Torque Arm question: Gondor no longer calls for aid [solved]

[Kaos]

Hi all,
For my current project i've installed a 420mm rear suspension
Made it a paralever (its a 2 valve) all sits and sat well till the rise that came with the new suspension.
The angle of the swingarm changed which now requires me to install a 280 mm torque arm.
The 4valve K is 300 mm and thus too long.
Do any of you know which model bmw has a 280mm torque arm?

Thanks in advance!

[Laitch]

I'm happy you thanked me in advance.

I was baffled by your problem but now I get it. You used a paralever assembly from an R model. The Bricks I've seen converted to paralever used the paralever assembly from a K model. It's possible you'll find an answer here, but maybe AI knows.
 
 

[Kaos]

I Could have been more clear about the assembly.
It is a K1100 swingarm and final drive and a k100 (and some R models)  torque arm.
The clock is from an R 1100, tha latter is not important.
AI just giving random answers leading me R1200 + arms because somewhere the number 28 is mentioned.
Downside is, i know k1200 models have a 265 mm arm and could go for that applying more tension to the suspension but then ill lose the center stand and i am not sure my right hand stand will be long enough.
But if it is as simple as "doesnt existi" i think ill just try to "unfold * a k1100 arm and make a shorter one.
Maybe cnc,.. dont know.

[Laitch]

It's time for you to post some photos, Kaos—a side profile of the rear drive assembly and the transmission to which it is joined, could be helpful. Marking your dimension challenges on the photo could be helpful, to me anyway.
 

[sooprvylyn]

This may work for you, but you might need to contact the manufacturer realm engineering to find one

https://www.bskspeedworks.co.uk/ram-strutt.html

[Kaos]

@Laitch here they are 
IMG_20241020_164416.jpg (51.82 kB . 721x576 - viewed 80 times)
IMG_20241020_164416.jpg (51.82 kB . 721x576 - viewed 77 times)
It a rather crappy angle, both picture as the final drive. Its all i have for now
@sooprvylyn, thanks i've came across this one in my search and have send them a message. Untill then i was hoping to find a genuine BMW part.

[Kaos]

Screenshot_2024-10-20-16-43-18-09_99c04817c0de5652397fc8b56c3b3817.jpg (31.95 kB . 382x576 - viewed 69 times)
Selected the same picture twice

[sooprvylyn]

Honestly the most cost effective option would be to cut and weld the oem arms. It wouldn't be too difficult to do, and you can grind the welds smooth after.  The oem arms have a nice straight section that would make it easy to do it seamlessly.

[sooprvylyn]

Here is the 2 piece stamped metal version of the k1100 swing arm....would be very easy to cut and weld this

https://www.ebay.com/itm/166724064368?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=Y3KahgikSQS&sssrc=4429486&ssuid=4ckt-K1fT_6&var=&widget_ver=artemis&media=COPY

[Kaos]

I have one of those, they're pretty easy to work with, shorten it and unfold, drill, cut and hamer into shape.
But that plan is my last resort. Firstly ill try to find a genuine part with the correct size. Then look at crafted or cnc parts depending on the price and lastly diy. Maybe even cut 2 cm from the current and get it welded.
But iam half suprised how hard it is to find all arm sizes.

[Laitch]

But iam half suprised how hard it is to find all arm sizes.

Which half is surprised?

Here are some questions the answers to which could possibly help my struggle in understanding of what's happening there. What differs in your modification that creates this torsion rod length problem when riders have successfully installed K1100 paralever gear onto 2V transmissions? Were the transmission rod mounts created and installed by you on your 2V transmission, were they already there and you drilled them, or did your 2V transmission already have them complete?

The BMW part fiche number of a K1004V black torsion road differs from the part number of a black torsion rod on a K1100. That generally means there could be a significant difference, like length, for example. Have you compared the lengths of a K1100 rod with a K100 4V rod.

[Kaos]

Usually when diving into modifications I am easely able to find sizes, parts and their respective bikes.
It just surprises me how difficult it is to find the lengths of the rods overall .
Which has me half surprised in this day and age.

When it comes to comparing, yes i am in possession of both a k1100 and k100 torque arm
How it came to be, installing a 420mm rear suspension vs the old 350mm suspension.
Before that install the k100 torque arm sat fine and the final drive was nicely aligned

And i had to drill the holes myself. But that didnt result in the current issue.
It was just that the original 350mm rear suspension made bike way to low.


IMG_20241016_174415.jpg (63.41 kB . 768x462 - viewed 79 times)
Saddle was just for checking the looks

Giving its not a racer, I went for an increased ride height. Hence 420mm

[sooprvylyn]

You are probably gonna have bigger problems than the swing arm strut length if you increased the shock length by 70mm. How tall are you that you needed so much more than the standard 25mm length increase of the rear shock?

I'm guessing you are gonna be putting a lot of stress on the drive shaft U joint that it's not really designed to handle.  Probably also pinching the swingarm boot at the gearbox.

[sooprvylyn]

Btw, I'm 6'5 and only added 25mm to my stock shock length.

[Kaos]

Ive checked the axle/shaft it runs clear.
On its own weight it sits at about 390mm - without me on it-
I am 190 cm which is 6.2 or 6.3 i think
Also My saddle is thin, so getting on and off is not the issue.
Only issue i am facing is the brake line which i had to order a new one for and the torque arm.

 The Grand mistake i made was measuring, drilling and installing when the 350 mm suspension was installed to find out it sits too low. - for people doing their research and stumbling upon this post; get a 385mm suspension and then start the process of measurement and drilling and whatever.

If necessary i can alter the suspension to sit at a different hight
And i do believe it -the arm- needs to be 290 mm.

So the final point being how it came to this, is "I messed up measuring the installation points with a wrong size suspension"

Doesnt change the fact i still need a 280mm arm.

[Kaos]

Upon further investigation, I realized that my initial assumption about the final drive’s alignment on the swingarm was incorrect.
After searching for terms such as torque rod, torque arm, and paralever strut (including various translations), I discovered that there are numerous names for this single component.
The shortest being 26.5 cm from the K1200, with lengths extending up to 300 mm and beyond. Nothing in between. which in turn makes it logical I was unable to find a paralever strut (the name according to BMW-Motorrad)

I also learned that shorter versions are used to adjust the ride height for improved handling. Having diven into several guides and forum posts about the conversion, led me to the conclusion that most conversions from mono to paralever result in the final drive sitting at an angle, similar to my setup. The exception is those conversions using the BSK Speedworks strut.

In my case, the swingarm points slightly more downward when the bike is on its center stand or lift, due to the longer suspension I have installed.
If I were to reduce the suspension resistance, the angle should align more closely with the expected position when loaded with my weight.
For now, I will maintain the suspension at 390 mm under its own weight, which is a 5 mm difference from the K1100, and will monitor its handling or if any mechanical abnormalities arise.

this is what we call "a storm in a glass of water".

[sooprvylyn]

My guy, this got posted less than a day ago.  You might want to get on this, might be a last opportunity to get hold of one.

[Laitch]

My guy, this got posted less than a day ago.  You might want to get on this, might be a last opportunity to get hold of one.

To what might the word Sold pertain at the start of the item description in that ad?

[Laitch]

this is what we call "a storm in a glass of water".

The British and some Americans might call that "a tempest in a teacup." Other Americans might call it "a hurricane in a Bud Light can."

[sooprvylyn]

Yep, you're right, missed that. Oops. Ah well.

[Kaos]

Cheers tho. I will keep an eye out for one of these in case of.