Hi all,
My 8 valve 100RT (60k miles) with a double adult chair feels reluctant to spin up over 4000 rpm.
At those revs I’m seeing about 65mph (100 kph) in top.
From all I’ve read that doesn’t sound right even with a heavy sidecar. 

The bike runs well in all other regards and mpg is a consistent 10 miles per litre.

Before starting diagnosis I had the valves shimmed back to spec. which has made the engine feel and sound better but hasn’t changed these two numbers.
It may be that I’m just backing off the gas too early (my other bikes are brit single and Big V so I’m not a natural revver). 

Before I start pushing rpm out of my comfort zone, any words of advice/caution?

Any views from our sidecar brethren on what I should be expecting to achieve through the gears.

Cheers, Stu

Words of advice: Don't worry about high RPMs.

Ks are high rev engines. Run it up to 8500 RPM and bounce it off of the rev limiter just to feel what it's like. You won't hurt anything.

The only thing that will change those numbers is a change of gearing in the read drive. Tyre size will make a slight difference.
The engine is limited to 8400RPM by a rev limiter in the ignition control unit. Reving them hard will use more fuel but wont hurt the engine.

According to BMW themselves (via Mick Walker's book 'BMW K-Series') the engine was designed to cope with 170hp+. You ain't gonna break it, unless you really try hard. Third gear, big handful and hold on to the throttle. On a solo that gets you into the fun zone...

Here's the power curve for the K100. When you've got the throttle pinned and you're paying attention you will feel it peak at about 6000 RPM.

Here is speed/gear data computed using a 2.91 final drive/K100 transmission as output from Anton Largiader's interactive final drive comparison table. A 3.00 will be slightly less steep.

65 mph at 4000rpm sounds about right for RT final drive gearing.  5000 should get you about 75mph, and at six grand you should be nicely up into the mid 80's.

Like the others have said, you need to learn to get the revs up.  These engines will run all day at the redline and love it.  I've read that these engines have been run in the factory for 24 hours at full load at 8500 rpm.

Love you guys. Every tech issue I’ve had you’ve given me deep engineering and experienced based guidance. Power curve question, you revert to big kids 

PS. I’ll go with your flow: gun it.

Dragon tickets are on sale... (hint). Good excuse to gun it .

Dai wrote:Dragon tickets are on sale... (hint). Good excuse to gun it .

Ordered last week. I’m sorting out some better lighting, heated grips, starter motor clean and spline lube. Assuming I don’t mess up, see you there.

My 1 and a half sidecar on K100RS (RT final drive, 1100 motor and 165/15 rear tyre) runs 5000rpm at 120kmh (75mph), its what they do. 5000 on a four sounds twice as busy as 5000 on a twin as there are twice as many firing strokes.

Not a fan of revving mine hard either but I don't have to either other than open highway.  I rarely run it over 5000, it goes well enough at those revs anyway. I dont find any advantage at all in revving it higher, just makes more noise.

At 10 miles per litre (16km/l) you are doing pretty well on a sidecar already.  Mine will do that on a good day, but usually a bit less.

Al

Thanks everybody,
I’ll stop fretting. I crossed my fingers and ran the motor gently up to 6 thou. So now I know it will do it I just need to train myself to push it a little harder.
Onwards with the Winter maint.
Stu

At some ppint in time you will be tooling along happily at 120kph, look down, and find you are in 4th gear.

hmmm. It may still be the case that I’m a revs pussy, but wouldn’t be surprised to find a bit of slippage too!

The K75's final drive gives about 4200 rpm at 60,mile an hour, but in doing that you get a first gear that allows you to walk beside the outfit not run or jog but walk, subtle things like that can help. Also at 60 to 70 she'll still be happy with her revs. Food for thought??

tinyspuds wrote:hmmm. It may still be the case that I’m a revs pussy, but wouldn’t be surprised to find a bit of slippage too!

Doubt it. I've seen worse in a K100 that was still gripping fine. The shite is being flung sideways and doesn't get a chance to contaminate the friction plate. Don't forget the back of the clutch is a bowl with no holes in it.

Dai wrote:

tinyspuds wrote:hmmm. It may still be the case that I’m a revs pussy, but wouldn’t be surprised to find a bit of slippage too!

Doubt it. I've seen worse in a K100 that was still gripping fine..

Thanks Dai,
I’m not wedded to the idea of dismantling the clutch and would much rather just button it all back up and get back to riding. But, uncoupling the chair and its associated infrastructure to get the trans out is not a job I esp want to repeat.
The underside of the bell has had a good coating of oil since I got the bike a year ago so I assume there must be a leaky trans or main seal so I think I have to go in and fix before it develops into something worse whether the friction plate is soiled or not.
Think I need to get to the friction plate at least and then take a view.
See you Feb.

tinyspuds wrote:See you Feb.

Oh, you will. Hopefully it'll be a bit of a longer chinwag than last time.