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17 Posts
Discussion Starter · #1 ·
This post is about a friend's 2014 300 track bike.

His oil is straight up chocolate milk. His instant thought is water pump or head gasket. His coolant is fine though (he runs distilled water for coolant)... If he was actually mixing fluids, wouldn't his coolant be contaminated too?

There was a post back from 2017 from someone here who had moisture in his oil, turning it to chocolate milk... Could this be what my friend has going on too, since he runs distilled water?

He already ordered everything for a new water pump... I'm trying to sort this out before he uses it if he doesn't need to, lol.


Premium Member
84' Goldwing Aspencade, 91' EX500, 98' Ninja 250 w/ 17' 300 engine, 07 EX500
194 Posts
Looks like the head gasket is going to me.

The moisture in the sight glass does have a slight milkshake look to it, but that's from not getting the up to temperature. This happens when one is just starting it up, when the bike is in storage, and/or short rides.

Your friend might what to do a compression test.

Assuming it's just starting, I'd say pull the head, and the cylinder jug, and lapp them both, and get a new gasket of course. Upon taking the head off you should see a bad head gasket. Lapping is a lost art for sure.

If it was me, I'd just get a good used engine, this will save a lot of down time, and then work on the bad engine in my own time, and have a spare engine. If anything I would learn about the engine.

I wish your friend good luck 馃

Premium Member
84' Goldwing Aspencade, 91' EX500, 98' Ninja 250 w/ 17' 300 engine, 07 EX500
194 Posts
Lapping valves, jug, and head write-up,

Okay this goes for the Ninja 500, but I'm sure the Ninja 250/300 is the same, if not please let me know.

The intake valves are case hardened to a thin level of hardness and much in the way of metal removal with destroy them.

Why do you think you need to lap them? if they are worn you need to re cut the seats and fit new valves ,no lapping required. If they are worn badly enough to need anything at all they develop a groove that offself is the detriment to flow. Lapping will make that worse.

Head Gasket repair

Lapping the head

A common failure of the EX engine is, a blown head gasket. The usual cause of this besides the obvious low water or frozen coolant reasons is, warpage of the mating surface between the head and the cylinders. The string of events leading to overheating is:

High pressure gas leaks from the combustion chamber into the coolant system, thereby over pressurizing it and blowing coolant overboard, then the coolant shortage causes overheating which causes even greater warp age, add on infanatum...

As well as the above, any engine that has had the head removed for any reason need to be re lapped. This engine is a very flexible unit because of the cam chain gallery down the middle. The only thing holding the two cylinders together is the very thin wall of the front and back sides of the chain gallery. 1/8鈥 if you鈥檙e lucky. This means that the engine works like two single cylinder engines running from a single crank held together by scotch tape. As long as they remain together they are usually fine, but once disassembled they need to be re flattened

The repair:

Unfortunately it is not a simple as replacing the head gasket. Because the 鈥済asket鈥 is not compressible, it is not able to absorb even slight distortion or warp age that may not even be detectable with the usual straight edge type of inspection. The up side of this is that you can re use the gasket.

Tools needed:

A lapping plate; usually a steel flat plate or a pain of flat plate glass. I鈥檝e used my table saw table successfully (the cast iron type)

Lapping compound: Valve lapping compound available at a Auto parts store

The means to wash the parts clean after lapping. A bucket of Kerosene is fine.

The Idea is to use the abrasive to grind down the high spots of the head and the cylinders till they are perfectly flat. See the pictures below.

The process move the part over the surface of the Lapp in a figure 8 motion

Clean and inspect your progress often. Shown is a partially cleaned surface
Automotive engine gasket Gas Auto part Event Circle

You are now ready for reassembly. Clean the old head gasket with lacquer thinner and Scotch brute or steel wool. Then repaint it with 1 coat of spray enamel on both sides (1 coat)

After assembly increase the Head Bolt torque to 40 lbs. ft.

Now鈥檚 a good time to degree you cams.

Freshly lapped set
Automotive engine gasket Gas Motor vehicle Engineering Automotive exterior

Shows the process and the lapp plate
Watch Gas Wood Auto part Machine

640 Posts
^ We did that process on our Ninja 500.

The symptoms were pressurizing of the cooling system, which forced coolant out of the radiator and into the coolant reservoir bottle - which overflowed.

I'm guessing a head gasket is the problem here as well. I'm not sure how his coolant (level) could be fine. That water had to come from somewhere.

I've seen where oil can get milky from condensation, but nothing like that.

317 Posts
I had the milky oil symptoms after doing work on my engine head, and accidentally (with or without knowing) some coolant poured into the head around the valves. So if there is any chance during routine maintenance that some coolant/water may have poured in there, it could be that if there are no other symptoms. In my case when this happened, I'd just have to ride the bike, and when I was done, open the oil filler cap to allow the steam to flow out. This would eventually sort this out, and then an oil change after almost all the moisture and milky stuff was gone.

Never had this happen during normal or track operation though. I did have a water pump mechanical seal failure this season, and although it is uncommon for both the oil and the water side of the seal to fail and allow cross contamination, it is possible, but more likely the head gasket as aforementioned. That is the only place the coolant is internal on the engine is around the cylinder block, if it's not the water pump.

I think the N300 head and cylinder block studs are TTY as well, so get fresh ones if you're going in there as well. Resurface the cylinder head and cylinder block if you're going in there too like mentioned above, I did this when I did my piston ring change and it came out perfect.

Good luck, hope this helps.

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