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kx450f blown up

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Hello All,

Here are a few pics of the motor from my friend's KX450F. This was a relatively low hour motor that always ran strong. Looks like the rod just decided to let go. Any ideas what, or why this may have happened? It looks like everything below the head gasket is junk now, even the transmission. Part of the rod and other metal broke through the case and gaffed up some of the trans gears too!

BlownMotor007.jpg

BlownMotor008.jpg

BlownMotor012.jpg

DPinDet

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just another reason i'll never buy a 4 broke. was the oil ect all changed reg? any signs of over heating?

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I think this was a common thing with the KXs' for a year or so.The top of the rod breaks off from the piston rocking. A little wear in the cylinder is all it takes.

YET...one more reason i'll never buy on of those new 4-stokes!

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Exactly. There was plenty of oil in the motor and no overheating at all. Nonetheless, a 2-stroke KX500 will be its replacement.

Anybody want to buy a good, ported head from this motor? It is about all that is still useable.

DPinDet

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That sucks but it is funny that so many people for get that 2 stokes explode as well. Maynot cost as much but can still be very expensive.

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2006 KX450f. Aftermarket piston with some kind of coating on it, not sure what brand. Mostly trail riding, with an occasional drag race here and there. Never raced.

DPinDet

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Funny how people who don´t like 4-strokes are always looking in the KXF forums. This is THUMPERtalk!

I think I´m gonna search all the 2-stroke parts of the forum and find a failure, then go on and on about how I don´t wanna buy a bike that could potentially break.

By the way, sorry ´bout the engine, that sucks...

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Funny how people who don´t like 4-strokes are always looking in the KXF forums. This is THUMPERtalk!

I think I´m gonna search all the 2-stroke parts of the forum and find a failure, then go on and on about how I don´t wanna buy a bike that could potentially break.

By the way, sorry ´bout the engine, that sucks...

exactly!

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2006 KX450f. Aftermarket piston with some kind of coating on it, not sure what brand. Mostly trail riding, with an occasional drag race here and there. Never raced.

DPinDet

Looks as though the aftermarket piston was at fault, being a four stroke does'nt seem to be the issue to me.

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Funny how people who don´t like 4-strokes are always looking in the KXF forums. This is THUMPERtalk!

I think I´m gonna search all the 2-stroke parts of the forum and find a failure, then go on and on about how I don´t wanna buy a bike that could potentially break.

By the way, sorry ´bout the engine, that sucks...

You dont need to look in the KXF forums to see new posts.I came on to this forum to help a fellow rider out.But I also switched back to a 2stroke,good luck with yours.

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This is the same thing that happened to our 2006 KX450 last Sunday. The top of the connecting rod broke apart, and destroyed the bottom end. The only thing that looks salvageable is the head, which has one stuck valve in it. I had recently replaced the top end preventatively to preclude the wrist pin failure. It lasted four rides after the new top end. Now I don't know what to do. It would cost a lot to replace or rebuild that engine. I suppose parting it out and buying another bike makes sense. I loved that bike, but I just don't trust those motors anymore. If you can't trust your connecting rod, something is seriously wrong with the design in my opinion.

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The piston was'nt the issue. The 06 had a sintered metal rod which was prone to breaking once there was even the slightest play in the bearing. The damage on the piston and cyl is from the rod breaking and whipping around in there. Some guys have put hundreds of hours on the stock rods, others not much. It all depends on the frequency of the oil changes, the compression ratio, and how hard you ride. And by the way, believe it or not, I have seen two strokes blow cranks and cylinders and cases etc.

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Funny how people who don´t like 4-strokes are always looking in the KXF forums. This is THUMPERtalk!

I think I´m gonna search all the 2-stroke parts of the forum and find a failure, then go on and on about how I don´t wanna buy a bike that could potentially break.

By the way, sorry ´bout the engine, that sucks...

I think its un-cool of people to come in and say "that's why I don't buy 4t" such and such. That would just piss me off.

Sucks to have that kind of failure man. The good side is that you can pick up a good 500 motor for almost the price of that head. The expensive part will be the welding and cutting of the frame. It should be well worth it to have a low maintenance 55 hp monster.

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I guess I got lucky. The shim from in between the crank and rod came out and seized the rod. The piston was slapping the weight for a while then it seized. No damage to the head, piston,cylinder or case. I would like to see how you do the conversion. I'm getting another 450 motor but may be in the future after I take some welding classes i could try and put a 500 in.

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This is the same thing that happened to our 2006 KX450 last Sunday. The top of the connecting rod broke apart, and destroyed the bottom end. The only thing that looks salvageable is the head, which has one stuck valve in it. I had recently replaced the top end preventatively to preclude the wrist pin failure. It lasted four rides after the new top end. Now I don't know what to do. It would cost a lot to replace or rebuild that engine. I suppose parting it out and buying another bike makes sense. I loved that bike, but I just don't trust those motors anymore. If you can't trust your connecting rod, something is seriously wrong with the design in my opinion.

just curious,what piston did you put in it?

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I decided to just rebuild it. going with kibblewhite valves, hotcrank, athena jug and piston kit.

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@WALENT 215 for about six months I had a high compression piston from Wiseco. Then I changed the cylinder and put in a 12:1 compression Wiseco. It went through 2 cylinders, 2 owners and about 3 years before it broke.

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