Redrive and Mounting
I chose to use Tracy Crook / Rotary Aviation's redrive, and I think this is the best option as long as Tracy keeps making them. It's reasonably priced, well manufactured, compact, and relatively light-weight.
The only drawback to this unit is the mounting plate - or lack thereof. The RD-1B (the best choice for this engine) ships with a rear mounting plate but no engine mount. Further, Tracy's mounting plate puts the starter on the bottom of the engine. This might be fine for an RV (Tracy's plane) but in a Cozy this area of the cowl is very tight.
CozyGirrrls to the rescue! Their engine mount solves the mounting issue, and they also sell a matching rear plate for the RD-1B that puts the starter on the side of the engine. Perfect!
Redrive
Tracy's installation guide is fairly direct, but I'll note a few things here that are related to the combination of this unit, the CozyGirrrls' plate, and the 3rd-gen RX7 engine.
First, I think it's a good idea to take apart the major components of the RD-1B to see how they fit together. The case is three elements: a front (rear, for a Cozy) housing that contains the prop shaft, a central ring section that holds the planetary gear set, and a front mounting plate with spacers for mounting the whole assembly to the engine.
Inside the case are a sun gear (the central gear that takes power off the engine), the planetary gear set (which receives power from the sun gear, and reduces its speed), and the ring gear (the outer gear, which transfers power from the planetary to the prop shaft).
Accessories include a pair of ball bearings that act as thrust bearings, a rear bushing to support the prop shaft, and a damper plate, which is just an aluminum plate with a splined hub riveted to it. The damper plate has outer holes with rubber shock absorbers in it, which match up to the flex plate to receive power from the engine.
Installation
Begin the installation with the damper plate. This is a fairly simple step – if you have the right flex plate. They're getting hard to find. Mazdatrix managed to dig up a used one for me. Try eBay, Craigslist, and the junkyard circuit as well.
Initially, I started by installing the original mounting plate as provided by Tracy. I actually had the CozyGirrrls' rear plate in the shop, but I had planned on selling it and using Tracy's until I discovered that the starter location was more important than I thought. Here are some pics of the process before I switched:
Mounting the CozyGirrrls' plate actually starts with the bottom plate. You don't permanently install it, but you need it to be in place to make sure everything else is lining up correctly. I went ahead and did the fitment for the mounting holes at this stage. To do that required me to drill 4 new holes and move 2. Fortunately, a die grinder I had bought for porting work (and never used) made quick work of moving the holes. Go slow - aluminum is soft, and will clog the die grinder cutter. Also, you don't want these holes to be sloppy.
Once you have that done you can mount the rear plate. If it's hard to get the sun gear installed in it, make sure your damper bolts are loose. Also, check for rust on the end of the sun gear shaft. I carefully lapped this with some 600 grit sandpaper to remove a bit of rust and this made the installation much easier.
After a trial fit and a check for desired end play, gear lash, and smooth rotation of the entire assembly, installation goes pretty quickly. Permatex both the rear and intermediate housing faces of the RD-1B. Grease the ball bearings. (I used assembly lube everywhere to protect the assembly from rust until I fill the system with oil. It may be several months before I get to do that - winter is coming.)
Slide on the intermediate housing, then the rear housing, working the gears a bit to get them to slide together smoothly. A few light taps with a mallet are fine, but if you encounter stiff resistance, stop and find out why. Stop and let the Permatex cure, then tighten the redrive bolts to their final torque of 5 ft lbs. Don't overtighten these.
Starter
I had some trouble initially getting my starter mounted. I bought the first starter on eBay, following Tracy Crook's description for the required unit precisely. When it arrived, it fit the redrive mounting plate perfectly… but was too close to the flex plate - so close that it touched, preventing the engine from turning! I was convinced I had bought the wrong unit, but when the second arrived identical to the first I decided that it wasn't really that big of a deal, and set about moving the unit.
If you have to do the same thing, it's really not that hard. You'll need a die grinder and a good cutting bit - I used a 1/2” dia cutter in a cheap 1/4” collet Harbor Freight die grinder, and it worked just fine. You'll also need some JB Weld to fill in the original mounting holes. I kept one of the two original holes to make mounting the unit easier.
You'll need a light shining down into the cavity where the starter meets the flex plate, and a small ruler (or a good eye for measurement). Finally, you'll need a small screwdriver or similar to extend the pinion of the starter. I had a set of metal picks that included a 90-degree right-angle tool and that worked like a charm.
Mount the starter in the central hole as best you can. If you can't even get it in there you probably DO have the wrong starter. Then insert the screwdriver or right-angle pick into the service hole on the side of the starter, and pry the pinion up. With a bit of practice you can get the pinion extended about 75% without much effort.
The pinion probably won't extend into the flex plate gears (because it's too close - hence this whole procedure). To fix that, measure the overlap and allow for a bit of additional tolerance. The FSM doesn't specify a tolerance here, so I allowed 2mm, which looked like it would allow the gears to mesh smoothly. All told, I needed to move my starter 6mm.
Mark a smooth arc along the center hole the distance you want to expand it. Then carefully cover the engine, PSRU, and all open components with plastic - you're about to make a mess. I found sheet plastic with aluminum tape did the best job. You REALLY do NOT want aluminum shavings in your engine, so take your time with this. Pay particular attention to the flex plate area, stuffing plastic into the gap to make sure no shavings can get into the gears or seals.
Grinding aluminum takes a lot of time - see my note in Shop Techniques and Helpful Tricks for some guidance. A die grinder works best here. Just take your time, make smooth passes, and stop every now and then to eyeball your work.
Once you've ground out the center hole, mount the starter again, this time using vice grips or clamps to hold it in position while you judge the new fit. Extend the pinion and check how well it meshes with the flex plate. You're done when you can extend the pinion and have it mesh smoothly with the flex plate. You may have to rock the flex plate back and forth a bit - remember, the pinion is normally spinning right now, which is why is has a bevel on its gear teeth, to help it mesh with the flex plate.
Once you're happy with the center hole's location, fill the upper hole with JB Weld. Attach the starter in position using the lower bolt, and once the JB Weld has cured, use the starter mounting hole as a guide to drill a new 10mm hole for the upper mount bolt.
What you do next might vary depending on the actual starter, redrive, and mounting plate combination you end up with. In my case, my redrive plate had its upper starter hole lined up with a bolt hole in the rear iron, and moving it shifted this alignment. This area needs to be supported, but I couldn't do it with the stock bolts without drilling and re-tapping the iron (which wasn't my idea of a good time) or building an offset bracket (not as hard, but still time-consuming).
Or you could try Plan C, my solution. Buy an M8-1.25 x 140mm bolt. Redrill the upper hole at a slight angle - it doesn't take much. Then run the longer, narrower bolt through the starter, the redrive plate support post, and the rear iron, and put a nut on the back of it. The smaller bolt will pass easily through all of the holes at the angle required provided, like I did, you only have to move the starter a few mm.
If you go with Plan C, you can finish it off by grinding two washers at a slight angle to take up the gaps under the bolt head and nut, and filling any air gaps in the holes with JB Weld. Use the bolt itself to set the clearance here - you can lightly coat it with Vaseline and re-install it after filling the holes to create a perfect fit.
Test Fit
Below you can see a trial-fit of some of the larger components.
Lifting my turtleback gave me the opportunity to stay more “stock” than I otherwise would have. (John Slade needed to modify his water pump and move his alternator to get everything to fit under the cowl line.) This saves a lot of time because three major subsystems (fuel, water, and alterator) can be more or less bolted back on and re-used. If your cowl line is lower, you may want to consult John and his site for guidance, particularly on modifying the water pump and alternator support bracket.
