Bellanca Engine Overhaul:
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After getting everything put back together and clean it is a bit scary to turn
the key for the first time. What if I screwed up during assembly?
The engine could not run, or worse loud nasty noises could occur and bits of
metal might fly off.
You start with pre-oiling the engine to ensure that it has lubrication before the oil pump starts drawing oil for the first time and fills up all the oil passages. Then fill with oil and any other fluids (such as hydraulic fluid). Then a final inspection and assurance from your mechanic.
I had to charge up my battery after several months of inactivity in order to crank, but once it cranked the engine caught after the first few blades. It took about 35 seconds to register initial oil pressure, which is ok, the magnetos were grounding safely, and the engine ran steady. It wouldn't idle slowly enough, though, which called for more investigation.
Turns out that the rubber intake manifold connector hoses were loose. Assembly to engine start took about a month. During that time the rubber connector hoses took a set and squeezed out around the clamps. This let outside air bleed in, effectively adding throttle to the engine and leaning the mixture downstream of the carburetor. The fix was simple - tighten up the clamps on the hoses. After that of course we had to readjust the idle speed and mixture on the carburetor.
This made for more ground running than is ideal with a fresh engine, but not an excessive amount. The first flight itself consisted of a normal taxi, run-up, and a somewhat shallow takeoff and high-power cruise. The Oil and cylinder temperatures were monitored and recorded to see the spike and decrease in temperatures that is expected with a successful break-in.
Two issues were noted: the oil pressure was on the low-end of normal, sitting at 30 psi. This is within the Continental acceptable range but it is better to see about 55 psi on a stable basis. The second issue was that the R.P.M. was running about 50 R.P.M. low at the full-increase propeller setting.
I flew around for about 40 minutes making a large circle north over a local lake, heading south towards Enumclaw, and then continuing on to Eatonville before getting ready to turn around north back to Renton. Performance overall was good. I was about 5 miles west of Eatonville at full cruise when a loud bang and buzz occurred!
Oh crap. The buzz is very loud, but the engine is running, and the airplane is flying without any buffet or other strange behavior. A quick scan of the instruments reveals nothing out of place - oil pressure, oil temp, R.P.M., manifold pressure, and CHT. I zoom upwards to gain some altitude, and turn towards the Eatonville airport. The buzz noise continues. Since nothing appears to be wrong with the engine, I throttle back a little to slow down and the noise diminishes slightly.
The panic is off, but the buzzing noise is loud enough that I don't want to continue the flight, so I head to Eatonville at the slowed-down speed, lower the gear right over the airport, and make a circling approach from high altitude in case the engine decided to quit during the descent. The landing was a little hot but not bad considering. I rolled out to the end and shut down to inspect, fearing a large oil spew down the side of the airplane.
Fortunately the engine had no problems. A very careful engine inspection reveals no leaks, no missing parts, and a full oil pan with no obvious metal chunks. Upon checking the airframe I discover that a piece of fabric finishing tape covering the windshield-to-fuselage seam on the left side (right by the pilot's seat) had peeled up on the leading edge. Airflow was getting under the tape and was making it vibrate. Fortunately the tape hadn't pulled up any other fabric and was still on the airplane.
After some cellphone consultation with my mechanic, who by this time was starting to get worried that I hadn't returned to home base on schedule, we decided that it was ok to make a temporary repair with some tape. I scrounged some duct tape from one of the airport locals, and applied it to the offending finish tape fabric, then started up and took off again.
The duct tape worked like a charm, although I kept the speed down on the return trip. Upon returning to Renton I put the plane away for the day, having had plenty of excitement!
Repairing the fabric tape that had peeled wasn't very difficult, although getting the finish paint to look good is harder.
Fixing the engine squawks proved more annoying. My engine is old enough that it has the old-style non-adjustable oil pressure relief valve which uses a fixed spring and plunger. The only adjustment for the pressure is to put washers under the spring. I decided to call up a junkyard and get a workable adjustable oil pressure relief plunger. That took a few days to arrive.
Unfortunately on the Bellanca there's not enough room between the back of the engine, where the oil pressure relief valve assembly is located, and the engine firewall. It is impossible to reach in from the side unless your hand is about 1/2" thin, so I had to get at it from below. This entails removing the carburetor and Y-pipe that connects the carburetor to the intake manifold runners on both sides of the engine.
After initially removing the relief valve spring and plunger to make sure there was no junk on the valve seat holding the valve open, the new valve was installed. Now it was a question of adjustment, which is a trial-and-error process.
I got good at taking the Y-pipe and carburetor controls on and off, since it took 5 tries to get the oil pressure plug adjusted just right at about 55 psi. The first time was too low, then too high, then too low, etc. About 3 hours after getting going, the pressure was set and the intake was back together for the last time.
Fixing the propeller R.P.M. problem was also annoying. After verifying that the problem wasn't the tachometer, using a visual propeller tachometer device, the problem turned out to be the propeller governor linkage. Upon inspection, the propeller control, which moves an arm attached to the governor via a complex bracket and bellcrank assembly, was not reaching full travel, so the governor control was not on the full-R.P.M. stop.
Prop governors are designed to have an adjustable control arm that can be moved to different radial positions to accommodate different installations. In my case, during the governor overhaul it looked like the arm was put back on at a slight different angle from the original angle. The fix was to remove the governor, take it back to the overhaul shop, and have them re-index the governor arm back a few notches to enable the bracket/control to reach full travel.
That part was easy, the downer is that to remove the governor on a Bellanca you have to remove the nose bowl, which means removing the propeller since the Bellanca nose bowls aren't split. Removing all of this is easy, re-installation is very time consuming. Re-installation of the propeller bolts, torquing them, and safety-wiring them is a "use the force, Luke" kind of job where the nose bowl must be installed before the propeller goes on, which means that you can't directly see what you're doing and you need about 3 extra elbows in your arm. After 3 hours of swearing, and a few puncture wounds from sharp safety wire ends punching into fingertips, the job was done. Someday I'm going to get around to splitting the nose bowl cowling so this job will be easier!
Overall getting the engine broken in and initially debugged was pretty painless. The next 5 flights were uneventful, and I recorded engine parameters and temperatures to monitor trends. The CHT readings did come down slightly and stabilize, indicating an initial breakin. Twenty flight hours later the first oil change had no metal in the filter, the spark plugs looked good, and a quick compression check yielded good readings all around.
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