rattle/buzzing noise

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rattle/buzzing noise

Postby jbowens2401 » 06:12 pm Oct 25 2010

So i got my wifes top end done on her kx100 friday night. i ran it thru two short heat cycles (the 1st until the cylinder was warm and the 2nd until the cylinder was a little warmer). i allowed 2 hours between the 1st and 2nd, then after the 2nd i let it cool overnight. the bike started great and sounded great thru both cycles (light blips of the throttle to vary rpm). the next morning, i let the bike warm up good and ran it pretty hard for about 20 minutes to seat the rings...it ran great! then, i parked the bike and let it cool down for a few hours. i took the pipe, tank, seat, ect off so i could retorque the head and cylinder nuts. also, i checked the compression and it was 155 (manual says between 120 and 180). the head nuts were still at 18 ftlb but the cylinder nuts had dropped to around 15 (retorqued to 18ftlb)? when my wife started the bike to ride it, we noticed a rattling/buzzing noise coming from the engine when the bike was revved and when riding above say 4,000 rpms. the bike still starts and runs great and has 155 psi on compression but i cant figure out what the damn noise is. sorry for the long post, but i wanted to give as much detail as possible. please, help me figure this out before i go crazy

thanks,

john
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Postby TWMOODY » 06:22 pm Oct 25 2010

I would check the exhaust springs to see if they are causing the noise.
Also by any chance do you have an aluminum skid plate on it ?
That can make the noise you describe, I have had that happen.
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Postby jbowens2401 » 07:32 pm Oct 25 2010

thanks for the feedback i just went out and took the skid plate off and held the pipe and springs with a glove while my wife started and lightly revved the bike. that damn noise is still there! any other ideas?
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Postby Griffbones » 07:40 pm Oct 25 2010

Yeah, pull the top end and inspect everything before you possibly make a bad situation worse. To me 150 PSI is certainly acceptable but not all that high for a new top end. Most of our KX100's normally ran around 160 -165.
I have had a piston completely destroyed yet still had good compression due to the fact that the damage all happened below the rings in the skirt of the piston.

If you are using a Wiseco piston, they need plenty of warm up time before revving them hard as the forged piston expands much faster than the water cooled cylinder. If adequate warm up time is not performed, cold seizures are very likely to happen.

Do your self a favor and pull the top end and just look, after all you are only out a $25 Moose top end gasket kit to check it and get some peace of mind.
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Postby Griffbones » 07:53 pm Oct 25 2010

Here are pics of a piston destroyed by the throttle being chopped at super high RPMs repeatedly with out pulling in the clutch. This starved the top end of lube at a time when it was at it's hottest and still spinning at very high RPM's
Image
Image

This engine still ran great believe it or not! The cylinder plating was damaged, but the bike still had good compression, but it did rattle horribly.

This is why you should take a look at your top end before it damages the cylinder like this piston did!

BTW this was on a 2007 KX100
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Postby jbowens2401 » 08:07 pm Oct 25 2010

wow! I think that pulling the head would be a great idea. I just pulled the exhaust and looked at the piston and it looked great. I've heard the exhaust side of the piston is where the damage will most likely occur first (especially in the case of overheating). The new top end has about 3 hours on it at this point.
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Postby jbowens2401 » 08:08 pm Oct 25 2010

what oil and ratio were you running?
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Postby Griffbones » 12:46 pm Oct 26 2010

This was not bad fuel or oil............Looong story!
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Postby jbowens2401 » 12:55 pm Oct 26 2010

okay so basically when you are coasting pull in the clutch and blip the throttle occasionally? is there anything in the powervalve system that could make this kind of noise...it was very clean so i didn't take it apart...i just disengaged the actualor arm to remove the cylinder. the main shaft seemed to move very smoothly.

thanks

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Postby KarlP » 01:02 pm Oct 26 2010

I had a similar experience on our KX100. Right after we got it the young son of one of my wifes friends took it for a blast up the street and siezed it.

The piston was not as bad as the one above but close.

I put a new piston and ring in and it was a bit noisy. I was concerned, but kept pushing it anyway. The noise has gone away or maybe I've gotten used to it.

NOT a recommendation.......just what happened.

I'm not sure I'd be in a big hurry to take it back apart.
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Postby jbowens2401 » 01:44 pm Oct 26 2010

thanks karlp, i'm really not wanting to take it back apart...i just want to know where the noise is coming from. i may take the seat, tank, and exhaust back off and reassemble to see if that helps because the noise started right after i took those items off to retorque the head and cylinder nuts. also, i may take the pipe off after each ride to look at the piston. do u know if there is anything in the powervalve system that could make this kind of noise...it was very clean so i didn't take it apart...i just disengaged the actualor arm to remove the cylinder. the main shaft seemed to move very smoothly. i wonder if these little guys have the kips rattle like our kdxs?
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Postby rbates9 » 05:25 pm Oct 26 2010

I just had the entire engine apart on my KDX and put a pile of parts in it. Started it up and it was making a buzzing noise. I checked every thing twice, then I had noticed that the right frame guard by the foot peg was bent in just enough to let the rear master cylinder vibrate on it. Bent the guard out and all was well. I would check every thing on the out side before I pulled the inside back apart.
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Postby Griffbones » 06:02 pm Oct 26 2010

It may or may not be the top end, but the top end is so easy and cheap to check. But yeah, check the pipe springs, exhaust pipe mountings, the upper engine mount (head stay) ect....... Did you by chance put a Wiseco piston in the cylinder to replace an OEM cast piston? It may simply be piston to cylinder clearance, did you measure it when you had it apart?

The power valves on the little KX's don't really make much noise, in fact they don't really do much period, pretty ineffective design really. In fact Pro Circuit makes a much better power valve for the KX 85's and 100's, one that actually effects the way the engine runs!

Yeah I had a son run that engine WFO as hard as it would go for 1/4 mile or more and then just chop the throttle closed, then run it as hard as it would go again and then chop the throttle closed, this happened repeatedly. That is when I got to explain some things to him about how a two stroke works. He was only about ten years old and did not know that he couldn't just let off the gas and coast from a high rate of speed like that.
No fuel or oil problem, strictly operator error, because dad had not explained this to him ahead of time.
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Postby Indawoods » 06:06 pm Oct 26 2010

That wouldn't have stopped me from getting MY ass whipped! :wink:
Just sayin...
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Postby Griffbones » 06:13 pm Oct 26 2010

>|<>QBB<
Indawoods wrote:That wouldn't have stopped me from getting MY ass whipped! :wink:
Just sayin...


He was just a little kid and had no idea. He was just havin' fun revin' her out and then letting off and coasting, so it was really my fault for not thinking to explain this to him before. Believe me he felt really bad, and this never happened again. Actually since he started riding at 7 years old (and is now almost 15 years old), I think this is about the only thing he has ever torn up. This kid is even easy on clutches! Again I take full responsibility for that one!
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Postby Indawoods » 06:20 pm Oct 26 2010

I know... we were brought up in medeval times anyway.... I feel for the kid.
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Postby Griffbones » 07:21 pm Oct 26 2010

>|<>QBB<
Indawoods wrote:I know... we were brought up in medeval times anyway.... I feel for the kid.


Ya got that right my friend. My dad would have whooped me too. :grin:
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Postby jbowens2401 » 08:03 pm Oct 26 2010

Griffbones, I did put a weisco kit back in along with a new wrist pin bearing and circlips. I took the cylinder to the local shop and had them check it with a bore gauge and they said it was still well within factory spec and they also said the plating was good. I really trust the guys there, so I think everything was okay. When you say warm up the engine properly, let me make sure I'm doing it right. I just start the bike and lightly blip the throttle until the cylinder is warmish hot to the touch. Is this correct? I'll recheck everything on the outside tomorrow afternoon and see if I can come up with anything. If not and I decide to pull the head and cylinder back apart would I need to go back with new rings?
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Postby Griffbones » 06:40 am Oct 27 2010

Yes, that sounds like you are doing a good job of warming it up. The rattle may not be the top end and it is hard to diagnose over the internet, so check every other possibility first.
But if you do have to go back into the top end it won't take long, and it is cheap to do. BTW if you see no damage in the top end, then there should be no problem re-using the rings with such low hours on them. You might want to pull the reed cage and look through the intake port too, as this can give a good look at the intake side of the skirt.
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Postby jbowens2401 » 09:24 am Oct 27 2010

thanks for the info, i will check the intake side of the piston this afternoon while im going through everything else. i'll report back what i find. thanks to everyone for their help.
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