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06 KX450F rebuilding

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Hi guys. I am rebuilding an 06 KX450F for a friend. He just got it. He rode it a few hours. It seemed to leak oil alot and it steamed and overheated and ended his day.  He ask me to fix it. I drained the oil. It looked ok. I washed the caked stuff off and I put new oil in it and topped up the rad. Took about 2 qts of coolant. Started up easily enough but as soon as it got warm, it steamed like the train on Back To The Future III. And coolant puked out of the overflow. Not sure if I can post a video here but I have one if you need to see. I see oil seeping out of the base and head gasket too.

There is a plastics Y tube in the coolant line that I found taped up with electrical tape. Huge crack that the PO taped to fix. It would leak coolant there and land on the header pipe. That is why the steam.

Drained the coolant. It was very dirty. Looked like oil but it was exhaust the pressurized the coolant.  That is why it puked out the over flow.

Took the head off and cylinder. Looks like the bottom of the head is messed up. That is where the exhaust was getting into the coolant. Cylinder looks ok.

Take a close look at the last picture.  Do

you think this is fixable? I'm hoping a machine shop can take a lick off. Maybe .005"? And it will be as god as new. 

Your thoughts? 

 

 

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Edited by Stablock67
Cylinder, not head

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I'd take it to a matching shop and they can check it for any cracks before they shave it a bit. .005 is a pretty small number. Probably be closer to .010

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Sand the head mating surface flat. Use a glass plate with some wet sand paper taped to it. Start with 240 or maybe 180 and go finer to end on 400. Use water. Works great and it's easy. You can plate sand the top of the cylinder too.

Swap the plastic Y joins for the later alum parts.

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Ok. Had the head shaved by a machine shop. Professional shop that do mostly dirtbikes. The took about .002 off.

They did a little work to the cylinder too for my new piston and rings. Put it all together and started up nicely on 3rd kick. Let it idle for 15 min. Then let it cool. Next day I rode it up and down the street and noticed a bunch of oil leaking from the one side out of the head gasket. Side by timing chain cover. Any ideas as to why?

I'm going to retorque the head and try it again i guess. Unless you guys tell me different.

Help! 

 

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Do you thigh ten the head in a X-pattern and little by little? 

It's important. It's good also to have a tourq wrench when tighten aliminium head. 

Now you need a new gasket, new every time when opening the head 

Edited by skorpan777

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How rough are the machining marks? That could cause a leak. Also a re used gasket (without copper coat). Or incorrect torque pattern. Or the top of the cylinder is warped. You can plate sand both surfaces.

 

 

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