Cam chain tensioner?


3 replies to this topic
  • xcape

Posted October 27, 2006 - 01:48 PM

#1

Just reading the crf250r forum and aparently a kx issue also....bikes blowing up as the tensioner fails??? Is it an issue with the YZ's? Did a search came up with nothing?

  • Ga426owner

Posted October 27, 2006 - 02:05 PM

#2

Just reading the crf250r forum and aparently a kx issue also....bikes blowing up as the tensioner fails??? Is it an issue with the YZ's? Did a search came up with nothing?


YZF's have no issues with tensioners.....until they are out of total adjustment

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  • grayracer513

Posted October 27, 2006 - 02:57 PM

#3

Did a search came up with nothing?

There's a reason for that. They don't fail. Some say that they have seen them fail, but it's extremely rare, and almost always in pure race engines. I have a standing challenge on this board that if anyone has one that has failed and been the cause of any engine damage to send it to me. No one has done so.

The device is outrageously simple. The plunger is keyed in the body so that it can move in an out of its bore, but cannot rotate. At the back end is a part that threads into the the plunger, is supported in a bearing, and driven clockwise (looking forward from the rear) by a spring. The instant any slack shows up, the spring winds the screw until the plunger is driven out far enough to take the slack up. The chain can no more push the plunger back against the screw and spring than you can make a bolt spin in its threads by pushing straight in on it. It's a de facto worm drive gear, and it simply cannot be back driven by the load it bears.

The only way for it to allow slack to develop is to have the threads (spiral cut gear teeth, in fact) "strip" under a load, or for either the plunger or screw to break, or, and this is a very remote possibility, for the spring to loose tension due to vibration at a harmonic frequency. Otherwise, it's essentially foolproof, stepless, and a great example of how effective simplicity can really be.

  • Ga426owner

Posted October 27, 2006 - 04:59 PM

#4

There's a reason for that. They don't fail. Some say that they have seen them fail, but it's extremely rare, and almost always in pure race engines. I have a standing challenge on this board that if anyone has one that has failed and been the cause of any engine damage to send it to me. No one has done so.

The device is outrageously simple. The plunger is keyed in the body so that it can move in an out of its bore, but cannot rotate. At the back end is a part that threads into the the plunger, is supported in a bearing, and driven clockwise (looking forward from the rear) by a spring. The instant any slack shows up, the spring winds the screw until the plunger is driven out far enough to take the slack up. The chain can no more push the plunger back against the screw and spring than you can make a bolt spin in its threads by pushing straight in on it. It's a de facto worm drive gear, and it simply cannot be back driven by the load it bears.

The only way for it to allow slack to develop is to have the threads (spiral cut gear teeth, in fact) "strip" under a load, or for either the plunger or screw to break, or, and this is a very remote possibility, for the spring to loose tension due to vibration at a harmonic frequency. Otherwise, it's essentially foolproof, stepless, and a great example of how effective simplicity can really be.


totally agree....why people think a manual CCT is better is beyond me.....:mad:





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