Jump to content

2008 KX450F Excessive Oil Lose From Breather Hose

Recommended Posts

Good Day All,

Please help or point me in a direction of someone who might have this answer.

I have a 2008 KX450F with less than 1 hour of time on it since completely rebuilt (cases split, piston, rings, cam chain etc, the bike was rebuilt with the same style modified parts that was in it before the rebuild). It will spit oil out of the breather hose while sitting on a stand after about two minutes and a couple throttle burps. When I say spitting out, it will run out almost like gulping from a quart bottle. I was not around the bike for the bike break in, but no one seemed to notice oil coming from the breather hose. I cannot verify if the problem was present then or not.

When talking about the engine being rebuilt or torn down, the work was done by a motorcycle mechanic. I did some of the test mentioned below.

Here are the events leading up to where the bike spits oil out sitting on a stand.

There was a transmission fork problem that surfaced right after the engine break and the engine was pulled apart two times since then.

(Because of some miss communications, we started this next paragraph with about 1200 cc of engine oil without a filter change.) After getting the transmission working properly, we noticed engine oil coming out the breather hose at a motocross practice track after a 10 lap session. It also looked like it was coming from behind the front drive sprocket. We washed the bike around the area, routed the breather hose to the other side of the engine, drained the engine oil (drained about 500 cc from the engine) and refilled the engine with 1000 cc of oil. We sent him back out for a lap or two to see if it was coming from the breather hose or a blown seal behind the front drive sprocket. It was definitely coming from behind the front drive sprocket but the breather hose had moved enough we could not tell for sure if it was still coming out there as well.

We changed the front drive sprocket seal. We also looked at the screen behind the cover that is behind the ignition rotor. It was not blocked with anything. (I did use a brake clean to spray through the screen. Could that have damaged the rubber supporting the screen?) We started the bike up on the stand for 30 seconds or so and no oil from the breather hose. Went to a local practice track, had him do one lap. There was oil all over everything right behind the breather hose. Again, drained the oil, this time, changed the oil filter, took the breather hose off the bike and made sure it was not blocked. Put in 1000 cc of oil, started it on the stand, and in about two minutes of running with a couple throttle burps, it started to pour out the breather as if it was being poured from a bottle. It was gulps, not a straight stream. As gross as it sounds, almost like a person puking.

Then we decided to check the rings. We put the engine on TDC, aligning the marks on both cams with the top of the case and the timing mark on the rotor to the site hole marks. We put 15 PSI into the engine and the pressure moved the piston. Then we realigned everything and tried again, but this time we had someone hold the piston in place by holding onto the 8mm nut to turn the engine with a T-Handle. If was very hard to try to hold this in place, almost looked like at times when a drill bit catches while drilling a hole. While he held it as best he could, at 15 PSI, we open the oil fill plug and checked for air at four locations (oil fill hole, end of the breather hose, the timing inspection hole in the ignition cover, the hole to turn the engine over in the ignition cover). We felt no air from any hole. Again it was difficult to keep the piston still and if we put more than 15 PSI into the engine it became impossible.

There were no issues before the engine rebuild, and I would say that when it came to the engine oil level, I would always put in about 1100 cc of oil because I could not mentally get past the idea of not seeing oil in the site glass.

This is our only bike and obviously we cannot ride it the way it is. Can you PLEASE help or point me in the right direction for help. My phone number is, 610.451.1222. My email is GregoryLamey@yahoo.com.


Link to comment
Share on other sites


I got a call from someone and they told me that the oil ring just did not seal and sometimes that just happens even with it being a new ring. Said if I take the engine apart, run a ball hone through the cylinder, take scotch guard over the oil rings, and reassemble it would be fine again. Said it happened to them and that was the fix.

Any thoughts ??


Link to comment
Share on other sites

Brake cleaner can do dammage to some kinds of rubber. But off the top of my head I would lean to a gasket was put on upside down backwards or something like that. That could cause a oil passage to be blocked not alowing it to drain or build excesive pressure.

Link to comment
Share on other sites

Check your oil transfer pump. If it is not working your bike will "puke" oil out of the breather hose. With the enging being taken apart so many times it is possible that the pin fell out and the impeller is not spinning, or that something got in the impeller and broke the shaft ears, The locating pins on the cover can easily come out during dis-assembly/assemble and get nto the impeller (don't ask how I know). It will be easy to lay the bike on it's side and pull the cover to inpspect the transfer pump impeller assembly to make sure all is good and rule it out. The stickies above have some good pics of the impeller assembly if you do a litle searching on cleaning the screen. Good Luck.


Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

  • Create New...