BMW K bikes (Bricks)

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1Back to top Go down   Engine mount rubber bushings Empty Engine mount rubber bushings Thu Nov 19, 2020 5:44 pm

BrickedOut

BrickedOut
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I recently took off my frame for some major modifications and decided to do a powder coating job to seal everything up. That meant I had to take out the front rubber mounts. Besides already being damaged, I made things even worse pulling them out and they’re fairly hard after over 20 years of service.

I looked online to see if they were available and was a bit surprised to find it was over $170 shipped for a pair of them. I’m not a big fan of that price so I thought I’d have a try at making my own using a polyurethane rubber casting.

Wanted to see if there is interest from others who also have damaged mounts or would simply like to replace the old hard rubber for better vibration damping. Planning on trying a few different methods with different rubber mixes to find what works best but I’m guessing I could make them for about $30/pair.

Not sure if there’s other rubber parts that have dwindling stock and equally high prices but I could possibly do the same for them if there’s enough interest.

Engine mount rubber bushings 45dc6610

    

2Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Thu Nov 19, 2020 8:05 pm

MartinW

MartinW
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Try Nolathane http://www.nolathane.com.au/ A engineering mate recommended that I replace my steel centre stand bushes with it. Apparently superior to most other types of bushes.
Regards Martin.


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K75s Hybrid
    

3Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Thu Nov 19, 2020 9:11 pm

BrickedOut

BrickedOut
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Unfortunately they don’t have anything in the correct size. It’s quite the odd size and shape which is why I’ve thought about going the custom route on my own.


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1995 K1100 LT
    

4Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Thu Nov 19, 2020 9:26 pm

MartinW

MartinW
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My engineering mate was going to get something close and then turn them down in the lathe. However some materials are a pain to machine and we haven't got around to trying yet. Too many projects.
Regards Martin.


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K75s Hybrid
    

5Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Fri Nov 20, 2020 7:56 pm

gorio

gorio
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Wondering what the part number is. Just want to check something.


__________________________________________________
1992 K100rs 16v
1997 R1100rt
2006 R1200rt
Past lives
Kawasaki Concours
1976 BMW R90s
1975 Ducati 860gt
1992 Honda VFR750
1985 Honda VF750
1982 Kawasaki 750GPZ
1975 Norton 850 Commando
    

6Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Fri Nov 20, 2020 8:34 pm

BrickedOut

BrickedOut
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46512312775


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1995 K1100 LT
    

7Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sat Nov 21, 2020 4:44 am

Suzi Q

Suzi Q
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I replaced them with flanged aluminium bushes - I was able to size the width of the flanges so's there was no pull on the frame when the bolts were tightened up. I know that it's easy and tempting to pull things slightly into line on assembly, but I think that this route - shimming the mountings - is a good way to minimise vibration. Not the question you were asking ('pologies) just mentioning an option.


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Sometimes I'm not really Suzi Quatro.
    

8Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sat Nov 21, 2020 7:12 pm

TacKler

TacKler
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I would be interested if you went down the custom route, just so I could have a couple in stock for my stash.  

I agree with Chris regarding "having no pull on the frame"  to prevent stresses and for vibration absorption, so a correct size is essential.  I don't agree with using aluminium though.  My R65 uses added on rubber bushings on the engine mount to minimise vibration at certain RPM which coincide with highway speeds.  

Putting my engineering cap on for a moment and thinking out loud here.  I could be on the wrong track but I would also expect the rubber allows distortion of the rubber mount in twisting of the whole of the drive drain which would be prevalent between engine crankcase through to the rear tyre road surface (tyre) contact.  However this would be taken up through backlash through various contact surface areas such as gears, etc through the whole drive train from front to rear.  If I remember correctly when K bikes first came out the twist caused by hard acceleration to the rear suspension was very noticeable.  I would also expect this "twisting" to be a factor in the original design of the moto.  

My brain now hurts after thinking about that.


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Red 1991 K75S
    

9Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sun Nov 22, 2020 12:06 am

BrickedOut

BrickedOut
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I’ve decided to go ahead and try making my own. Ordered some rubber mixes and will see if I can get a working mold. Will likely be about a month before I get to it though. I’m currently working on painting the frame, the case and the swingarm.

As far as the purpose of the bushing, I believe it’s just for vibration damping to uncouple the engine from the front of the frame (handlebars). What’s interesting is that the bushing has flared outer edges, unlike what you would find on most engine/frame mounts, and I assume this was done to keep the lateral vibes from our horizontally oriented pistons in check.

I believe what you were referring to is the jacking motion made by the rear end on acceleration due to the monolever effect. This squatting was mostly eliminated by the use of the paralever rear end so if that was the purpose of the rubber, the engineers likely would have gotten rid of it.


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1995 K1100 LT
    

10Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Mon Jan 25, 2021 10:10 pm

BrickedOut

BrickedOut
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To update on my progress with this side project, I created a mold and used some urethane rubber to get the rubber part of the bushing. Still requires the steel inner sleeve but it’s easy enough to burn off the old rubber and slip the new one over. The rubber mix I got ended up softer than I wanted though. I tried 44 shore A and it came out to close to a rubber band softness. Too soft for the frame mounts so I’m going to try something harder next. Incidentally this should work well to remake the mounts used for the ignition coils though. I’ve made a mold and will be making those and adding black dye to get them looking good. If anyone is interested, I’d be happy to make more to sell. Just hoping to recoup the cost of the rubber mix which isn’t exactly cheap.
Engine mount rubber bushings 3becad10
Engine mount rubber bushings 6a60c010


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1995 K1100 LT
    

11Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sat Jan 30, 2021 10:45 am

BrickedOut

BrickedOut
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Engine mount rubber bushings Cf995a10
Engine mount rubber bushings 43d5f610

Got the new rubber in and did a few edits to the dimensions of my moulds and I got the first set complete. They fit snugly on the original steel insert and have nearly the exact same shore hardness of rubber as far as I can tell to the touch. 
Best way to get the old rubber off is to burn it with a torch and use a metal brush to scrape the charred bits off.

If interested in a set of two, please reply or pm me.

Also for those who don’t have the original bushings and therefore don’t have the inner steel part, I could make some carbon composite plastic parts that would probably hold up to the load. Or you could always get new ones machined out of aluminum or mild steel.


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1995 K1100 LT
    

12Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sat Jan 30, 2021 12:06 pm

Point-Seven-five

Point-Seven-five
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PM sent.

You mentioned "jacking". I have many thousands of miles on five of these bikes with and without Paralever, and so far have never experienced this "jacking" effect that BMW mentions as the reason for the Paralever.

Maybe it's because I don't rev the piss out of the engine and pop the clutch to do burnouts to smoke the rear tire, but the only time I have ever seen this phenomenon is in videos of riderless shaft drive bikes on dynos. You will see the rear end rise slightly under acceleration without the weight transfer that normally occurs. I suspect that the reason I have never seen it on the road is that the jacking force is counteracted by this weight transfer under acceleration that makes the bike want to squat down on the rear wheel. If anything this jacking force is good thing in that it counters acceleration squat.

A lot of cost went into design and production of the Paralever, and I'm sure BMW wanted a way to capitalize on it as a feature. Personally, I suspect the initial reason for the Paralever design was to eliminate the spline wear at the final drive connection that was caused by the back and forth sliding action of the shaft splines on the final drive splines because the shaft had only a single u-joint. We've all seen the result of that wear, and some have had to pay the price to repair it.

By designing a drive shaft with two universal joints, the motion is virtually eliminated and the wear is minimized. Notice the greatly expanded service interval on Paralever splines. Now the Paralever added a bunch of cost to the bike for the extra parts complexity. Somehow this cost has to be justified, and maybe even turned into a selling point. Of course, BMW can't advertise that the old design was flawed, that's not very good for their reputation as being really super engineers. So one day the marketing boys got the brilliant idea to create this terrible "jacking" phenomena that someone saw when doing the dyno tests on new bikes. As it turned out, the geometric razzle dazzle of the Paralever reduced the effect. Bingo! They eliminate a design flaw and create an advertising campaign. And the rest, as they say, is history


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

13Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sat Jan 30, 2021 2:07 pm

Laitch

Laitch
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Point-Seven-five wrote:I have many thousands of miles on five of these bikes with and without Paralever, and so far have never experienced this "jacking" effect that BMW mentions as the reason for the Paralever.  
To be fair, BMW mentions the rubber cow effect, not jackingSmile


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1995 K75 81,000 miles
Engine mount rubber bushings Usa-lo10
    

14Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sat Jan 30, 2021 2:55 pm

Dai

Dai
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Many decades ago I designed and part-built an 'anti-jacking' backend for my now-defunct Moto Guzzi V1000G5. When I got to figuring out the best place to weld the mounting points at the front of the swingarm and realised I was going to have to cut and strengthen the frame to take them, I thought 'why the fck am I doing this?' and had to quietly admit to myself that it was more for show than go. I still have that swingarm and it's still in use but it's stripped of all the pretty addon parts I built for it.


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1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

15Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sat Jan 30, 2021 3:07 pm

cycleman

cycleman
Silver member
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chris846 wrote:I replaced them with flanged aluminium bushes - I was able to size the width of the flanges so's there was no pull on the frame when the bolts were tightened up. I know that it's easy and tempting to pull things slightly into line on assembly, but I think that this route - shimming the mountings - is a good way to minimise vibration. Not the question you were asking ('pologies) just mentioning an option.
Actually if you have a faired bike then the frame is shimmed at the front engine mounts. Non faired bikes didn't have the shims. Something to do with vibration.

I found this out from an old BMW service bulletin that advised to not put a fairing on a non faired original bike. It was something to do with vibration as the front frame mounts to the engine where shimed whereas on the non faired bikes they just tightened up the front frame mounts with no shims.

In addition if you have the engine & transmission out of a faired bike, you are supposed to torque the rear frame bolts to the transmission first and then measure the space at the front mounts and put in the proper shim. I have no idea if it really mattered, but BMW thought so, therefore the bulletin.

    

16Back to top Go down   Engine mount rubber bushings Empty Re: Engine mount rubber bushings Sat Jan 30, 2021 3:25 pm

Point-Seven-five

Point-Seven-five
Life time member
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Laitch wrote:
Point-Seven-five wrote:I have many thousands of miles on five of these bikes with and without Paralever, and so far have never experienced this "jacking" effect that BMW mentions as the reason for the Paralever.  
To be fair, BMW mentions the rubber cow effect, not jackingSmile

Is that anything like "rubber chicken"?

The article mentions stiffening the suspension under acceleration. Seems to me that's not a bad thing under hard acceleration. Helps to maintain steering geometry and ground clearance(pretty helpful in a turn). At least they admit that it reduces maintenance, albeit without mentioning splines.


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

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