Drive Chain Suddenly loose

Ok, so I'm fairly new to this whole repair thing on a bike therefore if you could dumb down any answers that would be awesome.

As for my issue, I was riding along the other day and all of a sudden my drive chain became very loose and kicked off of the rear sprocket. And I can't determine why this happened, any suggestions would be greatly appreciated.

With regards to the background on the issue here is what I have determined with the help of my uncle who is very mechanically inclined thus creating the mystery of the loose chain:

1. The front sprocket hasn't moved, or doesn't appear to have moved and isn't loose at all.

2. The rear tensioners also don't appear to have moved, nor has the rear tire slipped at all. (everything is as tight as it originally came.

3. According to the previous owner, he just put on a new chain, (I bought the bike in the begining of september) so there shouldn't be any strech in the chain and upon visual inspection the chain seems fine and well lubed.

However knowing the alarming rate at which parts seem to fall off this bike we were wondering if there should be a third sprocket somewhere along the chain (that may have fallen off) to take up the slack similar to what would be found on a bicycle?


Thanks in advance

Clearwind


Edit: the bike is a 1978 KZ650

nope no 3rd sprocket there. maybe the chain wasnt tight enough to begin with? you should have about 1 inch of play when its on the centerstand at rest. were the sprockets both replaced with the new chain? if not they should have been.count the notches on the swing arm to make sure the rear wheel is aligned properly...steve

Thanks for the quick response Steve.

A couple of things:

1. I've currently got about 9-10 inches of play in the chain, where as I had about 2-3 before.

2. when you say the notches in the swing arm are you referring to the stiffness settings on the shock absorbers? or something else? if you are referring to the shock absorbers they are set at the same amount on both sides currently.

As for whether or not the sprockets were replaced, I'm not sure as I didn't do the replacement on the chain, however neither of the sprockets look worn to me at this point.

Reply to #2: He means down on the swingarm at the chain adjusters, there are notches, that you match up with notches on your chain adjusters to make sure the wheel is moved back evenly.

It's also possible that the chain adjusters weren't tightened all the way and your whole axle moved a little. Just adjust your chain as per the owners manual or service manual , and see if it happens again.

The rear axle may have moved if it is loose.

You've got 9-10" of play in the chain. Gads, that's near impossible even if the adjusters moved all the way to their loosest setting. I'd count the links and see if a too long chain was fitted first. If it's right in links, it's probably just a junk chain. If it's not an oring chain, it's definately junk and needs to go bye-bye along with the sprockets.

another thought just came to me and it is this.. is your swingarm loose? put it on the centerstand and grab the rear wheel and try to push it back and forth side to side. it shouldnt have any play. i have had an adjuster come loose and damn thats a bad feeling! tighten those axle bolts tight

RonKZ650 wrote:

You've got 9-10" of play in the chain. Gads, that's near impossible even if the adjusters moved all the way to their loosest setting. I'd count the links and see if a too long chain was fitted first. If it's right in links, it's probably just a junk chain. If it's not an oring chain, it's definately junk and needs to go bye-bye along with the sprockets.

I'm with Ron on this, 8"-9" of play is simply impossible with a chain of the correct number of links. There's not that much adjustment available.

Maybe the previous owner fitted a 4000 psi tensile strength el cheapo industrial chain on the bike??

I am with other, there is no way you can have that much slack in the chain.
is there any chance of getting some picks of the chain and sprockets,
if the wheel moved that much I dont think the brakes would be working right,and the swing arm loose would make it almost impossible to ride.
I am betting on a cheap chain and they did not replace the sprockets, thus they are shot

Clearwind wrote:

... was riding along the other day and all of a sudden my drive chain became very loose and kicked off of the rear sprocket....

1. The front sprocket hasn't moved, or doesn't appear to have moved and isn't loose at all....

Is the chain still engaged with the front sprocket (meaning -- are the chain links still meshed with the front sprocket teeth underneath the engine cover)? Thinking maybe the chain has slipped off the front sprocket (i.e., countershaft sprocket), perhaps hung up inside on a damaged gunge cover (the thin metal cover that normally surrounds the sprocket).

Without removing the engine cover, could perhaps use a flashlight to look inside underneath the engine cover where the drive chain enters just before engaging the sprocket. Does everything appear normal?

Good Luck!

You should list your location and maybe someone could stop by and show you what is what. I agree with the others that having 8-9 inches of play would have the rear wheel falling off or almost falling off. I think with that much play and only having 2 inches a few days before could mean the chain fell off the front sprocket.