BMW K bikes (Bricks)

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FatRakoon

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My K100RS is a 1983 Model. It has a Reliant Regal Back axle.
The speedo does not work and so I need to do something there. I have plopped on a pushbike one for now, and its sort of about right-ish.

Now, my thing is, that the Trike does have a Mini Race Exhaust and so it does have a nice lovely howl at low speeds, however, when I do anything over about 40mph, the bike sounds like a demented banshee having an orgasm!

The revs are also seriously high too, suggesting that the gearing is not just a little off, but hugely off, and by some serious margin too!

Som, is a joint question, could I ask... What speed should I be getting and at what revs?

For example in 5th gear, if my ravs are at 4000 then what speed should I be seeing?

I am very much disabled and my rides have been very limited and I have yet to finish off the modifications to make me fully happy with the trike, but I have been out a few times for test runs, and on the expressway, I was running along with the traffic at around 70mph and I was revving in the 6000RPM area and the bike was souning like it was being murdered. It was silky smooth mind you, but hell was it painfully noisy.

Any thoughts?

    

2Back to top Go down    Calculatus eliminatus on Wed Jun 22, 2016 12:12 am

kennybob

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At 4000 rpm in 5th gear for a k100rs with a 130/90-17 rear tire, then the speedo would read 66 mph. For a k75S it would read 58 under these conditions.

The engine can handle the revs--maybe a stock muffler pipe will ease the ears, plus make more power with better fuel economy...but i understand about the attraction of a loud bike.

    

RicK G

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From what I can find a Reliant regal rear drive ratio is 4.38 - 1 This makes the ratio 1.5 times the standard K100 drive so at 6000 rpm you would be doing close to 65 mph which is far higher in revs than is needed. I would be trying to find a rear axle that has around 3.2 to 3.5 -1 ratio which would bring the reve down by about 40%.
I am not sure where you would find a suitable ratio drive as most of the small cars tend to have similar ratios or the more modern cars are front wheel drive.
A K100 engine would suffer any problems running at 6000rpm all day but fuel consumption would be poor to say the least.

As for the noise I would put 2 car type mufflers on it one about 1/2 the length of the other and separated by at least 12 inches of exhaust tube. This cuts down on the resonant frequencies that you tend to get with only one muffler.
1 1/2 inch exhaust tube would be all that is necessary but for show bigger diameter would be better.


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"Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats." from Mencken's 1919 Prejudices

Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

FatRakoon

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Thanks guys.
The axle is definitely a fair way off then?

This might explain why its a bit too easy to pull wheelies on it.

I am going to simply plonk a much bigger tyre onto the back wheels first.
I have a set of Wolfrace wheels from my old Focus that will plop straight onto it, and the wheels on it now are only 16" and the wolfrace wheels are 19" so that will ease it somewhat, but as for a new axle... Im not going to do that... I will use this as-is then, because in about a year or two, I am intending on getting myself a fully built custom trike based on a brand new bike. I only need this for a couple or three years.

( He says as if he can afford it - which he cannot LOL )

Thanks guys.

    

K75cster

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You are not going to hurt the engine at 6000rpm, they love it.
Good advice on the resonance thing from RickG, The thing to measure if you seek to lower the rpm at speed with be tyre aspect ratio. The 16" may be a 40% 50% 60% Don't know if you go to 75% like we do downunder. So moving to a 19" may advantage you or it may not that much if the 19's are all barely rim protectors. A 16" tyre can take a big tyre as in Tall. In here someplace was a long conversation on tyre circumference and the stock K100 17" came in at 2mts and a bit (2024 or something like that I cant remember), so having a wander around a tyre joint will give you plenty of info for thought mate.



Last edited by K75cster on Wed Jun 22, 2016 9:57 pm; edited 1 time in total (Reason for editing : changed to inch one of the %'s I got wrong)


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Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

FatRakoon

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Yes, I agree about the tyres.

I was told by a mate to look out for a different tyre first, before worrying too much about the wheel.

The only small semi-issue I have, is that the tyres that are on it, and the 4 tyres on the Wolfrace wheels, are all very very much brand new and there is absolutely zero tread gone.

The Wolfrace tyres for example were put on all 4 brand new only 3 days before the car went and popped on me and 2 of those days it was not used... Well under 100 miles.
The ones that are on it now, were put on by the guy selling it to me, for its MOT and while I have had the trike a good while now, I am disabled and I am just getting myself back on the road little by little and again, they have been to the local town maybe half a dozen times and thats a 4 mile round trip.

so, I am not going to just waste those tyres for nothing.

The wheel change I can do for zero outlay you see, although, the wheels needed a small plastic sort of washer type thingy to fit it to the focus... I dont know if it needs it for the Trike, but also the mudguard is very much hugging the tyre as it is, and its a welded on bit, so, I will need to do some altering to do anything to change the wheels or tyres.

Its all going to happen, but Im getting all my notes in order before I make any decisions and jumping in.

    

Holister

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Choosing a taller tyre on a 16" wheel will give you a marginal increase. For example the difference in height between a 200/40-16 and a 200/50-16 is only 10% of the tyre width which equals 20mm. This will add only 40mm to the tyre diameter and increase the circumference by only 7%. Going to a 200/60-16 would increase the circumference by 14%

Going from a 16" to 19" wheel will add more than 15% to the tyre circumference before you even look at a taller tyre option, and will probably bring your rpm at 65mph down by around 1000rpm. That's just a rough 'in my head' calculation.

Can you tell us what size tyres you have and what the clearance is to the mud guard and if the mud guard is mounted to the chassis or the axel.

I'mjust taking a guess here but there has to be a diff specialist that could swap your pinion gear out for a smaller one??

Just some thoughts to help you make a decision. Cheers


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1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

FatRakoon

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I will get you the exact wheel & Tyre sizes shortly.

Its 5am where I am and I am going out shortly to open the community centre up for the EU voting.
I'll take some notes and pics when I come back.

The MudGuard is welded onto the axle... The guy who did the work seemed to think that a welder is the be-all and end-all of everything and the stuff he welded up utterly ruined the thing. I have even had to have the oil filler and drain etc, all re-tapped because he welded EVERYTHING down. I have had all the seals and the brakes and bearings all done, since they rebuilt the back end for me and every nut and bolt had been welded to hide the serious issues underneath. Its all sorted now ( bar the gearbox/shaft seal - that was one we forgot and the one that was obviously leaking from day 1 LOL ).

Ok, where am I ? I dont half waffle sometimes... Oh yeah the mudguard.. Well. I will take some piccies of that too, so show the gap and the way its joined.

    

Dai

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@Holister wrote:I'm just taking a guess here but there has to be a diff specialist that could swap your pinion gear out for a smaller one??
Not possible on a Reliant diff. They've been out of production for years and in addition, if the diff has been put on right, it should be 'upside down' compared to the mounting on the original car (IIRC - it's been years since I had to deal with a Reliant-axled trike).


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'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

Point-Seven-five

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6000 rpm at 70mph isn't all that bad. My K75RT has gearing that runs 6000 rpm at an indicated 80 mph(actually 78).

A taller tire will help, but just remember that these engines love to rev and will do it happily all day. It's just something you have to get used to.


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Present:
1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

K75cster

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So it seems we are back with RickG and the Zorst amendment to satisfy you trikeing needs. In the short term atleast


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Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

FatRakoon

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Ok, just to let you lot klnow.

I have been talking to Lurch, and he is the guy who has done some of my work for me on this little freaky deaky beast...

He said that he will see what he can do and what he can come up with in regards to the revs. He has advised me, that the costs might very well me over what the job will be worth, and that it may simply be an easier job to completely redo the entire back end with a completely different axle.

We had a chat about the whole thing and we had a few options but he did also say that the exhaust being what it was, made it sound like it was doing more work than it actually was and that a lot of the issues are nto really too much to worry about. He said that the engine is revving high yes, but if it was quieter, then I would not be so concerned about it as I am, and sure, thats true. It has a Mini Racing can on it and so it does sound like a seriously tuned beast I grant you, but also a but like a farter too!

We are definitely going to try out the Wolferace wheels though... We already have them and they have great tyres on them and the only thing that will cost me, is time and it will help. Not much, but it just might be enough to get me to STFU to him about it. LOL.

I have however made a concious decision in the last couple of weeks, that the trike and the money I have thrown at it, have now gone way past what the thing is worth, and that now is the time to stop wasting money on it. I only need it to last me until I can afford to buy a new one that is fully built from new for me. ( in about 500 years time )

    

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