Any valve issuse withe the KX450F

[SADude]

I really like the look of the KX450F, I currently ride a kx250 largely because I have been scared of the valve issuse the 4-strokes have had.

Has anyone had valve problems with the KX450F and how does it handle technical trail riding??

 

[Britt Boyette]

You need to wait for the 07 model. It will be better suited for trail work as it will come with a 5 speed instead of the 4 speed 06 model. There has been a few issues with the early 06's but I don't think any were about valves. There was a faultly piston pin issue but I think that got resolved. The late 06's make for an awesome MX machine though! I also understand there will be a KDX450F in 07 which will be a great woods rocket.

 

[dirt bike dave]

I've ridden the '06 on some tight trails and taken its owner on some nasty trails. That motor is so impressive, I did not feel in need of a 5 speed.

The one I rode had the suspension done and was set up for MX, but I was very impressed with how it worked on the trail. The pegs seemed high to me, but I was able to hop on the bike and immediately go well on true single track.

I hear the dealers are making deals on left-over '06's. At the right price, I would take an '06 even if trails were all I ever rode. As for MX, the 450s have a huge motor advantage on any 250 two stroke. The KX450 is strong, that's for sure.

 

[Malden]

Your experience with the KX250F is the exception not the rule.

Rich, is this true for the 06 kx250f??? I have one and it has been absolutely flawless. I also know some local pros that have rode the wheels off of theirs and had no issues like the 05's. Im thinking of an 07 but dont want any problems. BTW there are a LOT of CRF 250's that i know have let go locally.
sorry if i im hijacking the original post

For what its worthI have no knowledge of kx450 valve problems in speaking with a half dozen owners when i was considering a 450.

 

[Rich Rohrich]

Rich, is this true for the 06 kx250f???

Yes. The '06 has the same valve recession problems as the previous years. Same goes for the '06 Suzuki and Honda 250Fs.

 

[Britt Boyette]

What can be done about these problems or any other valve related issues in the 250f?

 

[Rich Rohrich]

Stainless steel valves and high quality springs (like Kibblewhite) are one solution. High grade vapor deposit coated titanium valves (like Xceldyne) along with testing/changing the OEM valve springs every few hours is another approach. Either approach assumes valve seats that are cut concentric and to the proper width, something that RARELY happens at the Kawasaki or Suzuki factory , and has been a problem with the Honda 250Fs once in a while as well. I've never personally seen a brand new KXF/RMZ head come out of the box that didn't need the valves seats cut to make them right. I'm not the only one building cylinder heads who has complained about this.

Teaching young riders to not use the engine as a brake, and not mechanically driving the rpm past the rev limiter with the rear wheel helps a lot regardless of the parts inside the engine.

 

[Malden]

Ive often wondered if riding style contributed to premature wear of the valvetrain. Some guys are fast and seem to torture the motor and others are fast without the overrevving and popping. I tend to be easy on the motor which probably works in my favor. That and a rigorous maintenance schedule.
I witnessed a guy start a stone cold YZ250f a few months ago and proceed to hold it on the rev limiter like he was warming up a 125!!! It was a cold morning and it had a lean bog which he must have thought was a fouled plug....yikes!

Does anyone know if the mfg's have addressed the problems Rich mentioned for 07?? Is yamaha the only solid valvetrain from the factory????

 

[SADude]

Okay, so is the Yamaha the most reliable 450 motor? What would you say is the next best? Do the KTM's suffer similar problems?

 

[Rich Rohrich]

Okay, so is the Yamaha the most reliable 450 motor?

It has the most reliable valvetrain design

What would you say is the next best?

If you stay on top of the valvetrain the CRF450 has proven itself to be a very reliable engine.

Do the KTM's suffer similar problems?

The KTMs I've looked at suffered similar valve recession issues, and have a strong tendency to wear out the valve guides as well as breaking valve springs (spring issues mostly in SuperMoto). I tend not to deal with a lot of KTMs so I don't know if I'm seeing the exceptions or the rule, but based on a lot of feedback from a wide variety of sources, I'd say the KTM valvetrain is no more reliable than the Honda 450 or Suzuki 450. I have no experience with the new design 250 KTM.