BMW R series single cylinder bikes

[Interstellar0vdr]

I'm new to motorcycles, but very interested in the classic BMW bikes. I had previously made a post asking about other R series types, however, I've become really interested in the single cylinder bikes, particularly one I saw online that was a 1954 R25/3. I'm assuming that single cylinder bikes would be easier to work on, simply because it's smaller and less parts. I'm not super mechanically inclined, but I can do basic stuff on a car like change a tire or change oil. That being said, I figured I'd be able to do the work on a bike like this or at the very least, be able to learn how to do the work. I still need to get my license, but eventually I'd like to some day get a bike like the R25/3. Does anyone have any experience with these bikes and could speak to their reliability, ease of fixability, or any other helpful info? I know there are a few versions of the R25, hence the "/3", it's my assumption that the 3rd variation would be the best of the variants? I'm pretty sure BMW had the single cylinder bike up until the 1960s sometime, but I don't really know if anyone single is overall better than another, but I certainly like the way the 1954 R25/3 looked. Anyway, all feedback appreciated and hopefully I did not start rambling here!

[schrader7032]

I own a couple of the "complicated" bikes and one that you tag as being "simple". I'm not sure that the singles are an order of magnitude simple. Sure it only has one cylinder but you still have to set the valve clearances. It still has a "mysterious" DC electrical system...it doesn't get easier just because it's smaller. A transmission is a transmission...they all have intricacies that are unique to the bike. So, in general, I think you still need the appropriate mechanical skills to work on anything that is 40-60 years old.

The problem I've had with my R25/2 is that it vibrates quite a bit...it's just the nature of a single cylinder bike being more difficult to dynamically balance. I've had a few things depart the bike while riding, only to discover it gone when I got home. I typically do a quick check of things and nuts/bolts on the bike whenever I get back from a ride. So that's something that one has to live with.

You're correct that the "/" indicates a later version. After the R25/3, they dropped the "/" and just had the R26 and R27. All of the bikes were 250cc engines. One should note that the earlier bikes had very low horsepower with limited abilities to keep up with traffic. My single left the factory with 12HP. I'm a moving roadblock and only try and ride on off-hours when the roads might be more empty...I ride looking in the rearview mirrors a lot. The brakes on nearly non-existent and I have to prepare well ahead of time and anticipate situations because of it. The later single engine bikes got better with engine power and brakes.

I think you should look for a mid '60s R27. It will have as much as they could get into the singles, more power, better brakes, and the later models had the engines rubber mounted so they were smoother. With its capabilities, it will do pretty decent with traffic. I think this might be more enjoyable.

[Interstellar0vdr]

Much appreciated feedback! The bikes seem to more or less look the same as far as the R25 to R27, but there does seem to be something about the R25 series that looks a little smaller or sleeker, but maybe it's just me or the pictures I happen to be looking at. Looking at the specs, I think the R27 gas tank is just a little bigger so maybe that is what I'm noticing. Another thing I've seen on the R27 is that it looks like the part that covers the back tire is quite a bit higher from the tire than on that R25. I'm not sure if that has something to do with it being a later model or if it is something custom, but I think it looks better without that extra height over the rear tire.

[schrader7032]

There might be two reasons for the difference in the rear fender and tire. One is that when the rider is on the bike of say the R26 or R27, the suspension might compress a bit more and thus the extra distance might disappear. The other reason is the beginning with the R26, the rear suspension was a full swinging arm which has more range of motion and frankly a better ride. Prior to that, the rear suspension was called a plunger. I'm sure the suspension travel on the earlier singles is much less than the R26/R27. And the front suspension, Earles fork, on the R26/R27 are much better than my R25/2. To that I can attest!

[Interstellar0vdr]

Is there a particular reason you have the R25 type over the R26 or 27 if the later types are a bit better overall?

[schrader7032]

My R25/2 is the same age as me. I already had two twin cylinder bikes and figured I'd go for something a little "different". Somewhere on this forum I have my teardown of the bike. I think this is it:

viewtopic.php?f=7&t=8763&p=2042&hilit=teardown#p2042

[Interstellar0vdr]

It's a really nice looking bike! You don't see that green color very often either; looks good in that green, but I must say I do prefer the black.

[schrader7032]

I got the German papers for the bike. It was a police bike at a station between Frankfurt and Cologne and was retired from service in 1970. The frame should still be original color, but the tins were repainted by the previous owner...but I believe he was a skilled painter and used the right colors from Holt BMW.