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Home Repair And Restoration

Wibbly Wobbly Rear End

Repair Date 24 December 2019

By Ren Withnell

About 4 or 5 weeks ago I went from on the power to off the power. There was the usual snatch from the chain as the slack at the bottom becomes the slack at the top. Alongside this expected sensation was an unexpected sensation, the rear stepping out. Only microscopically so, I'm not talking a full on Marquez rear wheel steering into the bend here, just the merest hint.

The rear of Kawasaki's flagship H2R racing motorcycle
With over 300bhp at the rear the H2R can be a bit of a handful.

I'm not on a Kwakker H2R or a 'Blade. I'm not even on my 500, just my humble CBF125. While the CBF125 does have engine braking I suggest this wouldn't be the first choice of motorcycle for budding racers to practice rear wheel steering techniques on. It'll be these cold, wet, salted roads that are slippery. I'll just have to be more subtle on the throttle and easy on the corners.

For the next couple of weeks I notice this peculiar sensation but only rarely. No. No it's not right this, it just happened in a straight line approaching the lights. And it is always twitching to the right. It's as though when the chain snatches it pulls the rear wheel spindle on the chain side. Holy cow! I've forgotten to tighten my rear wheel spindle!!!

Nope. It is still set to 45 foot pounds. The chain alignment marks are still in alignment. Wheel bearings? Nope. There's no play in the rear wheel. Swing arm bearings? Nope. There's no play in the swing arm bearings (bushes, they're bushes not bearings). Headstock bearings? Nope. Front wheel bearings? Nope. I practically MOT the bike and all seems fine. Odd. How odd.

Coming home from work on Christmas eve I'm in first gear crawling through the traffic. I have my left foot resting on the gear lever. That's not right, when coming on and off the power I can feel the gear lever moving, microscopically so but it's there, for sure. 

Wait a minute. Hang on. Do NOT tell me the whole bloody engine is loose in the frame?!?! I gingerly complete the next 2 miles.

Nope. The motor is secure. So - what the duce? The footrest hangar is loose not the engine. The footrest is secured to the bike at 2 points, one to the frame and one through the swingarm bolt. It's all starting to make some sense now isn't it Ren. Yes Ren it is.

On the CBF125 we can see the plate that holds the footrest is held on by the swing arm bolt
The footrest hanger hangs off the swingarm bolt. 

If the footrest is loose and wobbling on the swingarm bolt I can reasonably deduce the swingarm bolt is loose. If the swingarm is loose I can reasonably deduce this is the cause of my rear end steering. Yes. Erm. The swingarm nut on the swingarm bolt is loose. By several threads loose. My Haynes manual suggest a torque of 40 ft-lbs for the swingarm bolt. It does not seem enough, not at all, yet I kow-tow to Honda's superior technical knowledge and torque it to 40 foot pounds (and an extra nudge for good luck).

What puzzles me is why could I not feel the loose swingarm when checking the bike? I would have expected while wobbling the rear wheel to have felt the swingarm moving? I know how to test these things I'm not stupid - ahem. I can only offer the excuse that the swingarm was only a bit loose on first inspection. Nice try Ren, nice try.

And why now? After 86,000 miles why would the swingarm come loose now? Admittedly there's no split pin, these nuts are similar to "nyloc" in as much as they have a metal "thing" that grabs the bolt. I suppose this "thing" has done it's job, the bolt has merely come loose not fallen out. Why now? Why not? Deep man... real deep.

Close up of a nut with a metal insert in the top to prevent the nut from falling off the bolt
It's not a "nyloc" but the principle is the same.

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Reader's Comments

nab301 said :-
Something for me to watch out for in about 84k miles time...
31/12/2019 08:32:12 UTC
Ren - The Ed¹ said :-
How long will it take you to cover those 84,000 miles nab301? You know, well, you don't actually have to wait that long before you check the swingarm bolt. If the mood takes you you could check it at 40,0000 miles.
02/01/2020 09:16:21 UTC
nab301 said :-
In my defence I do cover about 20k miles per year in total ( more than one bike) but I reckon I'll only average about 5k per year on the Honda , so 16.8 years I guess, by which time i'll be well into my 70's. Maybe i'll be glad of a lightweight all rounder assuming I'm still around and on two wheels !!

02/01/2020 08:30:58 UTC
Ren - The Ed¹ said :-
I hope you're getting around on two wheels when you're 70-odd too nab301. I think the diminutive 125 would be ideal too, you don't want to be hoiking around 250 kilos of 1100 BMW too often. This said in 16 years time we may well be all electric, probably not but I suspect electric will be a much more viable option.
03/01/2020 02:57:25 UTC
nab301 said :-
Electric could be good alright ,( although weight can be a problem) but range and charging points aside the prices are Imo out of reach for the great unwashed at the moment.


04/01/2020 08:02:30 UTC
Ren - The Ed¹ said :-
As, when, if the engineers and scientists can crack better batteries with a faster charge then that'll be the end of petrol engines save for enthusiasts. I should miss the tinkering and spannering that fossil fuelled internal combustion engines provide but then I rather fancy the idea of a quiet, torquey, reliable and relatively speaking simple velocipede. Of course the "cycle" parts will require maintenance (wheels, chain, suspension etc) so there'll be something for me to play with. It won't be the same as spending a whole weekend just to remove fairings, environmental controls, computers, sensors, cooling parts and various pipes just to set the tappets in the CB500X though.

I'll miss that... like a hole in the head.
05/01/2020 08:16:28 UTC

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