A buddy wants me to take a look at his Polaris Trail Boss 250 4X4. It has a 250cc 2 stroke single cylinder and when it idles it sounds like a 2 cylinder running on one and it knocks real bad.
My first impression is the timing is way off.
Any ideas?

 

Polaris engines are known to knock. I know mine knocks and ive had it checked out but nothing was wrong with it so i just bought a louder pipe and i dont here it anymore.

 

good problem solving
[img]i/expressions/face-icon-small-wink.gif[/img]

 

oldcrow, as far as the timing....no such thing on a 2 stroke. they do not have a cam. Mine also knocks...

 

It may be piston slap. mine knocks from this no big deal[img]i/expressions/face-icon-small-smile.gif[/img]

Jeff

 

two strokes have no ignition timing?

 

WHAT??? Ignition timing is what is used to insure the spark plug fires at the correct time.
What produces that spark? The stator, flywheel, coil, ect.
Same as a 4 stroke.
You are not always able to adjust it but it is there.

 

I have a 04.5 500HO and it sounds like a diesel! I otherwise love it though. Dobie

 

The stator plate is adjustable for ignition timing - a real pain to do since the flywheel has to be removed every time to make even the slightest adjustment.

From experience - especially if it has a Wiseco piston in it - they will knock to some degree. A lot of the Wiseco knock is actually piston slap as it requires a greater piston skirt to cylinder wall clearance than an OEM piston.

Something else that can cause a "knock" is the upper rod bearing may be getting a little sloppy

 

my bike has a serious death rattle and its just been rebuilt. guess thats just the nature of the beast. [img]i/expressions/face-icon-small-wink.gif[/img]

ross