Topic: CB450-- fuel and oil gushing out of crankcase breather

[paulages]

this isn't my bike, but one i sold to someone so i'm trying to help figure out what's going on. she called me saying that fuel was spraying everywhere, and that it was oily. i didn't really believe her description, as there are really only so many ways fuel and oil can get mixed up, right? i figured the tank-balancer tube had split or something.

well, i started the bike and sure enough, oily gas was gushing out of the breather hole. she apparently left the petcock on and a float stuck. that much i get. but i'm wondering if the rest of my guess-agnosis is correct. i'm thinking the crankcase and/or head and cam compartments pretty much filled with gas, and the gushing is from the excess pressure created when the top end is "oiled" with a really low viscosity oil/gas mixture which can't drain to the sump as fast as it will pump.

i plan to drain the "oil" as well as possible and recheck the carbs' float valves, but i can't help but wonder if the excess pressure could be caused by something else. i don't know the inside of the 450 engine, but it seems like the oil should drain back down the cam chain slot, like on the other hondas of the era.

sound logical? 

[mark]

...........
sound logical? 

Not only logical, but familiar as well.........

http://hondatwins.com/phpBB1/viewtopic.php?t=575

Good luck!

[paulages]

i remember seeing that thread on there, but never looked at it! guess i should have..

looking through that thread didn't tell me much more than that i'm not alone here though. i still wonder why the gas/oil isn't draining back to the sump quick enough to not spray out of the breather. checked the level at the dipstick and it wasn't that high.

[bill440cars]

           I'd be interested in knowing about this one myself. 



                                 
         

[kayaker43]

Its got to be a viscosity thing. I work with a lot of oil filled vacuum pumps that blow oil mist out the exhaust. the oil droplets are heavier than air so a simple exhaust trap that makes the air turn a few corners is enough to drop them out of the airstream.

There's a small hurricane going on inside the crankcase and a lot of gas thins the oil and changes it from a heavy mist to a fog or vapor that the baffles can't catch. Thick oil doesn't atomize well but gas sure does.

I would think a simple oil change would cure it? It may still take a few miles to burn off the residual gas and get back to normal?

I agree though that if it was run for very long that way, there is likely some scuffing to cam followers, pistons and crank bearings.

[paulages]

Its got to be a viscosity thing. I work with a lot of oil filled vacuum pumps that blow oil mist out the exhaust. the oil droplets are heavier than air so a simple exhaust trap that makes the air turn a few corners is enough to drop them out of the airstream.

There's a small hurricane going on inside the crankcase and a lot of gas thins the oil and changes it from a heavy mist to a fog or vapor that the baffles can't catch. Thick oil doesn't atomize well but gas sure does.

I would think a simple oil change would cure it? It may still take a few miles to burn off the residual gas and get back to normal?

I agree though that if it was run for very long that way, there is likely some scuffing to cam followers, pistons and crank bearings.

it wasn't run much at all this way, not even enough to warm up. i think it'll be fine, i just hope that the excess pressure is a viscosity or volume thing, and not some sort of blockage. the downward angle of the intake port doesn't help for gas leak problems.

[mark]

hmmmmm...

You might want to check the carb overflow hoses for blockage. We have a couple (at least) species of insect that just love to nest(leaf bits, mud, or both) in hose ends, bolt holes, and such.