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any idea why the kx250f valvetrain is so loud?

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i never realized how loud the valvetrain on my kx250f is till i bought a 2012 crf250r recently and realized how silent it was.

 

i have owned years 2005, 2008, 2009, 2010, and 2013 kx250f and they all had the same valvetrain noise. im not saying anything is mechanically wrong, but its really loud! and especially with steel valves. im wondering if anybody can supply an answer as to why the valvetrain is so noisy and if theres a way to quiet it down a bit? i notice on my 2013 that if i look down at the tank while on the gas, i can hear valvetrain like CRAZY, and at idle, my CRF has a silent valvetrain, where my KX at idle is still much louder.

 

specs on my 2013:

13.8:1 piston

pro circuit valves

pro circuit cams

pro circuit valve spring kit (with Ti retainers)

pro circuit porting

pro circuit ti-5 exhaust

oem timing chain

oem timing chain tensioner

oem timing chain sliders

 

i am not saying my valvetrain shouldnt be a little noisy. i realize aftermarket camshafts will produce some extra noise at basically every RPM. but its weird to me as to how quiet the honda is. i understand the honda is a unicam with a rocker but i still believe the kawi is louder than similar bikes like yamaha. any ideas?

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I never noticed on my 2011 KX250F. Maybe it vibrates at a frequency that your ears are sensitive too. The CRF must be making sound, because it is mechanical parts moving over one another. If you can, record both. We can then run them through an FFT which will tell us what the predominate frequencies are. You can also download software for your phone to measure relative dB to see if the CRF is actually quieter or if that is only your perception.

 

In the end, does it matter? The KX valve train is pretty robust and the motors make loads of useful hp.

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im not sure i'd dig this deep into it but could be a fun project. you made some valid points about frequencies and such. however the CRF does make sound. but its VERY VERY quiet. its hard for me to believe how quiet it is. i am beginning to think the KX head may use a thinner wall thickness in the timing chain area, and that the cam over bucket design is simply louder than the hondas unicam design. on a side note, my valve lash is set at .004 on both intake and exhaust. this is what pro circuit says to run with their modded heads. i would have thought the tighter tolerance would be quieter. but maybe not? im thinking about testing the dB trick just to have fun and see how it comes out.

 

Edited by imfasterthanyou

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Our 2012 kx250f made so much noise I thought something was wrong with it...I had just bought it so ended up taking it back to the dealer and basically told them something is wrong with it....they pulled it all apart and checked everything to find that everything was ok....we put plenty of hours on it after that with zero problems. I was told that kawi runs their wrist pin off center of the piston and that is what causes alot of the noise? Hmmm, I can't comment whether it's true or not but as you mention their motors are very noisy! They sure do run good though! Ha!

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wrist pins on center will make a lot of piston slap noise untill the piston has expanded from the engine warming up, then there is little to no piston slap. however the sound im talking about is all in the head! damn things are loud.

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Never noticed the valve train noise myself on our 07, 09, 11, and 12....we've also had 05, 09, 13 and 15 crf250 and they are definitely much quieter....after installing an rhc cam in the 13 the valve train noise was definitely apparent.

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did some dB testing today via the phone app. its really not a good app and i believe its because were trying to measure dB with an iphone speaker with no high quality and precision measurement capabilities. anyways i started the bikes, put my hand over the exhaust and held the phone near the head. this way it didnt measure exhaust note. 

 

CRF max: 60

CRF peak: 51

 

KXF max: 93

KXF peak: 52

 

its obvious that even with low quality dB measurement, that theres is a difference. however, i cant say how much as i dont think the difference SHOULD be that substantial. that would be a 33dB difference. i feel like i may have gotten one piece of exhaust note in there. or some type of ambient sound from somewhere else. we have numbers here, but they are not very reliable in my opinion. also, im beginning to think the KXF strikes a different frequency like stated above, versus the CRF. i came to this conclusion after taking video of the KXF head and the CRF head. listening to them back to make, there is a difference in sound and frequency. however the sound is not all that noticeable on the video. but to my ears, it is. 

 

in the past i ran the lucal oil-oil stabilizer. on the bottle it says it lowers engine noise and whatnot, it was on sale, figured why not. i ran this test on my 09. it did lower the sound a small bit but this is obviously due to the viscosity of that oil being in the 80W range. in my bike currently is 20-50w.

 

on a side note, the cams i am using now are around a .365 lift, the cams i have being custom made right now are in the .380 range. so regardless, i wont be able to get this sound to get any better. but i figure this would be something nice we can work on.

Edited by imfasterthanyou

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well ya got a extra came over the CRF. Ive never noticed my self and ive owed 4 of em.  I usually cant hear anything but drive chain slap.  hahaha

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I have a crf currently and had a 2012 KX and the CRF is quieter, I think its because of the unicam as rockers are not going to make the noise a cam makes.  

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I have a 2011 and its a little noisy as well at idle. It almost sounds like a knock or low squish clearance but I've been told it's completely normal for kawasakis. I'm not losing any power, not getting any smoke and the noise has been the same since the day I bought it. I'm not too worried about it at all anymore but I am coming due for a top end pretty soon so I guess we'll see.

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The KXF valve train is not only loud but it's the biggest and most important weak link to fix with the bike.   We have a half dozen of these for the race season last year and became very familiar with the bike.  Each of our bikes had a louder valve train than the YZFs we are on this year.   Each motor builder said to replace the entire valve train prior to riding.  So it's a known weak point.  

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Replacing the entire valve train prior to riding seems a bit excessive, not to mention ridiculously expensive. You're the first person I've ever heard say that and I'm at the track and shops pretty regularly. I'm not saying it's bogus information, but the average Joe isn't going to need to go through all of that. Kawasakis are notoriously louder (street, dirt, ATV etc...) than other bikes to begin with, but it doesn't mean you're going to detonate your bike. I have had multiple zx6rs, kxs, and kxfs with no "major" valve train issues. Hell, no issues whatsoever as a matter of fact aside from the occasional valve shims.

Edited by 40acres
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Replacing the entire valve train prior to riding seems a bit excessive, not to mention ridiculously expensive. You're the first person I've ever heard say that and I'm at the track and shops pretty regularly. I'm not saying it's bogus information, but the average Joe isn't going to need to go through all of that. Kawasakis are notoriously louder (street, dirt, ATV etc...) than other bikes to begin with, but it doesn't mean you're going to detonate your bike. I have had multiple zx6rs, kxs, and kxfs with no "major" valve train issues. Hell, no issues whatsoever as a matter of fact aside from the occasional valve shims.

 

 

i can second that. i just cant believe somebody would say to replace the entire kxf valvetrain prior to riding. ive owned four kx250f's of various years from their first year to 2013. never have i suffered a valvetrain failure aside from a valve guide breaking a small piece which still never bent a velve, hurt the piston, or the head at all. it was a really weird freak accident. my head currently is fully modded by pro circuit. but still using OEM valves. i asked pro circuit to use the OEM valves because they're an astronomical amount less than their del west counterpart. and with little to no real life performance gain out of it. as far as im concerned the stem is the same size, it uses the same keepers, the valve face is the same size, and the taper and blend coming from stem to face is damn near identical. both are titanium and the stockers will keep me from buying race fuel as i use a pro circuit piston at stock compression. and that persons remarks on the valvetrain is also the first time i've ever heard such a thing. but people have opinions and they favor the bikes they like too. 

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