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scrambler 500 slow cranking after camshaft replacement

15K views 65 replies 8 participants last post by  FPD218 
#1 ·
Hey guys i just replaced the camshaft on my 01 scrambler 500 and now it barely cranks over. Timing is set right and valves are set at .006. have any of you had this problem and what was the cause? it cranked over great before changing the camshaft. any help is appreciated. Thanks guys.
 
#2 ·
if it has the auto decompression feature it will have a steel ball bearing looking dude on the cam shaft with a little centrifugal weight and spring on the side and if it is not functioning correctly the ball bearing will not protrude from the cam causing it to NOT decompress the cylinder leaving you with hard turnovers....if it is working correctly the ball bearing will be protruding from the cam about 1/16-1/8” and as soon as the cam picks up speed the rotational force will pull the little weight outward causing the ball bearing to be flush or recessed in the cam no longer decompressing the cylinder
 
#5 ·
The cam can have the decompression ball and all associated part in tact but if the spring is facing the wrong way it will not decompress the cylinder (I ordered one a while back and it came assembled backwards from the manufacturer and caused exactly what you are describing)
 
#6 ·
So went back in a checked the compression ball on the camshsft and it is good. the ball is all the way out at resting position. one thing i did notice though is that the timing chain is really tight and i actually had a hard time getting the sprocket on the cam even with the tensioner out. is this normal for polaris or could the timing chain be binding?
 
#7 ·
The cam chain guide (not the tensioner side) but the front one just sits in a little cradle behind the stator plate and when you had the cam gear out there would have been enough slack to allow the guide to come out of the cradle causing your symptoms ie. tight chain and hard turnovers....if it falls out of its keeper it ends up between the keeper and crank gear puting extra tension on the chain and extra resistance when turning over
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#9 ·
Braaper don is right, but if you have told the complete story, it is not a concern. The guide cannot be removed or dislodged from it's seat unless the head was removed and head removal is not required to replace the cam, but the chain should not be real tight with the tensioner removed either. How easy does the cam rotate with the sprocket removed from the cam?
 
#11 ·
There is a nub on the upper end of the guide that sets into a notch in the top of the cylinder. The guide cannot be removed or unseated from the lower cradle without removing the cylinder head. It is the same for the Scrambler and Sportsman. If you can move the guide (any more than just perceptible movement) without removing the head, the guide is damaged and should be replaced.
 
#13 ·
There is slack in the chain - gear goes on very easily - then the tensioner device is installed - if I have to roll the engine over and I don't want to install the tensioner, I stick a finger, socket extension or whatever is handy to push the tensioner blade into the chain (the slack is on the back side of the chain and I just want to assure a worn chain does not jump the sprocket), but if the chain has enough slack to jump the teeth on the sprocket, it is worn out and needs to be replaced anyway.
 
#14 ·
Ok thanks. So im thinking this is my problem. mine is tight even with the tensioner out. in order to get the gear on i actually had to push up on the gear to get it on. mine was very difficult to put on. Ive never had this problem before and this is the first polaris I've done. Shoulve realized there was something wrong.
 
#17 ·
You have to remove the cylinder head to get the guide in the cradle - there is a nub on the top end of the guide that sets in notches in the cylinder and the head holds the guide in place.

I'm wondering if the chain is not meshed with the crank sprocket causing it to be tight.

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#18 ·
Well im still at it! Im not sure how but i managed to get some play inn the camshaft with the tensioner on but its still not right! Its still cranking really hard and it will break your hand trying to pull start it. ive tried other batterys to see if its the battery and no luck. The only way ive got it to turn over at a descent speed is by jumping the battery with my truck. BUT the truck has to be running or else it will wear my truck battery out too pretty quick. oknce i start the truhck up the battery the bike willb. turn over good. Something is definatly wrong and I'm not sure what. im al.ost to the point that i don't want to turn it over anymore because of the possibility of stretching the timing chain or messing up other things. I was thinking it could be a bad starter but its the same differance when trying to pull start it. I'm thinking its got to have something to do either with the new camshaft or timing/valves but ive triple checked all of it. Sorry for the long story but I'm getting frustrated. All i needed to do was change the camshaft and rockers and it turned into a shit storm!!
 
#19 ·
Well im still at it! Im not sure how but i managed to get some play in the camshaft chain with the tensioner on but its still not right! Its still cranking really hard and it will break your hand trying to pull start it. ive tried other batterys to see if its the battery and no luck. This thing will drain a fully charged known good battery in a few seconds. The only way ive got it to turn over at a descent speed is by jumping the battery with my truck. BUT the truck has to be running or else it will wear my truck battery out too pretty quick. once i start the truck up the bike will turn over good. Something is definatly wrong and I'm not sure what. im almost to the point that i don't want to turn it over anymore because of the possibility of stretching the timing chain or messing up other things. I was thinking it could be a bad starter but its the same differance when trying to pull start it. I'm thinking its got to have something to do either with the new camshaft or timing/valves but ive triple checked all of it. Sorry for the long story but I'm getting frustrated. All i needed to do was change the camshaft and rockers and it turned into a shit storm!!
 
#29 ·
  • thanks it pulls over easy with the plug out and cranks easy. it doesnt feel like anything's binding thats making it hard to pull over. you can feel the pressure from the compression and its like its struggling to get past it. I did pull the cam gear off though and checked for play in the front guide and i think theres a little too much play but not sure. Just would like to be sure thats the problem befor i tear it down. i left a video of the play below. if you could give me some input id appreciate.
 
#31 ·
Well, at least the top is in the right place and if it pulls over easily with the plug out, then I don't think the chain guide is the problem - how about a pic of the crankshaft position, the cam sprocket with at least one bolt in the sprocket and the compression release end of the cam?
 
#32 ·
ok will do. I've been working on 4 strokes for years and I've never dealt with this before. the only other thing besides valve train is battery or starter. But the fact that its a bear to pull makes me think its valves somehow. The compression lever is doing its job and i can see it liftinng the exhaust valve when it goes over the ball so im kinda stumped. Ill get those pics on here asap. Thanks for all your help with. its good having another set of eyes looking in.
 
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