Differences in Singles Models

[Kurt in S.A.]

I'm learning a few things and now wonder if someone could list some of the major differences in the singles, R24 thru the R27, especially the ones that make telling one model from another apart.  The location of the points was mentioned on the R27.  I know that the air cleaner system changed over time.  What about the spark plug location switching sides?  Was there always just one petcock and did it change sides?  And why the heck is it on the right side anyway...makes it difficult to reach over with the left hand and change to reserve or turn off when approaching the end of my ride.

I'd like to learn more about this era of the singles and be able to distinguish one from the other.

Thanks...Kurt in S.A.

[Kurt in S.A.]

[Taz]

Hello Kurt.

You may want to have a look at the table (Vergleichstabelle) for a start...I have put together some components and how to tell which model they belong to...in case you would see more parts in there just let me know...I will try to hunt down the information required and add it to the table then.

Best regards, Tas

[Kurt in S.A.]

Tas -

Pretty impressive...I figured there might be something out there.  I'll review and absorb!

Kurt in S.A.

[euro518]

Agreed, excellent table. I often use the Knittel & Slabon reference entitled Illustrated Buyer's Guide, BMW Motorcycle. Major (and some minor) differences are clearly laid out b/w the models. For example, the suspension b/w the R25 and R26 model is quite different - both rear plunger and Earles front). Also, the R27 has a system of three rubber engine mounts, including one on the top of the cylinder, unlike the R26 and previous models. I often use these major differences as a 'quick and dirty method'.

-Kevin

[Rawost]

Hello Kurt,
I recommend to look in the picture area (Menu>Foren>Bildergalerie)
Kind regards
Rainer

[rolf.soler]

Was there always just one petcock and did it change sides?  And why the heck is it on the right side anyway...makes it difficult to reach over with the left hand and change to reserve or turn off when approaching the end of my ride.

No, mine is on the left side....(long live R27 etc etc....)
But why don't you use your right hand to open/close the petcock ?
If your answer is "as soon as I release the throttle, RPM's and speed drops", then your throttle is not adjusted properly...The throttle should stay in position (not turn back) when you release it....makes sense in the pre-indicator-light era...you use your arm as a turn signal. So, if the throttle closes when released, you can only make left turns and will never make it to Germany 

[Kurt in S.A.]

Maybe that's why my gas mileage is bad, I'm always going in circles!!  Yes, if I release my hand, the throttle will go closed IIRC.  On my R69S, it does that too and I understand there's an internal spring that acts as a "cruise control".  I believe the previous owner of the R69S took things apart and ripped out that spring.  At one point, I plan on adding it back in.  Are the throttles on the singles the same way...is there supposed to be something in the throttle tube that slows the return?

Kurt in S.A.

[rolf.soler]

yes, a spring, at least in R26 and R27  , (and the R50, 69S etc.). The older R2x have different handles, but I beliebe they too have some cruise control system...
Check the catalogue for R50/69 etc, you will see the spring I mean; when you have it, it is just a trial and error process to adjust (shift the handle on the bar inward, towards center, until the handle stops turning back....with running engine it may be different)

[Kurt in S.A.]

Like this?



Kurt in S.A.

[mekgyver]

Yess 

[Kurt in S.A.]

You may want to have a look at the table (Vergleichstabelle) for a start...I have put together some components and how to tell which model they belong to...in case you would see more parts in there just let me know...I will try to hunt down the information required and add it to the table then.

Very interesting to see the changes over the years...little tweaks to continue making improvements...or to confound us!  I suppose one could say that the R27 had the best all rolled into it.

I did find at least one mistake.  For the R25/2 valves, it shows the intake/exhaust diameters being 32/32mm whereas all the other singels it's listed as 34/32.  I confirmed in my shop manual that the size of the intake valve is really 34mm.

Another entry that makes we wonder why it was changed for that model only.  This is the Kick Start lever.  For the R24 and R25/1, it lists no contact area of the lever at the downstroke when kicking it.  The R25/2 lists a "T shaped" section; so does the R26 and R27.  However, the table lists the R25/3 as having a "triangular shaped" section.  Did BMW really change the shape for this production run and then go back to the T-shape?

Kurt in S.A.

[rolf]

the 25/2 has 32/32! The only one with this....BMW hopes for better accelerating (mehr Drehmoment).