A Tale of Two Flywheels

by Ben N on March 22, 2010

Flywheels from the Mercedes 240D and Chevy S10

The second and third Sundays of the month are usually “EV Build Days” – but the friend who usually hosts them was out of town. Instead, I invited EV club members over to my house to help figure out the next steps in the “MerChevy” diesel truck conversion.

Rich was the first to show up, and the main guy I really wanted to talk to. We looked at the flywheels and started kicking around ideas. A couple other guys showed up as well, enough to get the ideas flowing, but few enough that we weren’t just tripping over each other.

The goal – figure out how to mate the Chevy transmission to the Mercedes engine.

The problem(s)? The Chevy clutch disc is too big to fit in the Mercedes flywheel. The Chevy flywheel can not be redrilled to fit the diesel engine. The Mercedes flywheel can not be drilled to fit the Chevy clutch cover.

We also pulled the bell housing off the automatic transmission from the Mercedes to take a closer look at that as well. Then I called up Hot Rod Jim, who lives just up the road from me and helped with machining on my Electro-Metro project. We decided to visit, so the guys and I hopped in the Rich’s truck, with flywheels et al in the back and zipped up the road.

We spent the next 20 minutes to half hour standing around the tailgate throwing around ideas. Here’s the two main things we came up with.

Option A: Find a clutch plate that will match the 26 spines of the Chevy transmission, but only be about 8″ diameter, (instead of the typical 9″) that will fit into the Mercedes flywheel. Buy a new Mercedes pressure plate and mount it on there. Done. (after that, a custom shaft bearing and engine to tranny adapter plate are still needed, but that’s the easy stuff.)

Option B: I know this one sounds crazy, but….. ¬†Sandwich the two flywheels together. Trim all that extra weight off the Mercedes flywheel (yipes! machining!) but carve a step into it. Put the S10 flywheel over the top of it, and press it down into the step in the other flywheel. Bolt the two together. I would now have a flywheel that fits the crankshaft of the Mercedes, and the clutch, pressure plate, and transmission of the Chevy. I would be able to use all (cheap and easily available) Chevy parts in the future. The weight should also be very close to the weight of the existing Mercedes manual tranny flywheel. Two machinists and a diesel mechanic were in on this conversation. They didn’t think it was crazy. I did, but that’s beside the point.

So now Rich is going to see if he can locate a clutch that will fit both the Mercedes flywheel and the Chevy tranny. If he can, this project starts to sound fairly doable. If not, it just got a whole lot more fun/interesting.

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