Gear and Shaft Repair

I discovered a problem inside the gearbox that I couldn't bring myself to ignore (despite sound advice suggesting this).

Someone inside the gearbox before me had installed the large gear on the countershaft backwards. This gear has a raised hub on one side to offset the gear away from the inside of the gearbox housing. It had been installed and run with the flat side towards the housing, causing the gear to rub into the housing (and vice-versa).

Damage to the inside of the case

The gear and its shoulder on the end of the shaft were discolored from heating. It was all quite scary looking and the gear had 0.015 of lateral runout caused by damage to both the gear and the shaft. I cobbled together a fixture for measuring the lateral and radial runout of the shaft and the gear and shaft together:

Measuring runout on the damaged gear and shaft

I took a 0.001 cut off the shaft's shoulder to true it up:


I faced the whole gear for balance (and vanity), and trued the hub face with a very light cut. This is the gear and shaft after the repairs:


I measured 0.002 lateral runout at the outer edge of the gear after the repairs. In back gear, there is a cyclic noise coming from the gear but it is not nearly as bad as before the repair. I think it is due to the gears having been worn-in in the damaged state for many years. I expect it will last for my lifetime.

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