Upgrading to a 210 hp. Continental IO-360

Before we started our rebuild project we took the Stinson on a final family trip from Vancouver Island to Alaska and the Yukon. The original 165 hp Franklin was hard pressed to get us out of Whitehorse. We like to fly on floats and we needed more power to do it safely with the whole family aboard. We considered three engines. The Franklin 220 or the Continental O-470 or IO-360. The O-470 would have been the cheapest and mogas compatible but we couldn't afford the 100+ lb. increase in weight. As for the Franklin, I was familiar with the type. Our old Frank never let us down, but I'd read of overheating problems and the entire conversion would have been in U.S. dollars. One more strike for the Franklin was the fact no one services the engine in Canada. I think the price is about the same for the Univair Conversions O-360/IO-360 and the 220 hp Franklin. The Univair conversions didn't interest me because only the 180 hp is available for my dash 2. If I was going to do it - I wanted at least 200 hp. This left the Continental IO-360. Similar weight to the Franklin, more fuel efficient, maintainable in Canada and those that had experience with the engine seemed to like it and the holder of the Tyee Aero Conversion, Canadian STC lives only a short drive up the road. We searched for quite awhile for an engine and one finally popped up in Alberta. What luck, an engine with Canadian paperwork would save a lot of hassles. I checked the Tyee STC blueprints for model conformance and purchased our IO-360-C.
What ever the choice you make. I'm sure you'll be pleased with the result. I still have the wonderful handling and stability you associate with a Stinson, but now I can count on unbelievable performance when I need it - An outstanding combination.

We placed our order with 50% down for our $12,500 Tyee engine conversion early in 2001 and were informed it would take about 6 weeks to get the parts together. Several weeks later I was informed that there was some stuff to drop off. I thought this was great, not much delay, I said I'd have the cheque ready for delivery. To my surprise all that was dropped off was a couple of thin books. I made the mistake of giving the final payment prior to receiving the goods. And would I pay for my stupidity! We waited and waited, made call after call and waited even longer. Month after month went by and not a single item was delivered. The rebuild went on hold for many months. As the one year mark approached we received a delivery which contained most of the parts but no supporting paperwork. Our first impression of the kit was not great. Installation documentation was poorly put together and contained several inaccuracies and for a so called complete kit there didn't seem to be much on the floor. Looking at it now, I have no idea what took so long as I later found out Tyee had the exhaust and engine mount manufactured years ago!

Not a lot for $12,500 even in Canadian dollars.

Some major irregularities cropped up as soon as I started putting the pieces on the engine. No lines were provided from the firewall forward although the kit specifies it contains the fuel system mods. No drawings for cabin heat box modification. Other fittings, switches and nuts were missing, engine-mount bolts were the wrong length, and the exhaust touched the engine mount on both sides! It was over a month before the STC holder showed up and attempted to address the exhaust and engine bolt problem... and it was months later before we received our MkII modified exhaust and new bolts. I gave up on the remaining promised hardware and purchased the items myself. I'll elaborate on our exhaust problems farther down this page.

On the lighter side, having most of the parts allowed us to finish prepping the wings and fuselage for close-up inspection and covering. It took only a day to install the fuel line modifications. Here I'm splicing the header tank into the main fuel line with AN flare fittings. The tank is secured to the upper fuselage frame with s.s. hose clamps.

While waiting for our exhaust to be modified we got on with installing our Cessna 337 baffling. Some trimming will be required in conjunction with the cowl installation.

1/4 inch vapor-return line runs from the fuel pump, through a check valve, to the header tank and from there to a T-fitting above the fuselage where the line splits to both tanks. Other than the check valve, there is no fuel shut off for the vapor-return line. In addition, I've heard another owner is experiencing serious venting problems with this setup. I believe this can be traced to the interconnection of the two tanks via the vapour-return T fitting in the ceiling. Normal return flows will probably migrate to the tank with the lower volume, however, the use of original positive pressure caps, could and likely will produce slightly different tank head pressures forcing fuel from the tank with the higher head pressure to the other. If the tank is anywhere near full your bound to vent fuel. The holder of the conversion has installed new caps, without pressure tubes, on his aircraft and he has not informed me of any such venting problems. New vented caps, are not included or part of the Tyee STC; however, I was promised a set with the kit. This, in addition to several other promised items were never delivered.

Vapor-return lines are secured to the fuel tank via AN fittings. A hole must be drilled into the upper edge of the fuel tank and an AN flange welded in place to accommodate the fuel return lines.

Some trimming is required on the inner-most wing rib to connect the fuel return line to the tank AN fitting.

Trying to accomplished as much as we can while still waiting for exhaust problems to be addressed. Note: Un-airworthy exhaust still installed. It was time to check the engine mount to firewall fit... and it did.

With the engine installed we could route control cables, finish power plant electrical connections, and finish the panel. No guidance is provided with the Tyee STC regarding engine gauge selection. I purchased Scott oil temp and pressure gauges but found the temperature bulb nut required grinding in order to fit. You'll also require a new tachometer - I purchased an electric Tach, from Aircraft Spruce, which is wired directly to the magneto selector switch/key. Also, you'll need manifold pressure and fuel flow gauges. I tried in vain to find a combination unit as found in many Cessna's and Maule's. In the end I used my old M.P. and purchased an electric gauge to indicate metered fuel pressure - 0-30 psi.

The engine doesn't look that big anymore. On the shop floor it looks big.. bigger than the Franklin. In reality, it's dimensionally smaller than the Franklin.

Here's a look at the original exhaust fit. It got even tighter when the correct engine mount bolts were installed and clamped down. Less than zero clearance on both sides.

Same crap-other side. The exhaust was modified by cutting/lengthening the down pipes and moving the muffler back about 6 inches. This allowed the down pipes to pass through the engine mount at a point farther to the rear where there is slightly more room between the mount tubes. The modified exhaust has 1/4 inch clearance on one tube and less than 1/8 inch on the other. This is entirely inadequate. We were correctly cautioned by our AME that the exhaust would crack our engine mount in less than a year if it was not modified further... I mean significantly. Ken, from Tyee Aero said he will fix the problem after I put the floats back on my aircraft, but I was not willing to wait, considering the seriousness of the design failure. After running the engine for 2 hrs we removed the exhaust and found the engine mounts badly marred and scorched on the left and right sides. To prevent further damage we had the exhaust tubes dented - not an ideal fix but hopefully this will prevent further contact.
I strongly caution anyone considering purchasing a Tyee Aero kit to make sure they are not receiving the original production exhaust. I know the STC holder had the exhaust made up years ago and he never fit one to his aircraft. I suspect they will all have to be redesigned.
I consider this exhaust to be the Achilles Heal of the Tyee engine conversion. We may have installed a more reliable and easier-to-maintain engine but we will undoubtedly pay the price, in engine mount and exhaust repairs, in the not-to-distant future. We've had our floats on for a while now and still no sign from Tyee on a fix to our exhaust problem! I'll provide an update here when and if we receive any action.

Front view.

One more time.

This is how the exhaust looks now. Not very pretty but at least it's not hitting the engine mount! We've temporarily protected the engine mount with fiberfax covered with metal tape.

Here you can see the IO-360-C starter/accessories drive. Contrary to the Tyee website, which appears to no longer be on line, and original blueprints provided by Tyee, they DO NOT have an STC for this and a few other IO-360 derivatives. The story just keeps getting better and better. Fortunately for me, Alberta Aero Engine, the company that overhauled the engine prior to us purchasing it, came to the rescue. They offered to rebuild the drive pack to IO-360-D specs and provide authorization to change the engine serial number to IO-360-CCD. This allowed us to qualify for the Tyee conversion. I would highly recommend Alberta Aero Engine - they, and Aircraft Spruce were the only companies we dealt with that didn't botch up at some point.

http://members.shaw.ca/flightlines.

As far as Tyee is concerned - perhaps paying up front isn't a good idea. I guess I'm a little naive, but I figured good faith on my part would be equally rewarded.
We encountered problems with companies other than Tyee Aero, but not to the same extent. After a two-month delay we received our Cleveland Chrome Brakes from Univair only to find Cleveland had sent steel disks instead - it was another 2 months before we got what we paid for... in their support, Univair customer service was outstanding.
We purchased our spinner, 80 inch constant-speed McCauley propeller and governor from the Prop Center in El Cajon, CA. It took us an unbelievably long time to receive our prop and there were further delays in the export documentation. Pete Grubb, the owner of the Prop Center, unfortunately cannot be trusted to deliver on time or in some cases at all... excuses ranged from - moving - buying a new home - can't find the parts I was going to sell you - I sent the stuff, must have been lost in the mail - etc, etc, etc... ad-nauseam! I've given up waiting for delivery of some promised parts.

Here's a look at our new 1/2 inch fuel line between the fuel strainer and the boost pump. The use of 90 degree fittings allows for a mild bend and short line.

With the new starter-accessories drive installed our engine becomes an IO-360-D engine and now eligible for the Tyee conversion. What a pain. Anyone considering purchasing the Tyee conversion should be aware of this shortcoming.

Here the cowls and baffling are finally installed. As you can see, the exhaust will allow easy access to the plugs, etc during routine maintenance.

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Copyright © 2003 David P. Miller
Last modified: March 23, 2004