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Discussion Starter #1
OK, I'm not naked, but I now have your attention. :tongue:

I need someone to tell me if my cam chain tensioner guide needs to be replaced. Please look at the photos below, and tell me what you think.





 

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OK, I'm not naked, but I now have your attention. :tongue:

I need someone to tell me if my cam chain tensioner guide needs to be replaced. Please look at the photos below, and tell me what you think.





you need to check the tolerances in your manual , then check the tensioner! but if it isnt broke ! dont mend it !! just a thought hope it helps :
 

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Discussion Starter #3
I don't know how you check tolerances on this. The cam chain tensioner sits at the bottom of the cylinder. This is off a 1980 KZ750. I'm trying to figure out if the plastic piece that keeps tension on the chain is worn excessively.

There is nothing in the OEM manual.
 

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Vintage bike addict
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Tina is there a picture of the tensioner in the oem manual. From the pictures it doesn't seem to be badly worn but I don't know how the plastic foot looks when new either. I do remember reading it only needs I think it was five pounds of pressure but can't recall if it was inch or foot pounds. Just enough to keep the slack out of the chain.
 

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Discussion Starter #5
The tensioner works fine, I just wondered about the groove worn in it.
 

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Vintage bike addict
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Since there doesn't appear to be any sharp or ragged edges. My GUESS is that most of that groove was there to begin with. Properly set and with the oil kept at the proper level there sould actually be very little to wear on it. If it were mine I'd use it. If I was doing the job for someone else, I'd put a new one in even if it looked identical. Just to minimize my liabilty. With all the work you've done so far, if it's not an easy to replace part. I'd get new if I could afford it. There should be others more experienced than I checking this thread who probably have better insight and advice.
 

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Gimme more twisties
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Looks alright to me but I'm no expert either.
The tension would be about right at the 5 to 8 foot pounds (not inches) if that helps a bit?
 

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Discussion Starter #8
It's right on the side of the case, easy to get to. Replacement cost is around $25, but something that may wait. Not like it's going anywhere real soon! :)
 

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Vintage bike addict
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Then lube the chain and put that goober together! Better to have a slightly worn working part than a new one that might have issues.
 

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Discussion Starter #10
The cam chain lives in motor oil, so it'll be good to go once I get the oil changed.
 

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Patriot Guardian
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How does it compare to the one from the 650?

On the big twins, you measure the tolerance by checking how deep the end of the pin is below the top end of the body when you remove the inspection cap.

Also, I'm not familiar with the 650/750, but on the twins, the tensioner itself does not directly contact the chain... it presses on the back of the guide, which presses on the chain... there should never be any actual wear on the tensioner, just the guide.
 

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Rich is correct, the tensioner does not contact the cam chain, it pushes on the rear sliding block (no. 15 in the pic below) which then keep the cam chain taut. The only way it could contact the chain is if the rubbing block is broken - looking through the tensioner hole in the block you shouldn´t be able to see the chain.

The tensioner is semi-selfadjusting so there aren´t really any specs to consider - the adjusting procedure should be in your manual but basically you rotate the engine to a certain point to put all cam chain slack at the rear, loosen the locknut to let the tensioner rod move out and then tighten the locknut again.

I tend to agree with Antiq, most of the groove was probably there to begin with, I would just run it - if I were to replace it I´d go for a manual APE tensioner from Z1Ent.

Btw, the 650 tensioner is slightly different as the pre-81 650s use a single roller cam chain and cam chain idler sprockets rather than rubbing/sliding blocks,
 

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Discussion Starter #13
To answer Rich, there is more wear on the plastic end of the 750 verses the 650. I'm assuming the wear is due to vibration between the contact points

I'm hoping that someone who has taken these apart with regularity, i.e. a mechanic, will tell me if this wear is normal, or needs replacement.

I appreciate everyones help.
 

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Navy Vet Search & Rescue
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I have to agree with Rich. There should not be any wear on it. All the wear should be on the guide block. I've had mine out on 2 different occasions and the only wear is the polished shine on the end. That amount of wear makes me think someone assembled the engine w/o the guide block and started it once or the guide wore out completely and allowed the chain to come in contact with that pin. If it were mine I'd take the cheap route and just fill it in with a welder and grind/polish it back smooth again. But thats just me and the fact that I could do that in about 20 minutes or wait a week for an order to be delivered. :biggrin:

P.S. Have you checked the guide to make sure it's ok? Also, my manual gives wear limits for the guide but nothing for the pin.
 

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Discussion Starter #15
Checking wear limits on the cam chain guide would entail taking the cylinder off, and I'm not going to do that.

With a 28 year old motor, who knows what it has gone through!
 

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Tina, looking at your tensioner rod (especially in the first pic) I doubt it has been in contact with the cam chain - if it had I would expect it to be more ground down all the way across, rather than hollowed out like your´s seems to be.

Using a mirror and a flashlight you should be able to take a peep through the tensioner opening in the block - if you see the rear side of the rubbing block you should be ok, if you see the cam chain it´s time to pull the top end and replace the rubbing block.

For what it´s worth the APE manual tensioner (pic below) does not have a rubber end, basically it´s just a plate with a bolt through it - if your tensioner rod sticks out long enough to press against the rubbing block and the rubbing block is intact you should be fine, rubber or not.

Btw, I think the 5 lbs (ft.lbs) referred to is the torque for the adjuster locking bolt, not the actual pressure of the tensioner, my 650 manual says the locking bolt should be torqued to 5 - 6.5 ft.lbs (6.8 - 8.7 Nm).

 

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Discussion Starter #17
I know it hasn't come in contact with the chain. Will try looking at the guide with a flashlight.

Looked, nothing wrong with the block that the plastic piece pushes against. So I'm guessing it's normal wear and tear.
 

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Scootter_man
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I thought the short bolt was only for to hold the paw back upon installation. And when the assembly is mounted you back the bolt out and let the tension of the spring extend the paw out, the small wedge and second spring. Then you just re-tighten the bolt back after it extends out. Thats how my 305 and 750 is made to do.
 

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Discussion Starter #19
I thought the short bolt was only for to hold the paw back upon installation. And when the assembly is mounted you back the bolt out and let the tension of the spring extend the paw out, the small wedge and second spring. Then you just re-tighten the bolt back after it extends out. Thats how my 305 and 750 is made to do.

You are correct. There is nothing wrong with my cam tensioner. It works correctly.
 
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