July 14th until this morning, August 19th! I know that there is no real excuse for wasting all that great weather over the past month, but I at least have a good REASON. I also had no time available to get at the August Skywriter until today. I worked out the numbers and in a 25 day period, I worked 250 hours! Fortunately, things have settled down now.

So, what was keeping me so busy? Well, that story begins in mid-May with the annual inspection of Iain & Dave Colquhoun’s beautiful 1953 Cessna 170B in Indus. Three hours into the inspection revealed an oil filter full of expensive shiny bits. Yup, it was producing metal. There seemed to be both magnetic and non-magnetic bits suggesting that the metal was coming from a couple of different places. Considering that the engine was last overhauled in the ‘60’s and was only a couple dozen hours from TBO, it was decided that the engine had to be removed.

For the next month, considerable time was spent talking to vendors and overhaul shops to try and determine the best course of action. There was a lot to consider. The simplest option was to sell the plane as-is and buy something else. However, the plane was an otherwise fine specimen of the classic design having a simple, but functional panel, a nice paint job and relative low total airframe hours.

The second option was to overhaul the original engine and reinstall it. This presented us with a couple of problems. First and foremost was whether or not the core components of the engine (ie. crankshaft, crankcase and camshaft) were reusable. Unfortunately, the 145 hp Continental C-145 and its replacement, the O-300 are no longer supported by the manufacturer. Parts are becoming more and more scarce and expensive as overhaul shops scrounge the few remaining serviceable, used items. Fortunately, this engine core was still rebuildable but would still be been quite expensive to overhaul.

Obviously, more than just the engine gets replaced when it’s time for overhaul. The aircraft manufacturer will usually recommend replacing the exhaust, baffles, engine controls and performing a nondestructive test of the engine mount. More often than not, the mounts come back with cracks that need to be repaired or replaced.

This brought us to the third option. Instead of reinstalling an orphaned engine, why not go with a newer, more powerful engine. The Lycoming O-360 is arguably the most reliable piston engine made. It’s only slightly heavier than the C-145 and produces 35 more horsepower! However, it is drastically different from the C-145 in that it’s a four-cylinder rather than a 6 and uses a rear Dynafocal mount system rather than the bed-style mount of the Continental. Obviously, it’s not a simple matter of replacing just the engine.

In fact, to use the O-360 on the 170B, the engine mount, exhaust, baffles, oil cooler, engine accessories, propeller and spinner all have to be replaced with new components. The cowl also needs significant modification to accommodate the wider engine and the large ring gear mounted up front.

Fortunately, there’s a kit for that! The one we considered was from Del-Air in California. The only things not included in the Del-Air kit were the engine, prop and a few minor hardware pieces salvaged from the Continental. Engine controls are reused as well.

Alberta Aero Engines in Edmonton offered to trade us an O-360 core for the C-145 core we removed, helping make this option more reasonable. The Continental overhaul was about 25% more than the Lycoming which also help offset the cost of the kit and new prop. The cost of replacing the baffles, exhaust and mount for the C-145 brought the cost difference between these two options even closer together. Finally, the performance and resale value of the O-360 powered 170 was significantly better than the C-145 powered plane. After considerable research and deliberation, it was decided that the 170B would receive a rebuilt Lycoming O-360-A4M using the DelAir kit.

The order for the engine, prop and kit were placed and initial indications were that the kit would arrive on the 7th of July and the engine on the 14th. Perfect! It would take a week or so to get the plane far enough along to install the engine. I also had a two week, fulltime teaching stint book in at SAIT for the first two weeks of August and my wife was going to be away in Newfoundland for the last two weeks of July leaving me to take care of the two pups. No problem. The kit would be mostly done by the time Renee left and finishing the estimated 95 hours of work should be easy to accomplish in the four weeks I had before classes started.

Well, we all know what happens with plans! The kit ACTUALLY showed up on July 21st and the engine on the 28th! I now had two weeks to do the install, two weeks in which I was responsible for getting the dogs out for two walks a day! Well, there was nothing for it but to dig in and get ‘er done. By the end of the two weeks, I still had lots of work to do, so I ended up spending my evenings and weekends while at SAIT either working in the shop or down in Indus. Iain was a big help in the last couple of weeks and spent nearly as much time in Indus working on the plane as I did.

The biggest part of the install was the cowl modification. A new two-piece nose cap for the cowl came to replace the original one. Holes had to be positioned and cut in the upper cowling to install the supplied blisters that accommodate the wider engine. The lower cowl was also equipped with a new air filter assembly. By the time it was all done, the cowl modifications made up about half the work required (and they still haven’t been painted!).

The kit also included new oil pressure, oil temperature, fuel pressure and ammeter gauges as the old ones simply don’t have the range of movement required for the new engine. The plane is fitted with both an engine driven fuel pump and an auxiliary electric pump as the original fuel lines will not deliver enough fuel through gravity alone. The fuel pumps are the simplest ways to get the required fuel flow without replacing the entire fuel system.

The tachometer needed to be reworked with a new green arc and red line. The O-360 is limited in this airframe to only 5 minutes at 180 hp. Maximum continuous power is 145. Of course, that gives plenty of time to take-off and climb, especially considering the new climb rate… oops, spoilers… you’ll need to keep reading for that information! 

By August 10th I had finally finished most of the install work and the weight and balance. We removed the bottom plugs and motored the engine to pre-oil the engine and confirm fuel pressure. On August 12th we ran the engine and everything went well except for a minor leak in the fuel pressure line and some minor adjustments to the idle and idle mixture settings.

We also got a reading on static RPM. The STC allows for a constant speed prop or one of two fixed pitch props. We chose the Sensenich fixed prop. The STC doesn’t specify a propeller pitch but instead, they give you a static RPM range that the engine must make at full power. For the Sensenich, the range is 2325-2425 RPM. We hit 2367… right in the middle of the range! This was great as it meant that the propeller didn’t have to come off for a repitch.

I spent two days working on the paperwork and by Wednesday evening everything was done. We hadn’t planned to fly that evening, but with the plane ready and an hour of daylight left, Iain and Dave decided it was time to see the fruits of our labour.

Not having flown the plane prior to the conversion, I wasn’t really sure what the benchmark should be. However, seeing the plane get airborne in the first 1/3 of runway 34 and be close to 500’ as it passed over Highway 22, I suspected that it was the performance was satisfactory, despite the 25°C air temperature.

As the plane taxied back and stopped, Dave jumped out with a huge grin on his face and said “Ken, jump in… you gotta try this out!” I did a circuit with Dave and saw what he was talking about. Again, we were off the ground in about 600-700’ after a very spirited acceleration. The climb rate touched 1200 fpm as we left the ground but stabilized at 1000 fpm. I asked Iain what the original performance was like and found out that they would take up about ¾ of the runway for take-off and generally see 300-400 fpm with the same load and OAT. We only did one circuit before landing just before official night so we didn’t get to investigate the cruise numbers.

So far, the only issue we’ve had post-installation was an oil leak at the oil temperature bulb. It took a while to track down but was easily fixed when we finally found the source. Iain and I did get out for another flight Saturday afternoon. The maximum cruise speed has improved from 95 mph to a solid 115 mph. Fuel burn has stabilized to about 9 gph, but they have been running the engine right at the maximum continuous power setting (2500 rpm) during the break-in period. I suspect that once they get the oil consumption stabilized and start running at a more sedate 2200-2300 rpm, they will likely see more economical numbers that the C-145. They have also commented that the new engine is quieter than the Continental. The only real negative to the project was the increase in weight. We saw about a 70 lb increase in empty weight with the new engine, which still leaves over 800 lbs useful, including unusable fuel.

Overall, they are quite happy with the conversion and have no regrets. From my perspective, I’d have no problems doing another Del-Air kit in the future. The STC also covers the Cessna 172 line, with the later models being a bit simpler as they already have a similar Lycoming O320 to begin with. Fortunately, I did get some experience with this kit earlier this spring when I annualled a 1956 C-172 with the same conversion. The owner was also gracious enough to give me access to the 172 while I was working on the 170, which was a big help.

With the combination of the 170 project and instructing at SAIT, the month was a bust for flying. Of course, with the end of the work comes the end of the fine summer flying weather. Oh well, my favorite time to fly is quickly approaching and I do plan on putting in a few hours over the next couple of months. Speaking of which, I will be teaching at SAIT again this fall, filling in for an instructor who is retiring at the end of August while they find his replacement.

Well, that’s it for this month. Remember that our first fall meeting will be on Wednesday, September 10th at 7 PM. I look forward to seeing everyone and hearing all your summer flying stories. 