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piston cracked at 70hrs

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Hi,

Recently the piston of my KLX450r cracked, it was still in one piece, but a large crack was across the piston which  caused a complete loss of compression.

I always thought that it would last minimal a 100hrs.

Luckily no further damage, I replaced it with a forged WISECO piston, and ON THE PIPE! again.

My question is, who has experienced this also at these running hrs.

I ride 90% motocross with it, run a 2014 KX450F exhaust.

Opened up the air box to the max, cut away the top, drilled holes to the side and rear, run a 170 main jet, and maintain and treat the bike well.

Regards,

Jan

 

piston KLX.jpeg

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Regardless of a position crack or just being worn I have known of a few 450s to make the 100hr mark. My 07 crf450r for example. Neither the timing chain nor the rings made it to 80hrs.

 

That is an impressive crack though

Edited by Zinergy

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Wow, mine made it waaaaaaay more than 100hrs.  At least you know what the inside of your engine looks like now.

 

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Lol, I wasn't curious  to the inside at all, but while I hat it apart I took the valves out to check them: still 100%.

 Even the valve clearance was just as it was when the Kawa left Japan:thumbsup:

I changed the timing chain for a new one, and will change the piston the next time after 50hrs.

My Kawasaki dealer also advises a 50hr interval.

Cheers,  ON THE PIPE!!

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Wow.  I dont know how many hours are on my bike ,  But i have over 5000 miles on the original engine. I bought it new in 08 and it has never been apart.   Runs great no compression loss.     I have never seen a piston crack down the center like that.  

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What year bike is this? Is this possibility why they updated to a boxed bridge piston in 2010?

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The bike is a 2008 model, I bought it new in 2014.

Did not know there had been an update on the piston, but now I have a WISECO piston in, so everything is safe.

It had been left sitting in a corner of the warehouse for 6 years, with zero hours on it.

The dealer totally forgot he had it in stock! the bike was covered with junk.

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The bike is a 2008 model, I bought it new in 2014.
Did not know there had been an update on the piston, but now I have a WISECO piston in, so everything is safe.
It had been left sitting in a corner of the warehouse for 6 years, with zero hours on it.
The dealer totally forgot he had it in stock! the bike was covered with junk.

Would guess lean if there’s a reason beyond just a bad piston forging. Bandsaw it open and look for a flaw. What’s the plug look like?

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The bike is a 2008 model, I bought it new in 2014.
Did not know there had been an update on the piston, but now I have a WISECO piston in, so everything is safe.
It had been left sitting in a corner of the warehouse for 6 years, with zero hours on it.
The dealer totally forgot he had it in stock! the bike was covered with junk.


The KXF has an update on the pistons from 09 to 10 with some reinforcements, over in the Kx450f forum they are claiming 300+ hours of harescrambles/ practice on a piston. Bad Piston or like others have said Lean

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I run a170 main jet and have the airbox opened to the max, cut the top of and drilled large holes in the  side and back.

Also run a 2014 kxf exhaust.  It probably could have run lean because I was railing berms at a deep sand motocross track with WOT in third gear all the time.

Even a Kawasaki cant stand this abuse I guess ;)

 

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I run a170 main jet and have the airbox opened to the max, cut the top of and drilled large holes in the  side and back.
Also run a 2014 kxf exhaust.  It probably could have run lean because I was railing berms at a deep sand motocross track with WOT in third gear all the time.
Even a Kawasaki cant stand this abuse I guess
 

What needle are you running?

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sorry for the late replay, 

A happy new year.

I run the standard needle with the clip 3rd position from top.

Do you recommend some other typ of needle? 

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sorry for the late replay, 
A happy new year.
I run the standard needle with the clip 3rd position from top.
Do you recommend some other typ of needle? 


My stock needle wasn’t adjustable. I recently did the NCVR for a ride and that was too Rich for 7500ft, now I’ve got a NCVS in there but winter interrupted my testing.

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