1988 LT80 Crankcase Full of Oil

[JohnnyB]

Greetings, 

Have a 88 LT80 that been sitting for a couple years. Bought a new piston, cylinder and head. Installed these, rolled it over and it quickly locks up.  Took carb apart. It was full of what appears to be 2 cycle oil. Cleaned it, but keeps locking up and 2 cycle oil continues to seap from exhaust port.  When i installed new cylinder, I noticed crankcase was full of oil.  I'm now wondering if that oil is what's getting sucked up into cylinder.  Should there be no oil in crankcase?  If that the case, how is crank and rod lubricated?  Sorry, never worked on a 2 stroke. Thanks!

[Mech]

I'm pretty sure the oil pump will have a spring loaded valve(check valve) to prevent oil from the oil tank draining straight through the pump and into the engine. The weight of oil under the influence of gravity isn't enough to open the valve, but the vacuum/pressure applied to the oil by the pump does open the valve. To test that valve you might be able to disconnect the hose going from the pump to the carb or inlet and watching to see there is no slow leak of oil from it. I say might because I'm not sure that will have a oil pipe, some models might pump oil through a hole in the cases to the main bearings. If the oil isn't leaking out of the hose it may be leaking from the pump into the engine due to wear, but, even with wear it should only leak when it's not running, if the check valve I described isn't working.

And..  All that said..  Are you sure it is oil overflowing out of the engine ? Those oil tanks don't hold much oil. Are you sure it's not fuel with a bit of oil in it ? Have you checked the fuel tap is operating properly ?

And to answer your questions.. The insides of older two-strokes were lubricated by oil mixed into the fuel in the fuel tank. In those models they got too much oil at light duty, or too little oil under sever conditions, depending how much oil you pre-mixed into the fuel. In later models they used a small oil pump to inject oil into the carb or inlet. The pump is adjusted by a cable from the throttle so that the pump puts out more oil at larger throttle settings. That tends to ensure the engine gets the right amount of oil for the load it's under. That system though still didn't distribute the oil to the critical places as well as we might hope so in even later designs they started pumping the oil straight to the main bearings and it got mixed and distributed with the fuel to lubricate the rod and pistons in the crankcase. Some models they used oil straight to the bearings, and to the carb or inlet, at the same time, using hoses or drilled passages.

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Edited May 26, 2024 by Mech

[JohnnyB]

First off, Thanks for the detailed reply.  The fluid I drained from the carb and seapping out the exhaust port is definitely straight 2 cycle oil.  It's blue and thick.  It will only crank over a few times before it "locks up".  I pull the spark plug and it's dripping with oil.  I turn it over without plug until no oil comes out, put the plug back in and the same thing happens.  I have fuel off and line from oil pump disconnected.  The oil tank is also empty after sitting which is why I thought it may have drained into carb and crankcase.  My thought was to just premix the gas as you mentioned was done prior to oil tanks.  I just bought the manual(I'll have print as its hard to read PDF on my phone), but not seeing anything about filling or draining crankcase.  There is oil about an inch from the bottom of cylinder once removed. I just don't understand where else oil filling the cylinder could be coming from after I drained carb and rolled it over without plug have fuel and oil injector disconnect.  I'll pull the cylinder off and take a photo. 

[Parham]

I have NO experience with 2-stroke...I just came to look at your post to see why "crankcase full of oil" would be considered a problem 🙂

 

[Mech]

#3 Yup well better check why oil is going straight through the oil pump...  Unless.. new thought.. Someone has got the hose from the oil tank going straight to the carb or engine, so it['s just draining all the time. That would explain the high flow rate. A pump should take weeks or months of slow leakage to fill a sump.

Check the plumbing !

 

[Gwbarm]

I have had this happen before on a 2 stroke scooter, it had been sitting for 10 plus years, it did the same as you describe lock up engine, took me forever to get all that 2 stroke oil out of the crankcase, and it still fowled 2 or 3 plugs before i got it right. I took the hoses all off and drained the oil tank, ran it on premix. Couldnt really disable the oil pump without tearing the engine down it ran off the crankshaft, and was not really on my high priority list, After deleting the oil supply i realized that this pump wasnt going to pump very long without oil and it was always turning when ever the engine was running. So hooked the oil back up to the pump, but instead of rounting into the carb i routed it back into the oil tank.  Didnt work well because oil was not getting into the crankcase VIA the carb it was from a bad seal at the oil pump. 

So my recommendation after all this howee is to replace the oil pump seal or pump itself, or dont store it with a full tank of oil. 

[JohnnyB]

My thought was it's so full, it's sucking it back up in the cylinder.  I don't have fuel or oil line connected, yet oil is still filling the cylinder to the point it won't turn over because of high compression. Oil also continues to leak out of exhaust port. After sitting a couple years, all the 2 cycle oil was gone from tank.  It filled the entire carburator including bowl.  I'm assuming the rest drained into crankcase.  I just don't see any fill, drain or level ports to confirm.

[JohnnyB]

Good thoughts.  I just picked the quad up and drained crankcase.  I'll replace oil pump and try again.  Thanks for everyone's help!

[Gwbarm]

I think that would be the best solution. Good luck!

[Mech]

I'd misunderstood and thought it kept filling the crankcase repeatedly.

If it's taken a couple of years to drain the tank then I think I'd just invert the bike and let the oil drain, then get it going.. It's likely be fine.

 

[JohnnyB]

Drained the oil out of crankcase and it rolls over now.  Just need to clean the carb and she if she fires up.  I'll provide an update within the next week.

[Gwbarm]

Good you had a drain, the one i was working on didnt have a crancase drain, and took forever to get it out with a syringe.

[JohnnyB]

Back in business.  Runs great again. Thanks for everyone's comments!

[Gwbarm]

Good  you got it going. Did you have to replace the pump.