Little (but Important) Things

The way our 503 had been set up on the trike, the gearbox was directed upwards. If we were to use it this way on the Gyrobee, the engine thrustline would have ended up much higher than the position of the vertical Center-of-Gravity/Mass:

First job was to rotate the gearbox so it is directed downward, significantly lowering the thrustline. We had never done this particular job before and a first look at an exploded view of the B-gearbox did not inspire confidence:

Fortunately, 99% of all this stuff stays together! To start, we needed some definitive guidance for getting the job done. Enter Rotax with an excellent guide on installation:

Installing the Rotax Model B Gearbox

Clicking on the link will download a set of instructions in PDF format. It is a dual language version (English and German) and quite complete. Only three tool items are necessary:

• A torque wrench

• A compatible 11 mm hex socket

• A compatible 13 mm hex socket

Here's what you do:

(1) Drain the gear oil from the box. If the engine is mounted on the gyro, drape plastic over the tail boom to avoid a real mess. Ventilation also helps as the gear oil stinks! Check the magnet on the drain plug. There should be some super-fine steel paste, but no obvious steel fragments. The lower drain plug and upper vent covers should be put aside for the moment.

(2) All bolt references refer to the illustration above. Use the 13mm socket to remove two #24 bolts (the longest), the two #25 bolts (mid-length), and the two #26 bolts (the shortest ones), and carefully pull the gearbox case half away from the half still mounted to the engine. Keep track of the bolts.

(3) Carefully remove the gasket and put it aside. If you are careful, it can be re-used, otherwise, have a new one on hand.

(4) Clean excess gear oil from both case halves.

(5) You will note that the remaining case half is bolted to the engine case with two bolts. Use the 11mm hex socket to remove these bolts.

(6) Pull straight back to remove the rest of the box.

(7) Rotate the box-case half 180-degrees and push in back on the alignment boss on the engine case. .

(8) Tighten the two interior bolts to 24 NM (210 ft/lbs.) using the torque wrench and the 11mm socket.

(9) Insert the #25 and #26 bolts (along with their washers) through the mounting holes on the loose case half. Arrange the gasket over the protruding bolts and slide the case-half into place and hand-tighten the bolts. Note that the #25 bolts are now at the bottom and the #26 bolts are at the top.

(10) Insert the #24 bolts but do not tighten at this time.

(11) Use the torque wrench and the 13mm socket to tighten the #25 and #26 bolts to 24 NM (210 ft/lbs.).

(12) Use the torque wrench and the 13mm socket to tighten the #24 bolts (washers under the heads) to 24 NM (210 ft./lbs.).

(14) Add SAE 140EP or SAE 85W-140 EP gear oil. About 300cc/ml will be required.

We will mount the prop and safety-wire the drain and overflow plugs later. For now, we can be happy the engine now looks "right", with a properly-oriented gear box:

Work on the seat is almost done, but I am waiting for completion of the custom seat cover. For the moment, I was content to mount the quadrant throttle and think about the mounting issues for the instrument pod.

Session time: ~1.5 hour      Total Time: ~22.5 hours