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O/T Lawnmower engine question?

Discussion in 'Off Topic Threads' started by Shooting Jack, Jul 27, 2011.

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  1. Shooting Jack

    Shooting Jack Active Member

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    I have a Poulan Pro rider model PB19H42LTS with a 19HP Briggs overhead valve engine. It has absolutely no compression. I removed the valve cover and it appears that both valves are opening properly. What would be the next thing to check? I did remove the plug and turn the engine over and saw that there was no compression, I also tried to stick a screwdriver through the plug hole to see if the piston was moving but couldn't get it into the cylinder. There is not block damage that I could see. Thanks for your help. Jackie B.

    PS. I wasn't there when the mower quit and all they could say was that it just quit with a little bit of smoke.
     
  2. grntitan

    grntitan Well-Known Member

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    Don't sound good. Hole in the piston? Broken connecting rod? Broken Crank? Does it turn over? If yes how easily?
     
  3. Shooting Jack

    Shooting Jack Active Member

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    Spins over very easily. The same as if you had removed the spark plug and spun it over.
     
  4. Pull & Mark

    Pull & Mark Well-Known Member

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    Valve's could be bend enough to get 0 compression. Ring/rings could have pulled off cyl. Hard to tell without taking it apart??? Were there any odd sounds first??? Clinking,clacking, tingging sounds or a loud bang and then nothing. Sounds odd it was running fine and then it just stoped and smoke. The motor had to make some kind of odd sound and then quit. This would be your biggest hint of the cause. Good Luck and Break=-em all. JEff
     
  5. Shooting Jack

    Shooting Jack Active Member

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    Thanks fellas, since I wasn't there and they didn't indicate any noise I don't have a clue. I believe that this engine has a removable head and that will be my next step I guess. I know an open valve will not allow compression to build and a friend told me that his did the same thing and was a broken pushrod which didn't allow the valve to close all the way. And now that I think about it I didn't check for valve lash which I will check next then remove the head. Thanks again. Jackie B.
     
  6. trap906

    trap906 Member

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    hey Jack, you said the valves were both moving properly.. next thing you need to do is check the valve lash. this is the clearance between the rocker arm and the valve stem. very common problem on the overhead valve briggs engines. rotate the engine until one valve is pushed all the way down or open. then using a .005 feeler gauge, check the clearance on the valve that is closed or all the way up. you can adjust the clearance by loosening the set screw and then turning the nut on the rocker arm, then rotate engine and repeat for other valve. you must only adjust a valve that is closed,don't matter which one you do first. the clearance must be very close to .005 no closer than .003 no looser than .007 as I said, very common problem with these engines as they are ran and wear the clearance will change. hope this helps
     
  7. grntitan

    grntitan Well-Known Member

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    If its not what they are indicating above with the valve timing, it may be much more serious.

    If it spins that easily i'd bet money the crank is spinning freely. In other words it no longer is pushing the piston up and down. Likely a broken connecting rod. If the rod is still connected to the crank and not the piston, you should be able to hear the rod slapping around inside the cylinder. If the rod broke off the crank(like the rod cap broke off) it may be hanging from the piston in the cylinder. One way or another, if its not simply valve timing its done i'm afraid.
     
  8. pyrdek

    pyrdek Well-Known Member

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    How about something much simpler. A blown head gasket. I had one of these on a B&S 11hp on the Deere. It made a distinct "huffing" sound and very low compression. Pulled the head and saw the gasket was blown.

    Bought a new gasket for this 25 year old engine (confirmed by the date code on the engine). Put it in and it is back in full operation. It does leak a bit of oil but I just keep topping it off and run it some more.
     
  9. Conn. Man

    Conn. Man Member

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    I seen crankshafts breaking in Brigg's motors.Best bet is get something flexible and put it in the spark plug hole to hit the top of the piston to see if it's moving.

    Sandy Holehouse.
     
  10. halfmile

    halfmile Well-Known Member

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    When you verify you have a piston, and valve lash is proper, put your thumb on the spark plug hole and roll the engine over. If there is not enough compression to push your thumb off the hole take it apart.

    HM
     
  11. Stl Flyn

    Stl Flyn Well-Known Member

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    With the spark plug removed, you will not have compression. I take it this is a twin cylinder, vertical shaft engine. I would bet the head gasket is the problem. Possibly in both cylinders, to varying degrees. Is there oil blowing through the breather, into the carb? The breather tube has a round cylinder on some models on top of the valve cover of which the tube comes out and goes into the top of the carburetor. There would be oil leaking out of that opening also between the tube and the hole on the valve cover. If the head gasket is leaking it allows pressure to the oil reservoir through the return ports. Usually this is the area of the gasket failer, between the cylinder and the oil return port. There should be excessive oil in the bottom of your air cleaner, and around the front of the engine. It could also be ring failer, but that is not as common a problem unless the oil was allowed below the dip stick. I just changed the neighbors head gaskets on his Kohler engine, which are known for blowing head gaskets within 200 hrs. of use. Change both head gaskets and also the breather gasket. Clean out the breather cylinder and tube with brake cleaner and you should be good to go. Do not mess with the valves, rockers, etc. You are just going to cause yourself more problems. The valves are functioning as you said.
     
  12. grntitan

    grntitan Well-Known Member

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    Make sure you let us know what it was.
     
  13. Shooting Jack

    Shooting Jack Active Member

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    It is a one cylinder and does not have any compression with the plug still in. I haven't had a chance to check it out today but will try later or first thing tomorrow. Jackie B.
     
  14. Stl Flyn

    Stl Flyn Well-Known Member

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    If it has one cylinder is is even easier to change the head gasket. I would take the head off and look at the gasket. Also make sure you are getting spark, and the cylinder is getting fuel. The engine should still crank over and run rough for a couple of cranks before it looses momentum and power to stop. You would hear some hissing and sputtering. That would be the compression leaving the cylinder when it should not be.
     
  15. sliverbulletexpress

    sliverbulletexpress TS Member

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    To have no compression at all it would be a hole in the piston, broken crank or rod not allowing the piston to move or a burnt valve with a big hole in it. With any of the other problems you would still have a little compression.

    I think it was said these engines have a reputation for broken cranks so that would be the most likely. You should be able to stick something small in the spark plug hole and tell if the piston moves up and down or not, betting not.
     
  16. birdtracker

    birdtracker Active Member

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    ethanol fuel strikes again. Birdtracker
     
  17. grntitan

    grntitan Well-Known Member

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    So what did you ever find out on this engine????
     
  18. Shooting Jack

    Shooting Jack Active Member

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    Broken rod end. Trashed unfortunately. Jackie B.
     
  19. grntitan

    grntitan Well-Known Member

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    Yep. Thats what i was afraid of.
     
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