Urgent Info Needed on Cam Chain Tensioner

[Guest]

Hi Guys (and gals). As some of you may be aware I have finally got my project going after 2 and a half years off the road.

I took the bike out for it's first ride on Saturday morning and was impressed with it's pulling power and low end torque. It seemed to be running fine. The carb setting seem to be spot on, it accelerates cleanly and briskly. And all this with just a bench synch. Only about 3 km covered on this ride.

I took it for a second run in the afternoon, a little further this time, probably about 10 km. When I got home the top end seemed to be making a lot of noise. On further investigation I found that the small nut holding the knurled knob on the cam chain tensioner had come adrift and the knurled knob had come off and was nowhere to be found. The small nut and the large spring were still residing under the carby bowls.

Fortunately I have a spare cam chain tensioner from which I can rob parts to do the repair.

I have the following questions:

1. I could not rotate the shaft which the knurled knob goes on, is this normal?

2. When this knurled knob fell off and hence released tension on it's shaft what problem did this cause if any?

3. Also when the knurled knob fell off wouldn't the plunger and it's spring have kept pressure on the slipper blade to maintain tension on the cam chain?

4. Also what is the relationship between the knurled knob shaft and the plunger shaft? How does this mechanism work in practice?

5. How do I fix the problem, is it good enough to just replace the knurled knob, rewind the spring 1 1/2 turns and refit the nut (with Loctite this time). I know I should have followed Bwringer's advice. Or do I need to remove the carbs, tensioner and reset it properly and then refit it again.

Any comments will be gratefully received.

[tkent02]

The spring on the sliding shaft should have kept tension, it should be OK. I would check the cam timing again just to make sure it didn't skip a tooth, but it should be fine. The wound spring only keeps the shaft from moving looser, gives it a ratcheting action, so it can only move tighter. The spring inside on the pushrod is the one that actually applies pressure to the chain. No need to reset the whole thing if it is still in there correctly. Wind the spring and put the knob back on with Locktite, have a ride, or have a beer, depending on your mood.

By the way the knob should only be able to turn counter clockwise, the spring keeps it all the way clockwise until it touches the ramp on the shaft, so it can't be rotated any further that way.

[ekim189]

washer?

hey Don... I have the same problem but i'm stuck out on the road and dont have parts. I melted mine black plastic knob off when i tried to idle the bike for a long time and it overheated! Can I just take that nut off and put a washer there in its place to hold back that spring? Is there a way around not buying a whole new piece so i can get back home quicker? Thanks Ya'll!!

[Nessism]

The spring on the sliding shaft should have kept tension, it should be OK. I would check the cam timing again just to make sure it didn't skip a tooth, but it should be fine. The wound spring only keeps the shaft from moving looser, gives it a ratcheting action, so it can only move tighter. The spring inside on the pushrod is the one that actually applies pressure to the chain. No need to reset the whole thing if it is still in there correctly. Wind the spring and put the knob back on with Locktite, have a ride, or have a beer, depending on your mood.

By the way the knob should only be able to turn counter clockwise, the spring keeps it all the way clockwise until it touches the ramp on the shaft, so it can't be rotated any further that way.

The noise is evidence the tensioner plunger backed off - hopefully not too far. I agree with the advice to check cam timing, and also to use loctite on the nut next time.

[tkent02]

The noise is evidence the tensioner plunger backed off - hopefully not too far. I agree with the advice to check cam timing, and also to use loctite on the nut next time.

You are not supposed to turn the knob when the engine is running, but of course I have done it to all of them as a test of the tensioner's function. Turn it counter clockwise as it idles, just a little bit until there is clattering from the chain, release the knob, the spring turns it clockwise, the noise goes away, now I know all is working as advertised. When the knob fell off Don's tensioner, the spring tension was released just as if the knob had been turned counterclockwise, I would expect to hear that same chain noise. As long as the cam timing didn't skip a tooth, no damage has been done inside the engine. I would be really surprised if either cam had skipped, but I would certainly check the cam timing to be sure.

Don, did you get your 699 ccs worth in the butt dyno department?

[Suzuki_Don]

Thanks guys for the quick replies.

If the cam chain tensioner has backed off, how do I get it to move back to reclaim it's original tension? Currently I cannot rotate the knurled knob anti-clock wise as Tom suggested (in fact it will not rotate in either direction. Is this a problem, does this mean something has jammed in there? Will refitting the knurled knob and rewinding the large external spring for the correct tension cause the plunger to obtain it's original tension on the cam chain?

I am going to pull the tank and check the timing to be on the safe side. I don't think the timing moved as I did not notice any drop in performance on the way home after the noise appeared.

[tkent02]

I don't know why you couldn't rotate the knob counter clockwise, I have never seen that.
You must have taken it apart when you did all of the engine work?
Did it look OK inside? No odd wear or stuck parts?

[Suzuki_Don]

I don't know why you couldn't rotate the knob counter clockwise, I have never seen that.
You must have taken it apart when you did all of the engine work?
Did it look OK inside? No odd wear or stuck parts?

Yes Tom I definitely took it apart and there was no abnormal wear. The tensioner behaved perfectly until the knurled knob fell off. I also replaced all seals in the tensioner when it was apart.

The butt dynometer is the only one I have. My son followed me in his EVO6 Mitsubishi turbo and he got p*ssed because I was out of sight after the first corner. It is extremely quick, and compared to the 550 motor has a lot more punch low down. It pulls strongly from 3k in 6th. It takes off from a standstill in 2nd and accelerates really hard. Mind you the gearing is about halfway between what the 550 was originally and the 650s are, so it is geared a bit lower than normal for a 650, but I do have the extra gear. Also no vibrations that I could detect, although I have not been on the highway at cruising speeds yet. I took it to 7k in 4th as part of the running in procedure and it got there pretty quickly.

Thanks for asking Tom.

[Suzuki_Don]

Problem Solved

Ok I could not get the adjuster shaft to move either clockwise or anti-clockwise. So I started the motor and it clattered like hell for about 5 seconds until I turned it off. I then checked to see if I could rotate the adjuster shaft. As luck would have it this time, I was able to rotate the adjuster shaft about 1/2 a revolution clockwise. So I left the shaft in this position and attached the external spring and fitted the knurled knob and rotated it 1 1/2 turns anti-clockwise to tension the spring. I then fitted the knurled knob over the two flats on the shaft and fitted the locknut, with loctite this time.

Started the motor and fantastic, no noise, and apparently no damage to the motor, and I don't think the chain skipped any teeth on the sprockets as the motor felt and revved the same as before.

Thanks to everyone. Thanks Tom for the good explanation of how things work in there. I did turn the knurled knob anti-clockwise with the motor running and there was cam chain noise and it went away when I released the knurled knob.