10 common mistakes Austin-Healey Sprite and MG Midget owners make

[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

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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Comments

MGWrench New Reader
9/2/22 11:58 a.m.

I couldn't have said them better myself!

Coder New Reader
9/5/22 10:30 a.m.

This article couldn't be more timely. I just bought a 67 sprite that needs a lot of work. Thanks for the warnings!

Teh E36 M3 UltraDork
9/5/22 2:06 p.m.

Don't embark on a very ambitious engine swap. They are never ever ever ever simple or easy or cheap.

NOHOME MegaDork
9/5/22 5:14 p.m.

Teh E36 M3 said:
Don't embark on a very ambitious engine swap. They are never ever ever ever simple or easy or cheap.

This statement applies to pretty much any engine swap in any car.

Did a Fiat 1600 DOHC into a Midget way back when and it must have been easy enough since I had little money and few tools at the time. We could debate how well done it was.

Teh E36 M3 UltraDork
9/5/22 6:01 p.m.

NOHOME said:
Teh E36 M3 said:
Don't embark on a very ambitious engine swap. They are never ever ever ever simple or easy or cheap.

This statement applies to pretty much any engine swap in any car.

Did a Fiat 1600 DOHC into a Midget way back when and it must have been easy enough since I had little money and few tools at the time. We could debate how well done it was.

Haha. Seriously. I did a 4age swap in 2003 and was 'done' in just over a week. And then spent 14 years sorting it. This time I'm 2 years into it and it's not running yet.

bosswrench New Reader
11/28/22 3:01 p.m.

In reply to Teh E36 M3 :

Agreed. A friend, having lost patience with the no-power Brit engine, swapped an RX-7 rotary into his Spridg. By the time he had it reliable, everything from the bellhousing back including the IRS, wheels & brakes were also RX-7. The noise was incredible even with a pipe that went from engine to rear bumper, made a 180 and halfway back up front, with several mufflers along the way. Would NOT recommend this for road trips. Fast, though.

joeymec New Reader
12/3/22 1:06 p.m.

After many Sprites and Midgets.... for me, the best engine upgrade was to go to a 1275 motor from the early 948s and 1098. You can tweak the 1275's to do just what you need them to do without upgrading rear axles shafts and the like due to overpowering. them. Remember...engine power is only as good as you can get it to the wheels! Overpowering these cars ( in my experience) is mostly an ego trip on how neat the engine swap is! Of course, if that is what you want to do, I would say go for it and like other's say.....it's never cheap and the sorting process gets extensive. An MGB or GT is a different story. V6 and V8 upgrades are more 'sortable'. Still, never cheap!!

Once again, just my opinion and 'not necessarily that of mgmt!!

joeymec New Reader
12/3/22 1:16 p.m.

In reply to Coder :

67 is the best year (in my opinion). It's last of the steel dash, first of the 1275 motor, no side marker lamps, no head restraints and not boogered up with smog controls. If yours is not a rust bucket and the tub is solid, it's worth putting back together. Everything, even today is still available most parts are interchangeable with other years. That of course depends on whether you are doing the work or paying someone else. That is the beauty of the Spridget. Lots of fun and driveability without being afraid of 'destroying a classic' which is what is happening today to most upper grade marques.

GrahamLine New Reader
8/8/23 1:29 p.m.

Had a Bermuda '72 and autocrossed it successfully for many years. The best engine improvements were replacing the pistons with 8.8:1 compression aluminum Hepolites, matching and polishing the intake and exhaust ports, and removing a thumb-sized piece of casting slag fused into the #4 cylinder intake.

A mechanical wizard set up the scrambled SUs and said "don't let anyone touch them." Car had about 45K miles when it came to me. Had I had more funds, I might have tried the close-ratio BMC gear set, or, even better, a 5-sp from a Datsun 1200/1400. The advantage of the later 1275s was the 3.9 rear axle which made the car much more pleasant at highway speeds.

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