BMW K bikes (Bricks)

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1Back to top Go down   Engine mount rubber bushings Empty Engine mount rubber bushings on 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 on 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 on 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 on 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 on Fri Nov 20, 2020 7:56 pm

gorio

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


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1992 K100rs 16v
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 on Fri Nov 20, 2020 8:34 pm

BrickedOut

BrickedOut
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active member
46512312775


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1995 K1100 LT
    

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

chris846

chris846
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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 on 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 on Sun Nov 22, 2020 12:06 am

BrickedOut

BrickedOut
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active member
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
    

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