Disaster-->My cam-chain broke

After finishing my bike about a month ago, I've been out riding and enjoying myself. A couple of days ago, the sun was shining and I fired up the bike and as it was warming up on the kick stand the engine came to a stop with a "clonk" :blink: I was hoping it was not anything serious, but from the sound of it it sounded expensive. Grinding the motor carefully with a terrible rattling sound confirmed that it was the cam chain. Why the f*!@ did this happen I ask myself?

The most obvious reason to me is the tension of the chain. I have felt unsure about the adjustment of the manual APE cam chain tensioner. I've heard and read that you are supposed to finger tighten it until and then back of one turn and it then be right. The problem is that this bad boy is so tightly stuck under the carbs that it can be a pain to adjust it without removing the carbs.

Here are some (not too good) photos of the current state of the APE cam tensioner. Can anyone see from this, if I have tightned it too much or too little?

Sorry to hear about this tommyboah.

Those chains are super hard to break. Did you use a one piece chain or was a master-link used?

You cannot tighten it by hand enough to break the chain. Was the chain making noise prior to the break. As mentioned the cam chains are very strong.

Put a stock tensioner back on there.

baldy110 wrote: You cannot tighten it by hand enough to break the chain. Was the chain making noise prior to the break. As mentioned the cam chains are very strong.

The chain didn't break while I was adjusting the tensioner I guess the chain might have been making some noise, a little hard to tell as the engine is not exactly noiseless to begin with.

I figure it would be easier to break a chain if it was to loose rather than too tight? If it was to tight wouldn't it simply wear through the rubber damper on tensioner?

The cam chain had only run about 300 miles as it was new when the engine was reassembled. Don't know if it is and endless chain or with a master link though, as I had a shop assemble the lower part of the engine. I will need to lock more closely at it. What I did see when disassembling the top last night was that the chain seemed to be physically broken, it was not a rivet that had simply fallen out.

I need to figure out why this happened so that I can prevent this from happening again.

See if theres a brand name stamped on the links of the chain,probably a cheap Chinese chain they sold you.

I would say its impossible for it to break at idle. Might have been too loose and let off throttle and it kinked. Need a picture of the chain

I took a picture of my adjuster.

peter1958 wrote:

I took a picture of my adjuster.

Thanks Pete for sharing your photo. Mine sure seems a lot more loose than yours. I bet there must have been too much slack and this made it break? The weirdest thing is that this happened while on the kick stand at 1500rpms warming up at no load. Maybe it had already started to go and this was enough to make it break?

Did the shop pull the engine out of the frame and split the crankcases, or just work on the top-end?

I adjust my manual cam chain tensioners with the valve cover off. I want to ensure the cam chain is tensioned properly - and it's easy to do after adjusting the tensioner by turning the crank forwards and then reversing while watching the cam chain and cams. You can see slack very quickly if there is any.

kz1000r2 engines so we have guide in cam cover aswell

If it is a KZ1000R2 motor, thats a Hy-vo cam chain.

Does anyone even make a heavy-duty cam chain for those motors???

I never saw any listed to my memory