gbalias

How long are your cranks lasting?

21 posts in this topic

I only ask because im doing some work on my 08 450.

 

new piston, cylinder, valves, cam chain, tensioner....etc. (top end stuff)

 

its got 180hrs on it.  never had an issue but one of the mechanics said even that theres no play on the bottom end bearing, its gonna be ready to blow anytime around 200hrs.  I thought this to be strange.  maybe a way to get me have him rebuild it?  

 

my '98 400 had who-knows-how-many hours on it.  never opened it.  my 2000 426 had another who-knows-how-many hours both desert and supermoto and never had to open it up.....

 

so what s a realistic expectation to have for a modern 4stroke in terms of the crank longevity?  i wold think with good maintenance the bottom end should last a lifetime.  I clean air filter before every ride, and oil and filter every 3 hrs or so.  

 

 

 

 

 

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heck...just realized this should go in the YZ thread....i dunno how that happened.  can it be moved?

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Why are you doing valves so early?  That may be an indication that the crank could be nearing end of life if you're sucking enough dust to kill your valves, but if you're doing them for preventative maintenance, they I would guess the crank is fine.  Probably don't need to change it until 3-400 hours.

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To many variables for a sure fire answer but in general 300-400hrs if its been trail ridden

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early?

 

 

i dunno...they are worn so im replacing them.  ive ridden trail, mx, desert and supermoto on this bike.  i have never hit the rev limiter though...im not too hard on it i dont think.

 

never found any shavings on the drain plug or in the filter area.  weird.

 

 

 

copy that though.  i just didnt want to feel i was getting sold a bottom end rebuild when it wasnt needed.

Edited by gbalias

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I had 10k miles 500hrs out of my 08 and it was still going fine when i sold it

That was all hare and hounds racing or practice track

Edited by GuyGraham

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I only ask because im doing some work on my 08 450.

 

new piston, cylinder, valves, cam chain, tensioner....etc. (top end stuff)

 

its got 180hrs on it.  never had an issue but one of the mechanics said even that theres no play on the bottom end bearing, its gonna be ready to blow anytime around 200hrs.  I thought this to be strange.  maybe a way to get me have him rebuild it?  

 

my '98 400 had who-knows-how-many hours on it.  never opened it.  my 2000 426 had another who-knows-how-many hours both desert and supermoto and never had to open it up.....

 

so what s a realistic expectation to have for a modern 4stroke in terms of the crank longevity?  i wold think with good maintenance the bottom end should last a lifetime.  I clean air filter before every ride, and oil and filter every 3 hrs or so.  

 

Your crank is fine

 

I would do a leak test on the head before replacing the valves at 180 hours...or at least a detailed inspection for mushrooming...

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Moved for you.

awesome, thanks.

 

 

 

while it was off i wanted everything else checked.  the valves started to move fairly rapidly as of lately so i stopped riding it...might as well  get everything else freshened up while i do the cyl and all that. 

so at least i can hope i wont ever have to open it again before i sell it....if i ever do.  lol

Edited by gbalias
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Can't really go on engine hours alone.  If you've got it apart check its condition based on the service limits listed in the manual.  That will give you an indicator of where you're at.  At least check what you can with the top end off, i.e. horizontal deflection of the rod, vertical deflection, play in the crank bearings, etc.  If they are out of spec or on the high end that will give you an idea where you're at.   

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Mine was still well within spec at 300 hours, and it's still running.  The test for big end clearance is shown in the spec section of your manual, dimension "F" in the diagram. 

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original cylinder wear @ 179.8hrs:

 

IMG_20160714_191528-X2.jpg

 

IMG_20160714_191516-X2.jpg

 

 

 

crank measurements are as follows:

 

D (big end side clearance): .012"

F (small end free play): .031"  

 

cyl measurements (cant have too much faith as i did it with transfer tools and mic)

small - 95.04mm

big - 95.10

 

you could feel with your finger the area that is worn (with no more crosshatching) vs that which is below the travel of the rings at the bottom.  as for the upper part that was badly worn...im guessing the increase in bore was allowing for the piston to rock in the cylinder, but the skirts didnt look too bad at all.

 

once i get the head back ill re assemble and ride!

 

thanks guys.

Edited by gbalias

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The pale gray "shadow" at the top of the bore is aluminum showing through a worn out spot in the plating.

 

If you got .031" on the "F" measurement and DID NOT allow the rod to move back and forth on the crank pin while doing it, your big end needs replacement.

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I'm confused.....i did not isolate movement on the big end while taking that measurement. So while moving the small end back and forth, the rod was also moving on the big end between the crank wheels. i guess the "D" measurement should also be factored?

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No, "D" is big end side clearance, to be measured with either a feeler gauge or a dial.  You can't just subtract this from the total movement if you allow the rod to shuffle back and forth as you measure "F" because the tilt of the rod will affect the amount the rod can move on the crank pin.  Hold the rod against one side and rock the top for your reading.

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well...cant say im doing it right for sure, but if i hold the rod REAL tight to one side, it doesnt wanna move at all.  obviously.  but if i let up an ever so slight amount of pressure on the big end while still holding to one side i get .010...maaybe .012" at the small end of side to side.  so the free play is a function of how tight im holding it at the big end.

 

but this doesnt make sense. without holding it to the side, the free play falls within the range specified in the manual.......  at .010, that is much less???  my manual says .020-.040" with a limit of .080" 

 

 

what the heck is going on? lol

Edited by gbalias

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By "don't allow it to move along the crank pin" I mean hold the rod as far to the left (or right) as possible while pushing the rod small end as far to the left AND right as is possible. 

 

Sorry about the confusion on the specs (mine). You're correct, it's well within range.

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copy that.  i guess ill continue to run it and monitor for next time i do the top end.  hopefully not for a long time.

 

 

do these things give any warning when the bottom end fails?  or is it from normal operating to total catastrophe?  ha

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