Ownership: Heart transplant

Our 150-horsepower Lycoming O-320-E2D soldiered on for 27 years and more than 2,000 hours after its last field overhaul. The engine is the same one the 172 left the Cessna factory with in 1975. The choices are plenty when it comes to engines for popular airplanes like the 172. Prices, as well, run the gamut from reasonable to more than the value of the airplane. While we drooled over a true 180-horsepower Lycoming O-360 replacement, reality left us with more affordable choices such as field overhauling our engine a second time or getting a factory rebuild from Lycoming (see “Overhaul Terminology,” sidebar).

Experience, wisdom, and age have made us much more cautious pilots than we were in our teens and 20s when this engine was last overhauled. Because of that, and the fact that our kids are now flying this airplane, we elected to go with the factory rebuild. While the original -E2D is a fine, reliable engine, we just didn’t feel comfortable pressing our luck for a third run to TBO, which would bring the lower-end components to the ripe old age of 70 at the rate we fly.

After some research, we found Ram Aircraft in Waco, Texas, holds a supplemental type certificate to replace the -E2D with a 160-horsepower O-320-D2J. The -D2J is a more modern engine with a more robust design than the already-pretty-bulletproof -E2D. The -D2J was stock equipment in the Cessna 172P. Ram offers a conversion package, including the STC paperwork, factory-new engine, and new propeller for around $40,000. Unfortunately, that put us over budget, so we elected to purchase just the STC paperwork for $515 and purchase a factory-rebuilt engine on our own through Air Power. That put us in the range of about $29,000—still a sizable purchase. The core upcharge for trading a -E2D for the -D2J is $1,500.

In the end, however, we got a modest 10-horsepower boost in performance with an engine designed from the beginning to be 160 horsepower, as opposed to modifying the -E2D with higher-compression pistons to get the same result. The -E2D was designed to run on 80-octane avgas, which went extinct in the late 1990s. The -D2J was designed to run on 100LL avgas and takes advantage of the added power that fuel can provide. The power boost requires repitching the propeller to absorb the extra power. Lycoming was working on a six-week lead time, which gave us time to attend to other chores, such as removing all the accessories for overhaul.

Since it had never been sent out for inspection, the engine mount was sent to Aero Fabricators for inspection and repaint. Some head-scratching was required to figure out how to ship such a huge contraption. Our mechanic overseeing this project, Frans DeBlois, at DeBlois Aerospace, suggested bolting it to some plywood and wrapping it all with plastic wrap. That worked, but the shipping came out to nearly $200 each way. Add in the $500 inspection/basic repair cost and it gets pretty close to the price of a new mount. In the end, a cracked tube was found and replaced, so we were glad to have sent it out, despite the hefty investment. Price this out carefully if you tread down the path of a project like this.

New hardware to hang the mount was also purchased from Cessna via Summit Aviation in Delaware. Accessing the bolts—especially the two lower ones—turned out to be one of the bigger challenges. They are located, blindly, within a stringer under the rudder pedals accessed by a slot cut in the stringer. A two-person job, in other words.

With the refurbished mount attached, we uncrated the rebuilt engine and hung it on the airframe. We used all new Barry engine mount isolators and hardware. Lycoming gives you six weeks to return your core engine and we used nearly all of it, given concurrent projects such as a new windshield and panel/interior work. It’s critical to pick off all the parts you need from the old engine while being careful to send the core back with all required parts and paperwork. We purchased our engine through Air Power, which simply holds onto a cashier’s check until your core is accepted by Lycoming. Once accepted, the uncashed check is returned to you. In the case of the O-320, the core charge is $16,000.

Baffling was removed from the old engine, inspected for condition, painted, and installed on the new engine. The -D2J is slightly different and required some modification to a few baffle pieces. For example, a new oil pressure line comes through the rear baffle to reach the front side of the engine. The -E2D oil pressure pickoff was on the back side of the engine. New baffle seals were purchased from Aircraft Spruce and Specialty Co. and affixed to the restored baffles. Several trial-and-error cowl fittings were needed to assure proper fit of the baffle seals to the cowling with no scalloping. Test fit the cowling before you hang the exhaust to make the removal and reinstall easier.

We got the exhaust hung with new hardware, airbox attached with new filter, attached a new starter and overhauled alternator—all the while reworking the baffling to properly surround all of the accessories. We also exchanged the original mixture cable for a vernier type for more precise leaning. One of the big challenges was rigging all the cables and wiring to mechanic DeBlois’ high standards. Lots of “do-overs” were required to get everything up to his spec. After all, he was signing off on this project.

Experience, wisdom, and age have made us much more cautious pilots than we were back in our teens and 20s when this engine was last overhauled.We hung the overhauled propeller and preoiled the engine by cranking the starter with the bottom plugs removed. It took three 10-second cranks to purge all of the air out of the oil system and get an oil pressure indication. We located a small oil leak and tightened the loose fitting causing it. We also found a small fuel leak in a primer line (another loose fitting). We then replaced the spark plugs and started the engine for the first time on our watch. (Lycoming ran it twice at the factory for a total of 1.5 hours.) It fired on the second blade and all was well—except for no charge from the alternator.

DeBlois troubleshot the alternator issue to a faulty overvoltage sensor, which apparently decided to quit working sometime while the airplane was down for the five-month project. So we waited for a new Zefftronics voltage regulator with built-in overvolt sensor. Once installed, we were happy to see a charge. We installed the cowling, did a longer ground run with a brief blast to full power, and removed the cowling to check for leaks or other issues. With all looking good, DeBlois said, “Go fly!”

A DIY project like this will likely be a long, laborious slog fraught with several frustrating low points. But when it’s all done, there is a satisfying high that comes from the accomplishment...We flew 30 minutes above the pattern of our local airport with no issues. We did take note of our Skyhawk’s newfound smoothness, thanks to the new engine, vibration isolators, and freshly overhauled propeller. Our Skyhawk was never a speed demon. Of the many 172s I’ve flown over the decades, it was the slowest. It cruised pretty reliably at 105 KTAS and that’s with the wheelpants installed. Now, however, we are seeing 110 to 115 KTAS. Takeoff and climb performance is about the same. The higher horsepower and repitched propeller are the big reasons for the speed increase. A tight, new engine versus a tired, old one is certainly another reason. Because the -D2J has a higher compression ratio, the fuel burn is the same as our old engine—nice bonus.

During the restoration, Air Parts of Lock Haven overhauled our original airspeed indicator—the dial was quite faded. They also supplied a new tachometer remarked to meet the Ram STC specification. Because of all the variables in airspeed and tachometer indications, we had to verify some of the perceived performance gains using GPS and old-fashioned time flown versus fuel used calculations.

A DIY project like this will likely be a long, laborious slog fraught with several frustrating low points. But when it’s all done, there is a satisfying high that comes from the accomplishment and the fact that you saved thousands of dollars in the process.