Riding lawn mower flywheel

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Old 07-09-19, 07:30 PM
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Riding lawn mower flywheel

I am having a problem keeping the flywheel in place after I replaced the key. It brakes the new key. I tighten the bolt as tight as I can get it and the key still breaks. What can I do to keep the key from breaking and the slots are not in line and it want crank.
 
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Old 07-09-19, 07:36 PM
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If the mower starts and runs fine and then it shears the key when you engage the blades, I would say that one of your blade pulleys is seized, or at least the blades may be locked up tight somehow.

You didn't provide any info on what you are doing when the key shears.
 
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Old 07-09-19, 08:13 PM
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Trying to crank the mower.
 
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Old 07-09-19, 08:19 PM
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The guys here will want to know the brand, size and model of your engine. It's possible that your engine needs a steel key. Also, you should be using a torque wrench to torque the nut to exact specifications.
 
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Old 07-09-19, 08:39 PM
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The crankshaft is conical where the flywheel seat. If the hole in the flywheel is worn badly it may not seat on the crankshaft. Then you couldn't tighten it properly.

Often the flywheel and shaft have been lubed which allows the flywheel to move on the shaft more freely than it should and shears the key. Make sure both the flywheel and crankshaft end are dry of lubricant. You can clean both with carb cleaner prior to installation.

Another problem is the proper alignment of the crank to flywheel when the end nut is torqued down. When you're ready to assemble the two parts insert the key in the slot on the crank and slide the flywheel on the crank and rotate it until you feel the flywheel slide over the key. Push it on the rest of the way and before you put the crank end nut on rotate the flywheel back and forth to make sure it's fully engaging the key. Now turn the nut on and torque it down.
 
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Old 07-09-19, 11:28 PM
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Did you put grease or something on the crankshaft to make it easy to take off? The key does not hold the flywheel to the crankshaft. It just makes you put the flywheel on in correct time. Friction holds it there, not the key. If there is oil, grease, never seize, or anything like that on it, it will shear almost immediately.
 
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Old 07-10-19, 04:50 AM
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As someone posted earlier, torque the flywheel to manufacturers specification. Over torquing the aluminum flywheel can crack the flywheel at the bore. Use an accurate torque wrench. Once cracked, the flywheel needs to be replaced.
 
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Old 07-10-19, 08:42 PM
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The model # is 31A807 Briggs & Stratton. What is the torque for the flywheel and do I need a steel pin?
 
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Old 07-10-19, 09:47 PM
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From what I can find, the flywheel nut is 100 ft lbs.

The part # for the flywheel key is 796335 (used before code date 12071800) or 591757 (used after code date 12071700).
 
 

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