1999 Yzf Catastrophic Engine Failure

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#1
this happened to my brothers yz400f. he started it up and let it warm up for a minute, then shut it off and put on his race gear. he restarted the bike and took off to do a slow lap (2nd gear maybe 1/3 throttle) and check out the track. half way around the track the bike locked up. he pushed back to the truck, went home and started to tear down the engine. the rod had broken about an inch below the pin. then went down with the crank, but when it came back up, it fell forward, missed the cylinder and went through both halfs of the engine case at the front motor mount. has this happened to anyone else? why did the rod brake? it was not even under a hard load at all. the rod looks good otherwise. no discoloring like it had ever become too hot. the bike is into its third year, but has very low time compared to some of my friends who ride theirs alot more. it has had the top done about a year ago. any ideas?
 

Tony Williams

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#2
That seems to be a weakness (albiet infrequent one) of the YZF 400 series. I believe the 426 has a heavier rod that you might consider as a replacement.
 
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#3
When you did the top end did you replace the piston with an OEM or an aftermarket piston?
 

bclapham

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#7
Chili said:
I'm just curious how Rich ended up replying to a 3.5 year old thread out of the blue?
must be a slow day at the powerplant!

isnt there a springfield in Illinois???? Doesnt Homer Simpson work at that powerplant??????
 
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#8
Chili said:
I'm just curious how Rich ended up replying to a 3.5 year old thread out of the blue?
:rotfl:
 
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#9
Chili said:
I'm just curious how Rich ended up replying to a 3.5 year old thread out of the blue?
Someone bumped it to the top and I didn't pay attention to the original post date. :bang: