*Improvised Pulley Repair*
18 September 2014
There are some times where replacement parts are unavailable through scarcity, cost or schedule. One such time was this past Sunday. I had intended to mow the lawn with my old Snapper riding mower. It had other plans. On engaging the drive it moved forward only with great effort and hesitation.
The cause became clear once the mower was lifted on the floor jack. These mowers use a disc drive in which a rubber coated pulley engages the main engine pulley at a right angle and speed is controlled by moving the driven pulley closer to or further from the center of the drive pulley. It was this driven pulley that was loose on its shaft. Being a Sunday afternoon, and given my full schedule this week, I decided to fix it with what was on hand. I hoped to get some of the yard mowed, and several acres take a while on one of these slow but steady machines.
I apologize for the lack of photographs, but I did not think to take any. I will paint the best word pictures that I can.
On removing the not-too-tight nylock nut that probably caused the failure, I could see significant damage. The hole in the center of the pulley was severely galled and the woodruff key that rode in the shaft was peened over. The pulley appeared to be cast of a zinc alloy. Thankfully, the primary transmission shaft on which it rides appeared unharmed.
As the pulley could not be welded, I scrounged around and found a large bolt of greater diameter than the shaft. After measuring it, I found an end mill with which to bore out the pulley, as no drill bit of that size was available. I bored the hole using the drill press. I cut a slug out of the bolt shoulder with a hacksaw, leaving it slightly longer than the depth of the pulley. The fit was close but not close enough, allowing the insert to move freely.
I took the two pieces over to a section of railroad rail, inserted the slug, and struck the slug on-end with a big ball-peen hammer until the fit was tight. I ground off the excess material using the bench grinder.
Not trusting the peened slug with regard to rotation, I returned to the drill press and drilled a 13/64" hole through the interface line made where the insert met the pulley and along the same axis as the shaft. I tapped the hole for 1/4"-20 UNC and inserted a bolt. I ground its head off flush. This bolt engages half with the pulley and half with the insert, preventing the pulley from turning on the insert.
Using a set of dividers, I found the center of the pulley and marked it. After drilling a pilot hole, I searched for a 5/8" bit to bore the pulley to fit the shaft. Not finding one, I resorted to using a rotabroach, which is intended for sheet metal work. Think of a small hole saw made of cobalt steel alloy. With sufficient cutting fluid and a very slow drill speed I was able to bore a surprisingly clean hole.
I filed a keyway with a square profiled needle file, which was probably the most tedious and unpleasant part of the job. I ensured that the keyway was deep enough but was sure not to file past the insert.
I used the remainder of the original key as a guide while grinding down a much larger key I had from an automobile crankshaft. I used vise-grips to hold the piece while grinding it on the bench grinder.
Reassembly was straightforward, though the fit was intentionally very tight. I hope the close fit will prevent a recurrence, taking much of the stress off of the nut.
I was able to mow about half of the lawn on Sunday evening. I ran out of light and almost ran out of gas. The mower ran fine and gave no trouble.Grundy
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