Two Stroke Motocross

Two Stroke Motocross Forum => General Two Stroke Talk => Topic started by: JaredRM250 on August 11, 2013, 05:21:06 PM

Title: What are the symptoms of the big end bearing worn?
Post by: JaredRM250 on August 11, 2013, 05:21:06 PM
I've been told by a dealer that my big end may be worn which is in a low houred bike. The bike does slightly rattle but if i pull in the clutch it nearly completely disappears.
Any thoughts on this much appreciated  :D
Cheers,
Jared.
Title: What are the symptoms of the big end bearing worn?
Post by: citabjockey on August 11, 2013, 09:18:20 PM
Easiest check is to remove the spark plug and the magneto cover.
Carefully rock the flywheel back and forth.

If you "feel" slop in that rotation at all then the big end bearing is gone.  If you can't then you probably would need at least a top end teardown to check with more precision.

Title: What are the symptoms of the big end bearing worn?
Post by: rbigair40 on August 11, 2013, 11:07:32 PM
That's just trans rattle that's normal don't worry , and a worn piston will trick you on the flywheel rock, unless it is completely gone the rod bearing that is .
Title: What are the symptoms of the big end bearing worn?
Post by: citabjockey on August 11, 2013, 11:13:59 PM
You can negate the warn piston issue by sticking a screwdriver down the spark plug hole. Feel that go up and down while you rotate the flywheel back and forth. Get the piston at about 1/2 stroke which maximizes the pistion travel per rotation of the flywheel. Now while feeling the screwdriver for up and down motion rotate the flywheel. If you get any discernible rotation out of it without the screwdriver moving then you have a bad big or little end bearing or bearing surface.
Title: What are the symptoms of the big end bearing worn?
Post by: evo550 on August 11, 2013, 11:47:29 PM
Do you mean, crank bearings or conrod bearing?
The only way to correctly determine wear is to check the specs and measure with correct instruments as per manual.
Title: What are the symptoms of the big end bearing worn?
Post by: Stusmoke on August 12, 2013, 09:19:56 AM
Pree much what everyone else said. When I got my new katoom, I got paranoid about the noise it made which was vid posted here: http://twostrokemotocross.com/forum/technical/engine-knocking/

Mine too drops right off if I pull the clutch.

With regards to big end wear, the easiest way to tell, like everyone said, is to give your flywheel a jiggle. If you're not sure with taht, then pull your cylinder off and take some feeler gauges to the big end from there. Compare to clearances in either your manual or what someone can quote from their manual. My POA would be: Flywheel check, pull cylinder and check for up/down play in the conrod (side to side is normal, to a certain extent) then feeler gauges if you're still not sure.

Good luck.
Title: What are the symptoms of the big end bearing worn?
Post by: JaredRM250 on August 14, 2013, 08:31:53 PM
Quote from: Stusmoke on August 12, 2013, 04:19:56 PM
Pree much what everyone else said. When I got my new katoom, I got paranoid about the noise it made which was vid posted here: http://twostrokemotocross.com/forum/technical/engine-knocking/

Mine too drops right off if I pull the clutch.

With regards to big end wear, the easiest way to tell, like everyone said, is to give your flywheel a jiggle. If you're not sure with taht, then pull your cylinder off and take some feeler gauges to the big end from there. Compare to clearances in either your manual or what someone can quote from their manual. My POA would be: Flywheel check, pull cylinder and check for up/down play in the conrod (side to side is normal, to a certain extent) then feeler gauges if you're still not sure.

Good luck.

Flywheel turns smoothly and bike starts 1st kick with plenty of power! All thats left to do is RIDE
Title: What are the symptoms of the big end bearing worn?
Post by: citabjockey on August 15, 2013, 12:18:43 AM
Mostly for con rod but really shot crank bearing could introduce rotational slop -- but will also allow the crank to wobble a bit.

Bottom line here with this check -

- if you feel sloppyness then you have a problem. You need to tear it down. End of story.
- if you don't feel slopppyness then you still *might* have a problem.  If there is other evidence then pull the jug. Otherwise, go ride.


Quote from: evo550 on August 12, 2013, 06:47:29 AM
Do you mean, crank bearings or conrod bearing?
The only way to correctly determine wear is to check the specs and measure with correct instruments as per manual.
Title: What are the symptoms of the big end bearing worn?
Post by: JaredRM250 on August 15, 2013, 12:11:05 PM
Quote from: citabjockey on August 15, 2013, 07:18:43 AM
Mostly for con rod but really shot crank bearing could introduce rotational slop -- but will also allow the crank to wobble a bit.

Bottom line here with this check -

- if you feel sloppyness then you have a problem. You need to tear it down. End of story.
- if you don't feel slopppyness then you still *might* have a problem.  If there is other evidence then pull the jug. Otherwise, go ride.


Quote from: evo550 on August 12, 2013, 06:47:29 AM
Do you mean, crank bearings or conrod bearing?
The only way to correctly determine wear is to check the specs and measure with correct instruments as per manual.

Ride is on the menu! thanks for your help guys
Title: What are the symptoms of the big end bearing worn?
Post by: SachsGS on August 15, 2013, 03:36:06 PM
If your conrod bigend bearing is worn you'll hear it "rapping" when the bike is running. Worn crank bearings have a "gravelly" sound. ;D
Title: What are the symptoms of the big end bearing worn?
Post by: JaredRM250 on August 16, 2013, 11:23:55 AM
Roll on ride time then!
Title: What are the symptoms of the big end bearing worn?
Post by: rm250guy on September 03, 2013, 12:23:33 PM
No doubt RM's make quite a bit of engine noise compared to some of the other 250's.  I have been hearing it for years....

Sounds like you may have a clutch issue and not a low end issue.  You can get the clutch to quiet down a bit by replacing the main clutch bearing (bearing, primary driven) and spacer.

I hope this helps.