Trying to figure out how i did this...

Trying to figure out how i did this... (now with a theory)

Noticed this tonight putting the bike up on the front and rear stands so I could start to do my shock swap (finally).

Yeah, I think I need a new part or two there.

I'm guessing that the jamb nuts were loose, or the chain too tight. But the axle hasn't visible moved since I torqued down the axle nut after replacing the tire.

 

You definitely do not want to ride this bike before you replace those parts. Tanrush on these forums recently bought a 1997 YZF-600 that was missing that hardware. The axle moved and the chain jumped over the front sprocket which took out the water pump and the clutch mechanism.

 

You have at least two problems here:

The axle should be installed from the sprocket side.

You are missing the bushing that rides in the slot of the swingarm--that lockwasher doesn't belong there. Each side has a bushing, no lockwashers.

Left side to right side: Axle-bushing----bushing-axlenut

 

It's grounded until its fixed, certainly not going to be riding it like this.

I must have swapped the axle direction at some point, I've always put it back as I found it, but did notice that the other '86 I have has the other direction. But it's probably been installed in this direction for at least 5k miles of riding.

And that's not a lock washer, but the bushi g that rides in the slot. But from the pic I can see how you could mistake it for a lock washer.

Luckily I can pull the parts off the other vfr temporarily until I get my hands on replacements.

 

Seems like that would only happen if some misguided or deranged fool tried to tighten the chain without loosening the axle first !?

Note that you cannot swaP SHOCKS while the rear is on a swingarm stand !!

 

I don't think I've ever seen that before. It could be that the axle was loose sometime in its life, or as squirrelman said, it was tightened with the axle nut not loosened. It might have had a hairline fracture for a long time and just finally gave it up.

 

Lgn001 - the adjuster is also bent, so I'm thinking it was pulled by the chain on swingarm movement, although the chain wasn't very tight (after destroying a transmission output shaft on a hawk, I keep the chains at the slack end of the range. A hairline crack is also possible, although the break surface appears uniformly clean, so it would have needed to stay closed. My only thought is that the chain is too taut (which would surprise me greatly, but I didn't have time to check it last night).

Squirrel - thanks for the warning, although it wasn't necessary. I put the rear up on my swingarm stand before I put the front on it's stand (steering-stem pin pitbull stand). this was just to get the bike up and level and stable, before I jack it from the center-stand point to remove the weight from the rear suspension. I found the cracked adjuster when I went to put it on the swingarm stand.

 

Could it be that the end cap was installed upside down? The 1100F has end caps very similar in design, and I seem to remember the holes having a slight offset left-to-right, although they are centered vertically. It doesn't seem like there would be enough "pull" with the axle tightened to bend the adjuster and break the end cap, but that would explain it.

 

Santa Cruz Mountain Metal Rats is my guess, something has been chewing on most of the metal bits in that photo....




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.

 

wonder what the old cush drive looks like? Like the metal rats thing, do they play music like the old band Ratt did?

 

Cush is new (about 5K miles ago). And was in great shape when I inspected them when I had the tire changed.

 

New parts ordered (hopefully all actually available). BikeBandit had everything but the adjuster itself. Dillion Brothers claimed to have everything (and cheaper by about 15%). Hopefully they can actually ship the adjuster that they claim they can. If not, I'll be looking for one off a parts bike. Ordered two new plates, and a replacement adjuster. We'll see what happens.

And hopefully tonight I'll have time to dig into the axle and check the torque on the axle nut.

My (perhaps incorrect) assumption is that the adjuster is only needed for locating the axle until it's fully torqued down, and that once torqued, it shouldn't move on it's own.

OTOH, a bit of statics (which I'm very rusty at), shows that at WOT in 1st, the chain has something like 1400 lbs of tension on it (70hp, 2.85:1 gear reduction, ~1-1.5" dia front sprocket), which results in either 1150lbs against the axle, or 1750lbs (depending on how that math works out, I don't actually remember how torque is applied at the fulcrum vs the other end, which has about 350 lbs applied at the contact patch).

But either way, that's a lot of force being applied to the axle shaft, and to be held by a the axle nut's normal force against the swingarm. So I can very much see the adjusters taking a lot of force, but that would also be force applied in the other direction on the brake side of the wheel (since the wheel and it's contact patch is going to act as a fulcrum creating a torque. So the adjusters can't be expected to take much force (since they work in tension only, so any force not handled by the axle is going to be pushing the brake-side adjust back out of the swingarm).

Therefore, not enough torque on the axle nut.

 

i've never seen one do that either.

i think your assumption is good--the maths may be a little off cause the sprocket is more like 3 inch diameter...

 

I meant 1-1.5" radius on the front sprocket... But they're still pretty hand-wavy. And definitely a lot of force on that. New parts ordered, let's hope they get here soon.

 

So, I have a theory.

I was looking at the bike over the weekend, and noticed that my relocated R/R (under the rear fender) had one very dirty bolt, and one verrrry shiny bolt, with a scratch pattern that made it clear it had tagged the tire.

So I'm thinking that as the rear shock went, I was getting more and more suspension movement. But the undersize (130/70-18) rear tire had *just* enough clearance. But when I replaced them with the proper size Avons (130/80), the big dips up on skyline that would compress the hell out of the suspension allowed the tire to contact the R/R bolt, and that would cause some interesting binding forces on the axle (since the contact patch with the ground certainly isn't going give up it's grip if there's enough dynamic force to fully compress the suspension).

Anyway, I put a paint dot on the bolt in question, and am keeping an eye on it. The new shock keeps the back end under a lot more control, but it's clearly something that I need to address at some point.