Chapter 23: Engine Mount Installation



Step 1:  Engine Mount Installation

It's great to finally bolt the engine mount to the firewall.  Since I have a fuel-injected engine, I went with an H-design dynafocal mount.  I could not use the standard Brock mount because its cross bracing (X-design) interferes with the fuel injection system.   I obtained my engine mount from AeroCad, who at the time employed the services of Velocity's welder.  I called Scott Swing at Velocity and sent them the dimensions and specifics from the M-29 drawing to ensure the mount was fabricated properly. 


Tips and Suggestions 


1.  Before drilling any holes in the firewall, I did some fit-checking to ensure the engine mount would be installed correctly.  I checked that the mount's footpads were over the four aluminum laminates in the firewall, and that the dynafocal cups were level side to side with the fuselage.  It must be hard to weld up an engine mount because none of the footpads were exactly dead on with plans coordinates.  All of my bolt holes went through the laminates, but 3 of 4 were off-center.   I guess you just have to get used to accounting for variances on things like this.  If I ever do this again, I'll certainly increase the size of the firewall's aluminum laminates in Chapter 4 from 1 inch to 2 inches square.


2.  When drilling the holes, I held the engine mount FIRMLY AGAINST the firewall and used the sleeves on the footpads as guides.  You want to do it this way to ensure the sleeve and the hole through the firewall/laminates are perfectly aligned.


3.  Once the engine was installed, the next step was to ensure the engine pointed straight out the back.  I did this by dropping plumb lines from the center line of the nose, firewall, and engine starter ring, then sighting down all strings.  The engine was pointed to the right of centerline by 3/32 of an inch.  So I'll need to tweak the alignment a bit with very thin washers under the mount's starboard footpads.  Evidently, the dynafocal ring is slightly off because I have verified time and time again that my firewall is square to the plane's centerline.


4.  It's always a good idea to get some tabs welded onto the mount for a grounding strap, cable clamps, etc.   I'd like to figure all this out and get the tabs welded on before powder coating the mount.  But the raw metal on the engine mount rusts really quickly.  So in the interim, I cleaned it up and painted it with zinc chromate to prevent further rusting.