Kx450f motor destroyed

Jbarros23
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Jbarros23
Edited Date/Time 11/13/2018 3:56pm
So motor had 25 hrs on it. Had my motor guy do a top end on it. First ride after rebuild this happened. Anyone seen a rod snap??


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Paul_Pitzonka
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Paul_Pitzonka 10/21/2018 11:05pm
10/21/2018 11:05pm
It happens, Rods normally break due to stress from prolonged use... yours shouldn’t have broken after 25 hrs... I’d be more concerned as to where the bolt/stud that’s jammed into the cases came from...
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grimsypro 10/22/2018 2:40am
10/22/2018 2:40am
Paul_Pitzonka wrote:
It happens, Rods normally break due to stress from prolonged use... yours shouldn’t have broken after 25 hrs... I’d be more concerned as to where the...
It happens, Rods normally break due to stress from prolonged use... yours shouldn’t have broken after 25 hrs... I’d be more concerned as to where the bolt/stud that’s jammed into the cases came from...
X2 would definitely be wondering why there's a bolt lodged in there!!
nage0139
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nage0139 10/22/2018 5:36am
10/22/2018 5:36am
My initial thought: that bolt got dropped into the crank when the motor was apart and caused it all.
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Jbarros23
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Jbarros23 10/22/2018 5:41am
10/22/2018 5:41am
It's a stock crank. The rod went through the cases and broke a case bolt. Bolt wasn't dropped into the motor
kb228
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kb228 10/22/2018 6:16am
10/22/2018 6:16am
Sounds like you need to find a new motor guy. Im sorry but that didnt happen on a 25 hour motor that was assembled correctly. My guess is excessive piston to cylinder clearance. Could have been a worn crank.
c0ncEpT
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c0ncEpT 10/22/2018 6:22am
10/22/2018 6:22am
kb228 wrote:
Sounds like you need to find a new motor guy. Im sorry but that didnt happen on a 25 hour motor that was assembled correctly. My...
Sounds like you need to find a new motor guy. Im sorry but that didnt happen on a 25 hour motor that was assembled correctly. My guess is excessive piston to cylinder clearance. Could have been a worn crank.
Your right. The guy that assembled the engine caused the rod to snap a the small end.

The small end of the rod doesn't break because of to much piston to wall clearance.
kb228
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kb228 10/22/2018 6:29am
10/22/2018 6:29am Edited Date/Time 10/22/2018 6:32am
kb228 wrote:
Sounds like you need to find a new motor guy. Im sorry but that didnt happen on a 25 hour motor that was assembled correctly. My...
Sounds like you need to find a new motor guy. Im sorry but that didnt happen on a 25 hour motor that was assembled correctly. My guess is excessive piston to cylinder clearance. Could have been a worn crank.
c0ncEpT wrote:
Your right. The guy that assembled the engine caused the rod to snap a the small end. The small end of the rod doesn't break because...
Your right. The guy that assembled the engine caused the rod to snap a the small end.

The small end of the rod doesn't break because of to much piston to wall clearance.
If the piston rattled and broke the cylinder wall and the piston itself... could have very well broken the rod.
mx317
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mx317 10/22/2018 7:03am
10/22/2018 7:03am
It's hard to tell without having it in my hands, but it almost looks like the wrist pin seized in the rod. That could break the rod.
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Jbarros23
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Jbarros23 10/22/2018 7:14am
10/22/2018 7:14am
The guy that did the topend never offered to look at it. When I called him to tell him the motor seized he automatically went to the crank, even though he said it was good when he looked at it. So now I'm stuck with this bike that needs a complete motor with only 25 hrs on it. Hard to prove he did something wrong
slipdog
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slipdog 10/22/2018 7:15am
10/22/2018 7:15am
Paw Paw 271 wrote:
There is no case bolt in that area.

Paw Paw
Yes there is. You can see the rod cut through the case from underneath it and pushed it out. The rod is still wedged in the case.
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kb228
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kb228 10/22/2018 7:43am
10/22/2018 7:43am
Jbarros23 wrote:
The guy that did the topend never offered to look at it. When I called him to tell him the motor seized he automatically went to...
The guy that did the topend never offered to look at it. When I called him to tell him the motor seized he automatically went to the crank, even though he said it was good when he looked at it. So now I'm stuck with this bike that needs a complete motor with only 25 hrs on it. Hard to prove he did something wrong
His response is shady. A reputable mechanic would take it back and find out what was wrong.
Jbarros23
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Jbarros23 10/22/2018 7:52am
10/22/2018 7:52am
Jbarros23 wrote:
The guy that did the topend never offered to look at it. When I called him to tell him the motor seized he automatically went to...
The guy that did the topend never offered to look at it. When I called him to tell him the motor seized he automatically went to the crank, even though he said it was good when he looked at it. So now I'm stuck with this bike that needs a complete motor with only 25 hrs on it. Hard to prove he did something wrong
kb228 wrote:
His response is shady. A reputable mechanic would take it back and find out what was wrong.
I agree. That's what pisses me off more than anything. Especially since I've given him close to $4,000 the last few months to build another motor and to freshen this one up
captmoto
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captmoto 10/22/2018 9:15am
10/22/2018 9:15am Edited Date/Time 10/22/2018 9:18am
That bolt doesn't belong there or it is a too long, wrong bolt. It looks like it went in and pushed the crankcase wall in and contacted the rod. A parts fiche will tell all. What year is the bike? How long did it run like this?

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Paw Paw 271
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Paw Paw 271 10/22/2018 9:21am
10/22/2018 9:21am
Like I said, there is no case bolt in that area. Look at the parts fiche.

Paw Paw
Jbarros23
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Jbarros23 10/22/2018 9:24am
10/22/2018 9:24am
It's a 2017 KX450F...its a Allen head near the counter sprocket
blaze 57
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blaze 57 10/22/2018 10:24am
10/22/2018 10:24am Edited Date/Time 10/22/2018 10:28am
Appears that bolt is the issue. I would be looking at where/how that got in there. I would have had the cases split by now out of sheer curiosity to see how that bolt ended up driving itself through like that.
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mx317
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mx317 10/22/2018 11:26am
10/22/2018 11:26am
blaze 57 wrote:
Appears that bolt is the issue. I would be looking at where/how that got in there. I would have had the cases split by now out...
Appears that bolt is the issue. I would be looking at where/how that got in there. I would have had the cases split by now out of sheer curiosity to see how that bolt ended up driving itself through like that.
The rod went through the cases and hit the bolt bending it up like that. There is a bolt behind the stator that bolts the cases together and it looks like this one.
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Paw Paw 271
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Paw Paw 271 10/22/2018 1:11pm
10/22/2018 1:11pm
blaze 57 wrote:
Appears that bolt is the issue. I would be looking at where/how that got in there. I would have had the cases split by now out...
Appears that bolt is the issue. I would be looking at where/how that got in there. I would have had the cases split by now out of sheer curiosity to see how that bolt ended up driving itself through like that.
mx317 wrote:
The rod went through the cases and hit the bolt bending it up like that. There is a bolt behind the stator that bolts the cases...
The rod went through the cases and hit the bolt bending it up like that. There is a bolt behind the stator that bolts the cases together and it looks like this one.
I don't think so.

Paw Paw
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NJKawi913
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NJKawi913 10/22/2018 1:35pm
10/22/2018 1:35pm
Here's my two cents. No one here can tell you exactly what happened without all the parts right in front of them. But we can all agree that there are no tell tale signs of a manufacture error. I have more expiernce in automotive engine building, but one thing I noticed here is that the carnage is pretty isolated to a few area.
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Tracktor
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Tracktor 10/22/2018 1:43pm
10/22/2018 1:43pm
Jbarros23 wrote:
The guy that did the topend never offered to look at it. When I called him to tell him the motor seized he automatically went to...
The guy that did the topend never offered to look at it. When I called him to tell him the motor seized he automatically went to the crank, even though he said it was good when he looked at it. So now I'm stuck with this bike that needs a complete motor with only 25 hrs on it. Hard to prove he did something wrong
kb228 wrote:
His response is shady. A reputable mechanic would take it back and find out what was wrong.
Jbarros23 wrote:
I agree. That's what pisses me off more than anything. Especially since I've given him close to $4,000 the last few months to build another motor...
I agree. That's what pisses me off more than anything. Especially since I've given him close to $4,000 the last few months to build another motor and to freshen this one up
Saw this happen to a local kid's KX250F after being gone through by a well known Norcal motor builder. I have no idea what actually happened though but results sound similar. Broken rod, low hours, fresh rebuild...........
mx317
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mx317 10/22/2018 3:46pm
10/22/2018 3:46pm
blaze 57 wrote:
Appears that bolt is the issue. I would be looking at where/how that got in there. I would have had the cases split by now out...
Appears that bolt is the issue. I would be looking at where/how that got in there. I would have had the cases split by now out of sheer curiosity to see how that bolt ended up driving itself through like that.
mx317 wrote:
The rod went through the cases and hit the bolt bending it up like that. There is a bolt behind the stator that bolts the cases...
The rod went through the cases and hit the bolt bending it up like that. There is a bolt behind the stator that bolts the cases together and it looks like this one.
Paw Paw 271 wrote:
I don't think so.

Paw Paw



Plain to see where the bolt goes from these pics.
Paw Paw 271
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Paw Paw 271 10/22/2018 6:10pm
10/22/2018 6:10pm
Please not the orientation of the bolt in the photo. It does not match the location of the only case bolt even close as it comes from the other case half and not the side of the case that the bolt is located in the photo. It would have had to have been pulled through the case into that position and I just don't think that the left case of the bolt in question would show it to be pulled through the case. It should have been pushed out of the case. I still contend that it is not a case bolt. I do feel the rod failed for some reason.
Now I have been wrong before and I have seen a lot of exploded engines, but this one looks odd. Most of the time a broken rod damages the cases in an outward fashion where this one seem to show and inward motion.

Paw Paw
Jbarros23
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Jbarros23 10/22/2018 6:14pm
10/22/2018 6:14pm
What advise would you guys have for me? Think there is anything I can do??
dkurtd
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dkurtd 10/22/2018 6:17pm
10/22/2018 6:17pm
Let's see a picture of the top of the piston. Also the combustion area of the head. I'm assuming that's an OEM piston.
Jbarros23
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Jbarros23 10/22/2018 6:27pm
10/22/2018 6:27pm
Dont have photos of the head or top of piston. But looked really good. Top of piston looked brand new

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