yz426 cam chain tension


1 reply to this topic
  • oilspot

Posted July 24, 2012 - 07:12 AM

#1

Just getting done putting a new piston and gaskets in my 2002 yz426. I found a great deal on a hotcams auto decompression cam so I'm in the process of getting that all wrapped up.
Here's my problem. I install the tensioner (that checks out by factory manual specs) and it doesn't seem to automatically get the cam chain tight enough. I can roll the tension on manually but I'm not sure I'm confortable doing it like that (i figure it's automatic for a reason).

So a few questions....
Does a cam chain tensioner automatically adjust tighter, and looser. Or does it just tighten up as needed.

And do the symptoms that I'm talking about indicate that the cam chain tensioner is bad.


And yes, I know the best way to go about it is to replace the cam chain and tensioner. Thing is it's raining here in the desert, riding is prime, and I don't have the cash to buy the tensioner and chain for about a month. I'm bummed that It's not ready to ride this afternoon!!!
At the same time I don't want to wait a month, buy the new tensioner, and have that not be the problem.

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  • grayracer513

Posted July 24, 2012 - 09:50 AM

#2

So a few questions....
Does a cam chain tensioner automatically adjust tighter, and looser. Or does it just tighten up as needed.

And do the symptoms that I'm talking about indicate that the cam chain tensioner is bad.


The tensioner will automatically take up any slack that might appear in the chain. It will not back off automatically, but there's no reason for it to do so.

The tensioner is a simple, spring loaded worm and sector gear arrangement. The spring drives a worm or screw gear inside the plunger, and rotates in response to any lack of resistance to the plunger extending farther. It runs on the slack side of the chain. As RPM increases, the tension on the chain between the crank and exhaust cam, and on the chain between the two cams, increases, which increases the slack on the back side. The tensioner then extends to take out the slack, and can't be pushed back any more than you can push a bolt through a nut.

The thing that screws up the works most often is when the chain develops tight, binding links. These will tend to "kink", or fail to straighten out entirely as they roll off the crank sprocket, making the back of the chain seem tighter than it really is. All it takes is for the engine to kick or roll back a little on startup or shutdown, and the reversal of the load on the chain to pull the kinks out, and you have a bunch of uncontrolled slack on the front and top side run of the chain, upon which it skips time.

The tensioner is simple to test. Wind it back to fully retracted. It should do so smoothly without snagging or catching as you turn the screw. Holding it retracted with your finger, you should be able to let it extend slowly, which it should also do smoothly without catching. You should also be able to push against it while extended any amount and not be able to push it back or get it to skip.

The chain is more often the culprit than the tensioner, but remember that the consequences of running the valves into the piston can be extremely expensive.





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