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Mechanical Engineering

Of MGBs and multidisciplinary machines

October 02, 2016

I was given a personal example of the power of a multidisciplinary approach to innovation a few weekends back when I found myself coincidentally working on very similar parts of cars built in two very different eras.

Let me explain. I own a 1974 MGB, a venerable albeit somewhat unreliable British convertible that has never run particularly well but recently began to stall and stutter even more alarmingly than usual.

Faced with a clearly sick car, I ran down a checklist of the MG’s typical mechanical maladies and traced the problem, with some trepidation, to an inability to properly set the fuel mixture. I say trepidation because the fuel mixture on an MGB – as was the case with all cars of that era - was controlled by a mechanical contraption known as a carburetor.

A million little pieces

Just a tiny bit of quick and overly simplified background. In basic theory, the job the carburetor is fairly straightforward. It mixes gasoline with air in order to create a balanced, more combustible mixture. Gasoline in its liquid form is surprisingly inflammable – but when it’s atomized in a fine mist into air in just the right proportion, it becomes the perfect fuel for driving the internal combustion engine. Any kid who has sprayed his mom’s hairspray past a lighter (not that I ever did that mind you) gets a pretty dramatic example of the impact of mixing fuel, air and flame. That’s the role for the carburetor – atomizing gas and mixing it with air. Sort of like a perfume sprayer. When you press down on the accelerator pedal, a cable opens up a valve in the carburetor allowing more air and fuel to mix and flow into your engine. Simple.

Simple in theory - but in practice for a car to run well it’s necessary to make fine adjustments to this mixture and flow rate, depending ideally on engine speed, load, ambient conditions, performance, whether or not you’re just trying to start, etc. In the 1974 MGB, this is brilliantly accomplished via an entirely mechanical carburetor. The necessary adjustments to fuel and air are all remarkably made via a Rube-Golberg-esque series of pistons, dashpots, springs, levers, needles, and magic pixie-dust. Well I made the last one up. I think.

As a mechanical engineer I can say that the MGB carburetor is an intimidating, magnificent and brilliant piece of engineering. Magnificent, brilliant, inspiring and entirely problematic. Unfortunately, as clever as the mechanical carburetor is, all that mechanism means a fair amount of cost, complexity and its associated reliability woes, which brought me to last weekend’s teardown and rebuild project. Even experienced MGB mechanics have been known to weep when faced with having to tinker with the carburetors. And ONE carburetor wasn’t enough for the engineers at Morris Garages – Noooo. They needed to add a second for good measure.

How many parts are there in an MGB carburetor? A hundred? A thousand? A million? Who knows. All I know is that I lost the better part of a day on this project – carefully photographing like an archeologist preserving a historic site, slowly disassembling, cleaning, replacing a few worn parts and then slowly reassembling the unit. When my car started again at the end of the day, I was thrilled and frankly somewhat surprised.

Computers, complexity and better cars

As a complete coincidence, that very same weekend I found myself making some adjustments to the throttle body on our Design Concepts race car – a 1996 Dodge Neon that we race in the CHUMPS endurance race series

The most creative and effective solutions to problems in innovation don’t always respect the boundaries we place on our design teams and their expertise

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