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  • Bobcat broken ring?

    My bobcat sat up for about a year without being cranked. Recently I tried to use it and couldn't get it to start. I ended up changing the carburetor with a new one. After changing the carb, it immediately started and ran fine for about 30 seconds followed by it bogging down with a solid stream of white smoke coming from exhaust. When I shut it down, I found oil coming from hose that's routed to inside breather cover coming from block. There was no gradual increase in smoke, it just came full stream all at once. I figure it has broken a ring, but just wanting to see what others think.
    MM 211
    Hobart stickmate AC/DC
    Miller Bobcat 225G
    CutMaster 39
    And a few other tools here and there

  • #2
    Something is pressurizing that crank case, so for sure a broken ring, that was likely siezed to the cylinder before you turned it over.
    Last edited by cruizer; 10-01-2014, 01:41 PM.

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    • #3
      Is this one of the older Bobcats with the tank above the motor? If gasoline was bleeding down thru the old carb into the crankcase, and filled the crankcase, it will also produce pure white smoke.
      Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

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      • #4
        Originally posted by JSFAB View Post
        Is this one of the older Bobcats with the tank above the motor? If gasoline was bleeding down thru the old carb into the crankcase, and filled the crankcase, it will also produce pure white smoke.


        I had the exact same thing happen on a loaner 5kw generator with a top mounted tank! Blowing white smoke while it ran for a while then would die. Checked the crank case, Full of gas! Drained, filled with oil, ran like a champ. And talk about the crank case was clean after that!! Instructed the owner to close the fuel line valve after each use to prevent future problems.
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        • #5
          Tanks in older bobcats are vented with the tanks in the lower body, I don't know how fuel would magically get into the crankcase. Ethanol in the fuel would have likely ate the carb bowl though.

          The vents in newer miller machines are using a solinoid. Hit the start switch, a tank mounted solinoid opens.

          The Lincoln and other equipment suppliers used a actual tank vent. Lincoln and others in thier infinate wisdom put these vent too low, so guys were continuously filling the tank necks up with fuel. this caused the unit to double fuel, hydro lock the engines, and get fuel into the crankcases over night.
          Last edited by cruizer; 10-01-2014, 01:39 PM.

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          • #6
            Originally posted by ja baudin View Post
            I had the exact same thing happen on a loaner 5kw generator with a top mounted tank! Blowing white smoke while it ran for a while then would die. Checked the crank case, Full of gas! Drained, filled with oil, ran like a champ. And talk about the crank case was clean after that!! Instructed the owner to close the fuel line valve after each use to prevent future problems.
            This happened on one of my gen sets, but they're both recoil start, and I couldn't pull the rope. I always close the valve and run the carb dry, but always isn't 100%.

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            • #7
              Pure white smoke on a diesel indicates unburned diesel exiting the exhaust. Could possibly be not warmed up enough, or a cracked ring, that cylinder isn't making enough compression to properly fire the fuel.

              Pure white smoke on a gas engine, indicates either water, or a crankcase full of gasoline. If it was a cracked ring, you would be getting blue or black smoke.

              Check your oil. If it's growing, or if you can't even see the level, probably gasoline in the crankcase
              Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

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              • #8
                Originally posted by thatsgre8t View Post
                My bobcat sat up for about a year without being cranked. Recently I tried to use it and couldn't get it to start. I ended up changing the carburetor with a new one. After changing the carb, it immediately started and ran fine for about 30 seconds followed by it bogging down with a solid stream of white smoke coming from exhaust. When I shut it down, I found oil coming from hose that's routed to inside breather cover coming from block. There was no gradual increase in smoke, it just came full stream all at once. I figure it has broken a ring, but just wanting to see what others think.

                First check the oil, ifit is in the level mark, and does not smell of gas, check the coolant, it is possible that the headgasket has a slight leak and is dumping into the combustion cylinder. If coolant is good do an engine bleed down test, a compression test will not always show a broken ring, a bleed down test will.
                Kevin
                Lincoln ranger 305g x2
                Ln25
                Miller spectrum 625
                Miller 30a spoolgun
                Wc115a
                Lincoln 210mp
                F550 imt service truck

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                • #9
                  Originally posted by Tryagn5 View Post
                  First check the oil, ifit is in the level mark, and does not smell of gas, check the coolant, it is possible that the headgasket has a slight leak and is dumping into the combustion cylinder. If coolant is good do an engine bleed down test, a compression test will not always show a broken ring, a bleed down test will.
                  Kevin
                  The BOBCAT is air cooled. No coolant.

                  Griff

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                  • #10
                    Originally posted by griff01 View Post
                    The BOBCAT is air cooled. No coolant.

                    Griff
                    Wow, older unit! Is it a wisconin v4 or onan? If its a wisconsin, do a compression test. Bettar yet run the engine and take a heat reading of the exhaust ports. Cool one will be the issue. Good thing about wisconsins are the jugs pop off so each cylinder can be repaired seperate. Bad part is parts are very pricey. If its an onan well...good luck!
                    Lincoln ranger 305g x2
                    Ln25
                    Miller spectrum 625
                    Miller 30a spoolgun
                    Wc115a
                    Lincoln 210mp
                    F550 imt service truck

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                    • #11
                      Gas in oil

                      I drained oil and it definitely had gas in it.
                      The fuel tank is at bottom of unit, not top.
                      Don't understand how fuel would have gotten in crankcase.
                      MM 211
                      Hobart stickmate AC/DC
                      Miller Bobcat 225G
                      CutMaster 39
                      And a few other tools here and there

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                      • #12
                        Originally posted by thatsgre8t View Post
                        I drained oil and it definitely had gas in it.
                        The fuel tank is at bottom of unit, not top.
                        Don't understand how fuel would have gotten in crankcase.

                        My mistake i thought bobcat meant skidsteer bobcat! I forget its a welder to. As for gas in the oil, when the carb goes bad sometimes the needle and seat stick open. As the engine is cranked the fuel pump fills the carb bowl then over flows the carb and dumps the gas into the cylinders. Some of it is pushed out the exhaust stroke but much more makes it pass the rings as the piston and rings are cool and not expanded to provide good ring seal. Now once the oil gets dilluted with gas it burn off the cylinder in the power stoke thus smoke. It would be a good idea to change the oil again.
                        Kevin
                        Lincoln ranger 305g x2
                        Ln25
                        Miller spectrum 625
                        Miller 30a spoolgun
                        Wc115a
                        Lincoln 210mp
                        F550 imt service truck

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                        • #13
                          Not a welder but an old Yazoo riding mower with a 16 hp single cylinder B&S. Mine did the same thing. Drained the oil and had an extra quart. When i could get it to start it ran super. Then next day it wouldn't turn over. Never thought to close the petcock on the tank but i do now and run her dry...Bob
                          Bob Wright

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                          • #14
                            Originally posted by griff01 View Post
                            The BOBCAT is air cooled. No coolant.

                            Griff
                            I realized (at least assumed) the OP was talking about a Miller Bobcat, and all Miller Bobcats are air cooled. I only mentioned the water, because it is a cause of white smoke, and also because it doesn't matter where the water is coming from.

                            A question to the OP, after draining and replacing the oil, is the engine still smoking?
                            Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

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                            • #15
                              Gas In Oil

                              A bad mechanical or vacuum operated fuel pump will put gas in the oil when the bladder goes bad.

                              Charley
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