Low compression/ Milky oil—HELP!

Hey So let me give you the background of my bike so I can rule out all possibilities.—it is a 2006 kx450f I just recently rebuilt the whole engine Crank/bearings/rod/piston/valves and the head got beat up by a dropped valve so I sent that away for repair. So basically the engine is %100 new. I rode it 4-5 time a total of 10-15 hours since ALL of that work…Now to the problem---

On my last ride I had white smoke while riding and it shut off. turned out to be coolant in my oil.

So far the only thing Ive changed is the water pump gasket on the outside. I though it might be the head, i.e a crack so I did a compression test and got VERY low readings. Every time I did it, it was BELOW 50 PSI but It holds it does not leak. What else could this be??

Maybe multiple things?

Cases not seal right?

Piston rings?

Head gasket installed incorrectly?

HELPPPPPPPPP!!

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Edited by Chrisj0806

A cylinder leak down test will tell you a lot about the condition of your combustion chamber. You can buy the tool (expensive), or you can make one (http://www.motorcycleproject.com/motorcycle/text/leakdown.html). You can skip the gauge part and just make/use the hose to find out where your leaking at. TDC on the compression stroke. Air out of the exhaust = leaking exhaust valve, air out the carb/injector block = leaking intake valve, Air out the oil fill = leaking rings, bubbles in the coolant = leaking head gasket.

To have coolant in the oil, possibly coolant in the combustion chamber (the white smoke, does it smell like burnt anti-freeze?), and low compression, I'm guessing a blown head gasket.

A cylinder leak down test will tell you a lot about the condition of your combustion chamber. You can buy the tool (expensive), or you can make one (http://www.motorcycl...t/leakdown.html). You can skip the gauge part and just make/use the hose to find out where your leaking at. TDC on the compression stroke. Air out of the exhaust = leaking exhaust valve, air out the carb/injector block = leaking intake valve, Air out the oil fill = leaking rings, bubbles in the coolant = leaking head gasket.

To have coolant in the oil, possibly coolant in the combustion chamber (the white smoke, does it smell like burnt anti-freeze?), and low compression, I'm guessing a blown head gasket.

Thanks for your time and input. I just did a leak down test (Put A hose into the spark plug hole with 10 PSi from my compressor) The only place it was leaking from was the breather hole in the side of the cylinder?? Does that mean anything??

Hmm, with the motor at TDC on the compression stroke it shouldn't leak air from anywhere, especially at 10psi (should test at more like 75-80psi, or 100psi to measure % of leakdown). And there isn't any breather hole in the cylinder that I'm aware of, only breather would be in the crankcase on the top back of the motor. There is a hole in the right (brake) side of the cylinder head on my 250F that I believe is to allow any water that might collect in the spark plug valley to drain out, but isn't connected in any way to the inside of the motor.

And there isn't any breather hole in the cylinder that I'm aware of, only breather would be in the crankcase on the top back of the motor. There is a hole in the right (brake) side of the cylinder head on my 250F that I believe is to allow any water that might collect in the spark plug valley to drain out, but isn't connected in any way to the inside of the motor.

Yeah you are correct. It is in the head but that is the only place air is coming from is the side of the head? Im confused now…

Can you post a pic?

Seeing the history of the bike I wonder if there is/was damage to the headbolt threads or if the head was not machined properly

Yes, a picture of exactly where the air is coming from would help a lot. Something isn't right, that's for sure.

this was my 1st thoughts too. did you check the head bolts? whole bunch more than 50psi in there under ignited compression to lift the head

Can you post a pic?

Seeing the history of the bike I wonder if there is/was damage to the headbolt threads or if the head was not machined properly

you wont get an accurate compression reading without wiring the decompressor open.

I think its the head gasket, maybe head not torqued correctly on rebuild, easy to see if you remove the head.

Can you post a pic?

Seeing the history of the bike I wonder if there is/was damage to the headbolt threads or if the head was not machined properly

Yes, a picture of exactly where the air is coming from would help a lot. Something isn't right, that's for sure.

I think its the head gasket, maybe head not torqued correctly on rebuild, easy to see if you remove the head.

OK so I pressurized the engine agin and listed/ sprayed soapy water and found nothing but one thing…. Air coming from one of the coolant hoses…so I opened the radiator and a big woosh of air came out. So It is getting into the radiator. Is that normal?

Here is the pic of the hole the air is coming from on the head it is in the top post.

Sounds like a cracked head.

OK so I pressurized the engine agin and listed/ sprayed soapy water and found nothing but one thing…. Air coming from one of the coolant hoses…so I opened the radiator and a big woosh of air came out. So It is getting into the radiator. Is that normal?

Here is the pic of the hole the air is coming from on the head it is in the top post.

No, it's not normal. I'm still betting on a blown head gasket which is letting the air cross from the combustion chamber into the water jacket. Also letting the pressurized coolant into the cylinder, and allowing it to move across into one or the other of the oil passages, along with causing your low compression reading. Did you re-torque the head bolts after you rode it for the first hour or 2? Sometimes you can get away without it, but a lot of times they need a re-torque to insure that such as this doesn't happen. There is also a chance that the head may be cracked given the prior damage and repair, but we'll hope for something cheap like the head gasket first. Pull the head off of it and see what's going on.

PS.. When you get the head off, lay it on a piece of glass, or use a straight edge, and see if it's setting flat. All the gasket mating surface should be completely flat. If the head is warped or not milled correctly, you should be able to see it. My 250F gives a usable warp limit of 0.05mm.

Edited by OLHILLBILLY

I would usually say head gasket also, but if it is blowing air from the spark plug drain hole I see no way for it to do this with just a blown gasket.

Edited by mx317

I could not see too much from the picture but would have to agree something in the head or gasket from what the OP found.

How robust are the bearings in these bikes? Engine has been run with coolant going through it for 'X' amount of time. Should this also be a consern?

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