Manual says to replace the piston at about 12.5 hours?


12 replies to this topic
  • yzUSMCf

Posted December 23, 2014 - 10:41 AM

#1

2014 yz450f

Really? Every 12 hours...

Opinions?

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  • yzUSMCf

Posted December 23, 2014 - 10:46 AM

#2

When is a realistic time to change out the piston??

I don't race but ride track and desert in the winter I stay off the Rev limiter

  • mch

Posted December 23, 2014 - 11:10 AM

#3

Depends on how you ride it.  Even the 2 strokes service intervals were very low hours according to the service manual.  I just changed the piston in my WR after about 400 hours and it's mostly desert and I don't red-line it.  That was kind of excessive, but I would think somewhere in the 100-200 hr range might be a little more realistic.  It really depends how hard you are on it (and I'm not real easy on mine).  I have no idea how many hours are on my YZ450 (07) that I bought used (and the suspension was pretty beat / muffler needed re-packing).  I already have 40 hours of my own without a new piston.  It doesn't make any funny cylinder noises like it's getting loose, so I will probably wait a little longer.


Edited by mch, December 23, 2014 - 11:13 AM.


  • yzUSMCf

Posted December 23, 2014 - 12:51 PM

#4

I'm thinking I'll throw in a new piston around 100 hours just to be safe

  • GHILL28

Posted December 23, 2014 - 12:55 PM

#5

Pretty sure that's just being extra safe.  Just in case someone seizes a piston at 20 hours they can point and say "should have replaced it at 12 hours, see here".



  • yzUSMCf

Posted December 23, 2014 - 06:22 PM

#6

That's what I was thinking. .

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  • Mtrain730

Posted December 23, 2014 - 08:20 PM

#7

I'm going for a 100 myself and I think that's me being carful. I think how you ride the bike makes a huge difference if you live on the rev limiter all the time I think a 100 is actually a lot if you just ride around the trails a couple hundred is probably not excessive. I'm gonna shoot for a hundred on my 450 because I race about a half dozen times a year and trail ride the rest of the time. It probably works out to be about 25/75 mx/ trail riding. My bike rarely sees the rev limiter so if I go a little over a hundred I'm sure I will be fine. I shoot for about 5 hrs with oil changes also I'm not one of those guys who changes my oil every 30 minutes either.

Edited by Mtrain730, December 23, 2014 - 08:30 PM.


  • grayracer513

Posted December 23, 2014 - 09:04 PM

#8

The manual is confusing and indistinct on that point.  It does say "replace" in the one column, but then also says "as required".

 

The downside of not replacing a piston in a 4-stroke built for and run at high RPM is not a risk of seizure, and in fact, seizures in YZF's are quite rare comared with other failure modes, and are generally the fault of failure or poor maintenance of the oiling system.  What does happen is two things.  The compression ring grooves wear, which allows the rings to twist out of square with the piston and cylinder, which leads to the rings "chewing at" the bore walls right at the top and bottom of the stroke, where the piston changes direction, and that causes deeper wear at those points in the bore.

 

The second problem is that as the skirt wears, the piston starts to "rock" front to rear as it goes past top and bottom center.  When this gets bad enough, the ring lands, that part of the piston between the rings, starts to contact the cylinder, which is not supposed to happen.  Interestingly, the rings are part of what stabilizes the piston at speed, and when they get weak, the rocking gets worse.  The eventual end result can be that the piston breaks a skirt and "rolls over" in the bore, the damage from which is almost always catastrophic. 

 

Still, I have yet to see a YZ450 piston with under 30 hours on it the looked anything like it needed to be replaced.  I did my own at well over 300, which, to be honest, was a little longer than I should have let it go, looking at it, but no collateral harm was done.



  • pomoco

Posted December 24, 2014 - 04:02 AM

#9

I just changed my piston that had 60 MX hours. It looked like brand new.

  • atomic410

Posted December 24, 2014 - 07:17 AM

#10

wow I'm glad I saw this.  I just got a 11 450 in sept and was told it had around 60 hours on it, believable because its really clean.  I put the tuner on it and it said 120!  It runs strong and pulls awesome doesnt burn oil etc, but I've been freaking about that 120 number.  Glad to know guys are putting big hours like this on these motors.  I'm coming from a 250 where 100 hours of woods seems absurd to me. 



  • Mtrain730

Posted December 24, 2014 - 07:40 AM

#11

The manual is confusing and indistinct on that point. It does say "replace" in the one column, but then also says "as required".

The downside of not replacing a piston in a 4-stroke built for and run at high RPM is not a risk of seizure, and in fact, seizures in YZF's are quite rare comared with other failure modes, and are generally the fault of failure or poor maintenance of the oiling system. What does happen is two things. The compression ring grooves wear, which allows the rings to twist out of square with the piston and cylinder, which leads to the rings "chewing at" the bore walls right at the top and bottom of the stroke, where the piston changes direction, and that causes deeper wear at those points in the bore.

The second problem is that as the skirt wears, the piston starts to "rock" front to rear as it goes past top and bottom center. When this gets bad enough, the ring lands, that part of the piston between the rings, starts to contact the cylinder, which is not supposed to happen. Interestingly, the rings are part of what stabilizes the piston at speed, and when they get weak, the rocking gets worse. The eventual end result can be that the piston breaks a skirt and "rolls over" in the bore, the damage from which is almost always catastrophic.

Still, I have yet to see a YZ450 piston with under 30 hours on it the looked anything like it needed to be replaced. I did my own at well over 300, which, to be honest, was a little longer than I should have let it go, looking at it, but no collateral harm was done.

. Thats great to hear About 300 hrs now your making me wonder if I'm jumping the gun doing mine at around 100. It's tough for me to make a educated guess when I should replace piston and rings or do any top end work for that matter because even though I know how many hours are on my bike the way I ride it varies extremely from hammering on it pretty good to just casual trail riding. I'm not in the habit of replacing new parts but don't want to cause damage with waiting to long either.

Edited by Mtrain730, December 24, 2014 - 07:44 AM.


  • yzUSMCf

Posted December 24, 2014 - 08:26 AM

#12

Good info! Thanks for pitching in guys! Keep it coming

  • mike_dean

Posted December 28, 2014 - 04:29 PM

#13

 A friend of mine has had 2 broken pistons on '08 and an '09 450, no engine damage, cracked on the under side near wrist pin. Was starting hard he pulled it apart found it, second bike he pulled apart to inspect because of what he found in his previous bike and found it. Both engines under 100 hrs, he runs them hard and ice races. My '06 well over 100 hrs and no problem, my '00 426  replaced first at 200hrs no problem, second piston 530hrs no problem. Seeing his engines made me worry about mine.


Edited by mike_dean, December 28, 2014 - 04:30 PM.






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