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  1. #1

    Join Date
    Apr 2013
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    Poulan

    Possible blown head gasket or piston rings?

    Hi,
    I'm a small engine repair novice, so bear with me. All of my knowledge I have gained recently from Google and the Briggs & Stratton website. I have a 22" cut Poulan push mower with a 158cc B&S single cylinder engine (10T500 series). Last season, after 4 years of working great post one trip to the shop, the engine started running rough. I took the carb off and gave it a good cleaning. In the process I messed up the throttle linkage and subsequently lost the springs. Not knowing any better, I taped the throttle wide open and finished out the season. I have a very small yard that takes 5 min to mow and probably mowed six or a little more times with the throttle like that. The engine produced some white smoke(not tons) but still ran well the last few times but I didn't think much of it. To prep for winter I put fresh gas with Stabil in the tank and ran it for 10 min. Then I changed the oil and put it away. The oil is slightly over filled, according to the dipstick, but not by much.

    This weekend, I fixed the linkage with new governor blade, linkage coil, and two springs per the B&S parts manual and pics from Google. The mower started with the gas I put in last fall but was constantly revving and producing white smoke with occasional slight black smoke when it choked down. It never died but would run rough when I decreased the throttle. I replaced the air filter (which wasn't that dirty to begin with) and different gas (though not fresh; It was what fresh last fall and stored in a new gas can all winter with Stabil). The spark plug was heavily fouled with a dry black appearance. I don't have a gap tester, but it doesn't look damaged. I wire brushed the spark plug and re-installed. The mower started on first pull. The revving is decreased/gone but now lots of white smoke and runs rough.

    The B&S website lists a number of things that could cause white/blue smoke, the three most likely(at least to me) include: overfilled crank case(not sure if my a slight over fill is enough to do this), blown head gasket, or worn cylinder/piston rings. Other websites/forums seem to provide conflicting various other opinions.

    Engine Burns Oil | White Smoke From Engine | Briggs & Stratton

    My plan is to get fresh gas and try it first. If that fails, I will buy a compression tester to check that the engine holds compression. I will check locally for the tester but will probably end up buying an inexpensive one online sometime this week. Is my plan reasonable or should I be looking for a different problem? If the engine doesn't hold compression, is either the gasket or the piston rings more likely than the other? If the engine does hold compression, where should I look next? I kind of want to figure this out on my own rather than take it to a shop but would be willing to admit defeat if I can't figure things out within the next few weeks. Thanks.

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  3. #2
    pugaltitude's Avatar
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    Re: Possible blown head gasket or piston rings?

    I think you could be hunting in the wrong place.
    Not many things go wrong with a model 10.
    It sounds like a carb diaphragm/gasket problem.
    Quite common on this engine.

    Clean the carb and fit briggs part 795083.
    Add fresh fuel, new sparkplug and the right oil.
    The only thing that could have caused damage is how high the rpm was when you taped the throttle linkage.
    The "best" engine you will ever own!

    Briggs & Stratton MST.

  4. #3

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    Toro

    Re: Possible blown head gasket or piston rings?

    Most common problem indicated by white smoke is water in the fuel. New fresh non ethanol fuel should help.
    This is only my opinion, and many will say it ain't worth a darn, as I'm only a retired grease monkey instructor and not a professional mechanic. Use what I post at your own risk as you know teachers only know book knowledge.

  5. #4

    Join Date
    Apr 2013
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    Poulan

    Re: Possible blown head gasket or piston rings?

    Thanks. I will try both of those before tearing anything apart. I was able to borrow a compression tester last night. Dry compression was 110 PSI, and wet was 120 PSI. Does that sound reasonable? I'll update the thread with the results of the new gas and carb diaphragm. Thanks again.

  6. #5

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    Re: Possible blown head gasket or piston rings?

    Those compression readings are what I would expect with today's engines.
    This is only my opinion, and many will say it ain't worth a darn, as I'm only a retired grease monkey instructor and not a professional mechanic. Use what I post at your own risk as you know teachers only know book knowledge.

  7. #6

    Join Date
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    Re: Possible blown head gasket or piston rings?

    Just wanted to update with how things worked out. I had to order the carburetor diaphragm. In the mean time, fresh gas got rid of the white smoke but it still was revving, despite the new throttle linkage and springs. I increased the tension on the big throttle spring and got it to run 90% better, but still a little rough sounding. With the new carburetor diaphragm it runs great. Thanks for your help!

  8. #7

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    Toro

    Re: Possible blown head gasket or piston rings?

    Glad you were able to work it out.
    This is only my opinion, and many will say it ain't worth a darn, as I'm only a retired grease monkey instructor and not a professional mechanic. Use what I post at your own risk as you know teachers only know book knowledge.

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