Blowing oil into airbox

[Junkie]

I recently picked up a 15 450XC-F in supermoto trim.

Bike has 44 hours on it, 10 hours on the big bore. It was a very nicely set up bike, lots of money in parts on it (Excel rims, Talon hubs, Berringer 6pot, FMF full Ti exhaust, Hinson slipper, etc) and very clean, with maintenance records, so I believe it was taken care of fairly well.

With high RPM I'm ending up with enough oil blown into the airbox that it'll leak down the subframe and then onto the frame.


I'm trying to figure out why.

Option 1 is that it's overfilled: when I checked the oil, I did so on a stand (K&L MC475, fairly large and flat). The stand is level, the frame isn't, so it might be too high of a level (as the bike leans forward and the sight glass is near the back). Even on it's wheels, it's leaning forward a little vs stock due to the supermoto conversion.

Option 2 is that the big bore simply moves enough air around in the crankcase that it blows some oil out the breather.

Option 3 is that there's something wrong, and I ought to tear down the top end and inspect.


Thoughts?

 

[mototireguy]

Combination of Option-1 and 2.

A little oil blow into the airbox is normal.

 

[byke]

Isn't that the standard symptom of blow by? Maybe the rings didn't seat well when the bb kit was installed. I'm assuming you'll put the bike on the ground at some point to check oil level and that side of things will work itself out.

 

[Junkie]

Well... even with it on the ground, it's leaned forward somewhat vs stock due to wheel size changes.

Current tire sizes are 125/75-16.5 front (works out to 23.9"), 165/55-17 rear (works out to 24.1"). Compare that to stock 80/100-21 (27.3"), 110/100-18 (26.7") and my front is a little lower than stock... if tires are true to size, no clue if they are.

 

[mototireguy]

Maybe the rings didn't seat well when the bb kit was installed.

Junkie can confirm but I think he's referring to the crankcase vent hose blowing oil into the airbox. Normal operation vents some oil mist/fumes into the airbox.

Unrelated to oil blowby past the piston rings.

 

[Junkie]

Oil is ending up in the airbox.

Excessive blowby can lead to some oil mist going past the rings, but it would take crazy amounts of blowby to cause the amount of oil I'm getting.

I'm thinking the most likely scenario is that it was overfilled. Gonna make sure level is correct and see if it continues.

 

[byke]

On the compression stroke, when rings haven't seated well, that pressure escapes by the rings and pressurizes the crankcase. The first question is whether or not it's normal and maybe it is for a bb sumo that's gets a workout and is slightly overfilled.

 

[fast4d]

over filled. 5 ktms I've owned they need to be checked after a ride (dry sump oil in tanks or frame) or they will read low
or
excessive blowby do leakdown test
or
remove the one way valve in the hose, install a screen fuel filter inline or couple of elbows and stuff with steel wool or equiv.
or
your hose comes from stator cover? balancer shaft seal is leaking causing excessive oil inside stator cover. all their twins have this. not sure about singles.

 

[Junkie]

I started the same thread on KTMTalk and Thumper Racing, the manufacturer of the big bore kit, replied. After PMing them with some info, I got this reply

It's easy to identifyour cylinders for the last 3 years plus our name/logo is lazer engraved on the outside of the cylinder on the timing chain side of the cylinder. before that we did use an electric pen to date and scribe our name on the bottom of the cylinder. I just looked up his order and it was placed in in May of 2015.

What concerns me is I show in August of 2016 he sent his ECU in for a reflash to the 520 kit which we didn't do when the kit was originally purchaced in 2015?? I hve no record of how fueling was done before he sent his ECU in for a remap to the 520 kit.

If the motor was run for any length of time with the stock 450 mapping as a 520 for the time in between when we sold the kit and the remap was done on his ecu there could have been significant issues and even cylinder damage due to underfueling. running stock mapping in the 520 will shorten the life of the kit to about 10 hours due to the exssesive lean condition of the fueing.

After verifying oil level a leak down would be the next thing to do that will tell you the condition of the cylinder and rings. I would also check fuel pressure and replace the small inline filter used in the tank quick disconnect just to be sure there are no fuel supply issues that could contribute to a lean condition.

 

[byke]

If it were me I wouldn't want a 520 big bore kit for sumo work.

 

[Junkie]

I realized I wasn't entirely clear in the first post - the bike has a 520 big bore kit on it, with ~10h on it.

 

[Ahab]

I have the same thing on one of my bikes. Checking oil after the first session appears to give a better reading than checking after a few minutes of idling. Don’t fill up to the max until you have ridden it

 

[dmfdmf]

Crankcase Vent Filter**

**for race applications only! ;-)

 

[kuksul08]

You can install an oil catch can to more easily quantify it and also keep it from getting in the airbox and making a mess.

 

[ratsblast]

No big deal, vent to ground. My Sporty puked tons of oil out the airbox before I routed it to the atmosphere. A high strung single might puke a bit of oil, as long as you have oil in the bike you are good. My BeLast pukes oil out the airbox.

 

[Junkie]

No big deal, vent to ground. My Sporty puked tons of oil out the airbox before I routed it to the atmosphere. A high strung single might puke a bit of oil, as long as you have oil in the bike you are good. My BeLast pukes oil out the airbox.

vent to ground on a bike that gets ridden on track? :rofl

 

[auntiebling]

if you point the vent tube up, it could be like an oil rooster tail... kinda like the intentional jet on a yamaha waverunner

 

[numist]

Depending on how much oil you get in the air box once you’ve compensated for the lowered front (maybe check it on a dirt bike stand if you have a box frame) you might consider an air oil separator. It’s the right solution for the problem but you don’t usually see them on bikes because it’s more $$ than a catch can. It’s easier on the engine and less mess than venting to the ground.

 

[Junkie]

the bottom of the frame isn't level

that may be the real cause: it was checked on the stand rather than on it's tires, so it was leaning forward some, which means the oil level would be higher than it should be

you can see there that the front is significantly closer to the ground than the rear

 

[ratsblast]

Put a baffled vent vertical then, the oil will condense in the vent tube and run back into engine.