Hit Tree Stump now Runs Rough


Old 10-03-04, 08:56 AM
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Hit Tree Stump now Runs Rough

I'm new to this forum, hope someone can help me out. I have a 4 year old Sears 21" lawnmower 6.5HP, after hitting a tree stump it now runs rough, and if it loads ups when cutting tall grass it will stall.

I heard that new engines have a timing key to protect against this type of scenario, any help would be appreciated, thanks!
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Old 10-03-04, 09:48 AM
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Hi xenon,
You will need to remove the shroud on the engine, this most likely will include the rope rewind assy fuel tank and perhaps the air breather housing. Under all of that you should find your flywheel. On top of that you may have a metal cup inside of which is a nut that holds on the flywheel. Remove the nut and the cup, and you should be able to view the shear key in the slot of the shaft that the flywheel mounts to. If it is sheared it should be barely so if the mower still runs.
Use caution holding the flywheel as the cooling fins will break if used as a leverage point. Suitable jigs are made or can be made usually of wood.
If you find the key sheared and need some more help replacing it, post back for a quick check list
Old 10-03-04, 10:10 AM
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Thanks Azis, I will try your suppgestions!
Old 10-03-04, 03:39 PM
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I'm hoping that azis is right that it is the flywheel key partially sheared but normally if you hit something with considerable force the key is designed to shear so much that the timing will be off enough that the motor won't start. This is the way to tell you something is wrong and it's time to fix it.
What I'm thinking is wrong is that you bent your crankshaft (I hope I'm wrong)
The best way to see if it's bent is to remove the sparkplug, depress the safety handle and while looking under the mower deck, mark a line of travel where the blade turns and see if it is equal all the way around. If it's bent, it may be slightly higher on one side of the deck than the other. Plus when the crank is bent, the motor is running off balance and you'll get the vibration.
Replacing a crank isn't hard but it may be pricey compared to buying a new mower. These above symptoms are the same as the 3 craftsman mowers I did this year (all with bent cranks)

Old 10-04-04, 01:21 PM
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i agree with snowman. my friend done the same thing this year to his mower and he is not sure if it is his crank or blade. i would say that his blade is bent and maybe his crank too. check both of them like snowman said. good luck.
Old 10-04-04, 10:49 PM
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Sometimes they bend, sometimes not, but for sure, the flywheel key is sheared.

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