Just got a 99 scrambler 400 4X4. It has quite a loud knock, and seems to go away at higher rpm's or i just cant hear it any more. I dont know if it is the motor or clutch, Any ideas how to fix it? Also, what would you all recommened doing as preventative maintenence, as far a fluids and such go. Anything else i should be concerned about with this machine?

Thanks for the help in advance

 

A knock could be almost anything. crank bearing, wristpin, clutch. If you can narrow down the area it's coming from that might help.

 

Well i pulled the clutch cover, and the belt, and wiggled the the clutch back and forth. It sounds like the knock is coming from the motor, because i can reproduce the knock just by moving the clutch back and forth, it kinda sounds like a sloppy piston. Is this common? I'm new to polaris atv's any recommendations to fix the problem? Also, what else should i do as maintenence? Thanks again

 

Probably your wrist pin, two strokes do wear out no matter what brand they are. not a huge deal if you can rebuild the motor yourself. just grab a piston, wrist pin and some gaskets and you should be good to go. have your cylinder checked since it may need to be bored over. Sometimes you can just hone the cylinder and put a stock size piston back in. when you get it apart take your finger and run it up the inside of the bore and if you feel a lip at the top you should have it machined.
As far as maintenence goes I would just put in a new plug and airfilter. then get a greese gun and greese all your shafts and swingarm and anything else you can find a fitting for. I use mobil 1 synthetic greese. also probably not a bad idea to change your hub fluid out. I use mobil 1 synthetic ATF but you'll get lot's of different suggestions on what to use. Polaris fluid is always a good choice if you don't mind spending the money. You can change the tranny fluid if you want to also. I'd use the polaris brand chain case lube for that one. People will suggest amsoil but for personal reasons that I will not get into here I refuse to use anything that says amsoil on it. That's pretty much it for maintenence. Another way to check the condition of the engine is to do a compression test but i'm not sure what the specs should be.