Topic: Dude, wheres my oil?

[mlinder]

SO, I changed oil a while back.
Didn't start it up till very recently. Oil level showed good, before I started it. Ran it a couple times now, up on the centerstand. Looked at oil today, none in there. At least none on the dipstick.
It not really lealing to any large degree, tiny leak at best. Wheres my oil? Is it in the engine? Need to know so I dont add more oil.

oh yeah, 69 cb750.

[ProTeal55]

As far as I am aware, CB750's have a dry-sump oiling system.
Basically that means that some of the oil is kept in the motor, and the "excess" is in the tank.
It is possibile when you ran the bike, the oil that was in the tank is now circulated thru the motor, and you need
to add more to "top off the tank" ? Oil just doesnt dissapear, unless you have a nice puddle under the bike 
I am sure some other members will chime in & help, but I am pretty sure thats the deal.

[kghost]

It is a dry sump engine.

The oil pump has a check valve that keeps the oil in the tank from flowing down into the engine when its not running.

(the tank is higher than the engine and gravity being the pesky beast that she is....)

If your bike has sat for a while it is entirely possible that the oil has drained into the engine thru the chexk valve that didn't quite seat.

Kick it thru with the kick starter and make sure its free.

Then fire it up and I think you'll find the oil is back.

[Bob Wessner]

SO, I changed oil a while back.
Didn't start it up till very recently. Oil level showed good, before I started it. Ran it a couple times now, up on the centerstand. Looked at oil today, none in there. At least none on the dipstick.
It not really lealing to any large degree, tiny leak at best. Wheres my oil? Is it in the engine? Need to know so I dont add more oil.

oh yeah, 69 cb750.

How much oil did you put in the tank when you did the change?

[mlinder]

SO, I changed oil a while back.
Didn't start it up till very recently. Oil level showed good, before I started it. Ran it a couple times now, up on the centerstand. Looked at oil today, none in there. At least none on the dipstick.
It not really lealing to any large degree, tiny leak at best. Wheres my oil? Is it in the engine? Need to know so I dont add more oil.

oh yeah, 69 cb750.

How much oil did you put in the tank when you did the change?

3 qts filled it up to high, much like yours....

[nickjtc]

Sounds like it might be an attack of the infamous wet-sumping. My Norton has a built-in check valve to stop it from happening, since it is a common 'complaint' with dry-sump old Brit iron. Never heard of it happening with Japanese machines though....

[kghost]

Sounds like it might be an attack of the infamous wet-sumping. My Norton has a built-in check valve to stop it from happening, since it is a common 'complaint' with dry-sump old Brit iron. Never heard of it happening with Japanese machines though....

Trust me...it does

[Bob Wessner]

Three qts, there's a famous number.  That's enough to run it on for sure. I would take it out, get it warmed up and recheck the oil level right after shut-down. It's definately wet sumping, quite common.

[mlinder]

Thanks for the help. I figured it was something like that.

[nickjtc]

Three qts, there's a famous number.  That's enough to run it on for sure. I would take it out, get it warmed up and recheck the oil level right after shut-down. It's definately wet sumping, quite common.

Not that this is an issue with my 650, but if a 750 crankcase fills up with oil are there issues with it getting pumped out of places it shouldn't when the motor is first started? Just curious.

[kghost]

not anywhere it wouldn't have been after the gears and crank get done slinging it around.

I suppose if it were really full you could hydraulic lock it....but I've never heard of it happening. Probably would take more than three quarts

[Boomologist]

My chopper does something similar. After an oil/filter change I add 3 qts to the oil tank. start the bike and run it for a minute or so. Shut it off and check the tank and it will take another full quart.(home made tank is a little bigger than stock tank) I know that oil filter doesn't hold a quart so I assume there is about a pint of oil remaining in the sump.
Also, after setting for a winter the oil tank will be down about two quarts  . Start it up and the oil magically reappears.

Another question; I worked on many aircraft that had dry sump engines for various reasons. Some were radial engines with no place for a sump(am I showing my age here), others were dry sump because it wouldn't be nice to suddenly flip an engine upside down with a crankcase full of oil.
But why are the CB750's dry sump? Hopefully it will never be upside down. The only reason I can figure is that they gain a little hp by not having the crank slapping the oil every revolution.

[Bob Wessner]

But why are the CB750's dry sump? The only reason I can figure is that they gain a little hp by not having the crank slapping the oil every revolution.

I always assumed it was to reduce the overall height of the engine package.. but you know what they say about assumptions. 

[Boomologist]

There is still the sump where the oil is picked up. This sump would probably hold close to two quarts if it wasn't being sucked out. So adding enough depth to the pan to add an additional quart would take about 3/4 inch. You would gain some room where the oil tank is and have less parts and check valves to worry about.

[nickjtc]

Isn't it something to do with better cooling too? The more oilways and pipes the oil has to flow through when it is not actually in the engine, the better chance it has of shedding heat...??

[Boomologist]

Yes, anytime you can get the oil out of the engine it will help cool it. If they really wanted to cool it they should have put fins on the tank.

[nickjtc]

Apparently that is the reason that the oil filter housing on the front of the 650 motor is bigger than previous bikes....more internal and external finning for better cooling.