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Discussion Starter #1 (Edited)
I picked up a 2006 Predator 500 pretty cheap because it had a loud'ish engine tick (top end) ..but it seemed to get quieter after riding it 10-15 minutes. She runs decent. starts up good... I figured easy fix! the valves needed adjusting..or cam chain was stretched. Well I pulled it apart and to my surprise all the valves were within spec. , and the timing chain was tight, the auto chain tensioner was doing its job. so I scratched me head, maybe Piston slap? I pulled out the bore scope, removed the spark plug .. besides some carbon on the top of the piston, the cylinder walls looked new! (I was told the motor was rebuilt 2 years ago and everything does look that way) THEN.. After re-timing her I started to hand turn the motor.. that's when I noticed on the down stroke the tension on the cam chain went slack a bit between the cam sprockets.. but on the upstroke it got tight again. Now im stumped. Thoughts?:hmmm:
 

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Check to make sure all the cam lobes are nice and smooth and the seats are clean. Sounds like something is holding back the intake cam from spinning until its forced to. Are all the valve springs in good shape and not broke or anything?

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Discussion Starter #3
Check to make sure all the cam lobes are nice and smooth and the seats are clean. Sounds like something is holding back the intake cam from spinning until its forced to. Are all the valve springs in good shape and not broke or anything?

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Yeah every thing looks pretty pristine in there. cams look almost new. springs good. what's most puzzling is that on the down stroke the chain gets loose and then re tightens on the upstroke. the chain tensioner only pushes out, not in, so thats the part Im scratching my head over, how the timing chain could get loose and tight again through the stroke. Is it possible that only one part of my timing chain is stretched??, and when that part comes around to meet the automatic tensioner , that's where it slacks out... maybe? im super stumped.
 

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If you have the valve cover off and are hand turning the Engine, You say on the down stroke the chain gets loose, So either its the stroke where the intake valves open (which would cause the rotation side of the chain to pull more because there is more resistance while trying to open the valves - if that makes sense) or its after TDC when the spark plug ignites. As the engine rotates, starting with TDC the piston goes down on the down stroke, as it goes down the intakes valves open and the piston sucks in the fuel/air mixture until the valves close at that point the piston hits BDC and starts to come back up (at this point all valves are closed) the Piston hits TDC again then rotates 14 degrees past TDC and thats when the spark plug ignites forcing the piston back down on the power stroke. Then the cylinder is full of spent fuel so the piston comes back up and the exhaust valves open and out goes the exhaust gasses.

The only thing I can think of is that one of the cams is binding or the cam chain is stretched or just needs to be re-tensioned, does that have one of the tensioners that has a lock nut on it? or is it constant spring tension. I would check the free standing length of that tensioner spring and compare to spec or a new one. The only thing that would create a load on that timing chain is the opening and closing of valves as it takes more power to push the valve down, That would tighten up more on the pulling side of the chain and loosen up the part of the chain that goes to intake cam, if the tensioner isn't taking 100% of the slack out then it wouldn't surprise me at all that you see it between the cam sprockets as that is where the chain has the most room to play.

Sorry a lot of that was me just rambling
 

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Discussion Starter #5
does that have one of the tensioners that has a lock nut on it? or is it constant spring tension.
Its a spring loaded ratchet style tensioner, once it pushes to take up any slack in the cam chain, it wont compress again. Since I cant see anything real obvious, Im thinking the cam chain itself must have a section in it that's stretched?? Maybe when the stretched section of the chain passes by the tensioner that's why im seeing the slack..then after I continue to turn the crank, the part of the chain that is not stretched passes by the tensioner it gets tight again?.. At any rate..Im going to order up a new cam chain and a new cam chain guide. I hope that's it. When I bought it, I was told that the motor was rebuilt a few years back because of a bent valve.. they did a new head assy, and cylinder assy, maybe they re-used the cam chain ..might explain the stretch in just a section of it?
 

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You're probably right about re using the chain, they probably never dove far enough into the engine to pull the chain off the crank side and just reused it. I agree on getting a new chain and guide, Let us know how it goes!
 

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Discussion Starter #7 (Edited)
You're probably right about re using the chain, they probably never dove far enough into the engine to pull the chain off the crank side and just reused it. I agree on getting a new chain and guide, Let us know how it goes!
yes. i'll keep ya posted. I ordered the parts this morning. It looks like the clutch basket will need to come off, and the sprocket behind the clutch. Also the lower sprocket the cam chain rides on has a sprocket in front of that ugh.. they sure don't make it easy lol . you know off hand if both , clutch basket nut, and the crank nut holding cam chain sprocket are regular threads, or are they backward threaded?

keep your fingers crossed for me.
 

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Discussion Starter #8
WoooHooo. pretty sure I found the problem. There is a long plastic cam chain guide that bolts on to the case behind the clutch basket..when I pulled the clutch basked the chain guide fell out..it broke about 2 inches up from where it bolts on. Im thinking that's the cause for the slack and the cause of my loud ticking noise. got a new one on order along with new cahin while its apart!

 

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That'll do it!
 
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