Kx450f motor destroyed

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10/21/2018 10:20 PM

PhotoSo 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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10/21/2018 10:21 PM

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10/21/2018 10:22 PM

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10/21/2018 10:23 PM

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10/21/2018 11:05 PM

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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10/22/2018 2:40 AM

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 bolt/stud that’s jammed into the cases came from...

X2 would definitely be wondering why there's a bolt lodged in there!!

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10/22/2018 5:14 AM

stock crank?

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Unleaded tastes a little tangy. Supreme is kinda sour, and diesel tastes pretty good.

10/22/2018 5:36 AM

My initial thought: that bolt got dropped into the crank when the motor was apart and caused it all.

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10/22/2018 5:41 AM

It's a stock crank. The rod went through the cases and broke a case bolt. Bolt wasn't dropped into the motor

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10/22/2018 6:16 AM

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.

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10/22/2018 6:17 AM

There is no case bolt in that area.

Paw Paw

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10/22/2018 6:22 AM

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 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.

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Race Bike: 2018 KTM 350SXF

Other Bikes: 1985 CR80R, 1990 CR250R, 1998 PW80, Specialized Fuse Comp 29.

Sold: 2016 YZ250F, 2012 CRF250R

10/22/2018 6:29 AM
Edited Date/Time: 10/22/2018 6:32 AM

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 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 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.

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10/22/2018 7:03 AM

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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Take it to the limit, one more time!

10/22/2018 7:14 AM

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

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10/22/2018 7:15 AM

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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10/22/2018 7:43 AM

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 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.

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10/22/2018 7:52 AM

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 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

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10/22/2018 9:15 AM
Edited Date/Time: 10/22/2018 9:18 AM

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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The older I get, the faster I was.

10/22/2018 9:21 AM

Like I said, there is no case bolt in that area. Look at the parts fiche.

Paw Paw

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10/22/2018 9:24 AM

It's a 2017 KX450F...its a Allen head near the counter sprocket

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10/22/2018 10:24 AM
Edited Date/Time: 10/22/2018 10:28 AM

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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10/22/2018 11:26 AM

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 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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Take it to the limit, one more time!

10/22/2018 1:11 PM

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 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 together and it looks like this one.

I don't think so.

Paw Paw

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10/22/2018 1:35 PM

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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I don't crash, I just run out of talent

10/22/2018 1:43 PM

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 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 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...........

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10/22/2018 3:46 PM

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 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 together and it looks like this one.

Paw Paw 271 wrote:

I don't think so.

Paw Paw

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Plain to see where the bolt goes from these pics.
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Take it to the limit, one more time!

10/22/2018 6:10 PM

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

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10/22/2018 6:14 PM

What advise would you guys have for me? Think there is anything I can do??

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10/22/2018 6:17 PM

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.

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2018 KX450F
2005 KX250
2003 KDX 220
1984 KX 80
1982 RM 80
1980 RM 80
1977 XR 75
1969 Honda Mini 50