07 YZ125 flywheel free play

Hi all,

This is my first post here so hopefully I can get some good advice!

I've recently picked up an 07 yz125 as a bit of fun and I've had a feel of the flywheel just as a rough guide to the condition of my bottom end and there is no up and down or side to side movement, but wen I rotate the flywheel back and forth quickly there is quite a loud rattle. I'm wondering if this is normal or whether my rod could have quite a lot of free play on the crankshaft. Any advice would be greatly appreciated! I havnt had a great deal of 2 stroke experience but the bike has done under 40 easy hours and has had the top end freshened once and as far as I can tell is still running pretty good!



There are a couple of possibilities.  First, you say it runs fine now.  If the rod is loose enough to rattle when you rotate the crank back and forth, it would make a horrible racket when running.  If it runs without excessive racket, it is unlikely your rod is this loose. You can pull the cylinder to check the rod.  It shouldn't have ANY vertical play, but some side to side is okay. But I would look at other possibilities first.  One possibility is that some crank roller bearings use a plastic cage, and the cage can break down and allow the rollers to move around some.  When you rotate the crank, as each roller goes "over the top", it can drop down onto the adjacent roller and you will hear a "click" sound.  You will hear this each time another roller goes over the top.  Another possibility is any "lash" between the crank primary gear and the clutch hub, or any other clutch issues such as loose clutch hub dampers or loose clutch basket bearings.   


A bike with under 40 hours shouldn't have a worn out rod or crank or clutch bearings, unless it was  run without oil or had a bunch of dirt run through it.   


Good Luck

Thanks Bill that sounds like some great advice.. When I get some time Ill pull the head of and have a quick look at things. The bike has had some dust through it is the previous owner was a bit lax on airfilter maintenance and after I bought the bike I found dirt in the airboot. Like you say though the bike still sounds pretty good to me and still goes well, no clutch slip either. Would rotating the flywheel make any noise or is it usually smooth and quiet to rotate. I'm not talking full rotations just little sharp short ones back and forward. Hopefully I'm just being paranoid haha.

Many thanks!

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