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Knocking Sound - YZ250

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Hi guys

Hoping you can help me out. I have a YZ250 2stroke 08 model.

I was riding the other day when I lost power & heard an electrical fast paced ticking type of noise. Bike stalled as I pulled the clutch in. It wouldn't start after that.

After taking it home I managed to get it started, but there's a loud knocking noise coming from the engine. The bike stalls almost instantly after starting.

Do you think this could be electrical related? Or is this wishful thinking. Had a new top-end installed around 30hours ago, with the cylinder re nicasil'd. That wasn't cheap! Really hoping it's not gonna be a big fix.

Any help is appreciated!

Thanks

Kyle

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Tis the price you pay for doing unnecessary rebuilds.  Before the rebuild, the bike was probably running perfectly fine and not even due for one I bet.

Edited by Honda_Power

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Hahaha, not quite. Piston was cracked.

Thanks for all the replies!

Damn, if your doing the wrenching it won't be to costly to repair.

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Tis the price you pay for doing unnecessary rebuilds.  Before the rebuild, the bike was probably running perfectly fine and not even due for one I bet.

:lame:

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What brand piston was installed? I've been having issues with Wiseco pistons lately in my personal shop rebuilds. I only use pro-x (basically oem) in my bikes with great results.

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What brand piston was installed? I've been having issues with Wiseco pistons lately in my personal shop rebuilds. I only use pro-x (basically oem) in my bikes with great results.

I'm not sure. Took it to a authorized Yamaha dealer though. Does everyone think it's most likely top-end related?

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Check and make sure your woodruff key didn't shear. It's the half moon pin holding the flywheel in position on the stator side crank shaft. Also, Take off your pipe and shine light into your exhaust port and inspect the piston. You will have to use the kickstarter to slowly position it into your view.

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Tis the price you pay for doing unnecessary rebuilds.  Before the rebuild, the bike was probably running perfectly fine and not even due for one I bet.

 

Dude, shut the eff up. You aren't even amusing anymore, now you've simply moved into the realm of annoyance.

 

Dont start it again, may cause a lot more damage. Pull head off and look.

 

Emphatically this. Knocking sounds mean something broke.

 

The bike has no head.

 I assure you it has a head. It's even removable... :lol:

Edited by Chokey
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Hahaha, not quite. Piston was cracked.

Thanks for all the replies!

 

 

How many hours on it? What was the clearance when it was installed? How many hours on the cylinder?

 

Cast pistons crack when they get too loose in the bore and start to slap. You need to have the cylinder measured, it may be time for a re-plate.

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My last yz250 gernaded too with about the same hours with excellent maintenance. Had new OE cylinder and piston. I thought it should have lasted longer.

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Tis the price you pay for doing unnecessary rebuilds. Before the rebuild, the bike was probably running perfectly fine and not even due for one I bet.

How low of an IQ do you have? Please, go get an OEM cast piston and throw it on a worn crank rod that works "fine". I promise everything will be okay, using your logic. Really, stfu, please.
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