Main Leg Lubrication

This blog cover the installation of greasing points into the main undercarriage leg

Overview
This builder decided to add greasing points to all high load pivots of the undercarriage for lubrication as required at bi-annuals /100 hourly.

Trailing Links

Bolt held in block, trimmed
then machined to length

All bolts were renewed to provide 100% bearing on links this required the purchase of a set of M6 x 90 mm Unbrako S/S bolts and remixing the factory supplied bolts. 

At installation M6 S/S spring washers were installed under each bolt head, this washer locks the bolt and arm together ensuring that all rotation occurs in the major attachment point located on the main gear leg. 

All bolts shanks were greased before installation.

Note: The changing of the bolts ensured that thread was not located in the working portion of components - shank support - thread retain. 

The center pivot blot was replaced with a M6 hex head to provide clearance to grease bolt on the main pivot mount. This was created by an unforeseen issue with clearance to the grease nipple on the main when the gear closes. [see note below]

Main Pivots
The boss face was drilled 3 mm through then drilled, tapped M5 to fit the grease nipple after facing the boss depth to 15.5 mm. To contain the grease at the rear a 1.5 mm cover was cut from 2024 aluminium sheet using a hole saw with the pilot hole filled using a 5 mm pop rivet and washer. 

Finally the cover was sealed with Permertex sealant, fixed onto the boss face using four [4] x M3 screws fitted into blind tapped holes. 

Note: After breaking a tap it was found 3:1 oil worked best as a tapping lubricant in this aluminium. A ratchet T wrench was purchased and proved to be perfect for this task.

Trial installation main pivots

The pivot arm was next filled using two [2] plugs of 25 mm thick builders foam foam cut with a ceramic hole saw. These plugs were pushed into the shaft and sealed with Permertex high temperature silicone.

Main Pivot Seal

Note: The hole saw was one in a bulk lot purchased to cut the holes for the seat belts with one perfect to produce the plugs. Plugs were fitted to prevent filling the arm with grease.

Hydraulic Cylinder Pivot
The rear of the cylinder mount was tapped M5 and a nipple fitted with a 12 mm hole drilled through the rib for access to the nipple. This position is not easy to access and will require a re-grease to be undertaken from the inside of the fuselage.

Note: Note sure about the access until the wings are mated

Drag Links

1/8'' Zerk drive nipple

Both drag link bolts are converted into grease bolts by drilling a 2 mm hole from the head side to the shank center with the head side redrilled to 1/8'' to accept the drive nipples, then finally a 1.5 mm hole was drilled to the pick up the end of the 2 mm hole and chamfered using a drill.

The M6 bolt hex was filled with silver solder and machined and drilled as outlined above with a nipple fitted. The disadvantage being it has to be tightened by clamping the head.

Cylinder is fitted with a stop collar to fix the stop point
stopping the gear just short of the top skin by about 5 mm

Stop Collar

The main M8 pivot bolt was drilled again as outlined above but it was found to foul the leg necessitating the machining of the head to a overall depth of 5 mm and the nipple reinstalled. The nipple overall height was reduced by 1 mm to improve overall clearance.

As noted above the center bolt in the trailing link group passed the nipple resulting in the cap head bolt beign replaced with a Grade 8.8 hex bolt - Murphy's Law in full application.

Another step forward

Comment
Doing it again the 1/16'' cover would be machined from 60 mm round and fitted with counter-sunk screws as the M5 rivet head made reinstallation tight.

All points where pressure lubricated and as expected more grease can be applied under pressure than by hand.

The limit switches will be covered in detail in a separate blog