Preparing The Rear Housing For Assembly
This starts with completely disassembling the housing by removing all the mechanical stops, limit switches, and the cam ring. Then the large bell gear can be pressed out of the housing to access the thrust bearing and seal. They are also removed from the housing for cleaning and inspection.
The seal and bearing must be removed because the original seal is installed backwards for our application.
The original Speed Reducer was designed to be operated in a horizontal position with the gearbox partially full of lubricant being splashed around, and the seal was installed to keep splashed lubricant (not flooded lubricant) in the case.
We are going to use it as a rotator in the vertical position (in most installations with this end of the unit on top) and we want the seal to keep water out of the case, instead of lubricant in. So, the seal needs to be reversed.
The bearing needs to be packed with waterproof grease because it can no longer be lubricated by case fluid when it is in a vertical orientation with this end up. We can't completely fill the gearbox with lubricant and maintain it's level up to the level required to lubricate the bearing. This also applies to the seal, the seal can't work without lubrication!
Complete Rear Housing at the beginning of the process on left. Bare Housing ready for rebuilding on Right.
The bare housing is first sandblasted. Then the holes that will allow water to easily get to the seal in the housing are sealed. Then the housing is primed and painted. The holes in the housing that were used for routing wires to power the motor are set up to be used as drain ports to allow water to drain out of rear cavity in the housing. The sandblasting is required to remove the oxide on the housing surface that prevents the hole sealing compound and paint from properly bonding to it.
When the housing is ready for assembly it looks like this:
Assembling The Rear Housing
In order to prepare the housing for final assembly the seal and thrust bearing needs to be installed.
These are the parts that need to be assembled:
The original seal is shown on the lower left, with its lip facing up. It needs to be installed with the lip facing down when installed in the housing, as shown here, to be set up for keeping water out of the gearbox.
The thrust bearing is on the lower right. The side of the bearing facing up in this photo needs to be facing down when installed in the housing for it to support the gear train properly.
Here is what the finished Rear Housing looks like with the seals and bearing installed:
The black ring at the bottom of the housing in this photo is the felt dust seal that goes into the groove at the rear end of the housing.
The Rear Housing is now ready for final assembly.
More About The Seal
The original seal is a unique size. There is no direct replacement for it. The sealing material is rawhide with a circumferential spring to press it against the sealing surface. Sometimes these seals are in amazingly good condition for their age and can provide sufficient grip on the sealing surface to produce an effective seal. Sometimes they are all screwed up and are unable to effect a seal.
When the original seal is not suitable for use, a new one needs to be installed. This requires machining the seal boss in the housing to accept the modern replacement seal.
On the right is the original seal. The replacement seal is on the left.
The seals in the K7NV rear housings are installed with an anaerobic sealing compound to prevent moisture from migrating in between the housing and seal body. They didn't need to seal this interface in the original units because it was a wet gearbox that ran in a horizontal position allowing the fluid to protect the area. The seal/housing interface is a prime site for galvanic corrosion when the unit is mounted in a vertical position. I have seen corrosion at this interface with every unit that has been in service.
More About The Thrust Bearing
MRC0017 Thrust Bearing
This bearing is a unique one that was made only for this application. There are no modern replacements for them. This is one of the reasons why it is so important to setup a prop pitch unit for use as a rotator in a manner that will prevent this bearing from getting ruined by corrosion. The same bearing is used to support the bevel gear in the adapter plate on the rear end of the Power Unit.
Every prop pitch that I have seen that was used by a ham as a rotator has had a severly corroded thrust bearing (or bearings if the adapter plate wasn't thrown away). I have several rear housings I'm still trying to get apart after months of soaking in penetrating oil because these bearings are welded together by rust. It's depressing!
I have found several bearings of similar design and nearly same size, but none of them can be made to work as a replacement. The price for these bearings that are close to the right size, but not useable, are around $130.
Fortunately, my bearing supplier made an exhaustive search and found a stash of these exact bearings and I bought them all so I could continue to be able to rebuild these things properly.