WR/YZ 426F Weirdness...Help?

SFO

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Feb 16, 2001
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I just pulled my 01wr426 apart to send Eric my cylinder for the O.S. bore connection.
Surprise, surprise when I got the head off.
The center intake valve has been clipping the edge of the piston cutout leaving a shiny rolled corner on the piston...
The small end of the rod is also starting to gall.
The piston pin is definetly toasted.

The book says .016-.039" freeplay at this junction.
This appears to be a misprint.
I would personally set it up at .0015-.002"...It is at .0015"...This is actual mesured clearance, the manual is a bit ambiguous here. It doesn't call out how they are applying their dimensioning to reality.
I hate designers...Just give me a drawing I will make it.
Has anyone seen these things on a stock bike?
Any insight would be considered.
 
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SFO

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Oh where oh where
Has my Rich Rohrich gone...
Oh where oh where can he be?

Yo man, the natives are at the gates!
 

Rich Rohrich

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First decent riding day in three weeks. PRIORITIES :)

This is pretty weird. The early versions of these engines had a TON of piston to valve clearance so it seems pretty odd. The center intake is about .050 shorter than the other valves in the steel valve engines. As silly as it probably sounds the first thing I thought of when I read this was, I WONDER what would happen if a long valve was used in the center intake. I KNOW, it sounds stupid :) Let me think about this one for a bit. Maybe there is something obvious that I'm missing post-ride :eek:
 

Shaw520

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Rich,... are saying that after a full day of roostin, that your brain is not quite functioning @ 100%,......:D......Its hard to lead the pack all day,..and then produce the marbles to sort out all these situations! :cool:
 

Rich Rohrich

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It's takes even more mental energy to NOT crash into every tree lining a motocross course. Today being a perfect example :)
 

will pattison

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what if his valve guide was worn, or the keepers, or the notches that the keepers engage? seems to me like that valve is gonna have to come out for an inspection so solve the mystery.

or...if the small end of the rod is going, could it be that the piston is flopping enough to strike the valve?

which came first, the chicken....

by the way, sfo, as much as i understand your ire with "designers", keep in mind that the people responsible for your frustration with the manual are a.) technical writers, b.) illustrators and c.) japanese. :silly:
 

SFO

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I wouldn't say that the small end was wasted, it is showing signs of galling.
The wrist pin took the brunt of the ugliness and is exhibiting a torn up surface finish.
The squish I measured before pulling the cylinder off was .030"-.055" below the deck of the cylinder without a gasket.
The edge of the cutout for the center valve was shiny, not the base of it.
I have run some tight set-ups before that left this area with a circle in the carbon.
When I put the larger piston in you know I am going to clay it.
It seems like the piston needed a larger diameter relief pocketon the center valve.
Is there a history with small end issues in this motor?
I will be charting the head at Kibblewhite this wk, I will report on the state of the guides and keeper grooves.
Rich, you should be getting my cams this week for the Ti comparison.
I guess I feel a little ruffled when I take my new bike apart and find issues.
Thanks for the time, Bill.
 

Rich Rohrich

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Originally posted by SFO
I wouldn't say that the small end was wasted, it is showing signs of galling.
The wrist pin took the brunt of the ugliness and is exhibiting a torn up surface finish.
The squish I measured before pulling the cylinder off was .030"-.055" below the deck of the cylinder without a gasket.

That's seems like the normal production clearance on WRs. The head gasket compresses to about .035" + - .001" . I've seen WR's average .060"-.080" total squish with YZs coming in about .010" less . The WRs used to come with a base gasket that was about .010" thicker, but I haven't checked the part numbers on the new ones.

Originally posted by SFO
Is there a history with small end issues in this motor?
I will be charting the head at Kibblewhite this wk, I will report on the state of the guides and keeper grooves.

It certainly hasn't been widespread if there is. Will has put some seriously high race miles on his YZFs with good results save for one crank issue. The stuff I've seen and the e-mails I get points to the crank/rod being pretty stout as long as good quality clean oil runs through the engine.

As soon as I get the cams I'll make a new more accurate fixture and I'll post the Cam Doctor numbers. It should prove ionteresting.
 

Jonny426

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WR wierdness

SFO, I was at the local bike emporium buying an oil filter for my ride today.I happened to overhear a friend of the owner ask if he'd seen any top end problems on the WR250. The owner said "no but I've heard of a few,on the 250 and 426." Yamaha it seems wants to blame any internal failures on lack of maintainence,but apparently they are standing behind their product unless it has definately been abused. You may want to pursue warrantee action thru your dealer. Jonny 426
 

SFO

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Feb 16, 2001
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Too funny...
I purchased an extended 2 year warranty as well.
It sounded just fine before I pulled it apart for the big bore kit.
I think might have a difficult time convincing Yamaha or my warranty company that I took my bike apart and found some problems,
but it sounds just fine!
I could put it back together and tell the tech, or bet him, that it has a bad rod.
I have been through this stuff before with Yamaha and Suzuki.
Thats why I bought the extended warranty.
Heck, I guess I will give them a call.
 

SFO

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Feb 16, 2001
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So Rich, what is the target squish on this bike?
I remember setting up my GS-1100 dragbikes at .040" and tz-250's at .035".
I was thinking about the standard compression piston, because I still want to run pump fuel.
Does the 13.5-1 require rocket fuel?
 

JEFF SAND

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May 24, 2001
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Rich,

You sleeping?
Cae Paeso Amiego, Muchacho


Squish?

I know, you know...
Short turn?



Seat preasure?


Ya gots me cammage, give me a set up and lets be right...???!!!



SFHO
 

Rich Rohrich

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Originally posted by SFO
So Rich, what is the target squish on this bike?
I remember setting up my GS-1100 dragbikes at .040" and tz-250's at .035".
I was thinking about the standard compression piston, because I still want to run pump fuel.
Does the 13.5-1 require rocket fuel?

I was happiest with my 420 (94mm bore) at .037" squish. At 800ft elevation and ~13.6:1 mine would run without knocking on pump fuel (93 octane MTBE Amoco) plus 2.5 ounces/gallon (about 1%) of C12 , or some equivalent octane booster. I only ran it that way for a short while because ALL YZFs and WRs run much better with proper race fuel run at 100% .

The complete 97mm Wiseco assembly weighs a total of 397 grams, which is 48 grams more than the 94mm assembly and 54 grams more than the OEM 92mm assembly so I'll be starting off at .045" squish with the 97mm to allow for any additional rod stretch that may occur, with the intention of dropping it below .040" if it looks to be safe. I don't know what the OEM 95mm assembly weighs so I might be acting overly cautious in this case.
 
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