12-29-2014, 09:43 AM
Went out and gave the screw/nut an oil and cranked the handle. It didn't want to move, so I double checked that the lock was off (which it was) and tried again. Tried working it both up and down and was able to get some movement but it wasn't easy. Then all of a sudden there was a loud crack, followed by a brief moment of panic and subsequent colourful language 
My concern was that perhaps I had broken the screw, or worse, cracked the casting. I rigged up the engine hoist and unscrewed the elevation nut from the pedestal and lifted the knee with the hoist. Once the nut was clear of the pedestal, I gave the handle another crank. The problem remained. However, I was pleased to have eliminated the screw/nut as the problem.
It then dawned upon me that the issue may be with the bearing retainer that bolts to the underside of the casting once the elevation screw has been installed. As the bearing was thicker, it finished flush with the bottom of the casting, so I installed the retainer upside down, as it had a raised section that was required for the thinner bearing but would not allow a flush fit with the current bearing. I stuck my head under the knee and saw a crack straight through the center of the retainer that confirmed my suspicion.
Originally, the space between the bearing and the retainer had enough clearance for the bearing retainer. With it installed upside down, it effectively locked down on the bearing carrier, causing the problem. I had installed this after I tested the elevation nut/screw, which is why I reported no issues the other day.
Well, I have a lathe, so making a new retainer is no problem! The old retainer. You can see where the bearing carrier has rubbed.
A suitable replacement found in the inventory. Top left of this picture you can see the other side of the original retainer, with the boss that fits against the outer race of the bearing. You can also see the crack!
Centre bored (oversize) to ensure that there is sufficient clearance for the carrier. After the hole was bored, it was dunked in the de-rust tank, which is why the metal looks very different (I didn't bother with a facing cut).
Bolt holes drilled.
Painted and installed.
My concern was that perhaps I had broken the screw, or worse, cracked the casting. I rigged up the engine hoist and unscrewed the elevation nut from the pedestal and lifted the knee with the hoist. Once the nut was clear of the pedestal, I gave the handle another crank. The problem remained. However, I was pleased to have eliminated the screw/nut as the problem.
It then dawned upon me that the issue may be with the bearing retainer that bolts to the underside of the casting once the elevation screw has been installed. As the bearing was thicker, it finished flush with the bottom of the casting, so I installed the retainer upside down, as it had a raised section that was required for the thinner bearing but would not allow a flush fit with the current bearing. I stuck my head under the knee and saw a crack straight through the center of the retainer that confirmed my suspicion.
Originally, the space between the bearing and the retainer had enough clearance for the bearing retainer. With it installed upside down, it effectively locked down on the bearing carrier, causing the problem. I had installed this after I tested the elevation nut/screw, which is why I reported no issues the other day.
Well, I have a lathe, so making a new retainer is no problem! The old retainer. You can see where the bearing carrier has rubbed.
A suitable replacement found in the inventory. Top left of this picture you can see the other side of the original retainer, with the boss that fits against the outer race of the bearing. You can also see the crack!
Centre bored (oversize) to ensure that there is sufficient clearance for the carrier. After the hole was bored, it was dunked in the de-rust tank, which is why the metal looks very different (I didn't bother with a facing cut).
Bolt holes drilled.
Painted and installed.
Hunting American dentists since 2015.