Dual swingarm, rear axle gap

[dusty]

I'm far from a frame specialist, or.. well, any sort of precise engineer, so it's difficult for me to say whether or not it's straight. I went out to take another look in the light of day, and did notice some peculiar ripples along certain flats, but I can't tell if they're from the factory or not. I say that (again, not a mechanical engineer) only because the ripples seem too uniform to be warping from shock, and because the top/bottom flats have no visual or tactile deformation - plus, the ripples seem formed in a way that should make the gap narrower as opposed to wider. The swingarm itself seems asymmetrical from the factory to accommodate the bulkier sprocket drive on the one side, so I couldn't think of any way to do a string test. There are zero apparent cracks or breaks in the welds or in the sheet metal itself (stripped the old paint off when refinishing, I imagine any crack would have stuck out like a sore thumb)

No chew damage on the inside flats where the conical spacer goes, for sure.

Inside left. The marks toward the end is just excess grease I didn't wipe off.


Outside left


Inside right


Overhead left


Outside right


Overheard right


Interesting in a way I guess: While looking up the cost of a new used swingarm, I noticed the same ripples on a few swingarms from 695s. THE MYSTERY DEEPENS.

[Howie]

The ripples are normal.  Engineer or not, you would need to compare it to a known good swing arm. 

Just a thought, don't do this until others chime in.  Tighten the axle nuts to the correct value, do not exceed the torque value.  If the gap disappears, check the wheel alignment.  Alignment is good, no problem.

[koko64]

If the caliper lines up ok with the disc centered and the gap is on the sprocket side, then it could be the wrong Cush Drive?

[dusty]

The ripples are normal.  Engineer or not, you would need to compare it to a known good swing arm. 

Just a thought, don't do this until others chime in.  Tighten the axle nuts to the correct value, do not exceed the torque value.  If the gap disappears, check the wheel alignment.  Alignment is good, no problem.

This was my thought as well, but I wasn't sure if I was just feeding into my eagerness to get this bike on the road. These swingarms seem pretty solidly built, I can't imagine the kind of force needed to permanently spread them even that small amount.

If the caliper lines up ok with the disc centered and the gap is on the sprocket side, then it could be the wrong Cush Drive?

Caliper lines up, but the sprocket does also when the wheel is fully to the left. I'll check the part number on the cush drive later, but I think it's the original one

[Speeddog]

Part numbers on a component are seldom for the *finished* part, they're for the raw casting or forging.
Not super helpful to anyone other than the factory and their vendors.

[dusty]

Fair enough! It'd be really useful if they did stamp it, though

Tightened up the rear axle to the greased 83 NM my manual specifies, all while sweating bullets. Undid the nuts afterwards and the swingarm sprung back out to the same gap, for what little that means. Front and rear sprockets are aligned according to my flat edge and string, and the notches for the chain adjuster are equal to whatever degree of accuracy those plates can provide. I'm a little nervous about it, but I'll have the frame and wheels checked for alignment at a proper shop when it goes for inspection.

Thanks guys, means a lot to get so many helpful responses.

[stopintime]

       https://www.profi-products.de/en/profi-cat-laser/motorcycle-chain-belt-alignment/3/chain-alignment-tool-se-cat?c=6

[koko64]

What was the outcome?

[dusty]

No idea really. Everything's tightened up and appears to be fine, but only time will tell - which is a terrifying prospect for such a big part of the bike

[Qomomoko]

any update?
Hope its holding up well or even better you got a "professional" opinion look at it and give the thumbs up
preferably with pictures of video

[dusty]

Nothing worth mentioning (for better and worse?)! Winter came pretty early last year, so I didn't get a chance to get it out to a frame specialist - not that I'd even know where to find one in the northeast. It's tracking straight at least without any odd behavior, but if it's there I'm sure it'll be one of those things you don't really notice until your bike is slinging you off.

Next up on the list is finding a decent replacement for the split/cored/re-baffled stock cans.