The Corvair Powered Zenair 601XL
March 20, 2004
Here's the last installment before we actually fly the airplane. Everybody in the hangar is pitching in and
burning the midnight oil to pull all the loose ends together. This first photo shows the cowling fully
assembled. It still has a few clecos in it. But many of the clecos in the photos are actually going through
nutplates. It's more done than it looks. It's a masterful job, and credit has to go to Kevin and Steve, who
pulled a couple of all nighters this past week on it.
Here's the front view, above. The two crease lines are the hinge points for the side sheet metal. Four
camlocks open up two square feet of cowling area for rapid inspection on each side.
Here's the 601's engine installed on its Motor Mount. It is a 2,700cc engine built with the best parts ever
installed in a spare-no-expense approach. This engine also has aluminum roller rockers. Even with this attitude,
all the parts and systems on the motor barely break $4,000. You could hardly buy a worn out, O-200 for this price.
This photo shows Gus safety wiring the fasteners on the 601's Deep Sump Aluminum Oil Pan. This Pan is
straight out of the inventory we sell; it has just been polished, which took about half an hour. Technically,
polished finishes radiate less heat, but it's arguable that it will also absorb less heat radiated off the
exhaust. It's all academic since we don't have temperature problems with any of our other flying installations. It
just looks nice. Notice that you can see Gus' reflection in the Pan.
Here's how I drill all the coarse thread fasteners for safety wire. This little jig is available from places
like Aircraft Spruce. There is a 1/4-20 stainless Allen in the jig above. With a regular drill, the proper
lubricant, and 1/16" $2.50 cobalt bit, I can do about 100 screws taking four to five seconds to drill each. The
little jig costs about $45, but is worth every penny. It does all sizes and types of fasteners.
Above is a close up view of the Motor Mount area on the case, and how our Deep Sump
Aluminum Pan fits around it. You can see how the gasket has been trimmed to match the pan. I have a lot of experience building
pans for Corvairs in flight applications. What makes this pan work with the Motor Mount cutout in it is the
.125" thick rail and the way that the vertical sidewall of the pan's sump acts as a stiffener down the whole
length of the pan. The pushrod tubes on this engine are ceramic coated.
The safety wired cover is above on a stock, rebuilt Corvair oil pump. This housing was in average condition,
and I installed a new gear set which we'd actually run previously in another engine. I carefully checked the
clearance on the pump by installing different gaskets in increasing thickness until the pump turned freely.
When the engine was installed, I checked the entire oil system by pre-oiling the engine with a half inch drill
and a dummy distributor. This setup would generate 40psi pressure at the equivalent of 600 engine rpm. 40psi
is where I have the relief set. Properly clearanced pumps can make exceptionally good pressure just off idle.
This engine is equipped with roller rockers. The longer studs required by these rockers, and their poly-locks
(the locking nut system for a roller rocker) dictate deeper valve covers than stock. Traditionally, people use
aluminum valve covers. Above is my solution: I milled away the center flat portion of the valve cover. Kevin
folded up two boxes which were 3/8" deep, out of .020 steel. I welded these on in place of the removed flat spot.
This was not a particularly easy weld bead. However, I welded the oil filler neck onto one of the valve covers,
and put breather fittings in it also.
Here is the modified valve cover installed, above. Also visible in this shot is the exhaust system. I made
it from one of our Exhaust Stub and Clamp Kits and some mild steel tubing. We had
it titanium-ceramic coated by the Moore brothers, a famous shop which does STC'd coating on aircraft parts,
including internal engine components, which is something we'll experiment with on another engine.
Just to show you that even professionals make mistakes sometimes, above is photographic proof. We forgot to
put a fastener in the flap torque tube. To avoid a lot of disassembly work, Steve, who at 5-foot-8 is the
smallest A&P in the shop, volunteered to fold himself up like a yoga guru and drill the hole behind the seat back.
It only took about an hour to line it up just right. He's a very resilient guy and was able to walk fully
upright the next day.