Hi all, just joined up here and have a problem with my 3LN1 fzr250. I was riding it the other day, and it developed a loud tapping/knocking noise. It was riding fine before and after the noise, and it didnt seem to make any performance difference, although I'm now having trouble starting it. Once the noise appeared, it got louder and louder until I stopped riding. I've turned the engine by hand and I couldn't hear it making any weird noises. It sounds like a metallic tap noise that seems to go up with the revs. Anyone got an idea what could cause this kind of noise? I looked at the oil and couldn't see any metal in it. I'm currently in the process of removing the engine to take a closer look, but I got stuck due to having no socket to remove the front sprocket(27mm i think?).
If it's more of a knocking sound then it is likely a big end gone and that noise is a piston hitting the head. More of a tapping could be a large valve clearance. Hope you sort it.
Well I've taken the head off it. I really can't see anything wrong yet. The pistons all go up and down fine without any noise. None of the valves look out of place, and when the cams were still installed the valves went up and down fine. Can anyone confirm what direction the crank needs to be turned? In one direction it turns fine. When I turn it the other, it still turns fine, with a bit more resistance and making a grinding noise which I have been told could just be the starter motor turning? Any ideas where I should look next?
Or it could have spun a main bearing. I had a GPZ600R do that to me. I rode it home but it never started again <!-- s --><img src="{SMILIES_PATH}/icon_mad.gif" alt="" title="Mad" /><!-- s --> Either way it defo sounds like a crank bearing issue! Chris
I just checked the pistons for any play and it looks like the piston closest to the alternator has a bit of play on the crank. If I pull on it up and down I can see it has some movement where it connects to the crank. Any idea what is involved in fixing this?
Tearing it down to the bare cases, unfortunately ... <!-- s:-? --><img src="{SMILIES_PATH}/icon_Eyecrazy.gif" alt=":-?" title="Eye Crazy" /><!-- s:-? -->
Yeah thought it would be a bit of work. That doesn't trouble me really. Do I need to replace the crank, or can I check it for wear and just replace the bearings itself?
The bearing shells are replaceable for a reason. IF the journals are good to go, simply replace any out-of-spec shells and carry on.
Think the chain is fine. 99% sure it is this one piston loose on the bearing and its making the tapping noise as it comes back down. I'm hoping it just needs a new cam bearing.
Uhhhh ... What? There are no piston bearings. The pistons ride on the wrist pins, which ride in the conrods. There are no cam bearings. The cams ride on the head, held in place by the cam caps. This is why the caps are considered an integral part of the head, and cannot be purchased (from Yamaha) separately.
No there aren't any bearings between conrod and piston in a four stroke, in two strokes it's the little end bearing. The bearing between conrod and crank is the Big-end bearing. The bearing between crank and engine casings is the Main bearing. I think stock is saying that he's '99% sure it is this one piston [and conrod] loose on the [big end] bearing and its making the tapping noise as it comes back down.' That would make sense. I have never heard of main bearings being a bolt in 'replacement part'. You may need to go to the next oversize bearing and get the crank reground. The tolerances on these things are stupidly small. Chris
