Automatic Cam Tensioners- A Discussion

[Lucien Harpress]

This is less of a question and more of a "gauge the waters on what people think", but I'm kind of curious about everyone's opinions on cam chain tensioners, especially people that have either worked on them a lot or seen a bunch of different styles. I realize this doesn't come up with our bikes at all, due to the belt driven cam setup, but belt tensioners like our Goldwings have is kind of outside the norm. Anyway....

What brought this up is the setup I have on my KZ1300. It's an automatic tensioning unit with a spring and anti-return features, but a lot of guys say it's arguably the weakest link in that particular motor. Most of the reason is that the mechanism to prevent the tensioner from backing out is a set of ball bearings set into a cone-shaped collar, Chinese-finger-trap style. The benefits are that you get constant, universal pressure on the cam chain, while the downside is that there is (supposedly) less of a positive locking mechanism than with a ratcheting type. I've heard plenty of guys say this type of tensioner is prone to failure, but oddly enough, I can't remember any actual case of a motor being trashed by an actual failure of the tensioner.

Of course, the third option is to trash both styles and get a manual tensioner.

So.... anybody have thoughts on any of this?

[robin1731]

I've seen more damage done by guys using manual tensioners than with the automatic style. Most guys get the too tight.

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[OCR]

Similar to the auto tensioner used in the later CL/CX V twins.
The main reason for failure is not replacing the cam chain before the tensioner reaches service limit and is then beat to pieces by chain backlash.

[Sidecar Bob]

Yeah, but with the CX's automatic tensioner adjuster there isn't anything to tell you that the chain (not the tensioner)(BTW: The actual "tensioner" is the blade that the adjuster pushes against the chain) has reached that limit unless you look at how far the tensioner is extended and since it doesn't require periodic adjustment it is very easy to forget to do that. When my 650's chain reached its service limit the only indication was a tapping noise from the rear of the engine. I knew that meant I needed to replace the camchain but when I opened it up I found that the tensioner adjuster was broken (probably what caused the noise).

With the CX manual tensioner adjuster it is impossible to set the tension too tight. You rotate the engine to the specified point (TDC left, compression), loosen the adjuster's screw, wait a couple of seconds for the spring to move the adjuster and re-tighten the screw. If you do it while you are checking the valve clearances it only takes about 5 seconds extra so there is no excuse for not doing it.

Given the choice of the CX auto adjuster or the CX manual adjuster I would choose the manual one every time.

BTW: My '78 and '83 GS400s had a different type of camchain tensioner adjuster. With them the tension was controlled by a spring loaded knob that automatically advanced a rod that pushed the tensioner against the chain to maintain even tension but IIRC, you were supposed to manually rotate the knob and release it to let it self adjust every so often. It was impossible to overtighten the chain with them too.

[robin1731]

snip...…….
With the CX manual tensioner adjuster it is impossible to set the tension too tight. You rotate the engine to the specified point (TDC left, compression), loosen the adjuster's screw, wait a couple of seconds for the spring to move the adjuster and re-tighten the screw. If you do it while you are checking the valve clearances it only takes about 5 seconds extra so there is no excuse for not doing it.

That isn't what I consider a manual tensioner. The manual tensioners they sell (aftermarket) are exactly that. You turn the screw in against the roller mechanism that pushes against the chain. No springs involved. Too many guys get them to tight and the roller just eats itself.

A spring loaded tensioner is not like that. Not what I think of when I say/hear manual tensioner.

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[Sidecar Bob]

The CX manual tensioner adjuster has to be manually adjusted. Once it has been adjusted and the bolt tightened the spring doesn't do anything (much the same as the GoldWing's belt tensioner springs).

It is obviously a superior design to the type you describe.

[Lucien Harpress]

This "fix" has also been brought up in KZ1300 circles before, too- converting the stock tensioner into a sort of "semi-auto" unit like you describe.

Basically, the stock KZ unit has a short screw that tightens against the plunger to hold it all the way in against the spring pressure. The idea is you build it, pre-set it, install it into the motor (with pistons 1 and... 3? I think? set at TDC), loosen the screw, plunger pops against cam chain, and then you re-tighten the holding screw. Which now is holding on to nothing, due to a slot cut into the plunger.

The "fix" is to replace that screw with a longer one, one long enough that it will tighten against the plunger no matter where it is located. You introduce a service interval where you to check your cam chain tension, but all you have to do is loosen the bolt, let the spring take up the slack from the last service interval (if any), then tighten it back down to hold the plunger again.

The only downside in my mind is that the clamping forces from the screw onto the plunger are lateral only- there's nothing stopping a hard enough jolt from sliding the plunger back anyway, sliding it across the bolt holding it. And if something is going to be bad enough to overcome the stock ball bearing holding mechanism, it would probably move the plunger against this bolt as well.

Other guys like to drill and tap the back end to put in a manually adjusted bolt and lockscrew, but you're only putting threads onto a housing MAYBE 1/8 inch thick.

(Like I said, when it comes to the 1300 this is a whole thing.)

[Sidecar Bob]

The "fix" is to replace that screw with a longer one, one long enough that it will tighten against the plunger no matter where it is located. You introduce a service interval where you to check your cam chain tension, but all you have to do is loosen the bolt, let the spring take up the slack from the last service interval (if any), then tighten it back down to hold the plunger again.

Which sounds a lot like the manual adjusters that the CX/GL500 have (& the belt tensioners on our 'Wings), except that the Honda ones were designed to work that way.

What kind of "jolt" are you talking about?

[Lucien Harpress]

Basically any kind of backlash on the cam chain for [insert reason here] that would cause the stock unit to fail. In my mind, anything that would cause the stock unit to fail would automatically cause the "fix" to fail as well. Between the ball bearings that are MEANT to keep the plunger from backing out, and the stop screw that's been added as insurance, the stop screw is the weaker failure point anyway. (From what I gather with my limited knowledge)