the engine was rebuilt-i keep thinking that this is a points only situation; that i might just need to find top dead center and gap the points (assuming they're not fried).
two things: when i pull in the spark advance, the engine dies, and yesterday it was only firing on the left cylinder. i figure that the spark is now already so retarded that the advance just shuts it down...

does that sound about right?

too bad that there's no vintage club member or mechanic in ireland or england to go to-but if you know of one in england i might be able to truck it over to him.

sending it to vech from ireland will be a tad pricey, i'd think!

[Darryl.Richman]

Barry, I know there are a couple Brits on the Kradrider list (a list for WWII German bikes) who have R12s or are interested in them. I seem to recall Drew Grant lives in Northumbria, and Anthony Evans (not sure where exactly).

I sent you the scan of the owner's manual; hope it helps you.

Regarding points, a magneto bike should never erode the points, unless the condensor is dead. (Unfortunately, if the condensor is dead, you have to R&R the whole mag, as it's buried inside.) If the condensor is dead, the bike will not rev well and you'll notice quite visible arcing across the points when they open. It's easy to see with the bike running in a darkened garage, with the cap removed from the points chamber.

If one cylinder dies, then it's likely that there's something wrong with that cylinder. The valve settings might have come loose on one of the valves; I would check that first. (I've had this happen a couple times and the cylinder runs crappy first and then doesn't run at all.) I've also had a pretty new Bosch plug quit working -- that will do it, too.

Bruce, that's very confusing news. I noticed the measurements on the timing diagram in the R12 book. I also noticed that they're different between the R12 and the R17. However, in my edition of the english manual, dated October 1936, the text agrees with the diagram (says 7-8mm). The spec for the R17 is 12-14mm.

Craig Vechorik has said that he transfers the timing marks from an R50/2 to the R12 flywheel and has good success. I believe the F mark on an R50 is at 39 degrees btdc (and the static timing mark for idle is at 9dbtdc).

[Bruce Frey]

You should receive an email shortly with the R12 info. If you don't belong to The BMW Club of UK and Ireland, you should consider it. They have a vintage section.

Peter Dunn, who is also a member of this club, should be able to point you towards someone. There is a fellow by the name of John Lawes who is knowledgable about plunger frame bikes (he is also a CJ dealer), but I don't know if he knows much about the previous generations. I have heard of another fellow by the name of Harvey from another group who sounds as if he shoud be avoided.

cheers,

Bruce

[Darryl.Richman]

Barry, it also occurs to me that you might find Erik Bahl's website helpful. He restored an R12 and took a lot of photos from beginning to end, and produced a very useful description of all the work he did.

[Barry Robin]

i know eric's site very well-i'd check in most every week to see how he was getting on with the R12. sort of like a must-see t.v.show, i'd eagerly await each new episode...

funny thing: i just back from taking it out through the dublin streets, and it performed beautifully! it pulled just fine, idled fairly correctly and did everything the way it's supposed to. too bad it might not tomorrow. sometimes it feels like a freind who goes off their meds occasionally-you never know what you'll get.

thank to both you and bruce for the pdf files; they'll come in more than handy.
i think the next step is to either rebuild the carb or to swap it over to a dual carb system using those re-pop grazins from ebay...

[Peter D. Nettesheim]

Gents,
I have been away from the forum otherwise I would have put my two cents in earlier. The set up of the timing is simplistic in theory and operation. First you need to avoid tying to use knowledge of later BMW timing. The exact method is laid out in the R12 manual (which is available in english). This is the process:

1)Set either cylinder to TDC (do you know how to determine which cylinder is at TDC?).
2)rotate the engine in reverse direction to its normal operating rotation till the point where the piston is at a distance from the top of the cylinder the prescribed amount (I don't have this figure off the top of my head but can easily find it in the manual if necessary. I have only seen one dimension for the r12 and the spec on all sport machines is different). In addition, all this stuff about precise 7mm or 8mm is insignificant. Why? Two reasons. The timing of the engine is based upon the precise position of the timing advance mechanism, which varies and you have not even addressed the fact that the timing will likely be in perfect position when the chain cannot even be placed over the sprocket on the front of the magneto. Are you aware that there are two different magneto timing sprockets to take up for this varience (don't tell me you have both types in stock). Don't be hung up on precisely 7 or 8 mm since quite honestly I don't believe you will be capable of getting it to within even 3mm.
You won't need to anyway to get proper performance.
3)set the magneto so that the points are just opening when the timing advance ring is at full advance.
4)Here's the one people forget. You must now remove the ignition wire from the magneto on the side that is to get spark and confirm you see a small brass strip on the backlite distribution ring otherwise your timing will be off by 180 degrees. Do you understand? Both plugs do not fire at once!
5) Shim and then install the magneto for proper chain tension.
6)If you have done the above correct, you can forget all about the timing marks on the flywheel and the rest of that BS. The above is exactly how the factory has given instruction and all the rest is just extra information of no importance.
Good luck and write me at BMWMUSEUM@HOTMAIL with any questions.
Peter D. Nettesheim

[Peter D. Nettesheim]

Your carb issue should be easy to resolve. Start by installing new jets of the proper size. Let me know the results and we can pick up from there.
Peter D. Nettesheim

[VBMWMO]

here's a quick one for those with R11/12's with Sum carbs:

i replaced the float and it's idling fast...
the brass float bowl-what direction does it go?; the dome towards the top or the bottom?

senile dementia at it's best!