Prometheus Unbound


The drivetrain is probably the simplest part of the project, from a planning standpoint, but there are some unique challenges to actually building it.

I'll be keeping the existing clutch and manual transmission, coupling the motor side of the clutch directly to the electric motor. There exist specialty adapters made to do this (expensive!), and many hobbyists build their adapters from thick aluminum plate (also quite expensive). Instead of doing that, I'll be casting one. This will save weight and money, and allow me to build the adapter plate out of a high-strength silicon casting alloy instead of out of 6061 plate. Since I have the skills and facilities to do both the casting and machining without contracting it out, here is one of the places where I anticipate I can save a significant amount of money over most hobbyists.

The disadvantage to this approach, of course, is that it takes time. I can easily get a technical diagram of the motor-side mounting holes from the manufacturer, but the exact layout of the clutch and transmission bellhousing is more difficult to find. Since I want to minimize the time the truck is inoperable, this presents a challenge: I can't start on the pattern work without knowing that information.


I've started in on the disassembly of the existing truck's drivetrain.

Existing engine mounted in truck

Here's a picture after a lot of disassembly work on smaller parts. I've drained the fluids, removed the hood, radiator, battery, and parts of the A/C system, and disconnected and labeled a whole snarl of wiring. Almost everything here will not be used in the final version.

Removed radiator

Lots of removed parts. I'm trying to keep the valuable things in condition good enough to sell.

Removed exhaust system

To remove this, I just sliced the pipe with an angle grinder. Note the big hole in the muffler, which was making this truck a bit noisy to drive around. Of course, it'll be almost silent when I'm done with it.

Removed gas tank

The gas tank was a real pain to take out--it took me almost an entire day. No angle grinders here--I had to use bolt cutters to cut the straps and a hacksaw to cut through a big steel framing member (no, not an integral part of the chassis!) under the tank. The bolts were situated in such a way that I would have had to move around a whole mess of brake line to take it out the way it's meant to come out.

Brace under the transmission

Now, on to the fun stuff. This inconveniently-situated steel beam holds the transmission up. Fun fact: The heads of the bolts attaching this beam are imperial-sized, but the nuts that go on them are metric! I don't know how such a mixed-up fastener comes into being, but it makes disassembly that much harder. The whole truck has been like that--no consistency in the fasteners whatsoever.

Dropping the drive shaft

After much careful, delicate work with a crowbar and sledgehammer, the transmission and engine have scooted forward enough to let the driveshaft drop out. We had tried to disconnect the rear end previously, but it was stuck fast.

In order to get to this point, I had to cut out part of one engine mount in order to shift the engine forward enough to unbolt the other mount, in order to shift the engine forward enough to unbolt the first mount so that the starter would clear and the engine could come forward still more. The purpose of all this was to get to the top bolts on the transmission bellhousing, which of course are completely inaccessible with the transmission in place. The Haynes repair manual suggests removing the cab of the vehicle . . .

Hoisting the engine

Here's what's pulling from the top. That's the crane from my big furnace holding the weight of the engine, with about 450 lbs of barbells in addition to the 200-lb furnace body to counterbalance the rig. The come-along is anchored to my mill, and its purpose is to pull the cart away from the vehicle. With over half a ton of weight on the rather-melted furnace wheels, they roll poorly at best.

Removed engine

Removing the transmission bolts just didn't cut it--there were more bolts between the transmission bellhousing and the oil pan, and just about impossible to remove with the transmission in the vehicle. So, we hoisted it up and out, let the truck off the jack stands, and rolled it out from underneath. I don't know how much weight is here in the engine, but it's a lot. Enough to tip my crane forward and require additional human ballast despite the heavy load of weights. With all the fluids it's leaking all over the floor, I'm more than glad to get rid of it.

Engine compartment without engine

Lots more space in there now that the engine is gone. Most of what's still there will go too. The electric motor will hardly take up space at all, so I'll have to find a use for the rest. I might put some batteries up front.

Update 6-28-09

Even more stuff is gone now, though disassembly hasn't been my primary goal since the engine came out.

Missing bumper

I'm in the process right now of tracing the wiring and getting rid of the parts of the electrical system that had to do with the engine. To get to everything, I've had to do more disassembly than I really wanted to. Here, you can see the grill and front bumper are off.

Interior without the seat

And in the inside, you can see that I've removed the seat (probably a good thing: it was nasty under there! Amazing how much crud can accumulate in ten years or so . . .) and a lot of the trim pieces on the dash. In addition to tracing the electrical system, I also wanted to replace the stock heater core with my own version, or at least take a good look at it and determine whether or not to reuse it, but after seeing how hard it is to get to (the entire dash has to come out), I've decided instead to just leave it in place. It will be thoroughly flushed before running the coolant from the controller through it, since contaminants could make the water conductive and cause leakage currents. The supplementary electric heater will probably go where the A/C heat exchanger went. I'll have to build a heat-resistant enclosure for the elements, because right now, that enclosure is all plastic.

EV Components

EV components have started to show up.


First off, thirty feet of 4/0 gauge welding cable (eBay) and some solder-on cable ends (WeldingDepot).

Motor crate

Then a crate containing the motor and DC-DC converter (Cloud Electric). The motor is an Advanced DC #FB1-4001a, the largest that's readily available.

DC-DC Converter

This is the converter, an Iota 45 amp model (comparable in size and power to a hefty computer power supply). It's designed to run on 120VAC, but can also run on 144VDC, and is specifically designed to smart-charge 12V lead-acid batteries as well as supply 12V power to whatever may need it.

Motor test

Here's the motor, with a cable assembled to select the rotation direction (those cable ends take a lot of solder to put on, and I really need some washers because the holes are too big) and a 12V deep-cycle connected to test. It spools smoothly up to about 1000 RPM unloaded at this voltage, with a dramatic shower of sparks as the connection is made. Stall current at this voltage is in the range of several hundred amps.

Motor to Transmission Adapter

There are three main components that need to be made to mate the motor to the stock transmission: a coupler that attaches the flywheel to the motor shaft, an aluminum casting that will fill the space between the motor and transmission and hold the coupler's external bearing, and a steel plate that will mate the casting to the transmission's bolt holes. I could do it without the separate steel plate, but the bellhousing end of the transmission is about 18" in diameter and I can't swing something big enough to mate to it on my lathe. The steel plate will reduce that to a little under 12".

Starting to machine the coupler

Here's the coupler, being machined from a piece of 3" diameter 4140 steel round. I'm in luck, since the flywheel-to-engine bolt circle needs a flange exactly 3" diameter, and I had this stock left over from my latest muller rebuild. That nose fits the hole in the center of the flywheel, and I'm boring a hole for the end of the transmission's shaft.

Machining the coupler

Here's an action shot, roughing out the mounting flange for the flywheel. The shaft of the coupler is reduced to 50mm (a little less than 2") for an outboard bearing. This bearing will take the thrust loads from the clutch and any radial loads from an unbalanced mechanism, and the outside of the bearing will be mounted in the aluminum casting that attaches the motor to the transmission and its adapter plate.

Flywheel with the ring gear removed

Changing tacks for a bit, here's the flywheel. I heated it up (quite a bit, hence the nice blue oxide colors) and water-quenched the center to get the ring gear off.

Machining the flywheel

Another action shot, this time machining the exterior of the flywheel. It's mounted on the partially-completed coupler, which is of course held in the chuck. I had some pretty severe problems with ringing on that large unsupported surface, but since I'm machining the "back" of the flywheel, it doesn't matter that the surface isn't smooth.

Finished machining of the flywheel

This is the finished flywheel (except it hasn't been re-balanced). I removed about seven or eight pounds of metal and a lot of rotational inertia. It's still about 0.400" thick, so it shouldn't have any structural problems from the removed metal. Evidence of the chatter problems is also pretty visible.

Motor and transmission together

The motor, transmission, and coupler together. Everything appears to fit as designed. I put it together like this so I could take measurements for the adapter casting pattern . . .

Adapter pattern

. . . Which is here. This is extremely rough, of course--a lot of sanding and a lot of wood filler are still needed. Also visible is the outboard bearing. That piece of sheet aluminum is there to define the parting line--there's a larger cavity on the other side to fit into a boss on the motor. This pattern is drag-side up, the way I plan to cast it. One riser directly above the center thick section where the bearing goes, and a gate into the edge, should make this a pretty standard double-roll casting. (All my large molds seem to be double-roll for some reason, as if they weren't hard enough to roll once. This one needs to be so the casting is formed in the cope, because that's the way the draft on the outside goes. I don't want to flip the casting over to put it in the drag, because that would leave two large cores suspended from the cope sand.)