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Hello all,while mowing the other day the transmission pully fell off.
I picked up a 7/16-20x4 in bolt to put it back on but that does not seem to be the size.
Would you know the size of the bolt. I am now wondering if the th part where the thread goes in is cut. Please see the images.
Thanks,
Ram

That should be the size. More than likely the threads were damaged as the old bolt loosened and fell out. Carefully restoring the threads with a tap is probably needed.

Thanks, I bought a another standard bolt(vs matrix), that seems to go few threads but stops after using 3 threads leaving half an inch of bolt outside. Further tightening turns the pully. Let me try restoring the thread.

Just make you got the right length too. IE they do get put in the wrong bins at you local hardware stores.

PN 501606501
7/16-20 x 4 Grade 5 and apply blue Loctite. OEM part comes with Loctite already applied.
And don't forget to install the 7/16" lock washer.
Torque to 55 ft-lbs.

Yes the length seems to be correct. I ordered OEM on searsdirect, same part number as you have mentioned but they have not shipped it yet(screen print).
Do you have a recommendation of a local store where I can get the exact bolt?
Thanks
Ram

Grade 5 bolts will have 3 radial lines on the bolt head. Grade 8 bolts will have 6 radial lines on the bolt head. Can be purchased at any hardware store, Menards, Lowe’s, Home Depot, etc.

As Rivets said just about any hardware store have them.

Thanks

Get the same grade as came in it. Don't go caveman and get all grade 8. If they break off, you will have hell getting them out.

Grade 5 is plenty on a lawn mower.

I don’t know what it came with, I will go with grade 5, thanks

And check the depth of the hole in your crankshaft as your original bolt could have broken off inside the crankshaft
The hole should be the full length of the bolt + 6 threads length
The pulleys rarely bottom out on the crank shaft so you will need to slide the pulley on the shove some thing up the hole that is near the minor diameter of the original bolt then mark it with your third paw and compare that to the new bolt .
And a silly mistake is not to get the pulley in the key way properly

I tried with grade 5 bolt, still having trouble tightening it past 2 threads. It looks like the bolt is a size bigger but I am sure the size is as per recommendation. Please see the screen print.

Have you tried running a tap in those threads to make sure they are clean?

Good morning everyone. I was able to get the bolt from my friend who had an old lawn mower that was not being used. When I compared that with the bolt I had, I see the threads on that was fine thread. That worked fine. Thanks Riverts for the suggestion on using roctite, I initially fixed without that and the bolt became loose after 10 mins of mowing but after applying threadlocker green and leaving it for 12 hours, the bolt stayed there there just fine.
Thanks everyone, especially Riverts and Startrec.
Are there any recommendations for typical maintenance of lawn mower? I change the oil, filters, sharpen blades, but this bolt getting loose was unique