Tech Tips @ CB750.org - Checking the oil on a CB750K SOHC

Checking the oil on a CB750K SOHC

Have you ever added oil to your oil tank thinking that it was too low, just to find that when you start the engine, it was now over filled? If so, don't feel foolish. You are not the first person to make this mistake. Your oil level should always be checked after the engine has been run (warm) and not when it has been sitting(cold). Overfilling will cause the excess oil to empty out through the breather system and overflow onto the ground right in front of your rear tire causing some very unusual and dangerous handling characteristics.

The CB 750 is one of a few Japanese motorcycles that incorporated a dry sump oiling system. This system is use by many British bikes as well as Harley Davidsons. Dry sump systems are also very popular with auto racing enthusiasts. All these machines have a separate oil tank that stores the majority of the oil. About one third of the oil capacity is stored in the engine case. The advantage to this system is that the volume of oil can be increased without enlarging the engine cases. It also allows the oil to cool, which keeps the engine cooler. The downsides to dry sump systems are two-fold. First, the oil tank needs to be connected to the engine via oil lines that can leak or even worse break. If this should occur, your engine will quickly meet its demise! The second problem is "wet sumping". Wet sumping is a condition that is caused by the oil pump check ball allowing the oil in the tank to empty into the engine when not in use, causing the engine case to overfill. When this occurs, the oil level in the tank will appear low or empty giving you the impression that you need to add oil to maintain the proper level. As soon as you start the engine, the excess oil in the cases will be pumped back into the oil tank. Now the extra volume of oil has no place to go, except out the breather and on to the ground.

Remember to always check your oil level, keeping in mind that having too much oil can be as bad as not having enough!

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