SOHC.co.uk Forums > CB750

Dry sump!

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Johnny4428:
What controls the amount of oil in the sump of the 750? I drained oil and refilled tank, started up ran for a short while and the oil disappeared completely off the dip stick. Topped the oil up again. Since drained the sump again just to see amount of oil, and took 2 litres of oil out. Is this normal?

Rob62:
Sounds like you may be making it more complicated than it is. The pump controls the oil, all you need to do is fill the tank with the specified amount, run the motor and check that the pump is working (you can see the oil returning to the tank and foaming slightly with the cap removed) and then when its all cooled down re check the level....

Johnny4428:
Thanks Rob, I don’t have any experience with these dry sumps other than the Matchless I have, very simple system. Just not convinced the oil was being pumped back to tank! Certainly comes up to oil pressure and circulates in engine.

Rob62:
I dont think you can tell straight after firing up...but once its been running a bit and you look into the top of the tank you will see some foaming as the oil returns....

K2-K6:
There's a check valve in the oil pump that prevents the tank running through to fill the engine when it's not running,  that should make the level stay consistent in the tank during normal use. Failure here is similar to the old British bike condition of "wet sumping" which riders checked for if their bike was of this type and had stood for a period of time.

When you change the oil and filter during service on the 750 through,  the initial "fill" to top level on dipstick would drop a fair bit as soon as you start it as it will initially fill the filter housing from this volume,  but shouldn't ordinarily drop below the minimum mark on the dipstick. 

All being normal you should get a consistent "read" of level on dipstick whether it's running or not. Significant variations would suggest you'd need to look further into how it's working.

It's only a significant risk if the level drops so low that there's no head of oil to feed the pump.

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