Topic: oil air lock?

[Bill K]

 Helping a friend with his 78F build. Engine built back in bike, after adding oil to the tank it just stays there. We pulled the drain plug and the pan in dry. Do we need to burp this thing or what? I didnt have any issue like this when i did my build a few years back.  Any help appreciated .... Thanks!

[Grabcon]

If I understand these motors and oil systems the oil pump moves the oil. It will not move from the oil tank to the crank case unless the oil pump moves the oil. Before starting kick it over a few times to see if the oil gets to the crank case.

There are cases where if these bike sit for a long time the oil will seep past the check valve an fill the crank case, but it should not happen over night.

Look in the CB750 Shop manual in the Engine Mechanical section. It shows a diagram of the lubrication system. The one I down loaded from this site show the diagram on page 26.

[lucky]

Helping a friend with his 78F build. Engine built back in bike, after adding oil to the tank it just stays there. We pulled the drain plug and the pan in dry. Do we need to burp this thing or what? I didnt have any issue like this when i did my build a few years back.  Any help appreciated .... Thanks!

You need a workshop manual.
The CB750 is a DRY SUMP engine like a porche or some airplane engines.
The oil is stored in the tank not in the engine.

[Bailgang]

I had the same issue with my kids 73 750. I knew it was a dry sump but it was the first time I ever dealt with a dry sump and didn't know what to expect. Before actually firing it up I turned it over with the ign off during which time oil level in tank dropped which told me the oil pump got the idea and all was well.

[wrenchmuch]

Air can be introduced to the tank return line or the pump and will prevent the pump from priming . Some remove the pump and immerse it in oil while rotating the pump gear back and forth until the bubble is dispelled . You can also try introducing a little pressure to the tank while cranking the engine .
Remove the plugs when doing this . Revs will drop slightly when the pump primes (you'll hear it ). I capped the fill hole with my fingers and put the air line between my fingers to get pressure into the tank . Crank while introducing the pressure ( assistant required ) . By pressurizing this way you can't put too much pressure in the tank . This method has worked twice for me . Your results may vary . 

[Bill K]

  I'm not new to these bikes, I have a workshop manual and my budy has Hondamans book. I'm very much aware of the DRY SUMP and how it works. I just thought it was strange how the oil just sit in the tank, never ran into this before. We cranked it with the switch off. Thanks for the suggestion of some air pressure in the tank wrenchmunch, we'll give that a try.