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YZ250 Rattle

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So I have a 1996 YZ250 and Im thinking its about time for a rebuild, I dont know how many hours are on the bike in total but since ive had it ive put probably 20 hours or more on it. But it has this rattle to it and Im concerned that the connecting rod has free play where it connects to the crank shaft. Ive taken the stator cover off so I was able to have direct access to turning the crank, and when the piston goes to TDC and you turn the crank back and forth, it feels like something is knocking. Im taking the cylinder off this winter to see if a top end rebuild is needed, but either way something isnt right. Also ive been looking at trying to find new levers, and the master cylinder on the bike has an old design and I have not been able to find good levers that match the design. Im looking at getting ASV Breakaway levers but their design does not fit my bike. So im considering just getting a master cylinder off of a newer YZ and using it instead but my concern is will a newer master cylinder work with the old caliper?

 

Oh and heres a video of the bike, If you listen carefully then you can hear the rattle the whole time during the video. Skip to 2:42 to hear it clearly. 

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Sounds pretty normal to me. Or maybe im not hearing it. The older bikes can be pretty rattley sounding. I have 2 2002 250s.

Does the rattle change when the bike is cold vs hot?

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sounds like a bit of piston slap.

 

have a peek at the piston and cylinder through the exhaust port, also run a compression test.

 

might be nothing but the 2 above will give you an idea if its fine or time for a top end.

 

newer masters should work fine, just remember to record the year so you can get the proper rebuild kit when needed, or a new owner needs one.

Edited by Excitable

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Sounds pretty normal to me. Or maybe im not hearing it. The older bikes can be pretty rattley sounding. I have 2 2002 250s.

Does the rattle change when the bike is cold vs hot?

No the rattle stays the same volume if the bike is cold or hot. I will take a look at what youre talking about though. Compression seems fine though as its quite stiff to kick the bike over from anything but TDC. Maybe this is an issue?

Edited by TrailRider85

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For reference I took videos of 2 2002 YZ250s running.

 

This frst 1 is a completely rebuilt motor.  Most new bearings in the transmission and clutch and waterpump etc.  New crank, rod, and bearing.  About 40 some hours on this complete rebuild.  The top end is a 295 with about 10 hours on it.  The motor is literally brand new.  No expense spared.  You can here how rattly it sounds though.

 

http://www.youtube.com/watch?v=3t_RjYx5szA

 

This 2nd bike is a totally stock motor with (guessing) 50 hours on it.  I have owned it the last 20 hours of its life.  Motor never been cracked.  Still rattly.  It has a PC Works pipe (and stock bore) on it so sounds a tiny bit different when revved.

 

https://www.youtube.com/watch?v=vY6Xvw9GtH0

 

The rattly sound I thought I heard in your video is/was the same as my bikes.

 

A little back story.  After I rebuilt my motor I thought I was hearing a horrible rattle in it.  You know how you're always more in tune with noises after a big maintenance project.  Luckily I had the other bike to compare it to.  I also listened to a couple other YZs at the track.  All the same to me.

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Mhh yeah Ill make a note of that after my rebuild is finished, but good thing I took it apart anyway because there was certainly things that were wrong. Thanks for the help though 🙂

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Yeah I listed to your video again after I made mine. They're different noises. I can believe the piston on slap was making that noise. But not the crank bearings.

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