Avoid used YZFs that have had their valves adjusted???


8 replies to this topic
  • x2468

Posted July 22, 2010 - 09:08 PM

#1

Well im back in the hunt for a new dirt steed and the yz450f 06+ is still at the top of my list as far as what i want. Last time that happened was summer 08 and i did tons of research, but i ended up getting a nice yz250.

Anyway, I remember most of the questions I asked then and their answers. One thing I don't quite remember is the question that i just possed in the subject. I remember someone telling me (i think it was Grey but not sure) that once the valves have required adjusting, the likelyhood that they will continue to go down hill from there is high. eventually leading to the need for a new valve train and head. Or maybe it's only the case if the valve seats have worn not the valves?? I don't remember....

Either way, should i avoid 06+ Yz450fs that have had their valves adjusted already???

  • matt4x4

Posted July 23, 2010 - 05:23 AM

#2

Any bike that was ridden will need to have it's valves adjusted, period. No getting around that. Buy brand new if you want to get one that hasn't had it's valves adjusted.
Once the shims get to the smaller end of allowable spec, you are looking at new valves and having the seats rescut, nothing wrong with that, normal maintenance.
You will only need a new head if the bike has a catastorphic valve/cam/engine failure which can happen on any bike or if the bike is/was not properly maintained.

  • grayracer513

Posted July 23, 2010 - 07:51 AM

#3

Either way, should i avoid 06+ Yz450fs that have had their valves adjusted already???


Depends on how much adjustment was required. Any more than one shim size smaller is a pretty sure sign the valve needs replacing.

We have two '06's here, both over 100 hours, neither of them needs its first reshim yet. OTOH, just because it's never been adjusted is no sign it doesn't need it. A bike that hasn't had its valve clearance checked regularly is just as suspect.

  • myoung

Posted July 24, 2010 - 09:31 AM

#4

Any bike that was ridden will need to have it's valves adjusted, period. No getting around that. Buy brand new if you want to get one that hasn't had it's valves adjusted.
Once the shims get to the smaller end of allowable spec, you are looking at new valves and having the seats rescut, nothing wrong with that, normal maintenance.
You will only need a new head if the bike has a catastorphic valve/cam/engine failure which can happen on any bike or if the bike is/was not properly maintained.


I don't know, my '09 was set at the tight end of clearance by Yamaha leaving no room for wear. They were within spec, but I went ahead and adjusted them to give a little room. I've already been told I didn't need to mess with them if they were within spec, but it made me feel more comfortable. I'm only at 45 hours now, but everything is still where I left it. :smirk:

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  • yzfrider1

Posted July 24, 2010 - 10:20 AM

#5

Once the coating wears off the valve, it will start to mushroom. It's at that point you want to start thinking about replacement. The higher the rpm, the more likely the valve has worn off the coating. The only way to know is to inspect the valve. Is it reasonable to do that when looking at a bike, not really. If your going to buy a used 4 stroke, this is a risk you take, no matter how clean the bike is.

  • x2468

Posted July 24, 2010 - 08:31 PM

#6

Once the coating wears off the valve, it will start to mushroom. It's at that point you want to start thinking about replacement. The higher the rpm, the more likely the valve has worn off the coating. The only way to know is to inspect the valve. Is it reasonable to do that when looking at a bike, not really. If your going to buy a used 4 stroke, this is a risk you take, no matter how clean the bike is.


at what point does that likely happen? the coating wearing off the valves that is

  • yzfrider1

Posted July 24, 2010 - 09:11 PM

#7

at what point does that likely happen? the coating wearing off the valves that is



Depends. Several factores.

  • grayracer513

Posted July 25, 2010 - 07:36 AM

#8

at what point does that likely happen? the coating wearing off the valves that is

Valve life in a YZ450 is very good under normal circumstances. I had an '03 that never did need the first valve adjustment in the whole 300+ hours (over 4 years) I owned it. A race bike, running at higher revs more of the time, will not last as long as one ridden primarily for recreation (unless you're a goon or something).

What wears the valve is the accumulated total number of times it closes against the seat. Valves are not affected by the load placed on the engine, or by anything other than just closing down on the seat. Closing at a higher rate of speed accelerates the wear, so high rpm operation both speeds up the wear rate and increases the number of closings the valve experiences. Even so, Yamaha usually has outstanding valve life. Dirt is also a factor. If it looks as if the air filter is poorly serviced or in bad condition, that would be a reason to avoid buying the bike.

The trouble with the coating is that it is so thin that there is no real indication that it is wearing until it's worn out. The giveaway is when the valve clearance won't stay set for more than 10 hours, or when it needs a shim two sizes smaller than it came with to start. If you set the clearance, then check it again 5-10 hours later and find that it has gotten tighter, the valve is bad. If it stays where you set it, the wear was more likely the seat than the valve face, and you should be OK for a while longer.

  • almostinvincible119

Posted July 25, 2010 - 08:29 PM

#9

Had an 06, 200 hours, valves adjusted 3 times and I had a modded head and high comp piston. Its all about how you ride it IMO





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