13BTT-REW FD3S Rebuild -- Overview

06-12-2009


I am installing a 3rd generation (FD3S, 13BTT-REW) rotary engine in my Cozy. I've decided to give the rebuild a try myself, and send it out to a rebuilder only if I run into trouble. I'm documenting here what that process looked like. It seems like there are lots of guides floating around, but none take you through the entire process right from the very first step.

This is quite an involved process, and along the way I learned something very important. This work is absolutely within reach for somebody who is committed to doing the job properly, has the time to spend, and is handy with a wrench. But it's a mistake to think that because the rotary is a "simpler" engine that it's actually any easier, faster, or cheaper to rebuild than a piston engine.

I've heard all those arguments about "fewer moving parts", but by my count, the rotary actually has more parts than a piston engine. Each rotor has 49 (FORTY NINE) little seals, springs, and other bits that sit around it. Double that (two rotors), and add all the bits on and in the housings, and that's just the inside of the core. Servicing the engine also requires an array of special tools. Sometimes you can get away without them, but frequently not. Each costs from $100-$200, and you still need the socket sets, power and air tools, and other bits you'd need to rebuild a piston engine.

Some of the parts themselves are also very expensive. The eccentric shaft is $450 - drop it (it's REALLY heavy) and that's an expensive doorstop. If you lose oil pressure in a car, you can damage all sorts of things, but usually the engine will keep running for a while, then overheat. You get a slow workup to the final problem, and if you crack a head gasket, you can at least try to repair it - you might not lose the whole block. But in a rotary, a loss of oil pressure CAN cause the rotor bearings to seize onto the eccentric shaft. In the process, the engine can more or less eat itself, taking out a lot of surrounding parts in the process. Lots of expensive paperweights.

In the end, I have yet to see a convincing and compelling argument about safety, cost, or simplicity that was based on a serious and detailed analysis of every system. You want a rotary, fine. But you're not ditching the piston engine's problems - you're just trading them for a new set.

In my mind, any arguments about the rotary being a safer or better or even cheaper engine just don't wash. If you're going to do this, and you're going to be really honest with yourself, there is only one good reason to use a rotary, especially in an aircraft. This is a very elegant piece of engineering, and it's just cool. There, I said it, I'm being honest. You can argue about forward-hinged canopies all day long. But they're cool, and so is the rotary.