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Discussion Starter #1
Jeff has already seen the start of this post in the "general" area. Anyways, I have oil leaking from the center bolt on my cam chain tensioner on my 86 Gixxer 750. Jeff mentioned I could easily remove that bolt and replace the o-ring on it without worrying about the tension coming off my cam chain. I've never done this before and so read the section in my Haynes manual thoroughly. Here's where my additonal questions for Jeff or anyone else who would like to help come in:

I guess the part that worries me is where it says in my manual "Once you start to remove the tensioner bolts you must remove the tensioner all the way and reset it before tightening the bolts. The tensioner extends and locks in place, so if you loosen the bolts partway and retighten them, the tensioner or cam chain will be damaged."

The manual only shows the removal procedure for the whole tensioner assembly- not just the center bolt. I guess I'd feel better if I knew exactly how the whole thing worked as I had thought that center bolt was the one that adjusted the tension on the cam chain. Could you guys give me a brief lesson on how this device works?



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the part when they say 'when you start to remove the tensioner bolts you must remove the tensioner all the way and reset it', they're referring to the two tensioner bolts that are holding the tensioner body in place against the cylinder, and not the large central bolt.




here's how it works. the bolt (13) is pushing against the long spring (15) which in turn pushes against the tensioner rod. this way, it will take up slack in the cam chain. now, you can't really see it in this picture (the haynes should have clear pictures, though), but the rod has teeth on its top edge. these teeth engage a spring loaded ratchet pawl, and the teeth are machined in such a way so that the tensioner rod cannot move backwards unless you lift up the pawl by hand - the rod can only normally move forwards (to take up cam chain slack). when the tensioner body is installed in the motor, the ratchet pawl can't move upwards (disengaging the teeth) because of the way the tensioner cavity is machined.

so, if you leave the tensioner body secured to the motor, but unscrew the bolt (13), it releases the long spring, but since the function of the spring is to push the tensioner rod forward to take up any slack in the cam chain, you can remove this bolt without worrying about the tensioner rod moving backward and releasing tension on the cam chain (because it is prevented from moving backwards by the ratchet pawl). in fact, you could ride around with that long spring removed from the motor, and the bike would run fine - it's just that if the cam chain wears a little and becomes more slack, the tensioner rod will no longer take up that extra slack because the spring isn't there to push it against the cam chain guide.

the gasket you want to replace is 14.

what the haynes manual meant when it said 'resetting the tensioner', they mean removing the bolt (13) and spring, and removing the two bolts that hold the tensioner body on the motor, and removing the entire tensioner. then, you would lift up the ratchet pawl (remember, it's spring loaded and normally engages the teeth on the tensioner rod), and this frees the tensioner rod to move both forwards AND backwards. you would then move the rod all the way backwards (out), and then reinstall the tensioner body onto the motor. (you would NOT want to start the motor at this point because there is ZERO tension on the cam chain, because the tensioner rod is fully out.)
when the tensioner body is bolted to the motor, you then would insert the long spring. when you do this, you will hear a 'zipping' sound, and this is the sound of the tensioner rod moving forwards (it makes the sound because of the teeth moving rapidly under the ratchet pawl) until the cam chain guide hits the cam chain. you would then put the gasket (14) and center bolt (13) back on. you have just 'reset' the tensioner.

so, bottom line - if your tensioner is good, removing the bolt (13) to replace the gasket (14) will not release tension on the cam chain. the tension is maintained because the tensioner rod, once it moves forward to a certain position, cannot move backwards because it's held in place by the ratchet pawl.

the only realistic way in which this tensioner can fail is if something happened to the ratchet pawl (say, its spring broke, or the pivot pin fell out), or if the tensioner rod teeth were somehow damaged in such a way that the rod would move backwards despite the pawl engaging them.

but believe me, if the tensioner rod were free to move backwards (against the long spring 15), you'd know. the long spring isn't nearly strong enough to withstand the whipping of the slack side of the cam chain - the chain would jump the cam sprockets the very next time you decelerated (when the force exerted by the cam chain on the cam chain guide and tensioner is at its greatest), and you'd end up with bent valves, or worse.

hope my explanation was clear.


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[This message has been edited by jeff (edited 03-17-2001).]
 

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Discussion Starter #3
Jeff, you rock, thanks a lot for the effort put into that post
I feel much better knowing the whole picture now.

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no problem.

when you're putting the long spring back in, though, if you feel the spring pushing the tensioner rod forwards and hear the telltale 'zipping' sound, and you have not removed and reset the tensioner, then the tensioner's bad and needs to be replaced. the tensioner rod shouldn't move back when you remove the spring - the 'zipping' sound means that it did.

again, it is highly unlikely that this will happen, because if the tensioner were bad you would have noticed some serious problems the last time you rode the bike (loss of power, the sound of pistons hitting valves, etc
).


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Jeff, I received my gasket today and only now have I realized there is a problem. I have the right gasket- I verified it with the schematic on bikebandit- but I do not have the appropriate tensioner cap bolt for the gasket to fit on. I have a bolt with about a 14 mm head and a 14 mm nut on this bolt- the bolt is screwed into the center of the tensioner body up to where the nut is placed. I'll be taking the bolt out tomorrow but I'm thinking that a past owner rigged this up as a replacement to the tensioner cap bolt- why they did this is what worries me. Hopefully the spring will be behind the bolt, working properly and pushing on the rachet- then I'll just need to purchase the proper tensioner cap bolt. I just hope the bolt isn't pushing directly on the rachet with no spring in between and they were using this adjustable set-up to maintain cam chain tension. Have you ever heard of a set-up like this?

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Are you sure it's not a manual adjusting tensioner like the ones from APE. They make it so you tighten the center bolt and lock it down with a locknut. I have one on my 88 since the tensioners are prone to failure.

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[This message has been edited by OldSchoolGixxer (edited 03-31-2001).]
 

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Discussion Starter #7
It very well may be, I am not familiar with the manual ones and was not aware there were any available. If it is this how do I stop the oil leaking from around that 14 mm center bolt then? Is the spring that pushes on the rachet mechanism behind that bolt or do the manual ones push directly on the rachet itself?

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yeah, that sounds like a manual tensioner. the big center bolt on the stock tensioner screws all the way into the tensioner body.

i think there's supposed to be a small o-ring behind the nut, if you turn it out you should be able to see it.

BE CAREFUL - the way a manual tensioner works is, the bolt that is going into the tensioner IS the tensioner rod! if you back out the bolt (after backing out the locknut), you're releasing tension on the cam chain. there is no ratcheting mechanism with a manual tensioner - just the long bolt. turning it in increases tension on the chain, turning it out reduces it. the nut serves to 'lock' the bolt/rod in position.

manual tensioners need to be checked and adjusted every so often. or, if you hear cam chain noise develop, it'll need to be adjusted.

the manual tensioner shouldn't be overtightened or undertightened. i think ape (who makes manual tensioners) says something like turn the bolt in until it's finger tight, then back it out 1/4 turn, or something similar.



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Okay, thanks guys. I'll have a closer look tomorrow. I sure wish I had a instruction manual for this...sigh. I guess I can take the bolt all the way out and try to keep the lock nut in the same spot- that'll get me in the ballpark of the same setting when I put it back in.

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[This message has been edited by Talisian (edited 04-01-2001).]
 
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