2002 Cr250r Low Rpm Knock

[MOTOHEAD64]

I have a 02 cr250 that I have owned for about a year. I noticed a knock at low rpm's the last time I was riding. It only happens as the motor is ideling down, and it knocks once or twice and then stops. It is not a constant knock, meaning it doesn't do it every time the bike idels down, but enough to be noticed. Is there anyone who has had this happen? Or who knows what could be causing this? I am thinking it is signs of the motor being tired and needing a rebuild. Just want some advice on where to start. Thanks!

 

[MOTOHEAD64]

Thanks, but this is a two stroke it does not have cams.

 

[IndyMX]

Oh crap.. I see that now...

Could be piston slap then... Tear down the top end and do some measurin.

 

[MOTOHEAD64]

What exactly is piston slap?

 

[whenfoxforks-ruled]

Its kinda self explanatory. Your piston is not supposed to slap. The skirt wears, the rings wear. What does the manual recommend for replacement on engine hours? Running longer than recommended is how the cylinder gets oval.

 

[MOTOHEAD64]

The thing is I'm not sure how many hours are on the motor, or even when the last time the top end was done. I am all for rebuilding the top end. I just didn't know if piston slap had something to do with the lower end of the motor. Like the crank, rod, or bearings being worn out.

 

[IndyMX]

Piston slap has to do with the piston. Hence the name... It's the skirt wearing out, actually slapping against the cylinder wall. Excessive clearance.

 

[MOTOHEAD64]

Thanks Indy. I will pull it apart and check it out.

 

[steve.emma]

i have the same bike and it makes that exact same noise..... i dont believe its piston slap. on mine it doesnt happen at idle, only when on over run and even then it wont always do it. my piston and rings are in good condition. i used to worry about it when i first got the bike but now i kinda just accept it. i think its more of a characteristic than a fault.

 

[whenfoxforks-ruled]

It could be that the pipe does not keep the sound and pressure waves in sync, ideally they should be. It will affect performance and make an odd sound. Do both bikes have a stock exhaust system with good packing in the silencer?

 

[MOTOHEAD64]

I am running a FMF exhaust system front to rear. My turbine core muffler/sparky got punched in a little from looping it up a hill. It's not bad but I guess it could make it loose a little back pressure.
The only other bike that I have heard this same noise on was 1987 250r three wheeler. It was my Dads and he never tore it down to see what it was. He also never maintained it. Not a trait I got from him. I want my bikes to be tip top always, and if something is out of the ordinary I want to know why. I am still going to tear the bike down, if not just for my own knowledge that everything internaly is good. I just don't want to end up sitting in a canyon with a blown motor. That knowledge is at least worth the price of a gasket kit. Right?

 

[IndyMX]

I am running a FMF exhaust system front to rear. My turbine core muffler/sparky got punched in a little from looping it up a hill. It's not bad but I guess it could make it loose a little back pressure.
The only other bike that I have heard this same noise on was 1987 250r three wheeler. It was my Dads and he never tore it down to see what it was. He also never maintained it. Not a trait I got from him. I want my bikes to be tip top always, and if something is out of the ordinary I want to know why. I am still going to tear the bike down, if not just for my own knowledge that everything internaly is good. I just don't want to end up sitting in a canyon with a blown motor. That knowledge is at least worth the price of a gasket kit. Right?

You should tear it down once in a while anyway.. Just to be on the safe side.

Yeah, who wants to be any distance from the truck with a blown motor..

 

[BigRedAF]

Honda has had problems with egg shaped bores in the past. I tore down a new bike in 1986 due to excessive noise and measured the cylinder with a dial bore indicator. It was .002 top and bottom and was as bad as .0045 in the center causing piston rock. We ordered an other cylinder and it too was crap. The third cylinder came from a Honda support team and it was perfect. I had the same problem back in 2002 with an other CR250.

If you find out that yours is egg shaped due to wear or poor plating a new piston wont solve your knock. You can get it re plated and that will return it to new tolerances and solve your knock if that happens to be what's causing your issues. Generally re plating is less money than a new cylinder and if it wrong they will fix it.

 

[Matt Fisher]

The 02+ CR250's will occasionally make a clacking sound when chopping the throttle as the RC's servo motor snaps the powervalve shut. Pull the side cover off the valve and use your hand to quickly snap the valve shut, you'll likely hear the noise you're referring to.

 

[steve.emma]

cheers Matt, that could be exactly the noise i have. will try what you suggested and see if it sounds the same. i am pretty sure the noise i have has nothing to do with sound/pressure waves in the exhaust, and its not constant or regular enough to be piston slap in my opinion. :cool:

 

[MOTOHEAD64]

Thanks everyone for your input on my situation. I do beleive the noise was piston slap. I tore in to the motor this weekend and found a couple problems. Even though the knock wasn't constant, meaning it knocked a couple times and then stoped(it did this about five times in about eight hours worth of riding). There is a wear mark on the exhuast side of the piston and barel where it looks like the piston was hitting the cylinder. I also found slight movement in the rod to crank journal while grabbing the rod and twisting it. Though I wasn't able to feel any up and down movement, I'm sure under more pressure it could have some. That being said I have decided to go ahead and rebuild the whole motor. It's worth it to me to know I will be on a reliable machine.

 

[whenfoxforks-ruled]

When you can get a complete engine kit for a 250 for a little over 400 dollars, what the heck! http://www.motosport.com/offroad/pr...prodId=287414&sMMY=HONDA;CR250;2002&cat0=DIRT