Cam chain slipped

[Ray Rockett]

I am pretty sure that the cam chain is off on the xs650 I just bought. I didn't realize until I went to tune the bike. First I found the chain tensioner was super loose then I couldn't get both valves to open on one cylinder at tdc. I have couple of questions for anybody who wouldn't mind helping me out.

Is this engine damaged? Salvageable?

I've never done anything more than periodic maintenance and basic tuning, how time consuming is something like this (assuming worst possible scenario) to repair, is this something I should even try to do myself?

Thanks in advance to anybody willing to help me out.

Ray

Oh and by the way, this is a great site. I've learned a few things already, I think...

 

[5twins]

First off, the valves don't open at TDC, they close. But, even though both cylinders are moving up and down together, they are on different strokes. One cylinder will be at TDC on it's compression stroke and both valves will be fully closed. There should be some play in each rocker. At the same time, the other cylinder will be at TDC on it's exhaust stroke. The exhaust valve will be almost closed and the intake valve will just be beginning to open. Both rocker arms will be tight with no play. This is why when you go to set the valve clearances, you can only do one cylinder at that TDC setting. To do the other, you need to rotate the motor a full revolution or 360° and bring it to the TDC mark again. Now that other cylinder will be at TDC on it's compression stroke and it's valves can be set.

But, if you still think your cam chain has jumped teeth on the cam sprocket, throwing the cam timing off, there's a way to check it without taking too much apart .....

http://www.650motorcycles.com/CamTiming2.html

Fixing this isn't too difficult but there is quite a bit of work involved. The motor needs to come out so the topend can be opened up. And, if the chain is so stretched out that it can jump teeth, it's probably best to replace it.

 

[Ray Rockett]

Thank you for your help. I used the info in the link you included to determine that the cam chain was off.

I got the engine out and the cam chain reset. But I can't get the groove on the cam sprocket centered perfectly above the cam bearings. I am off by a little over a mm either to the front, or the back if I shift the orientation of the two sprockets by a tooth. What am I doing wrong here?

 

[5twins]

Choose the tooth that puts the mark closest to (or at) vertical with the cam chain tensioner on the back of the cylinders snugged up. The cam chain tensioner removes the slack from the chain by pushing on the backside of it. This will roll the sprocket back a little. If you can't get things aligned even with the tensioner applied, that's really telling you the chain is stretched out and needs replacing.

 

[retiredgentleman]

Look on the right side of the camshaft gear. You will see a small punch mark. With engine at TDC, that punch mark should be
exactly even with the top surface of the head.

 

[Ray Rockett]

I must need a new chain then, thanks for that info.

I'll have a look for that punch mark, it is a bit difficult to measure exact center for that notch, that sounds easier to reference.

 

[retiredgentleman]

Yes, the notch is only an approximate reference mark. What I see as 12:00 may look like 11:45 or 12:15 to you, and vice versa.The punch mark is an exact reference mark. There is no possibility of error using the punch mark.

 

[Ray Rockett]

I am looking good by the mark. Thank you.