o7 dumping oil out of vent PLEASE HELP

yesterday when i was putting my bike up i dropped it when i got off and oil started coming out of the vent on top of the engine. later that night i go out and fill it back up with oil and let it run for a few minuets, no oil came. out. today i get it out and it wouldnt start for nothing, when it did, it started loosing oil out of the vent again. i dont know what to do, im scared if i have to rebuild it. if anyone can help that would be really great.

:smirk: your "scared" haha

sorry just sounded funny.

I honestly would not worry about it, wouldn't hurt to make sure the oil level is in check and top up if necessary.

The breather is basically a direct and unfiltered/unobstructed hose to the inside of the valve cover, where raw oil is being used to lubricate your cams, bearings tappets etc. Point being if the bike tips, oil will probably come out if there happens to be some left up there, and it's nothing to worry about.

I'm trueblues dad.

Its not just oil draining off the top end. Its more like the oil is getting pumped out the top end. It would probably pump a quart in just a matter of minutes. I'm wondering if it broke a ring. Letting compression blow oil out the top end. Thats where the "fear of rebuild" has come from.

You are probably not going to like this but oil coming out of the vent hose is a sign that you need a rebuild. What is happening is the ring/piston/cylinder seal is not keeping the compression above the piston. Its blowing by and forcing oil from the bottom end up to the top end and out the vent. Being a 07 it's probably time. Just my guess. A shop can do a leak down test to be sure.

Just for fun, let's try draining the oil entirely from both the front and rear drains, then add back exactly 1 quart. See what happens.

I was going to say the same thing. Gray is there a reason that the Yamaha does this ? cause if you think about it its just gravity feed back to the bottom or is there enough pressure in the motor to force just a little out ? I've had the same thing happen with just 50 to 100 ml overfill.

The engine is designed as a "dry sump" oiling system in which oil draining away from the crank and top end (and in Yamaha's case, the transmission as well) is picked up by a second oil pump and returned to an external tank or a reservoir built into the engine. With the second and third generation YZ450 (aluminum frames), there is NO extra room in the reservoir for any additional oil, and any more than a few cc overfill will be forced back to the sump by way of the pressure balance line that runs from the top of the tank to the right engine cover. That raises the oil level in the sump to the point that the crank will drag in it and throw it around in the engine, and if there's lot too much, it can cause interference with the oil running down from the top. thus leading to oil out the vent.

So before anyone panics, let's check the oil in the bike to be sure it's correct.

The engine is designed as a "dry sump" oiling system in which oil draining away from the crank and top end (and in Yamaha's case, the transmission as well) is picked up by a second oil pump and returned to an external tank or a reservoir built into the engine. With the second and third generation YZ450 (aluminum frames), there is NO extra room in the reservoir for any additional oil, and any more than a few cc overfill will be forced back to the sump by way of the pressure balance line that runs from the top of the tank to the right engine cover. That raises the oil level in the sump to the point that the crank will drag in it and throw it around in the engine, and if there's lot too much, it can cause interference with the oil running down from the top. thus leading to oil out the vent.

So before anyone panics, let's check the oil in the bike to be sure it's correct.

Thanks Gray! thought you would know...:smirk:

Were going to give that a try first. After doing more talking with him (trueblue) I really believe its way over full.

Sure enough, it was way over full. Teenagers!! Gotta love em!! Thanks to all!!

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