Topic: Oil leak from oil tank?

[bhambren]

Hey, folks.  New, first time owner and brand new to this group.  I just bought a survivor '76 CB750 Four - a life-long dream.  Runs great but has a massive oil leak on the right side.  Best I can tell is that it's leaking from the bottom of the oil tank.  The supply and return lines from the oil pump are dry and clean on the outside.  I thought the culprit was a missing vacuum line but after fixing that, still losing tons of oil. 

It only leaks when running - to the tune of about a quart every 10 miles, so it's quite a mess.  I wouldn't have suspected the tank is breached except the bottom of it - the seam - is the highest point on the motor where fresh, leaked oil presents itself.  The oil tank drain plug is snug and dry.  Bottom of the motor is clean and dry.

I haven't removed the oil tank yet.  Thought I'd check with you folks for advice on whether I'm on the right track and possible testing, fixes or replacements.  Used tanks on ebay are reasonably priced but hard to know whether I'm getting a dud.  Thanks in advance for any advice you have for this newbie.

[disco]

Not uncommon. The oil tank in my ‘76K developed a small pin hole too. I guess it was unridden for a while & condensation caused it? Anyway brazed it up fairly easily & it’s been OK since.

[ekpent]

  Make sure that the hose coming out of the breather on the back of the engine valve cover is not plugged up and free to breathe to the atmosphere. I did a 1975 750 that spewed oil and a  paper wasp had blocked that hose. Pic of some of the crud in it. Hose coming off the back of the engine needs to be clear also and hooked to the oil tank. Also make sure the tank is not overfilled and has the correct amount of oil in it.
PS-Welcome to the forum !

[bhambren]

Holy Cow!  You guys may have a laugh at this.  I guess I messed up.  I routed a hose from the back of the motor to the back of the valve cover.  I guess I need to undo that.  Might be why the leak seemed to worsen after I did that.  So that nipple on the back of the block routes to the oil tank?  There's a hose coming down from the bottom of the oil tank just pointed at the ground near where the carb drain lines go.  Is that the orifice that connects to the back of the motor?  Thanks so much for the help, guys!
Matt

[ekpent]

 Yes redo the hoses as you described. Valve cover hose open to atmosphere and oil tank to lower back case nipple. See if that fixes it.

[scottly]

There is a nipple on the back of the oil tank that is the same size as the nipple on the back of the crankcase; this is actually a drain from the oil/air separator, and it's normal for oil to come out of the tank and drain into the case when the engine is running. The attached pic is a K1 tank, without the battery box blocking the view; your tank may be different. The nipple on the valve cover should have larger hose that routes over the top of the carbs, and down near the carb drain lines, like the tank vent hose you've described. Make sure the vent hoses are routed towards the right side, so any oil expelled doesn't go under the rear tire.
 

[PeWe]

My K6 oil tank has no vent to air as the earlier. 2 x Oil lines to/from pump. Spigot for hose to rear of the case.

Correct oil level?
Check when engine is warm, after a 20-30 minute ride. The pump might allow oil to flow to case when parked. Oil level look low, more oil in tank when cold that will overfill the tank when warm.

[bhambren]

Many heartfelt thanks for the info and feedback.  Will try what’s suggested and report on results. 

[bhambren]

Looks like my tank isn’t bad after all... connected the lines as instructed and working like a champ!  Now on to other challenges!  Thank again, everyone!