Stripped Crank Shaft internal thread for flywheel

[vrotsos991]

I have a Snapper Series 11 that I purchased as a fixer upper. It has a Briggs 12.5 HP 286707 motor. The motor had the beautify cover taken off, the crankshaft extension was removed and stripped as well.

After further investigation I found that the crankshaft female thread was stripped. This is a 9/16-18 thread. I tried to chase the threads but was unsuccessful. It seems that the material the crank is made out of is to hard to form thread, and the tap kept wanting to go in at an angle.

I need to install a bolt to maintain pressure on the flywheel so that it will not come off obviously. What options do I have since I can not tap this material? Is there a filler that can be used to fill that cavity and then I can drill and tap it to install a bolt? Any ideas?

 

[bertsmobile1]

Put it in the parts bin and go look for a new project or a mower with a hole in the crank.
The cost of doing a perminant repair wil be greater than the cost of replacing the crank.
B & S cranks are reasonably cheap so you can replace the crank, takes a bit of time but not too expensive to do.

 

[motoman]

Perhaps a long shot, but you probably tried to start the tap by hand. The last stand diy attempt is to (somehow) lock down the crankshaft on a drill table . ( I assume you do not have access to a mill table. Even a low end Chinese pedestal drill has a base that "may" be aligned with the drill chuck. So either build this up (always dead flat) or lower the drill table such that the crank shaft can be firmly clamped and aligned with the drill chuck. A thread "chaser" is your tool of choice, not a tap, if possible. This is because a tap will remove material (the buggered threads), while you want to restore the thread. A chasing tap will force the thread back into position and also burnish and smooth the threads. A chaser can be found on line.

Place the chaser in the drill chuck and bring it down near the female thread. Leave the table or fixture loose so that slight alignment corrections can be made as the chaser enters. DO NOT USE THE MOTOR, THIS IS A MANUAL EXERCISE. Once the chaser enters the thread squarely lock down the piece. One hand lightly pressures the downfeed handle while the other turns the chuck with chaser. Use lubricant. Try leaving the chuck key in for leverage. Proceed and when backing out the chaser clean the swarf, if any, from the chaser and blow out the thread hole. When I do this I find there is a point where the threads are supportive and the workpiece can be removed and held in a vise . Then the conventional tap wrench can be used (still use the chaser, not tap). :2cents: