Craftsman 15.5 hp OHV won't restart

Discussion in 'Mechanic and Repair' started by rnorquay, Nov 3, 2007.

  1. rnorquay

    rnorquay LawnSite Member
    Messages: 3

    Please help

    I have a Craftsman 15.5 hp with a Briggs&Stratton 2N8707-0173 engine.
    Engine usually backfires when stopping, but now refuses to start. It does not even try it just spins.
    I have:
    Checked Oil, fuel.
    Removed flywheel bolt and checked the key.
    Removed and cleaned the carb.
    Checked the solinoid at the base of the carb is retracting when the ignition is turned on.
    Checked the spark by holding the sparkpulg against the engine. It was weak so replaced the coil and now is very bright.
    Checked the valve clearences, the inlet valve had a gap of approx 1/4 inch, not sure how it was running but the end cap was still in place so adjusted it by eye to approx 1mm.
    In desperation tried pouring gas in the carb while cranking the engine but nothing.
    Finally tried spraying easy start which resulted in the engine backfiring twice.

    I don't have a way to test compression but it was running fine prior to stopping.

    Any ideas?
  2. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

  3. rnorquay

    rnorquay LawnSite Member
    Messages: 3

    Hi Restrorob

    Thank you for your reply. I checked the valve clearances as in your link and it was the exhaust valve (not the inlet) that was way out before. I set them both to 0.005" but it made no difference. I also check the spark plug gap and set it to 0.3 but made not difference. One thing I did notice while cranking the engine was that there was a lot of pressure comming out of the engine breather tube.
    I have another question, how does the decompression valve work on this engine? Could this be the problem or is it time to buy a new ride on?

    Thanks in advance
  4. leeker

    leeker LawnSite Member
    Messages: 51

    Not sure what Restrorob next suggestion will be, but i have to think you have a compression related problem still. it could be a push rod that is bent,(did you happen to take the push rods out and look at them when you set the valves, they will bend a little and still stay on the rocker arm without you knowing this when you set the valves). Do you have any way to do a leak down test?. if this unit has been backfiring and you checked the flywheel key and set the valves i would look at the push rods next and then do a leak down test if the push rods are fine.
  5. rnorquay

    rnorquay LawnSite Member
    Messages: 3

    Hi Leeker

    Thank you for your reply, yes the push rod on the inlset valve is bent and I agree that it needs to be replaced but why won't the engine start after compensating for the bend with the adjustment on the rocker arm? Also what causes the rod to bend? Is it a sign of bigger engine problems?

  6. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    With the bent push-rod the valve doesn't open far enough and stay open long enough to allow the proper amount of air/fuel mixture to enter the combustion chamber.

    If the engine was ran long enough without proper valve adjustments the push-rod could ride up out of the indentation area on the rocker thus bending the rod.

    You also could have a gummed up valve guide and the valve stuck at one point. Swing the rockers sideways and push on both valve stems (with the piston rotated down in the cylinder) and make sure they move freely, If they do replace the bent push-rod and adjust to spec and see if it doesn't start right up.
  7. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    Dumping straight gas in the carb won't do anything, when you cleaned the carb did you pull off the bowl and clean all that out, including teh j.e.t.?

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