ElectroClassic EV
Classic Cars Reborn into the Electric Future

Mating Game

The transaxle is now refurbished and shiny, and the grand moment of coupling it to the AC50 electric drive motor has arrived. I just received two essential items from Canadian EV: the hub and the adapter plate. The hub is used to mount the clutch and flywheel to the AC50 electric motor. The custom adapter will then mate the motor to the Porsche transaxle.

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The hub is custom machined to exactly fit the electric motor shaft with a square key. A nice design feature seats the hub flush against the motor front bearing, eliminating any possible wobble, and sparing the locking screws from the forces of the clutch.

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The red forged aluminum adapter matches the motor mounting holes to the bolt pattern of the 914 transaxle, and must be installed on the motor before the flywheel is mounted.

A Word on Flywheels

In an internal combustion engine, the cylinders are timed to fire in succession, like a galloping horse. This creates sequential bursts of angular torque that must be smoothed out for the engine to run evenly.  The inertia of the flywheel’s spinning mass does exactly that, evening out the rotation of the crankshaft. But an electric motor already has a very regular and smooth power profile, making the flywheel irrelevant and literally dead weight. Because the flywheel’s mass resists the motor’s effort to accelerate the car, valuable electrons are wasted. A general rule of thumb states that each pound of flywheel weight is the equivalent of an extra 100 lbs of car weight. For more on this subject, UUC Motorwerks has an in-depth explanation.

One EV solution is to marry the motor shaft directly to the transmission drive shaft, eliminating the flywheel and clutch altogether. A gas engine needs a clutch to shift gears, but an EV has full torque available at all motor speeds, and can be left in 2nd or 3rd gear for all driving requirements – except reverse. But because shifting in or out of reverse usually happens at a standstill, and more importantly because electric motors don’t idle, reverse doesn”t require a clutch. I almost talked myself into removing it, but the clutch stays because I want the option of using 5th gear on the open highway, and 1st gear on Fargo Street. How else will anybody know how fast an electric Porsche will go, or how steep it will climb?

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Deciding to keep my flywheel and clutch didn’t help with the rotational inertia problem. The racing crowd addresses the issue with lightweight racing flywheels, which are very expensive. A common and thriftier method is removing unwanted mass from the existing flywheel. This sounded like a good idea, so I turned to RIMCO in Santa Ana. They are experts in air-cooled engines, and routinely lighten stock flywheels. They threw my flywheel on their lathe and removed the unneeded starter teeth, as well as another 5 lbs, reducing it from 17 to 11 lbs. That’s an equivalent of 600 lbs of vehicle weight, according to the formula. They then precision balanced it, of course.

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Here is the lightened flywheel, mounted on the motor.  Notice the missing starter teeth ring.  Installing the flywheel was not any different than installing on the gas engine, except that without the starter teeth, it required other means to lock the flywheel while torquing down the mounting bolts. I threaded a couple clutch mounting bolts into the flywheel and used a breaker bar against them as a stop lever.

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While the flywheel was being lightened, RIMCO determined the clutch pressure plate and disc still had a good amount of life in them, so I am reusing them here. A pilot tool helped align the clutch disc while bolting the pressure plate onto the flywheel. Here you can see the motor and transaxle engaged in their mating dance, with the axle shaft preparing to dock into the splined collar in the clutch disc. It’s a love story.

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And that is how EV babies are made.  The white three-phase main wires on the right were later rotated to the top of the motor, where the terminals were more accessible, and where there would be less interference with the future battery racks. This involved removing the flywheel and turning the motor 90 degrees on the adapter, so that the transaxle side of the adapter kept the same orientation.

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Installing the coupled pair in the car was much easier than yanking the stock gas engine and tranny. Due in no small part to my buddy Steve dropping by to lend a hand and some unfailing common sense. The AC50 has a much smaller footprint and profile than the stock gas engine, making it much easier to maneuver. First the whole assembly is positioned level on the floor jack and rolled under the car into position. Even though my jackstands were at maximum height, we had to angle the bell housing in through the rear wheel well. The jack was raised so the rear transaxle mounting feet just reached the brackets on the undercarriage, and then rolled slightly backward so the transaxle docked with the mounting bolts. I medium-tightened them just to hold position for the meantime. Then the jack was raised just enough to allow the lower cross-member to be installed under the motor. The motor’s end will rest on a small block of wood until the L-bracket is fabricated.

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The CV joints needed a good once-over before going back in the car. I stumbled on an excellent YouTube video showing the teardown, inspection and reassembly of 914 CV joints, which motivated me to roll up my sleeves. I took each joint apart, cleaned, bagged and marked them individually to identify their position on the axles. It turns out that both left side joints were badly worn and required replacement. Auto Atlanta sells reconditioned CV joints complete with boot and bolts, but I was able to talk them into selling me just the splined joints alone. Since the right side joints were being reused, I took the video’s advice and swapped the inner and outer joints for greater longevity. Now each bearing will wear on the opposite, fresh side of the spider race. It’s possible to pull and replace the CVs without removing the stub axle, but over-torquing and breaking a flange bolt forced me to remove it anyway, so I could extract the broken end. I had added peace-of-mind watching the axle-side CV flanges seat properly over the roll pins, which is impossible to see with the stub axle installed.

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Now that everything is in correct position, I torqued down the motor cross-member and transmission mounting bolts. Next up is refabrication of the motor mount L-bracket. Can’t wait to spit out a CAD file for the plasma cutter!

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4 Responses to “Mating Game”

  1. This is so exciting! Such excellent writing. Thanks, Mark!

  2. Ohhhh – a plasma cutter. That sounds so sexy. I’ve always wanted one of those. – Fordy

  3. Great blog, keep up the good work. I converted an old Citroen myself and decided to retain the clutch also, easier shifting, but also for safety: what if the electronics get crazy? At least I have the clutch to disconnect the motor. In practice (I have the AC 50 motor also, with the Curtis controller) you will use 2nd gear most of the time, and for 4th and 5th the motor lacks the power/torque. Nice guys at CanEV by the way.


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