Seems like an unusual R 65 I have!

[Dizerens5]

I’ve forgotten about BMWs, the last time I had one (R60/5) was 35 years ago. But I’ve just bought a beautifully rebuilt 1978 R 65. Looks like it just rolled out of the showroom and rides like it too. Lovely. But it’s not quite what it says on the box. Instead of the buzzy motor I expected it turns at a gentle, comfortable 3,000 rpm at 65 mph in 5th. Should be more like 4,200 rpm! Final gear ratio raised? Maybe but I’d then expect 1st gear to be much too high. It isn’t. Anyway the rear drive housing is still stamped 31:9. And surely changing the rear bevels (and the speedometer) would have cost somebody about what the whole motorcycle was worth, if it was well used already. Does anyone have an idea about what is going on here? Thanks.

[nhmaf]

Are you SURE that you are going 65 MPH?

My LS's is ticking over ~ 4500 RPM @ that speed.  HAve you timed a fixed distance travelled or measured with a GPS (or perhaps your speedometer is the incorrect ratio - check the small "w" number near the lower end/corner of the speed dial and report back what it says)

I suppose it is possible that someone swapped out the internals of an 3:1 rear end into your 3.44:1 rear end housing, but it doesn't seem very likely.   Maybe it isn't even an R65 engine ?

Do the numbers match on engine and frame?

[Dave 2]

Hi and welcome, I also sold my R60/5 35 years ago. (mistake!) When I take my 1983 R65LS to work tomorrow, I'll check out your observations. I've only been riding it for a month, but off hand I'd say your 5th speed gearing is higher than mine. With the number of certifiable BMW techno-maniacs in this group you should get an explanation coming along. Dave 2

[Lucky_Lou]

My well have a transplant in there if the ratios were altered you would know about it at the bottom end low ratios check the engine/frame number here
http://www.realoem.com/bmw/select.do?vin=6346898&part=&kind=M&series=K56&body=ohne&arch=0
Lou

[montmil]

Possibilities abound! Wrong speedometer, dragging speedo cable, correct speedometer has some sorta interior drag malfunction, tach incorrect.

No way your R65LS or non-LS will perform at those numbers. I have two R65s and I''d love to sip fuel at 3000rpm and 65mph  

Welcome to the herd.   Monte

Here's a useful table for '70-on Airheads. It's the final drive ratio info, and the handy rpm column will let you determine what's in your final drive regardless of what's stamped on the outside:

Gear set     Ratio     Approximate RPM at 55mph
32/9           3.56      3734
31/9           3.44      3608
37/11         3.36      3525
32/10         3.20      3357
34/11         3.09      3241
33/11         3.00      3147
32/11         2.91      3050

[Bengt_Phorqs]

Too good to be true.  At first blush it seems you have a R100 engine with a high speed final drive.  How about some pix?  And like it was mentioned, what is the s/n on the engine?  The R100 will fit into the R65 frame.  If that's the case, you got yourself a pretty cool hybrid.  You can probably win some bar bets with that bike.

[Dizerens5]

Thanks everyone. I think my speedometer is about right because a) mileage recordings (odometer) agree with those on my car and my other motorcycle and b) going at 65 on the dial I steadily overtake the modern big trucks which in this country (Britain) normally go at 60. The ref number on the speedo dial is W 1276. The little handbook gives a ratio of 1.267 -  is there is typo here maybe? I have no means of checking rpm but seat-of-the-pants suggests it's about right too. In 5th gear I need to go around 50 at least. Below 45 the whole motorcycle starts to "shake its head" as the engine begins to labor at low rpm (around 2,400 on the dial). Engine and frame serials are both 6340800 indicating a Sept. 1978 build. No sign of alterations.

[Rob Valdez 79 R65]

I used to think 85 MPH was my "sweet spot" as my bike liked to cruise that speed.

Then I put a GPS receiver on my bike and learned the ugly truth about the accuracy of those speedometers.
The odometer was always spot-on, however, when matched against the 1/10th mile markers along the freeway.

I am currently rebuilding my bike, and just last week I removed the speedometer cable, as it won't be a part of the rebuild.


And [size=18]NEVER[/size] lug your engine!  (lots of throttle at low RPM in too high of a gear).  This is very bad for the engine.

[nhmaf]

If your R65 engine is lugging at just under 45 mph in top gear, then there is definitely something different about your bike.   The speedometer is driven by the transmission's output shaft, so if that is indeed spinning at the same RPM as the speedometer is calibrated for 65 MPH, yet the engine is going too slow in RPM, must mean that you have a rebuilt transmission with an extra tall gearset inside.   This would be a "rara avis" or rare bird, indeed - but it does seem to fit the available evidence at the moment.   I've heard of very few places where one could get the transmission ratios changed on this side of the pond, but there are some.

The W1276 speedo is the correct one for a 31/9 or 3.44 final drive ratio.  The other R65 speedo seen is W1318 for a 32/9 or 3.56 final drive as I have on my LS.   It give good strong take off, but top end and fuel mileage drop a bit.

[Altritter]

And NEVER lug your engine!  (lots of throttle at low RPM in too high of a gear).  This is very bad for the engine

That was true of the old VW Beetle twin-boxer, also. John Muir (he of the "Compleat Idiot" maintenance book) vowed that more Beetle engines were ruined by lugging than by over-revving. (As if a stock Beetle could be over-revved!   )

[Dizerens5]

Thanks again. We have a BMW club with meetings 2x monthly about 40 miles away. I have joined  and will go along hoping to find a member who knows R 65s and who can take a ride and give an opinion! Maybe just a tacho failure but it's a very good ride anyway. Certainly better than my old R60/5 years ago. Now that was a bike needing a lot of rpm!

[Bengt_Phorqs]

And NEVER lug your engine!(lots of throttle at low RPM in too high of a gear).This is very bad for the engine.  

OK, I give up, not that I would lug my engine, but just exactly what are the negative physics involved in lugging?

[nhmaf]

The following is my understanding of the subject vis-a-vis airhead engines:

The airhead engines do not have an overly generous oil distribution system at lower rpms. Under low rpm/high torque loads it is believed that the lower output of the oil pump may not get enough oil to the bearings.   As RPMs increase, the pump's output increases quite a bit, so for these engines, running at 4000-5000 RPM (given adequate wind speed to keep cool) is much easier/lower wear on them than chugging around town at 2000 RPM.    

I don't know if the oilheads are the same, probably not.  But, no matter how "agricultural" some may think they appear or how broad their torque curve, these aren't Harley or John Deere engines.

[Bengt_Phorqs]

Thanks Mike, that explanation makes sense to me.  Good thing they are buzzy little engines relatively speaking.

[Dizerens5]

With most road vehicles this should not really be a problem as lugging the engine (over here we say making it labour!) feels  and sounds so unpleasant that I suppose not many want to do it. Even in a car it's pretty obvious. Although I do remember a business associate who always put his car into top gear (4th in those days) as soon as he was rolling. Poor car, I really felt for it....