knocking

[yamarider88]

hey guys my friend and i just finished rebuilding our top ends together and we finished mine first no problem went through all the heat cycles rode it around and it's all good. then on my friends (2005 cr 250) we put it together just as we had mine and started it and it started making a loud knocking sound at idle we turned it off and decided we would let it cool down and then start it again. the next time we started it he rode down the street and came back and it was still making the noise but not quite as loud or often. told him we should take it apart but he insisted he ride it one more time and he got on it pretty hard and came back and it wasn't knocking any more but just didn't quite sound right. also his would not idle until we turned the idle way up and even then it still was idling weak. what did we do wrong? he waited a really long time to do his top end this is the first time it's ever been done in either of our bikes since they were new.

 

[Filthy_McNasty]

A knocking sound from an engine is never good news, and no way in hell would I just ignore it and ride the bike. Something got put together wrong or doesn't have correct clearances, or you didn't replace a part that was worn out...whatever the cause of the knocking, it needs to be investigated. The alternative is to ride the bike and pray that nothing happens, and take the chance that your $150 top-end rebuild doesn't turn into a $700 complete engine rebuild just because your friend doesn't care enough about his bike to fix it correctly.

What the heck, it's his bike, just let him blow the thing up. Sometimes that's the only way to teach people that they're being stupid.

 

[N3WFI3]

check for air leaks first i guess, around the head and base gaskets and the carb intake

 

[_JOE_]

What the heck, it's his bike, just let him blow the thing up. Sometimes that's the only way to teach people that they're being stupid.

Isn't that the truth?!

 

[yamarider88]

yea i told him the problem would most likely escalate to a higher level if we didn't figure it out before he starts riding it again. we checked the carb and head for leaks and found non. need to check the flywheel and see how that looks see if theres any play in it to tell if the bottom end is ready. the dunes are just so freaking hard on our bikes i swear it's so much work to have fun but heck it's a blast.

 

[N3WFI3]

ya i was thinking it had to do with the bottom end
like the bearings or something

 

[Rotorranch]

If it wasn't knocking before you worked on it, I'd guess it was something you did while working on it. :nod:

Maybe you put the piston in backwards? :whoa:

Rotor

 

[yamarider88]

no i made sure it went in the right way did just what the book said to and we lined the ring up with the little hole were the ring ends meet.

 

[Rotorranch]

But was it knocking BEFORE you worked on it?

Rotor

 

[yamarider88]

nope it wasn't running at all his ring was gone it didn't stick out at all it was same diameter as the piston and his bike would not idle you had to pull start it to get enough compression to start it.

 

[Filthy_McNasty]

So the top-end was completely worn out. I would hazard a guess that the lower end is also completely worn out, but with the wasted top-end it had before the rebuild, it had so much piston slap that you couldn't hear the lower end knocking, and it didn't make enough power to make the loose rod bearings knock very loud anyway.... :laugh:

 

[Isobareng]

Well...... first remove the mag cover and look for a up and down movement of the fly wheel any at all is bad. then check that the power valves are installed properly. if that is good remove the cylinder and check the rod crank bearing and wrist pin bearing. while the cylinder is off see if you can feel any crank movement thru the the right hand side main bearing.

hope this helps

D

 

[yamarider88]

he has probably all ready done this if his brothers helped him out when he took his bike home but i'll tell him. i was at his house a week ago and we fired it up and took it around the golf course he lives behind and (not on it around it is dirt and no houses) it sounded fine and ripped so maybe it's all good but i guess we'll see in march when we go to moab.