Chapter 23 - Section 2

Mounting the Engine


Building the Engine Stand

I was surprised that the Plan recommends against using an engine hoist to mount the engine. Instead, the Plan recommends building an engine stand. I went to Harbor Freight and bought 4 medium duty cast iron casters (275 lb payload each) for the engine stand. The cost for each caster is ~$6 and the 2 x 4 lumber comes to ~$11. I spent a couple evenings and completed the stand. It turned out to the exact dimensions per Plan and its pretty rugged.


[Hindsight] I had to modify the engine mount for my engine. The upper horizontal support beams were too far apart. In addition, I had to add custom support blocks to keep the engine level, and I had to shorten the stand to make room for bolting the engine mount onto the engine.









Engine sitting sturdily on my 'modified' engine stand. I just don't see how I can handle the engine without the help of an engine hoist according to Plan. It happened that Harbor Freight had an engine hoist for sale for $149...perfect timing. The cheapest one did the job. 


[Hindsight] This is one of the few recommendations from Plan you may want to reconsider. The weight of the engine made it difficult to maneuver, let alone lining it up against the fire wall.











Engine Mount

I ordered the engine mount (heavy duty) from the Cozy Girls and it arrived after a few months. I was anxious to find out how it will fit to the hard points in my firewall. It took me a little time to remove it out of the crate and lay the engine mount footprint right on top of my hard points. They lined up perfectly!









Bolting the Engine Mount onto the Firewall

After the engine arrived, it was time to attach the engine mount onto the firewall. I laid the mount on a flat surface, with a translucent paper in between. I traced out the mount footprints onto the paper. In addition, I slipped a 3/8" drill bit (that has a pointed tip) through the mount's bolt holes and pierced a hole onto the paper. These holes will be used to establish the mount position on the firewall.


I drew out the mounting positions (per Plan) of the engine mount onto the firewall. I based my measurement using the top of the longerons, the 17.4"WL from the center section spar and the centerline of the fuselage. My mounting positions are now about 1/8" above the center of my hard points. I do not know how the hard point drifted out of position during the prior assembly steps ... its the same on all 4 hard points. At least it is symmetrical. You can see my 'round' hard point relative to the engine mount hole.



Regardless, I taped the translucent paper (with the pierced holes) on top of those positions. With the help of a wood block, hot glue and bondo, I bondoed the engine mount in position (on the firewall). I re-measured its position against Plan - though the only tangible position to measure is the center of the mounting holes. I was not quite sure how to get the 1.5o tilt with the mount at this time. I may have to re-visit this alignment position later on...


With the engine mount bondoed in place, I used a center drill bit to establish its mounting hole location for subsequent drilling. I used a 3/8" pilot point Cobalt drill bit (DeWalt, Lowes) and lots of machining oil to complete the bolt holes. I chose a lower power hand drill because my hard point is round and it was pointed out to me (early on) that I may end up spinning the hard point. Therefore, I took time to drill my bolt holes without incident! It is gratifying to see that the big moment for mounting the engine is drawing near. 


Protecting the Engine Mount

With the engine mount sitting around for a couple of months, I noticed a few rust spots starting to appear. I figured I better do something about it before it gets out of hand. First, I brushed the entire mount with a Scotch pad. Then I wiped the mount down with Acetone because I have quite a bit of splattered machine oil around the bolt holes. The Acetone worked out well because it actually cleaned up quite a bit of the dirt residue from the manufacturer.


I sprayed a light coat of primer on the mount. I used Rust-Oleum Engine Primer (Autozone) because it's supposed to resist heat up to 500oF. Hopefully, my engine mount does not have to see this kind of heat... After the Primer cured, I added a light coat of white Rust-Oleum engine enamel. Again, its supposed to survive to 500oF as well.




Bolting the Engine Mount to the Engine

I decided to bolt the engine mount onto the engine first before attempting to mount the engine to the firewall. Lining up the bolts and Lord Mounts to the engine was quite a challenge. I was beginning to think I got the wrong mount...feels like it was at least 3/8" off. It turns out that the bolts enter the engine bolt holes at such an angle, you must slide all 4 bolts in together (a bit at a time). I ended up inserting all 4 bolts onto the engine first. Secondly, I hung the engine mount onto the bolts. Then half of the Lord rings - one at a time, the center post and the outer half of the Lord rings. I have to do quite a bit of jogging, shifting etc. to get them all in place and tightened. I also looked up the torque value for 7/16" bolts and torqued them down.


Putting it in the second time was much easier. I couldn't understand why it was so difficult the first time...


Mounting the Engine to the Firewall

I tried to mount the engine to the firewall with the engine hoist alone. It was difficult to line up the bolts through the engine mount and the pre-drilled holes in the firewall because the engine does not 'hang' level to the firewall holes. It was almost impossible to roll the engine 'level' to the firewall holes while it is hanging freely on the engine hoist. I eventually laid the engine back onto the engine stand (built earlier) and followed the Plan's recommendations. That worked out well.


My 50 lb. weight was barely enough to keep the plane from tipping. I had to get extra weights from WalMart, otherwise, it would not be a joyous day. After all the maneuvering, I cannot imagine getting the engine from delivery to mounting it onto the firewall without using both the engine stand and the engine hoist!




Engine Position Relative to Thrust Line

Throughout the engine preparation and mounting process, I kept wondering if I could ever secure the engine in-line with the planned thrust line. It was not clear in the Plans where the thrust line really was...A visit to the Cozy forum reviews a ton of information. Evidently, even if the engine is off a bit, it does not affect the performance of the plane much. However, it would be nice if I can have my engine mounted close to the Plan. I finally found the information I was looking for...According to Nat, 'the thrust line on the Mark IV is WL21.5 at FS135 and inclined up toward the rear 1-1/2 degrees'. I can work with that...


First I set the plane straight and level. Then I measured the height of the longerons (47.75") and the center point of my prop extension (47.25") above ground. The difference (0.5") is the relative height of my prop center to the longeron - which is at WL23. In other words, my prop center is 1/2" lower than the longeron (i.e. WL22.5").


The distance from the firewall to the aft face of the prop extension is 40.4". Since the firewall is at FS124.25", the aft face of my prop extension is at FS164.65".


Per Nat's thrust line equation (Cozy Archive 06/12/1998) and a little trigonometry, I projected that thrust line, towards the rear - it passes FS164.65 at WL22.28".


In comparison, my engine is 0.22" above the thrust line. A quick measurement with my digital level showed 1 degree tilt down - it should be 1.5 degrees down. This can be corrected by adding an appropriate thickness washer to the lower engine mount bolts. Though not exactly to Plan, I believe my engine location is pretty close with little performance concerns down the road!


Prop Clearance Calculation

At the back of our Cozy Plans, it stated that the maximum prop dimension is 70". It also shows that the clearance height is 10 degrees projected rearwards at FS110. As I measured above, my prop location is at FS164.65. Using the Plans' equation, minimum required clearance at FS164.65 should be 9.64" above ground. Since my prop extension center is at 47.25" above ground (above), the maximum prop RADIUS I can use can be calculated to be 37.61" (47.25" - 9.64") or prop diameter of 75.22". Obviously I won't be using that long of a prop - most likely 68" instead. That means I should have a good margin for error (~5") to prevent prop strike, I hope!