Air from the oil cap

[Lou Ras]

Hi
I just replaced the crankcase cover gasket and was running the bike on the centre stand while topping up with oil. There is a significant wind (air) blowing from the oil cap when the bike is running. Is this normal? It doesn't use oil and the exhausts burn light greyish white. No loss of power or increase in consumption. Any suggestions??
Thanx

[Lucky]

Yeah, one suggestion: leave the cap on while the bike is running.

why are you adding oil while the bike is running? You can't 'top off the oil' this way.

[Extent]

^^^^

Ya it'ld be really easy to overfill it that way, actually you're guaranteed to overfill it if you don't let it settle after the engine has been shut off.  FWIW tho the air is probably normal, you can get quite a bit of air moving up thru the crankcase vents that go to the air box, I imagine that it could come out the fill cap just as easily if it wasn't closed up.

[louthepou]

Hi Lou Ras,

Yep, gotta stop the bike to top up, otherwise you'll put one gallon too many.

The "wind" is due to the fact that when the pistons move up and down, the volume of the "bottom" part of the engine changes. Think about it - a piston moving down is pushing the air underneath, and when the oil cap is removed, there's a place for that pushed air to escape.

Funny story: forgot to put the cap on once, started the bike, reved the engine then sprayed ooil all over my leg. Doh!

Louis

[Lou Ras]

Ok, I did not describe correctly. I let the bike run, switch it off. Wait a few minutes and then top it up. You did answer my question though. If this happens to my car it is time to replace the piston rings - that's what got me worried.

[QBS]

Don't worry.  Be happy.  If it ain't broke, don't fix it.

Cheers.

[silicon_toad2000]

You'll find in a car you can get quite a bit of blowby before it start using a lot of oil.
Being that the oil cap on the vision is basically in the sump copmpared to a car which is in the rocker cover, I would expect a lot more air moving about at the oil plug for the vision.
If you are worried about it, you could do a compression test just for peace of mind.

[jasonm.]

You are overfilling the engine if you do not let it fully warm up...run for 20 minutes or miles. It takes 30 minutes for the oil to come up to the line after a complete warm up.

[Lou Ras]

How would I know if the engine is overfilled ??? ??? ??? Has it got some kind of overflow ???

[h2olawyer]

There are a couple methods to check if your oil is overfilled.  First, check the sight glass.  There are two small lines molded onto the left crankcase cover.  One is for low oil level & the other denotes the high level - about even with the top of the sight glass.

The other way - look in your airbox.  If you have a fair amount of oil coming up through the breathers from each cylinder, into the airbox, the most likely - though not sole - cause is overfilled oil.

H2O

[QBS]

The easy way to determine if your V is over filled is to enlist the aid of at least one or preferably two worthy assistants to  lean the bike over to its' right side while you kneel beside it and observe the sight glass.

A properly filled V will begin to reveal its oil level line immediately after it passes from its veritcal balance point and is headed toward leaning over to the right side.  The further the bike must be leaned over to the right to reveal the oil level line, the greater it is over filled.

After the level line has revealed itself, estimate about much oil that degree of lean represents and then clean the area around the oil drain plug and then carefully drain that much oil into a very clean container.  Do the level reveal procedure again and drain as nessessary until the oil level line is visable in the site glass when the bike is at its central balance point.

Put the bike on its center stand on level ground and use your drained oil to carefully and slowly bring the oil level line up to just touching the top of the site glass window.  The bike is now properly filled.

Cheers.

[louthepou]

Better aim at the top "full" mark in that window; one a long time ago (1987) I destroyed my first Vision engine for keeping the oil level too low, too many times for too long.

Louis