bad knocking sound...

[Xrider06]

My 250R started making a bad knocking sound coming from the cylinder. I'm not sure what this is but a few people thot it was a rod bearing or something. Even tho it made this sound it still ran completely normal. I took the topend apart and looked at the bearing on the top of the rod and it looks fine as far as i can tell so do you think it could be a bearing in the bottom end or something different? Please help me. Any info is greatly appreciated.

[Antony250R]

No one really knows what the famous 250r engine knock is. I have heard so many different answers. I think it's piston slap because on mine the knocking sound gets
quieter as the engine warms up.

[wilkin250r]

It could be the main crank bearings in the lower end. Pull off the left side cover (stator side), and see if the flywheel and crank wiggle up and down.

I just had this problem. I had a slight knock in the engine, I thought it might have been the rod, but the entire top end was in perfect shape, the wrist pin and bearing were good, everything.

Then, when trying to pull the flywheel, I felt the whole thing jiggle up and down. That's when I knew...

[Rich250RRacer]

Originally posted by wilkin250r
It could be the main crank bearings in the lower end. Pull off the left side cover (stator side), and see if the flywheel and crank wiggle up and down.

I just had this problem. I had a slight knock in the engine, I thought it might have been the rod, but the entire top end was in perfect shape, the wrist pin and bearing were good, everything.

Then, when trying to pull the flywheel, I felt the whole thing jiggle up and down. That's when I knew...

Watch the journal on the stator side, they are known to wear. It will show the same symtoms as a bad bearing. The crank should fit tight in this bearing (light press fit), requiring the special tool from Honda to install the crank. If the journal is worn the crank will just slide into the bearing.

[wilkin250r]

If the journal is bad on mine, then I have nothing left. I have nearly 1/8 inch play back up and down....

[Xrider06]

thanks i think il try that because everything else looks fine

[LT250Racer609]

its a rattling comming from the cylinder right??


if so its the piston slapping around and normally as the quad warms up its get a little quieter...this could also be because of worn rings or wristpin also if the engine is knocking

[2FIFTYR]

ok a two stroke with an expansion chamber pulls a fresh mix of fuel and air into the pipe and is forced back into the cylinder when the pressure in the pipe is high enough acting somewhat likea turbo charger. My theory is that the pipe at a cooler temperature doesnot have enough energy to keep the fuel moving and force back into the cylinder until the engine warms up.

and sits down in the pipe and eventually burns in the pipe causing a back fire.

[Jester]

:confused: ^^

[machwon]

Bad counter balencer bearings can also make a knocking noise. Be sure and check it all while you're in there.

[baseballplaya23]

Originally posted by 2FIFTYR
ok a two stroke with an expansion chamber pulls a fresh mix of fuel and air into the pipe and is forced back into the cylinder when the pressure in the pipe is high enough acting somewhat likea turbo charger. My theory is that the pipe at a cooler temperature doesnot have enough energy to keep the fuel moving and force back into the cylinder until the engine warms up.

and sits down in the pipe and eventually burns in the pipe causing a back fire.
umm and that would cause a knocking sound like he is talking about? wtf? :huh

[wilkin250r]

Originally posted by 2FIFTYR
ok a two stroke with an expansion chamber pulls a fresh mix of fuel and air into the pipe and is forced back into the cylinder when the pressure in the pipe is high enough acting somewhat likea turbo charger. My theory is that the pipe at a cooler temperature doesnot have enough energy to keep the fuel moving and force back into the cylinder until the engine warms up.

and sits down in the pipe and eventually burns in the pipe causing a back fire.

Anybody that is dumb enough to be on the pipe before the engine warms up deserves a seized motor...

[dynofox]

There was a knocking sound in my R's motor and after a complete tear down (bottom end too) I found the noise was caused by piston slap. My cylinder was still on it's original bore, not bad for being 20 years old. :)

[greatwhite04]

So how do you fix piston slap? What is it slappin' against? What will happen if you don't fix it?

[2FIFTYR]

THanks for jumpin down my throat but the theory is there. it could cause a knock sound like that ( IN THEORY!) one thing i left out because i was in a hurry is that when the pipe is warm it maybe pulling a little bit too much fuel in to the pipe and not being able to push it back in fast enough. Like I said before this is just a theory that is possible. So next time you come full bear being pissed off read what the writting says.

[wicked265R]

^^ it still wouldnt make a knocking nose from that. Well lets just settle it here, thats not a great "theory".
I'd say its probably piston slap too. how old's the top end? I had knocking nose from my piston hitting my head a little from the wrong size gasket put on the head. check for that too. let us know how it goes :D

[Xrider06]

the thing has been bored but only about .10 or .20 over. The bore still looks real good and the piston was kinda black on top but other than that its good too. i just got the thing a few months ago but i know that it wasnt bored out more than 2 or 3 years ago. it had a fresh piston and rings and everything put in in 04 and it only had a few hours on it when i got it so its still fairly fresh.

if it is piston slap or whatever, what do i need to do to fix it? it never did it b4 and i put prolly 15 or 20 hours on it so why would it just start. im pretty sure it wouldnt be the gasket so what else could it be?