Elevator Push Tube - Part 1

The elevator is controlled by a push pull tube on bearing mounted bell cranks with all connections made with threaded rod ends fitted at both ends .Begin by removing the front remand which is held in by a series of temporary rivets. The front edge has a angle fully riveted to the panel - do not drill these rivets only the ones into the riveted to the skin and longeron. Remove the panel and place to one side for future installation.

Front Bellcrank

Install the front bracket and bell crank onto the rear spar mount with four AN3-7A bolts.

The rear bell crank on mine required an amount of fine tuning before installation. The mounting centers pre-drill into the mounting bulkhead is a 60 x 20 grid. Measuring the assembled bell-crank assembly unit it was 61 x 20. It was dissembled and the two packer washers between the bearing and bracket filled down by 0.5 mm [0.020''] to achieve the correct centers. Reassemble loosely to aid assembly.

Install rear bearing to ensure a bolts are correct - For information Click Here

Rear Bellcrank

On this kit the top two bolts fouled on the reinforcing brackets on both sides. The best solution was to file one of the bolt heads flats providing the correct clearance at assembly. All bolts used are AN3-7A . 

You will require a large degree of patience or hands with the ability to emulate a snake to install the bolts. The best technique was to insert a bolt through the selected mounting hole and with one hand inserted through the 100 mm fanged hole a washer or nut is guided on to the respective bolt using a combination of both hands - it's really quite easy, really.

Once the bracket is installed time to calculate  the length of the tube. At this point I noted that one end was badly damaged and mild panic set in with thoughts of  "I cannot remember hitting this that hard".  Once calm returned it was determined that the tube was oversize and only one end was damaged.

This leads to a simple warning that this tube is very light and can be damaged easily by striking a prepared edge so exhibit some care in handling.

The overall length has to be calculated and the center so the center distance has to be determined. A cheap tape measure has a hole drilled a 1/4'' diameter at the 100 mm mark, this is secured to the front bell-crank using a bolt and then extend the tape to the rear bell-crank. While holding the bell-crank in its correct location with a bolt fitted into the lower mounting hole, mark its center onto the back side of the tape with a Sharpe pen. Rechecked to verify the marks position and then removed to the workbench to calculate the tube length. The timber block is to lock the bell-crank into it correct location while pulling on the tape.

The calculation is fairly straight forward using a few basic parameters. The threaded length of the rod end is 22 mm and 5 mm was allowed for lock nut with and minimum engagement into the mounting resulted in a nominal 10 mm projection from the mounting with the threaded rod now in its mid position. The assembled length is measured for both fittings and this was deducted from the theoretical center to center measurement taken with the tape. Remembering to deduct the 100 mm from the measurement read from the tape measure.

Mark cut point with a Sharpe pen and then wrap a strip of cardboard wrap it twice, secure the end with a length of tape. Align the edges of the cardboard to create a straight line through the tube - mark the perimeter with the Sharpie pen. 

Following the line a series of cuts are made while rotating the tube in steps, try to cut as deeply as possible without penetrating the tube. Repeat until a full revolution of the tube is completed. At this point use the saw to cut straight through the tube using the groove as the guide. The tube will cut easily so it all happens quickly. To finish off check with a square and carefully dress the edge to remove any inaccuracy's with the cut.  Polish the edges at both ends with 400 aluminium open cut. Remove all the plastic wrap and wash with thinners. Finally polish out any mill marks or scratches with 400 grit aluminium open cut, clean and prime.

Yes it fitted...!

Calculation sheet

With this kit one of the fittings was size for size fit and was therefore quite tight to assemble. This requires a hammer to drive it into the end of the tube. Fit a AN4 bolt fully into the tapped hole then tap the fitting lightly into the open end. Rotate after each few taps and recheck alignment until engaged sufficiently to ensure a straight insertion. At this point a few sharp blows will drive the fitting home. Once installed fix the fittings to the tube as outlined in the factory notes and drawings.

Fixed with two rows - eight rivets in total - both ends