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Old 09-14-2016, 07:02 AM
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Default Strange ticking sound from newly rebuilt 2002 YZ250F

     

Hopefully someone here can help solve this strange tick. My son bought a used non-running 2002 YZ250F. After disassembly, we determined that the engine was a 2003 model. No difference really other than it has auto-decompression, nice!

We replaced the cylinder and piston with a standard sized Cylinder Works kit and inspected the crank and bottom end, which turned out to be fine. We didn't replace the cam chain as it appeared undamaged. We also cleaned and rebuilt the carb which had 2 year old gas still sitting in it.

So, now to the point...we got the timing set and checked the valves. The previous owner had installed KibbleWhite valves and springs. Four out of 5 seemed to be set too tight compared to the spec so we adjusted them, 0.17-0.22 for exhaust and 0.10-0.15 for the intake. Once rebuilt she started up on the first kick and sounded great. Now, after running for about 30 minutes the bike has developed a strange tick. You can really hear it with the seat removed and it's much louder at the air box. It also takes more kicks to start now. We haven't checked the valves again, could that be it? I've included a video link below so you can hear it. Any help is greatly appreciated, thanks!!

youtu.be/0bFYR5itm2E
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Old 09-14-2016, 08:23 AM
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That sounds completely normal to me, the YZF engines have always made a lot of noise. If you have an aluminum skid plate on the bike it will magnify the noise to an extent as well. The sound you are hearing with the seat removed is just the intake sucking air like it's supposed to do. Go fire up a newer YZF with the air filter where the gas cap traditionally is and you can hear it plain as day. I also heard the same sound on my KX 450F when running it with no airbox and just a pod filter for snowbike use.
That said, even if the cam chain looks good it may be stretched beyond the service limit. Do you really want to risk a $2k plus engine rebuild on a $20 part? I'd definitely replace the cam chain as cheap insurance. Also make sure the tensioner is doing it's job.
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Old 09-14-2016, 09:28 AM
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You may want to go back and replace the cam chain. They wear out and will have no signs of wear as they stretch.
Yes recheck your valve clearances.
Are the valve clearances posted in thousands of an inch or mm?

Paw Paw
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Old 09-17-2016, 11:58 AM
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Thanks for the info! We are going to check the valves again and then replace the cam chain today or tomorrow, depending on our schedule. Once that's done and it's back together we will also check that the oil pump is working. Hopefully she will be running soon!
Thanks again!!
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Old 09-18-2016, 05:22 PM
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Check intake valves.
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Old 09-18-2016, 06:47 PM
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Well, we got the new cam chain on last night and checked the valve clearances and the timing. After putting it all back together it fired right up. It sounded great! There was no ticking and she ran great when we took her out to the trails today. We did notice that the old cam chain has a spot that didn't bend well, almost like it was crimped a bit in that section. Not sure if that was the problem, but glad we got it fixed.

Thank you for all the help, everyone, we greatly appreciate it!!
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