Oil Line Shut Off To Prevent Wet Sumping?

[86FJNJ]

I'm new to SOHC CB750's, I noticed that when my bike sat for a while a lot of oil drained from the tank back into the case, likely overfilling the case which from what I read is called wet sumping on these models. In my cafe rebuild I'm going with a custom oil tank and 8AN lines. In order to prevent wet sumping should I install an 8AN shut off valuve in both the feed and return lines that I can close when the bike is being stored for long term? Yes, I know I would need to ensure I never start the bike with these in the closed position. If I don't go that route, is it bad to start the engine with that extra oi in the case or is there a simple way to purge the excess oil from in the case before starting without having to drain the case and refill? Does the wet sumping happen from both the feed and return line or just on the feed line?

 

[dirtdigger]

Two things...the oil pump has a check valve on the tank suction side in the stock oil system configuration. They go bad and cause the oil to drain to the sump. The other thing that hardly anybody knows is the design of the stock oil tank prevents oil drain back on the oil return to tank side. The return side would ideally dump into the top of the tank or near the top of the tank. Cut open a stock tank and you will see what I mean. so yes it cant wetsump from both lines if the tank design is incorrect.

 

[86FJNJ]

thanks dirtdigger, the oil draining into my case happened with the stock tank so perhaps the check valve is bad. On the custom tank I'll make sure the return dumps to the rear of the tank towards the top. But what are your thoughts on my idea of an 8an oil shut off like this? I could mount the valves right next to the key and starter button so it's part of the start cycle to ensure they are open.

https://nitrousoutlet.com/products/...FLDhOM_fEe_vA67OJhMcz2921rSHRZv4aAko_EALw_wcB

Or, if I let nature take it's course is there a go to method to purge the extra oil from the case other than draining and refilling? Or if I don't do anything and start the bike with more oil in the case will it just blow out of the crank case breather? I could ensure I route that to an area on the rear side and put a can to catch the overflow on start up.

 

[dirtdigger]

if the tank is built right and the checkvalve in the oil pump work there is no need for a valve of any kind. You will always have some oil in the engine sump but if it all drains the check valve is bad and needs fixed. As long as you still have some oil in the tank to supply the oil pressure pump you can start it and let the scavenge pump do its job. If the tank is empty and you start it you will be running the engine dry with no oil pressure. Its normal for the oil to drain down a certain amount especially if it sits for a long time. In that instance I just drain from the sump and fill the oil tank, not a big deal and saves you engine from damage from no oil.

The only crankcase breather is in the valve cover and it will never get that full of oil. The only other breather should be in the oil tank and it shouldnt overflow there either unless its overfull to start with.

Thousands of the engines are running in custom bikes with no valves and no catch cans so I think you are overthinking things and just need to make sure oil tank and oil pumps are working as they should no need to overcomplicate things

 

[86FJNJ]

ok and fair point but dont know unless I ask, I do tend to overthink things but better safe than sorry, thanks!

 

[dirtdigger]

no problem