I'm new here so you'll have to excuse me if there's already a thread way back covering this.

Use my K only for long trips but possibly like many others feel that the gearing is too low. It's doing 4400rpm at 100kms per hr.
There's a "Cycleworld K100" page on the web and it says the rpm at 60mph is 3720 with a final 4.71 ratio.

This sounds much better and so I'm wondering if the about diff option talked about in the Dec 1983 copy of "The Classic Motorcycle" (british) ever became available.

Bike is a 1983 RS (engine no. 104EA39832203) and I can't see any marking on the casing to indicate present ratio.

An RS had a 2.81 rear drive and on the top of the drive near the 4 bolts that hold it to the swinging arm the numbers 31/11 should be stamped. That ratio works out to about 103kph at 4000rpm or very close.
Its the lowest ratio that can easily be used in a monolever drive.

Tks Rick - didn't see that you had replied before I posted.

So it's 2.81 but I still think that the revs are about 4400 at 100 kph or is the rev counter out. 
Is now running a M Marathon 140/80 because i couldn't get an orig sized 130/90 but i think that only increases revs by about 100 rpm at 100kph.
I'll send you the C M C test if you want it because it's not available via the web. As you probably know this mag was edited by Bob Currie who had a phenomenal knowledge of anything brit but was a bigot when it came to anything else.

Why don't you come up to the mountain bike ride  https://www.k100-forum.com/t8326p100-a-ride-through-the-northern-tablelands-2014#105142

If that's the Nov 22 ride - yes I think I will, but I'll need to get that rear replacement disc back before then.

Is this your polite way of saying that i need to get away from all this theoretical stuff and just ride the thing.

I'm going down to Sydney the weekend before on the K RS because it's so comfy and have managed to cover myself (for club rego purposes) by getting an invite to the Classic Italian Bikes gala day in Melbourne on the 16th. So if bike is OK to go after this, then I'll be a starter. Where are you leaving from and what time?

what about my query?   did some of the early K RSs come with clear i.e non black engine cases

My spares bike is a 1984 K100RS. Engine cases, swing arm, final drive, fork legs and footrest hangers are all raw silver. All seems outwardly identical to my 1984 K100RT. Final drive is different ratio from RT and its 31/11.

The difference in ratios from RT is small, about 4000rpm at 100kmh is what I have on the RT and LT. Ratio same on RT and LT. Changing to RS final drive doesn't seem worth it unless you are doing a change anyway. I think there was a change in the number of splines on the end of the drive shaft so just check what years can be swapped.

This all applies only to 8 valve engines and Monolever final drive, the one with the 4 bolts at the end of the swing arm!

Nah just come up and say Hi and put some faces to names. All the info is in the link I will be there at Smithy's place on Saturday and Sunday nights, some may stay in town (Guyra) and we would probably meet them the at corner Wards Mistake Road and Ebor Road on Sunday.
I think the change to black was at the introduction of the 87 models in Sept 86.
The change over with regard to rear drive spline count was Sept 85 when they went from 16 spline to 20 spline.

werewasi wrote:I'll send you the C M C test if you want it because it's not available via the web. As you probably know this mag was edited by Bob Currie who had a phenomenal knowledge of anything brit but was a bigot when it came to anything else.

Ain't that the truth!! I spent a lot of the late-Eighties and most of the Nineties contributing to just about all of the British monthly motorcycle magazines; Classic Motorcycle was the only one that wouldn't take anything I wrote because I concentrated mostly on Italian and German machinery. Never had any problems anywhere else.

RicK G wrote:The change over with regard to rear drive spline count was Sept 85 when they went from 16 spline to 20 spline.

:smoke::smoke:   ?? ......and in the middle of the week.

The 20 spline FD was used from Feb -86 and onwards.

werewasi wrote:what about my query?   did some of the early K RSs come with clear i.e non black engine cases

The first RS that came with black FD was the SE model in -87, on the std RS
silver was still used untill -89 or -90/16V.

Here's a picture from the '83 brochure which shows a black sump.

Paul.

Inge K. wrote:

werewasi wrote:what about my query?   did some of the early K RSs come with clear i.e non black engine cases

The first RS that came with black FD was the SE model in -87, on the std RS
silver was still used untill -89 or -90/16V.

It is nice to have a first, 1987 K100RS SE all black

Dai wrote:

Ain't that the truth!! I spent a lot of the late-Eighties and most of the Nineties contributing to just about all of the British monthly motorcycle magazines; Classic Motorcycle was the only one that wouldn't take anything I wrote because I concentrated mostly on Italian and German machinery. Never had any problems anywhere else.

Actually I think he died in about 88 or 89 because I've got an 89 mag that has a new editor listed, but from what you say, things didn't change in spite of this.

He's an enigmatic character - so much knowledge but so pig headed. He was actually a sargeant major in a brit army motorcycle rebuilding workshop during ww2 -called Bs (cos not armoured vehicles.)  Imagine getting caught by him putting rings in the wrong way.


Al these figures that testers quote for rpm are crazy.

Now i see in the road test i offered that on P34 of The Classic Motor Cycle""that the tester (Mike Woollett)  says "and at 100mph the engine was buzzing round at a busy 5000 rpm""  

If only.

I would have been utterly ashamed to have got my facts that wrong.

Anyway; this entire thread made me go and take a wire brush to the sh!te covering my bevel drive. I was a bit relieved to find it is an RS one. I'd bought it as such but that was back before I really knew what I was looking at.

[quote="sidecar paul"][url=https://servimg.com/view/17238339/425][img]https://i.servimg.com/u/f39/17/23/83/39/sam_0410.jpg[/img][/url]
Here's a picture from the '83 brochure which shows a black sump.

Paul.[/quote]
Yes the Wootton bike had the same silver cases and a black sump. I actually think that unpainted cases look the best (with the exception of that black 87 special) and would like to get the black off the 86 RS I have.
Is this a silly move?

Here, I'm strangely confused about the logic BMW used to put the shorter, quicker gears on the touring model, and the taller, slower gears on the sport bike. 

From what I gather, they wanted additional torque on the touring bike for 2-up riding, and a sport model with higher top-end speed.

But, the logic appears wrong to me. If I had an RS I'd want an LT rear end for quickness off the line and in the curves. And, if i owned an LT I'd want the RS rear end for the opposite reason--lower RPMs when touring. Of course I have an RT, which is designed for sport touring, so the quicker RT rear end is fine by me. 

No, if you had an RS you wouldn't want the gearing to be any shorter (lower) because they pull well enough out of any corner or gradient already. What i want on the RS is to feel on long trips that the motor isn't working as hard as it seems to be now. Unfortunately (unlike the 75) there is a vibration phase between about 95 kph (57mph) and 105kph that is not pleasant and higher gearing would shift this. Any non freeway roads in Australia are generally posted at 100kph and I've just come to the conclusion that if you go faster than this, you'll invariably get booked. CTP (third party personal injury ) premiums in NSW are now linked to your driving record so there is even more fallout. So vib free 100 is what i want.
The culprits in all of this gearing saga are the US brethren because it seems that the original gearing of the bikes was chosen to accomodate the US demand for 'performance' which the japanese bikes in 1983 were delivering. Quick standing 1/4s were the order of the day. 
Unless my tacho is wrong the K is doing 4400 at 100kph (62MPH) - too much for a 90hp motor.

How can I get the tacho properly calibrated?

You might be able to get a set of paralever gears and adapt them but as for monolever gears 31/11 is as far as you can go in that direction.
There are a set of 2.75 in one of the paralevers it may be the K1100RS or one of the R series and the 1200RS had 2.62 which is what I have in the K1100LT and there is a set of 2.53 or close to that from the R1200C.
I hunted for 12 months for a set of 2.53 but came up blank and after some hunting one of the US guys put me onto some 2.62 in US which I got very cheaply.

werewasi wrote:What i want on the RS is to feel on long trips that the motor isn't working as hard as it seems to be now.

The motor is reputed to be capable of sustaining 7000 RPM for sustained periods of time, as these bikes were designed for the German highways -- high speed and long distances.  I don't believe the motor is working hard.
 

werewasi wrote: Unless my tacho is wrong the K is doing 4400 at 100kph (62MPH) - too much for a 90hp motor.  How can I get the tacho properly calibrated?

I'm not aware of a means to calibrate the tach because it is directly measuring the pulses sent to the primary of coil #1.  There is a possibility that your tach needle is off, but unlikely.  What you can adjust is the speedometer.  The speedometer is calibrated from the factory to indicate about 10% faster than you are actually going.  Using Karamba, you can get the speed indication exactly right, which is equivalent to raising the RPMs and shifting the resonant vibration.  Read this post about Karamba.

tks Rick.   despite your giving me this info about 2.62 what i am hearing is that not poss for monolever. correct?

rm - the speedo is spot on - maybe 1kph (at 100) out (GPS checked) so it's fine. Tks for the Karamba link.. 

If what you are saying - that the tacho pulse comes off the coil and can't be wrong, (and I'm definitely doing 100kph) then the only conclusion one could draw is that mine must be correct at this roadspeed and that an earlier poster in this thread who said that his was revving lower must be wrong !!!!!!!!!   In fact what is so slack is that Wootton TCMC) and the Cycleworld people published figures that were pure fantasy.

My problem is that I'm conditioned to low revving motors because of using them daily - A diesel engined Ranger and a Honda NC that only revs at 3200 at 100kph - and you become attuned to this stuff. 

I'm right though in saying that the K is vibey between 95 and 105 kph aren't I, or have I only got 3 pistons doing something?

I am not saying that the 2.62 or any of the paralever gears wont go into a monolever but that at the very least some mods would be needed to the pinion shaft, shorten it by something like 10mm. I have never delved into a swap so there may well be other things to be considered.

I agree that they always seem to be over reving and I found that I was always looking for an extra gear.

However I have found that I got a significant improvement in fuel consumption after fitting the 2.62 gears as against the 2.91 that was factory fitted but I lost that improvement and more after fitting a set of K1200RS cams.
One other thing that can be done with an 8V is to fit top gear for a 16v which will slightly lower the revs as well.
8V 1.67 & 16V 1.61 ratio input to output shaft.
I am not sure all the stuffing about is worth it, I did mine and all it did was move the buzz to a slightly different speed which still gets annoying when at that speed.

If your bike is pulling 4400rpm at 100k you might have a 3.2:1 ratio from a K75rt in there?

When 88KE and myself went to France he was just after putting the FD from his K75 onto the K100LT due to wear issue and no time to get the right one. Its a perfect fit. Your 4400 at 100 sounds very close to this. I could be wrong in this but as far as I know the internals are same and you can rebuild a FD with different ratios and the number on the casing will then be wrong.

I have an RS FD looking at me and thinking. . . Its even got a good disk on it so a very simple swap. However the vibtation issue is there. Our roads have a 100 kph speed limit so having the vibe at 110 is ok because the motorway limit is 120. As long as it stays between 100 and 120 its good. Just be careful in case you push it to somewhere you don't want. If a much lower ratio and a rebuilt 5th gear puts it to 130 then its fine, but if it puts it where you ride then its bad. France you have 90 110 and 130 so it may be a different choice there.

I find that at 4800 which is 120kph the K is perfect but tempts you to higher, just like Italian jobbies!!

[quote="K75cster"]If your bike is pulling 4400rpm at 100k you might have a 3.2:1 ratio from a K75rt in there?[/quote]

and quote:

I find that at 4800 which is 120kph the K is perfect but tempts you to higher, just like Italian jobbies!!

These two statements seem to confirm that my K has not got the original gearing in it. To ascertain what it is, can i rotate the motor (when i have the rocker cover off) 360 degrees and count off the number or revolutions the back wheel does?

Yes but you would have to take into consideration the transmission ratios as well

Not sure,  i get it Rick. 

if what i am trying to do is see if the wheel revolutions are different from say the other K100RS that i have, and therefore there has been some alteration of the gearing as C75ster suggests, this will be apparent when i do my spin thing.
If there is a difference, then I have the option of pulling out the gearbox and trying to ascertain what exactly is in there. This is the only way i can find out ?????????

Is my methodology for doing the spin test correct.

Additionally I would like to come on the 23rd ride but have a problem because my k is on club plates and because this is not CLUB ride, then.........
Clarence Valley E M C really hot on this issue and want verification before putting entry in ride book. 
Can't come on NC - just too painful.
Need to buy more bikes obviously.

will any other club be listing this ride????

If you want to find out the ratio by counting the engine revolutions and rear wheel revolutions then you will need to take into consideration the top gear ratio in the gearbox to do the calculations because 5th gear is 1.67 - 1 not 1 - 1 as in car gearboxes

Can't think of any club that would be involved in the ride.

At the risk of being tedious

022575 says that 4400 at 100 sounds like what his mate got when he put the K75 FD in and C75ster thinks 
that its a 75 FD in there.

Can you explain to me what happens when bods change the FD. 

1 -  Do you swap the whole thing over - outer casing and all 
2 -  put the replacement internals into the original casing.

If 1 , why would i stiil have an FD casing that said 32/11
If 2,  if I took the FD off and peeked inside what would tell me what ratio it actually was ?

As i understand it, the RS originally had a FD of 2.81. Now it poss that it's 3.21.  
My mainframe says that this is an increase of 14.2%

so does this mean that at 100kph, the bike will be now doing 114% of the revs that an other unmolested K RSs are doing.?

Rick
and if i turn up on my bohmerland, will i be lynched?

Being 30 years old there can be a lot of changes in that time. The usual is to swap the complete drive but maybe bearings were needed and the only gears available were 3.20  32/10 so in they went and that what was traded and nothing said.
If you took the final drive off it would be easy to check the ratio by 10 turns of the input shaft.
My maths says 10% higher but all the same it's reving a lot higher than it needs to.

I doubt they would lynch you after all Saxon will be on his (choke cough) Triumph Rocket 3

I would suspect rather than taking a gearbox apart, go get a known RS final drive and put it on. Just make sure its the right 16 or 20 spline input. A final drive swap is a lot easier than getting a gearbox off and opening it up. If that solves the problem then you know you have a K75 unit. If it doesn't then there is a gearing issue but my money is on the FD unit as a gearbox rebuild is more hassle than a gearbox swap which would be much more likely [now wondering is there a K75 gearbox in there..]. .

The K75 was a direct swap from the K75 to the K100, no modifications whatsoever.

I saw a FD being rebuilt and its so easy to do, maybe at some point it was done just with some parts off a shelf..

If it's a K75 drive it will be a 20 spline they never had a 16 spline shaft.

You won't find any different ratios inside a K gearbox, the ratio variations are in the final drive.



Paul.

The 16v bikes have a 1.61 5th gear and the 8v bikes a 1.67 5th gear. The difference is the helical cut gear on the input shaft behind the shock absorber has 30 teeth on a 16v and 29 on an 8v.

[quote="Inge K."][quote="RicK G"]The change over with regard to rear drive spline count was Sept 85 when they went from 16 spline to 20 spline.[/quote]
Rick
:smoke::smoke:   ?? ......and in the middle of the week.

The 20 spline FD was used from Feb -86 and onwards.[/quote]


Ok so we have a slight difference of 'fact' here but that doesn't matter too much 

If there was a change from a 16 to 20 spline and the RS is an 83, then how could it ever have accomodated a 75 FD (unless only internals transposed) because someone has just said that the 75s only came with a 20 spline.

If i have also an 86 Rs then I can't shift the FD over because won't it be a 20 spline and the 83 bike a 16 spline? Or is it a case of the 'internals being able to be transposed? And how easy is that or rather how hard?

So if you're wondering why i want to do all this, the answer is that i want to shift that vib buzz up past 100kph, and it probably will give better economy too. ( and i have a 2nd FD)

Anyway, thanks for your contributions to my understanding of K stuff. This is a great forum and there's none of that that 'talking down' to dummies.

So what would happen if someone also changed the drive shaft from 16 to 20 spline................I know it might mean a change on the gearbox end but that may not be impossible, especially of there was a change of gearbox for some reason.

All that is required to change from a 16 spline to a 20 spline final drive is the drive itself and drive shaft.
The swinging arm and gearbox quite happily accommodate either.
Nowdays it is virtually impossible to get a replacement 16 spline shaft so when it knackered you will find the easy way is to use drive and shaft from a later model.
Quite often you may be away from home when it fails and you take what you can get just to get moving.

Werewasi the figures I have indicate as follows, an ordinary 130/90/17 will have a circumference of 2080mm and at 100kph is 100,000mts/h divided by 2080mm x 2.91 x 1.67 divided by 60mins = 3893rpm F/D will indicate 31/11 stamped on it. for a 3.2:1 K75 it will read, 100,000mts/h divided by 2080 x 3.2 x 1.67 divided by 60mins = 4282 rpm and F/D is stamped 32/10 so an rs should be 100kph divided by 2080mm x 2.81 x 1.67(the gearbox 5th gear ratio) divided by 60mins =3760rpm F/D is stamped 32/11 F/D, but this is the actual rpm via a calculator, so the 4400rpm is about spot on for the 75 F/D. If you have another F/D from another bike or perhaps the origional F/D it would be expected the previous owner had bought the 75 F/D to get back on the road when the tail shaft did the splines in sometime in the last 30 years. I cant help with a 140/80/17 as I dont have one to measure. With the 75F/D you will find the bike will idle away without any throttle because it is geared low enough to basically walk beside at idle in 1st gear. with the rt or rs the F/D will cause the bike to launch itself when the clutch it let out due to the taller gearing, no bother though, if you are just looking to change the rpm to avoid the buzz, then this post should help you pick a F/D to do just that. otherwise the buzz is managed by many other tweaks mentioned in other post's.  So to swap to the other F/D would just require another tailshaft with matching teeth to the F/d you have spare, if its different to the one on it. regards

For two years I rode my bike with similar thinking; lower RPMs, less vibration, and better gas mileage. With the stock exhaust being so quiet, it lulled me me into believing the bike was running properly between 3000 and 4000 RPM. On occasions when I revved the engine, the bike just didn't sound right. The muffler was too quiet and I couldn't get the feeling of higher RPMs. There was also vibration to deal with, so in the end I just kept playing it safe at lower RPMs. 

Once I put on tuned headers, suddenly the bike likes being above 4000rpm. The performance boost from the Euro cam is a great feeling. It cruises nicely on the freeway in 5th gear at 5000RPM, but also runs smoothly at 4400-4500RPM (don't ask me how). I did add end-bar weights and lowered the handlebars so my weight is shifted slightly forward. Everything is most comfortable, no vibration to speak of (except on the rear foot-pegs).

So, go figure. I don't know if it's me, or the K100. Quirky, and hard to figure what this bike was truly intended for.

C75ster,
I'm going to go through all that stuff and try and get my head around it but because i've had a few wines tonight and my brain is knackered, I'm struggling. I appreciate this info but can you do a little punctuation job on it because i want to understand it properly.

just to help i have this

                           circumference       revolutions per km 
130/90/17               2091.79mm           478.09
140/80/17               2062.26mm           485.38 

Difference 1.5%     

BeforeI forget all this stuff I need to get it down on paper so;

Went out to my 86 RS this afternoon thinking that I would pull the final drive off it, change it over to the suspect 83 RS and then see what revs the bike was doing.(with supposedly what would have been an original FD in it)
Straight away I saw that the 86 had 31/11 on casing whereas 83 had 32/11 (despite its suspect internals) 
Then when I had the 86 FD on bench I found that the 86 had a 20 spline shaft whereas it is probable that the 83 has 16, although i wont know until I pull it off, so being able to do a swop seems doubtful. Maybe tomorrow when I'm feeling in love with bikes again I'll get the 83 FD off. 

I turned the shaft 14 times and the hub rotated just shy of 5 times - say 20 degrees short of a full 5th revolution.

So what does that say.




Why didn't i just stay on my Velosolex and as a woman?

No worries, the posted numbers above are a calculated rpm figure for 100kph so a F/D with 32/12 is 3505rpm @100kph indicating a 2.62:1 ratio, I'm using a stock tyre circumference of 2080mm 130/90/17
a F/D with 32/11 is 3760rpm @ 100kph indicating 2.81:1 stock rs,
a F/D with 31/11 is 3893rpm @ 100kph indicating 2.91:1 stock rt,
a F/D with 32/10 is 4282rpm @ 100kph indicating 3.2:1 stock K75
So if the taco is reading correct the rpm will tell you how far out the speedo is or how much the tacho is out if you can check you speed at 100k with someone. hope that's easier to chew through.

OK just read that bit about the 140/80/17 at 2062mm
32/12 is 3536
32/11 is 3793
31/11 is 3927
32/10 is 4319
that's the calculated rpm on the 2062mm circumference trye

I went out and had a look at my K and realised that when I sit on it the tyre is 'flattened' a bit...reducing the overall circumference slightly thereby increasing the RPMs slightly......I know on my K on 130/90/17 BT45 I hit 100kmh at exactly 4,000rpm. The relationship then to 4,400 with the K75 makes sense. But now I know by doing a reverse calculation exactly how much the K sits down on the rear tyre when its loaded. A soft tyre would flatten a lot more thereby altering the gearing. Is this to be the new 'variable gearing' option on the K?

I do have an RS final drive looking at me and its also 84 so presumably its a straight swap. As in if it still has original 16 spline shaft in both bikes.

That was a very useful calculation and makes the comparisons very clear.

Sorry guys.
i put the wrong figs up above for the casings so i have changed to 83 --32/11 and 86 31/11.

so that now makes me ask why the 86 (if 31/11) has fitted, what you have just shown above is an RT FD - not an RS!!!!!!!!!!
Can you translate the 14 turns of input shaft into a nearly 5 turns of hub and tell me what gearing this constitutes.
I'm definitely going to pull the 83 FD tomorrow and do 14 turns of input shaft and see how many times the hub turns. So if someone can do the math, this should solve the mystery of exactly what is in that FD, although the general consensus already is, that its got a K75FD in it.

K75ster. your figs in 2nd paragrap can't be right.

A 180/80 has a smaller circumference (2060mm) so the revs would be GREATER not less. 3760rpm would INCREASE to 3816.

it's quite difficult to count the turns of the input shaft so i thought of getting two small thin bits of wood and clamping these to either 'side' of the shaft using a picture frame G clamp (small)?.

anyone got a better idea


I just divided 14 by 4.9 (turns of hub) and came up with 2.85. Eureka. -  that's the FD fig or close to it. so if i do the turning exercise more precisely, then it should be poss to tell what the exact FD ratio is in that 83 RS.

In fact if I turn the shaft, say 30 times, i'm more likely to get a more accurate figure correlating to the number of hub turns. 

all those in favour say............

yep updated post 50 after reading the 140 tyre is 2062, but it appears you've got the calculator out so you're on to it, now you know the theoretical the difference must be tired wiring or instruments binnacle, what willyou do to clarify which is off

K75cster wrote:yep updated post 50 after reading the 140 tyre is 2062, but it appears you've got the calculator out so you're on to it, now you know the theoretical the difference must be tired wiring or instruments binnacle, what willyou do to clarify which is off

Don't forget the 'squat' factor reduces the effective diameter from the theoretical and increases the RPM. Its very minor as it will vary very slightly with tyre pressure.
That's how the QE2, drawing 32, feet hit rocks at 40 feet.....someone forgot....

Agree.  
bike is doing 4400 rpm at 100kph (GPS and speedo same. so if 1.5% is due to smaller rolling circumference of 140/80, then the revs on a 130/90 would be about 4330. Still means i am 500 more than an RS on 2.81.

Are you saying that 'tired wiring' from the coil could affect tacho reading. What's that mean???

[quote="92KK 84WW Olaf"]
That's how the QE2, drawing 32, feet hit rocks at 40 feet.....someone forgot....[/quote]

re the QE2 and the 'squat' factor'. Wouldn't the water pressure at 32' tend to compress the hull and therefore LESSEN the draught by 2.6 inches.

I was thinking F/D impulse sender to tacho, the speedo read correct with the gps so that really leaves the tacho or the wiring to it from the sender, or a rebuilt diff with 75 ratios in it. 4400rpm is more 75 reading than rt readings, so thats a hard one to reason. the 5 turns to 14 on the diff seems to read 2.66666 very close to that 2.62 number given in rickg's post earlier. then again minus the 20degrees or so gives it very close to 2.62 actual, it will be interesting to hear what spline is in the tailshaft, be interesting if its a 16tooth like the 86 should be.

14/5 is 2.8 !!!!!!

Think you meant to say' it will be interesting..........      in 83'   - because I now know what's in the 86 (the 14 to 4.9 turns hub) 
Because the 83 appears to have been fooled around with, I will most probably find that its got a 20 spline shaft rather than its original 16. In fact, if its a 75 FD, it MUST be 20.

86 didnt have a 16 spline - it changed over to 20 that year and Rick said in post 32 that ALL 75s had a 20 spline.