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O/T Aligning the rings on a lawn mower engine

Discussion in 'Off Topic Threads' started by joe kuhn, Jul 11, 2010.

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  1. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Piston is horizontal. Does it matter how I align the gaps on the rings before I put the piston back in?

    Interesting that the magneto fires every revolution on a four stroke engine like this. This means the spark plug sparks after the compression stroke AND after the exhaust stroke. I didn't know my lawn mower 'wastes a spark'. Hah!

    Correction: the spark plug fires WITH the compression stroke and the exhaust stroke.
     
  2. stokinpls

    stokinpls Well-Known Member

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    They won't stay, but start them out with the gaps 180 degrees apart. If it has three rings, try 120 degrees. If it were a two-cycle it would likely have pins in the grooves to keep them from rotating. Nothing like a little grease-monkeyin' to get your mind off of what's going on in Washington. ;-) Good luck.
     
  3. halfmile

    halfmile Well-Known Member

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    I hate to be a nit picker but I don't think your mower will run very good with a negative spark advance.

    It should fire just before TDC on the compression stroke. Some engines use as much as 39 degrees advance.

    I always put the rings opposite of each other, too.

    HM
     
  4. Tron

    Tron Supporting Vendor Supporting Vendor

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    Gaps, 180 apart. If it's a Briggs motor there will be a little notch on the piston face and that MUST face towards the flywheel (top of engine).

    Best O' luck to you.
     
  5. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    It has 3 rings, so 120 degrees it is.

    HM - it's just me generalizing. I didn't measure anything... I'm still amazed it fires two sparks in four strokes. Doesn't that seem odd to you? One is wasted.

    Hi Tron - having a ball taking my first lawn mower engine apart. Showing the boy what's going on, but he's more interested in wheels for his skateboard. It's a Tecumseh in a Sears mower. Found it on the curb and put it in the shed for a rainy day project. Of course he wants me to fix it so he can have an easier time mowing since it's a self propelled mower. The thing was smoking bad when we got it. 3 of the 7 bolts between the oil pan & main housing were loose. Oil gasket was blown. A few scratches on the piston and cylinder, but not bad. Minor scoring where the piston connects to the crank. Rest looks ok except for terrible carbon buildup on head and piston which I'm removing. Don't know source of carbon - rings look ok to me. 50 bucks for new gaskets and we should be in business. If it works for a season, I'll be happy. Boy has 2 more mowings to pay off the last skate board. He's going through a pair of skate shoes about every month and likewise for a board. I won't have to mow for the rest of my life. Wait till I dump all those fast food receipts in his lap when he tries to shove me into a nursing home. Plan ahead my friend.

    Da Kuhner
     
  6. oldgahchamp

    oldgahchamp Active Member

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    Joe Kuhn. There was a reason the mower was on the curb. TECUMSEH!!. Put it back on the curb where it belongs or tip it upside down and plant flowers in it. Larry
     
  7. trapperpg

    trapperpg Member

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    Waste spark comes from flywheel magnet passing magneto 2 times for each complete firing cycle.
    phil
     
  8. slipping into darkness

    slipping into darkness TS Member

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    I drag a Briggs out of the dump and was told to give up on bringing it back to life and use it as a boat anchor, guess what its a year later and purrs like a brigs never has. hows that for proper English. I'm sure you will be successful. "slid"
     
  9. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Next question is how much torque do I use on the head bolts? The two on the side were real tight, the rest directly over the piston weren't as tight. I'd rather not spend $11 for 'documentation' I may never use again. Thanks.

    Will have to borrow a torgue wrench. Maybe not. Maybe I'll just guess.

    Fixed a Briggs 3.5 horse last week. It needed new gaskets between the carb and the gas tank. Guy at work tipped me off. $3.50 + $8 shipping. The rubber gasket has a little bubble in it that regulates the gas/air mixture somehow and that sometimes get stretched. Johnny says to me - how come it sounds wierd now? Reason is it's running as it should.

    Internet parts ordering is great.
     
  10. halfmile

    halfmile Well-Known Member

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    Nothing new about wasted spark systems.

    Harley sportsters used a John Deere Magneto (Fairbanks Morse) years ago, and it could have the plug leads reversed and still work normally.

    Most of the Hyundai, Kia, etc present day asian compacts use a wasted spark system. the coil is mounted on the plug and has a lead to the other cylinder of the pair. There are 2 coils serving 4 cylinders.

    And the damn leads cost 29 bucks for 2.

    HM
     
  11. timb99

    timb99 Well-Known Member

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    Joe

    Technically...

    A "motor" is an electrical device

    Your Tecumseh is an internal combustion "engine"
     
  12. ouch

    ouch Member

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    Put a couple drops of oil on each head bolt and torque to 160 inch pounds = 14 foot pounds.



    You should hone the cylinder wall slightly to help the rings seat = seal. Top ring end gap should be about .007 inch , second ring gap about .017 inch.


    While your at it you could lap the valves. Tecumsehs are fine engines. Richard
     
  13. 9point3

    9point3 Well-Known Member

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    Timb99,

    Technically you are only somewhat right

    A motor by definition is not always an electrical device

    Ever hear of a pneumatic motor or a hydraulic motor?
     
  14. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    As long as it cuts the grass.

    What's it mean to 'lap' the valves? I cleaned them up and they look pretty good.

    The guy at the auto parts store said I don't need any sealer on the gaskets. I'm ok with that.

    The rings aren't new, but I'll hit the cylinder wall with some sand paper before re-assembly. That aluminum is pretty soft.

    2 coils serving 4 cyclinders! What a hoot.

    Thanks guys.
     
  15. HSLDS

    HSLDS Well-Known Member

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    Motors have the energy which drives them created EXTERNALLY (compressor, electrical generator, hydraulic pump), while engines develop the energy which drives them INTERNALLY - typically by burning a fuel inside.
     
  16. HSLDS

    HSLDS Well-Known Member

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    Valve lapping involves releasing the valve keeper to remove the spring tension, then coating the edge of the valve with an abrasive. A tool (basically a suction cup with a handle on it) is used to rotate the valves against their seats - this 'uniforms' the edge of the valve and it's seat so they mate perfectly - essentially making a better seal during operation.

    Valve lash will need to be checked after doing this (clearance between the valve and the lifter/push rod) - you can guesstimate this by measuring the clearance BEFORE lapping - and returning to this number when done - a friendly repair shop can tell you the clearance for your specific engine.

    Getting the lash right is tougher than the lapping in lawnmower engines in that there is typically no adjustment in them - you will need to file/grind at the gap between the valve and lifter.
     
  17. gdbabin

    gdbabin TS Member

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    Not always HSLDS (but you know this of course),


    "An external combustion engine (EC engine) is a heat engine where an (internal) working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work.[1] The fluid is then cooled, compressed and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine)."



    It sounds to me that Joe isn't too concerned about lapping valves or the detailed technology surrounding mechanics. He just appears to want his mower to run. Thankfully they aren't the most sophisticated of contraptions. Knock off the carbon, new spark plug, clean carb and you can't go wrong by much.


    When I was a pre-teen lad I loved taking old horizontal shaft engines apart and "fixing" them up for my home-made go carts. One of the best mods was removal of the governor, which I don't recommend in your case Joe! Ah the good ole days.......


    Guy B.
     
  18. Quack Shot

    Quack Shot Active Member

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    The spark is never wasted unless you don't hold on to the wire tightly. :)

    Waste spark has been around for a LOOOOONG time. Newer vehicles with the "coil packs" fire two cylinders as a pair. One on compression and the other on exhaust. The higher resistance is in the compressed cylinder and the gap under atmosheric is negligable. Next rotation, the cylinders trade roles. The ignition on that lawnmower will fire once each revolution. It takes two revolutions and only one spark is required, since there is only one power stroke for two revolutions.
     
  19. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Appreciate the difference between motors and engines. I didn't know the correct term is 'engine' when the power source is internal. So air compressors are motors. Wording has been fixed.

    Sorry guys, but I'm going to just put 'er back together when the gaskets come. Valves will have to be as they are. Everything looks good.

    Car guy at work says cars run spark off the cam (exceptions noted above), not the main crankshaft, so they don't 'waste a spark'. Mowers would be way too complicated with that kind of a set up and it doesn't cost anything because it's just a magneto generating the spark.

    Parts are on the way...14 ft pounds for the head bolts...ok.
     
  20. HSLDS

    HSLDS Well-Known Member

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    Guy B.,

    You are correct - I should have specified INTERNAL combustion engine...

    We could add Sterling Cycle engines to the mix as well...

    David D
     
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