Tech Tips: Austin-Healey Sprite and MG Midget

[Editor's Note: This article first appeared in our July 2016 issue. Some information may be different.]

Not much more than badges and a few fancier cosmetic appointments differentiate the Midget from the Sprite. Known together as Spridgets, these fraternal-twin cars feature simple technology that nearly anyone can understand and wrench on. Modifications and dramatic improvements are easy to make. Unfortunately, some well-intentioned “upgrades” have problematic results. Here are tips for avoiding several common Spridget blunders.

[Turning a tired Bugeye Sprite race car into a street hooligan]

Expert: Paul Dierschow

Sports Car Craftsmen
(303) 422-9272

Don’t change the car from steel to wire wheels without changing the entire rear axle housing. The wire-wheel axles are nearly an inch shorter, and although they will move the car if installed in a steel-wheel axle housing, the amount of axle spline engaging the differential side gear will be next to nothing.

Don’t use axles from a 948cc-or 1098cc-engined car if you have any performance ambitions whatsoever. They are made from material that is quite inferior to that used for 1275cc- or 1500cc-powered cars. They’re guaranteed to let you down when you least need or expect it.

Don’t spin the rear wheels when driving from an unpaved area onto a hard road. The shock generated by the abrupt change of traction is almost guaranteed to snap the right-rear axle shaft effortlessly. Again, severe disappointment may ensue.

Don’t change a drum-brake car to disc brakes without changing over to the rear brakes and master cylinder from a disc-brake car as well. The front-to-rear brake bias will be changed to be far less than ideal if only the front brakes are changed. Do the whole job.

Don’t plan to put a 1098cc engine onto a smooth-case transmission that was behind a 948. The 1098 clutch won’t fit inside the bell housing without very extensive modifications.

Don’t try to solve a clutch-release problem by lengthening the slave cylinder pushrod. The release bearing fork will hit the back of the bell housing’s opening and bend it easily due to the force generated by the hydraulic pressure within the system. Instead of making the problem worse, fix the original problem, which is usually a worn-out release bearing or master cylinder pushrod.

Don’t use the wrong radiator cap on a vertical flow radiator. They take a 1-inch-deep cap that is hard to distinguish from the common 3/4-inch-deep one found in most other cars. This will cause the car to boil over easily, as it will not seal the cooling system and thus prevent the coolant’s boiling temperature from rising properly.

Don’t fill the radiator in a cross-flow car through the pressure cap on the surge tank. That will only partially fill the coolant system, and hot running will quickly result.

Don’t upgrade to the wrong alloy wheel. Too much positive offset will cause the tire to foul the rear wheel arch; too much negative will foul the leaf springs. Your choices are limited.

Don’t buy a generic fuel pump just because it’s cheap. Most will produce far too much fuel pressure, which will overwhelm the carb float needles and then initiate serious driveability problems. Attempting to resolve this with a pressure regulator frequently produces further problems, including leaking or inaccurate settings. Just ante up for the real SU pump and be done with it.

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