Gas in crankcase: what does it MEAN?

[knewsom]

Hey guys,

Not sure if I smelled gas in the oil in my 78 (which, by the way, I'm purchasing tomorrow after a compression check), smelled oily, and I think I smelled gas, but it might've just been in the air - my fingers didn't smell like gas after dipping them in the oil really, but this sparked my curiosity - what if there WAS gas in the crankcase? what does it MEAN? Basically that the oil is doing nothing? Gas just cuts the viscosity of oil, yes? If one HAD gas in the crankcase, what would one best do about it?

Cheers,
Kris

[JWSanders]

Drain and replace, including the filter.

As long as it wasnt run very long with gas in it, it should be ok. I don't want to think about the ugliness associated with leaving it in too long...and all the associated grinding, knocking, and death sounds it will start making.

Should do that after you get the bike anyway. As well as all the other fluids -- brake, front gear, rear gear, and forks if you feel really frisky. They're all cheap enough that it's worth the peace of mind knowing you have fresh everything.

Good luck on the compression check!

[mason79]

i guess i'm an old timer when it comes to gas in the oil, your carbs are overflowing, valve worn, sinking float, or worn o-ring for 80's and newer, does that sound right to you?

[prometheus578]

"I've got gas."

Gas in the oil denotes two things. Vacuum petcock leaking when off, or the float needles are leaking. (Carb float bowl fills up and overflows. Fuel comes out the carb into the airbox, or drains forward into the cylinder then down past the rings into the crankcase)
With the tank full o' fuel, pull the fuel lines that run to the carbs. Stare at the petcock fer a spell. If it doesn't leak... keep starin' at it a while longer. If it still doesn't leak... then it should be OK.
That leaves the float needle valves as the culpret. when you pull the carbs to clean them, which you will, replace the float needles. (about $4.95 per from just about any bike shop) Use some chrome polish and Q tips and clean out the seat where the needles live. Make sure that you flush the seat and the fuel line with spray carb cleaner to remove the polish when done.
The needles get a "wear ring" on their tips from use, and also from sitting against their sealing hole... like when the bike sits for years. Petcocks can also leak fuel over several years of sitting, but be perfectly fine for everyday/monthly use.
One final thought (Yeah... like I ever have a final thought) Bikes that don't run (no spark) can also get fuel in the crankcase by the owner trying to start it... crankin' and crankin' for days, but that's not too common. My bet's on the float needles.

what if there WAS gas in the crankcase? what does it MEAN? Basically that the oil is doing nothing? Gas just cuts the viscosity of oil, yes?

Gas obviously thins out the earl. You've gone from 10w40 to 10w nothing. This may be causing your knocking, if there's enough fuel in the oil.
Your crank, cams, etc, ride in their little holes on a cushion of oil under pressure. Oil pressure is what keeps the crank, rods, etc from rubbing directly again' the bearing surfaces. The oil under pressure is forced next to these surfaces, where it then squirts past and out after doing it's job. If the oil's too thin... it will squirt out under pressure a lot easier, and not provide the cushioning effect.

[scalded dog]

Take a green limb off a tree, about as big as a pencil or smaller, dip it in the oil, put a flame under it, if it burns, there is gas in the oil, if not, you should be fine. Later 'Dog

[knewsom]

Awesome, thanks so much for all the great info! I'm the sorta guy who needs to UNDERSTAND something in order to remember it.

Neat trick to see if there's gas in the crankcase, I'll def. try that before starting the bike again.

I think I can talk the dude into delivering it to my house via pickup truck, but if I can't, and I have to ride the bike home... The front tire has a lot of cracks and is pretty sketchy looking. Should I take it STRAIGHT to a place where I can get a new front tire before even taking it home?

Cheers,
Kris

[scalded dog]

Front tire, it's always better to be safe. These bikes are awesome, you won't regret buying it. Later 'Dog

[mason79]

i notice with the gas in oil sydrome that the crankcase got pretty clean and the black stuff inside the engine settled on the bottom, could this be good, or did it do irrepairable harm?

i read some guys like to use engine flush for oil changes, is this not the same concept?

[John]

Running the engine AT IDLE with gas in the oil should'nt be any worse than running some Berrymans B-12 through the system. The fuel will help to dissolve any sludge in the oil gallies, and help to rinse away the deposits that have developed in some of the nooks and crannies where the oil will pool and collect.

[mason79]

i took a long flat tip screwdriver and stuck it in the oil filler, put a lighter to it and it would not catch on fire, but the oil sure is dirty,i thought there may be gas in it from my suspect carb work,

i just changed it, with no miles on the oil, just foolin with it tryin to get it started thats all, and now that it starts all the time should i change the oil again? it looks dark in the view hole...

[TopCatGr58]

Hey Mason,

You shouldn't need to change it yet. The oil can look bad in the view window due to sludge buildup IN THE WINDOW. Next time you have the clutch cover off, you can clean that window. You can try to clean it now by either getting some LONG Q-tips, may still need to tie them to the end of a screwdriver, and stick it down inside the crankcase cover, there are slots in the backside of the metal that holds the window in place, you can fit the Q-tip in between those spaces to scrub the window.

Try using the side stand, you may need to put something under a wheel to get enough tilt angle to drop the oil below the window!

However, there might still be lots of sludge in the bottom oil/tranny pan, and after putting in fresh oil, the oil mixed with the sludge, freeing it up, and getting it mixed in, dirtying up the new oil! The tranny pan can be removed, cleaned and replaced without pulling the engine, but might have to pull the pipes depending on which ones you have, and how they are laid out!
T.C.

[mason79]

hello topcat!

there was soooo much gas in the oil when it was drained, i peered down the filler with a flashlight and i was squeaky clean, virgin machined parts!

the view window i cleaned and while on the side stand is clear, can the oil go a thousand miles while it mixed with the sediment from the 91 octane engine flush?

i think i have a leak, i thought i fixed by changing out the shifter cover gasket, i did not know there was oil behind it, (should have hello, oil leak)on the floor it went what a mess, luckly the drain pan was 2 seconds away. 2 seconds ia a long time sometimes.

then i traced the leak to the engine pressure sender, it flows down to the frame, i thighen it, but it statred again, is this common?

can i putr any 'ol oring or is this a yamaha part number?