Old Mower- Engine difficult to spin when spark plug is in...

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  #1  
Old 08-18-08, 05:27 PM
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Unhappy Old Mower- Engine difficult to spin when spark plug is in...

Old-as-Moses Lowe's 42" mower with a B+S 15hp engine


When I take the spark plug out (I read somewhere that when an engine is difficult to turn over, you can spray into the spark plug wd40 or whatever), the engine spins freely. When I put the plug back in, every 5 rotations or so, it is too difficult for the starter to overcome and spin.

The mower sat for a million years in someone's backyard, before I picked it up for free...
 
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Old 08-18-08, 06:11 PM
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Since you say it's a 15 hp I will assume it's a over head valve.

If so check the valve clearance;


Remove the valve cover then rotate the engine over by hand until you reach top dead center compression stroke, Then remove the spark plug. Once at TDC insert a small screw driver in the plug hole touching the piston and rotate clockwise past TDC until you see the screw driver move down inside the hole 1/4". Now loosen the jam screw in the center of the adjustment nut and adjust to .005-.007" both intake and exhaust. Hold the adjuster nut with your wrench while tightening the jam screw. It may take a couple times to get it right because when tightening the jam screw it could throw the adjustment out so check after tightening.

If the valve clearance is within specs there could be a problem with the compression release on the camshaft.


Good Luck
 
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Old 08-18-08, 07:11 PM
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my mower has the spark plug on the front (so I suppose it's a different kind of valve), Should I still try this? (by having someone else work with the screwdriver?
 
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Old 08-18-08, 11:02 PM
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Originally Posted by junkmower08 View Post
my mower has the spark plug on the front (so I suppose it's a different kind of valve), Should I still try this? (by having someone else work with the screwdriver?
ok you got a sidevalve engine which is the most common engine your going to find on a mower. can you post the model number of the tractor and engine.
 
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Old 08-19-08, 12:20 AM
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They all have the plug up front. Yours is an overhead valve engine if it's a 15 horse single cylinder. It needs the valves adjusted.
 
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Old 08-21-08, 06:52 PM
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Battery?

Are you sure the battery is good enough? My Briggs OHV 14.5 HP lawnmower would not spin over, even with a 1 month old battery. I tried to jump it off another lawnmower, still wouldn't spin over. I took the plug out and it spun over fine, real fast, everything looked good. Thinking the cylinder was full of oil, I pulled the head off. Dry as a bone. I figured the starter must have a dead spot, but I tried one last time to jump it off the truck anyway. It fired right up. The battery didn't have enough juice to spin it over with full compression, and the other battery didn't have enough to start the engine through the jumper cables. I learned three things that day:

1. Jump the lawnmower off a car or truck, not another lawnmower. The alternators on these little Briggs don't have enough current for this and you'll end up with two dead batteries.
2. Just because the battery is pretty new doesn't mean it isn't dead.
3. Buy a battery charger and put it on your lawnmower batteries every month or so if they're not being used regularly.
 
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Old 08-21-08, 07:24 PM
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You can overload a starter with current and burn it up. If the compression release is not working properly due to excessive valve lash, it will act like the starter is dragging.

If you shoot enough amps through the starter, you may get it to crank over but you will shorten the life of your starter.

Lawn and garden batteries have sufficient current to properly crank the engine, provided the engine is in proper working order.

Adjust your valves as 31YTech advised and you should be alright, provided you have not already damaged your starter.

Best of Luck...
 
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