If you are building a taildragger, you may skip this task, or apply the guidelines to the main gear installation.
The nose gear leg will need to be drilled for the single 5/16" mounting bolt. A hole needs to be drilled through the top knob of the nose gear leg from front to rear. This hole must be a precise fit for the 5/16" bolt to avoid nose gear shimmy, so we will drill it slightly undersized and ream it to 0.310". Note that the "axle" part of the nose gear actually sits perpendicular to the floor, not parallel with it, as the main gear legs are oriented. This axle passes vertically through the nose gear fork. Gather the related parts and review the blueprints to become familiar with the orientation and relationship of the parts.
The nose gear leg fits into a tube in the engine mount. This tube will have a pilot hole drilled through it on one side. You can pre-drill the nose-gear leg in a drill press, then align the holes when you install the leg in the mount tube and hand-drill the final hole.
To assure that the hole is drilled straight, the leg should be marked then securely clamped in a drill press vise for drilling.
A simple means of marking the gear leg is to lay it across a wide drawer such as a toolbox cabinet drawer. The weight of the axle part of the leg will hang directly downward, swinging the leg perpendicular to the floor (or gravitational center of the earth anyway). Using a small level or plumb bob, mark a vertical centerline where the bolt will pass through the gear leg. Also mark a point to start drilling on the top face of the gear leg knob. Consult the plans for orientation.
Move the gear leg to a strong drill press vise and clamp it into position. Verify that the line remains perpendicular to the floor with a small square against the drill press base plate. Secure the gear leg in the vise and the vise to the drill press base plate.
Drill a pilot hole through the gear leg using a 3/16" cobalt, carbide, or titanium drill bit. Use a slow drill speed and apply steady pressure. If the drill bit sings or you see signs of overheating, stop and apply a drop of machine oil or dip the hot drill bit in Boelube drilling paste before proceeding. When the pilot hole is done, verify that the hole is in alignment. If not, a small amount of repositioning in the vise may be possible before continuing with the next size drill. Several increments of drill sizes should be used to allow gradual correction if you have fouled up the alignment. Best to get it right the first time! The alignment is critical because a small amount of misalignment in rotation will be very noticable at the tip of the leg. Also, play in the bolt is not good, so only increase the hole size to that of the bolt. Most bolts are a few thousandths under the actual named dimension.
Make a second pass through the hole with a 19/64" drill bit and 0.310" reamer. This is the final size. Debur the hole and chamfer the edges.
Reamers can be obtained through many sources, a few are listed below:
- MSC industrial supply (incredibly fast order delivery) - www.mscdirect.com
- McMaster-Carr - p/n 8803A47 for 12 bucks US.
- DORMER catalog - .3105" (close enough) p/n 0250525
TIP: Use only new drill bits of good quality cobalt or titanium. The most common problem when drilling this hole is to continue applying pressure to a dull drill bit. This can cause the drill to chatter and "walk" slightly off center. You must use good quality bits, securely clamped in a large drill press vise. If you are not equipped to make this hole, take the gear leg and mounting bolt to a local machine shop. You want your nose gear to run straight! A machine shop can drill a very precise hole to give you a perfect push-fit for the bolt.
The weight of the powerplant will cause the landing gear to compress. You need to prepare for this so as to avoid possibly denting the bottom fuselage skin or other parts. Your wheels should have their bearings greased and be installed before hanging the motor. You can remove them as needed later. Remove any saw horses or other objects from underneath the plane which might dent the fuselage belly. As weight is added to the nose, the tail section will tend to rise. Be certain you have enough overhead clearance to avoid damaging your airframe. If convenient, remove and store the empennage.
Assemble the nose gear leg and wheel assembly. You may choose to install the nose wheel now, before installing the gear leg, or later. If you defer wheel installation, be sure to protect the nose gear leg so the threads are not damaged.
Remove a Badly Placed Plate-Nut
If you installed the fuel pump backing plate on your firewall (specified by Vans for Lycoming motors and the Facett pump), the lower plate nut will need to be removed as it interferes with the engine mount tube. Drill out the rivets, remove the plate nut and fill the holes with dead-rivets or screws and nuts.
If you are installing an optional cabin heater, now would be the time to complete the installation. It is easier to work on the heater before the engine is in the way. Return to and complete this first Checklist when you are ready to continue.
At this point you are ready to hang your motor on the firewall. Check the following details.
[ ] Have you installed your optional Cabin Heater main box (the valve and hoses will come later)?
[ ] Have you obtained all tools, parts and materials required for hanging the motor?
[ ] Do you have the correct Engine Mount Bolts?
[ ] Do you have a 19/64" drill and 0.310" reamer for your portable electric drill?
[ ] Is the workspace suitable for the task?
[ ] Is an Assistant available and briefed?
[ ] Are the Wheels and Tires assembled?
[ ] Nose gear leg, fork, and wheel are ready to install?
[ ] Firewall is fully riveted and clean?
[ ] Rectangular stainless steel firewall recess is installed and sealed?
[ ] Hoist and sling are ready to go?
[ ] Safety measures have been considered?
[ ] Enter time and date in your Engine Logbook under "Initial Installation" including engine year, size, type, model and serial number.
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