Valves closed down on 250F

[MWEISSEN]

My son's 2001 YZ250F suddenly came down with a case of no start. After cleaning the carb and trying again tonight, no go. The bike give a few revs of ignition, but not much more until it finally floods out completely. Normally it's a 2-3 kick starter.

We then checked the valve clearance. In March all was OK, now the center intake clearance is at less then .05mm, the the two exhaust valves were tight. The major concern is the center intake valve. I can re-shim and bring it back in line, but why did it get so tight so quickly? This bike went for two years with no change in the valve clearance, even after a top end rebuild this winter (the March check - OK one was off because I initially didn't get the shim in right..)

Can the experts here help me with a root cause for the what appears to be sudden valve tightening? Thanks for your help!

 

[MWEISSEN]

Oh by the way, I understand that the lowered clearance typically caused by the valves pounding into the seat. My question is what would cause it to seemlingly accelerate?

 

[SFO]

What was replaced w/ your head rebuild?
Were the seats recut?

 

[MWEISSEN]

SFO, I just replaced the piston and rings. A leak-down test indicated the valves were fine, so I left them alone.

 

[MWEISSEN]

Uh, never mind....this head is going out for repair or replacement.

 

[DEANSFASTWAY]

The Ti valves are treated on the surface ,once that wears down the softerTi ismore susceptible to the pounding. They really dont like to be overheated either. We have alot of sand out here and woods and the Fs get really hot.

 

[MWEISSEN]

I will be purchasing a new head and valves. While doing so, should I stick with stock TI valves, or go to an aftermarket valve? Also, is the profile of the '03 exhaust cam the same as '01? I may have to buy a new cam as well, and this of course is an option (to go with auto-decompression.)

 

[DEANSFASTWAY]

MW are you sure you need a new head , Why? Definetly go with thew 03 cam .The bike will start by hand. Maybe Mike Perry or Rich can school you on the valves Ive always used just new Yam Ti Valves in the 250Fs for fear of dropping a valve on overrev. But The Ti valves are real expensive. DEAN

 

[MWEISSEN]

Yeah, I'm going with a new head. The cam bearing surface between the exhaust valved is all galled up. The aluminum has peaned over so bad that I can't get the valve buckets out and the oil passage is partially filled in. Why I don't know yet, but while I'm waiting for parts I'll be checking out the oil pump and passages.

Thanks for the advice on the valves!

 

[SFO]

These heads are repairable, the cam surface can be reclearanced.
This is a common problem, if you don't want to repair your head I would be interested in it.
The OEM yamaha ti valves are 70+$ each and KMPI can give you a better price I believe for a Tensilite Ti replacement valve.

 

[DEANSFASTWAY]

SFO want some 426 or DRZ ? send me a PM.

 

[Brewster]

That should be KPMI http://www.blackdiamondvalves.com/Default.htm

Brewster

The OEM yamaha ti valves are 70+$ each and KMPI can give you a better price I believe for a Tensilite Ti replacement valve. [/B][/QUOTE]

 

[MWEISSEN]

I'm looking for one more piece of advice please:

The exhaust cam has some heat bluing on the roller bearing outer race, and the surface between the valves is shiny from the head galling, but doesn't have any lines in it. Should I replace the cam?

 

[DEANSFASTWAY]

Yeah try an 03 model cam.Theyre cheap and the bearing comes with it.

 

[ACGUY]

Hey MW,

How much oil came out of this bike when you drained it? Any metal in the filter? Was it oil starved to cause the bluing and sudden wear? If so, you may want to check the crank too.

Bob

 

[MWEISSEN]

No, I checked the oil level when I drained it, and got the full amount. I'm 99% sure I put the cam cap back on incorrectly when I rebuilt it earlier in the year.

 

[Pathfinder4]

I ran two 2001 bikes for a year. One developed valve clearance problems quickly and we played with it for months. The other took a year before center valve got out.

They were stolen and we replaced them with 2002 and 2003.

You MUST put in 03 cam on your 01 - well worth it.

Good luck.