Engine Rattle

phranticness · Feb 3, 2006

K gotta question for ya fella's. I just rebuilt the top end on my 99' kx 125, It runs great, I went through a full day of break in. I noticed last weekend, after the previous day of break in, an odd rattle from the moter. Under moderate load, Slightly after the powerband begins to kick in(probably when the exhaust valve opens) a ting type noise, almost like pinging but it only lasts for a second or so. when I had the top end apart I noticed the exhaust valve seems to have a little excessive clearance. The noise could be ratttle from the pipe springs, I'm just not sure. I read that 98' kx's had a problem with the power valve hitting the piston but that was resolved in 99'. This noise sounds very simular to pinging, but does'nt have the duration of spark Knock. Any thoughts? I appreciate any imput.................................happy trails

kwiktsi · Feb 3, 2006

Having never experienced your exact issue myself on a 2 stroke, I cannot say for certian- but from my years of tuning cars and such, I know that knock can occur once it hits it's highest load and then go away immediately after. It does not necessarily keep knocking- once the high load is off, it may settle down. Could be what is happening to you. I know with turbo cars and such, depending on tune, they can knock the instant boost hits due to the increased load (and pressure, but we are talking about loads here, not cyl. pressure :) ), but once you get over that "hump", it will stop.

could be that right when it hits powerband, it is pinging due to the instant heavy load and then when it starts rolling a bit faster, the load is lessened and it stops. I hope I explained this right :).
Joe

MOTOX888 · Feb 3, 2006

what octane fuel are you running?.........maybe try a higher octane
you should always use premuim pump fuel or higher on a two stroke

phranticness · Feb 3, 2006

thank you for the imputs, I run 92 octane, I don't believe it's pinging, It's just a noise thats of around the same frequency. I will try a can of octane boost to rule that out. I really don't think it's pinging though. The noise was not present before the top end overhaul, and I have cleaned the power valve and its ports, makeing clearences larger, thats why I suspect the valve. I feel it might be the power valve clanging. It's kinna a metal to metal ting, but not consant enought to be any part of the rotateing mass. any 99' or newer kx owners (KIPS valve system) experience this noise or any problems with power valve noise? again, thanks for all the imput

MOTOX888 · Feb 3, 2006

STAY AWAY FROM OCTANE BOOSTERS!!!!!!!!!
THEYRE A JOKE........THEY WILL DO MORE HARM THAN GOOD!!
maybe the powervalve parts are worn beyond the limit......did u measure the clearances? the last thing that you need to happen is for the powervalve to catch on the piston.......ouch

phranticness · Feb 4, 2006

honestly I did not measure the powervalve componants. I installed them in the cylinder and moved them manually, they work freely. I read the spec on clearance with the piston, darn if I can remember what it was now, but I know that visually it had more clearance between the end of the valve and the piston than spec.It was at least .050. But the valve did kinna fit loose in it's bore. K I went riding after work again yesterday. I have to note that this noise is not getting louder or more pronounced, or happoning any more often. I also noticed that I can make it under decel compression braking. Again this is only intermittantly happoning.

wornknobby · Feb 5, 2006

does it go away if you pull the clutch in?

does it do it while in neatrua?

snb73 · Feb 6, 2006

phranticness,

I bought an 03 a few years ago and had the same problem. During the test ride the bike had noticable vibration. I did some reading and most riders said the KX vibrates alot. When I got the bike home and took everything apart for a good cleaning and to lube all bearings. I found all of the engine mounts were loose. The head mount (cylinder head to frame) was loose and one side was cracked. These are hidden by the gas tank.

Check all your engine mount bolts for proper torque. Don't forget the swingarm blot and the head stays.

Hope this helps, Steve.

phranticness · Feb 6, 2006

Hmmmm, good thought. I haven't tried either of those things. I went riding up in the Mendocino national forrest yesterday, did'nt get any worse. That suggestion brings up a thought though. My clutch hub fingers were notched bad. I filed the notches smooth to get rid of it hanging up. mabey the excessive play from the disc tabs to the hub fingers is the rattle? I'll check the bolt torque on the moter mounts as well. At this point I'm not gonna sweat it unless it gets more pronounced, and I'll keep this thread updated. thanks for all the imput.

mikej43 · Mar 28, 2006

Ping type noise

One time I was jetting a used bike after a pipe mod. Had a "Ping Like Noise" but not true ping noise. It was present only at the end of 3rd and 4th gear. Tried making the usaual needle,piolet,main jet changes. Even tried working with the choke to figure it out. No luck.

It turned out to be the Pipe Guard. The flanges on the pipe guard would vibrate against the pipe at high revs only. Any one have a two stroke .WAV file of a bike pinging. A sampe noise at that time might have pointed me away from trying to fix a Non-True pinging noise.

What I am trying to same is hinted at in your discussion. May be the ping like noise, isn't cylinder pinging at all.

Hope it helps.

mj

thing2_and_thing1 · Mar 28, 2006

I noticed a bad rattle on my KX250 not too long ago and thought...Damn :ohmy: ! I got off the bike a rapped the throttle a few times while kneeling beside and found it to be the exhaust where it enters the head. I could tell for sure by pulling back on the pipe (WITH A GLOVE) a hit the throttle and no noise. A new gasket and springs and it is all good.

mczehr · Mar 29, 2006

I am expiriencing the same problem with my 03 kx 125. I rebuilt top and bottom this winter and have the same noise. I dont think it is a pinging sound. This was present before the rebuild and at the time I thought it was the crank because of the vibration that was also present. Now it is getting worse and the vibration is bad. I didnt torque the motor mounts to spec could this be the problem? I am going to check them today but I know there tight but perhaps to tight. Any help would be great. I think we all have a similar problem. Please post any success that you have.

robwbright · Mar 29, 2006

My RM has had a rattle/ping sound that I think is similar to what you're talking about. It's had it both before and after I had it overbored.

I think it's just noisy, and I've seen other posts here about other RM125 owners having the same.

In your case it could be nothing or it could be something. ;)

I'd let someone more experienced have a listen.

phranticness · Mar 29, 2006

No worrys

Well, It's been a month or two and the noise has got no worse, I'm convinced it's pipe rattle, I just thought I'd update.

I got a new growl though, but thats for a different thread.

thanks for all the imput fella's

promuppetmower · Mar 30, 2006

my bike has been doing that since i bought it in like neutral it sounds like something is in the exhaust pipe just ratteling around.

250twostroke · Jun 18, 2007

i think the power valves could have a little extra clearence...but because they are getting more oil on them as you ride it more it is just getting quiter (closing the clearence) my rm 125 is making the same damn noise and it is driving me crazy..i will probably be changing out my power valves

Engine Rattle

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