tecumseh timing

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  #1  
Old 05-01-07, 11:39 AM
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Unhappy tecumseh timing

I have a Craftsman tiller that is about 25 years old, with a 6 HP Tecumseh horizontal shaft motor. For some reason, it sheared off the Woodruff key that aligns the flywheel to the crankshaft. I bought a new key, and that one sheared off immediately again. I believe the timing must be off for the engine to kick back and shear the key. I can't find the Tecumseh engine model number to try to find the timing setting. The Sears tiller number is 917-252370, the Sears motor number is 143-716342. There is a small tag bolted to the motor that says SBH351A and SER 4049F.
 
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Old 05-01-07, 12:00 PM
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Chances are the ignition timing is not off, unless you have manually shifted the stator yourself. I'd say you are not torquing the flywheel nut to spec and the lack of such is allowing the key to shear. Torque is critical!!! Based on the 143.716342 engine number you gave, this should be a 8-horse engine, not a 6-horse, with a cast iron flywheel. And, if in fact so, the nut torque will be 40 foot pounds. If you do, in fact, have a timing issue then the timing point is .090" BTDC (Before Top Dead Center). By the way, the "SBH" indicates that this engine has had a shortblock installed at some point and then would mean that the stator was, at some point, installed on the new shortblock and could then be off time. Do you know the procedure to time the stator? And what tools will be necessary?
 
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Old 05-01-07, 09:50 PM
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The tiller was purchased from a Sears repair installation, so it may have been a shortblock replacement. The owner's manual definitely says 6HP. I'm not sure how you mean the timing setting. I'm used to cars being degrees before TDC, not thousandths of an inch. How should it be set? I believe it may be off, because the engine is not starting easily, and it has a new spark plug.
 
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Old 05-02-07, 08:02 AM
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Remove the cylinder head; Set up a dial indicator to indicate the position of the piston; Set piston at .090" BTDC on compression stroke; Remove flywheel; Remove all wires from contact points post; Set points at .020"; Using an ohms/continuity meter, place the positive lead of meter on the points post and the ground lead to a suitable ground point on the engine; NOTE: if you have continuity at this point, all is OK - timing is correct. If no continuity you'll need to loosen the two screws (bolts) that hold the stator to the cylinder block and rotate it in whichever direction to obtain continuity (points closed). This may take several attempts for those who have never done this before. You need to loosen the screws only to the point that you'll be able to move the stator (with a light-weight brass hammer is best) as the setting will likely change when you re-tighten the screws back down and takes a good feel to get it (timing) on the money.
 
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Old 05-05-07, 05:27 AM
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Any new news yet, whwiech?
 
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