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MG MGA - T 9 Gearbox and Aluminum Flywheel

I recently c/tacated Hi-Gear engineering regarding a T9 G/Box and an aluminum flywheel to go with it. They have advised me not to fit it due to lack of mass and inertia which can give rise to transmission line rotational ocillations making some vibration and noise. Chatter can sometimes be heard due to the loss of flywheel effect as this is what a flywheel is supposed to do. Q/ Has anyone out there come across this who has this set up with the T9G/Box and flywheel?? Clive..
c allen

I hate to be pedantic but to make a flywheel out of lighter material is a total contradiction of the mechanism design. A flywheel stores energy by weight and rotational speed reduce the former makes no sense.....Has anyone tried plastic?
Neil Ferguson

I don't think mass of the flywheel has anything to do with clutch chatter, but it certain does affect the driving character of the car. With a heavy enough flywheel you could pop the clutch at idle, and it would squeak the tires a bit and drive off without stalling the engine. A lighter flywheel has the advantage of spooling the engine up quicker, so you get a little better acceleration in the lower gears.

But there is a practical limit to lightening the flywheel. If the flywheel is too light there becomes a very fine line between "it's not moving yet", and "aw s**t, I killed it". With low flywheel mass you have to be very careful with a bit of extra throttle and feathering the clutch, to avoid either spinning tires or killing the engine.

Years ago I changed my MGA flywheel to the later production spec (late MGA and all MGB), reducing weight from 28 pounds to 20 pounds. I like it a lot for street use and mild competition. Reduction of a couple more pounds may or may not be of much benefit, but a 14 pound flywheel is definitely "hairy" for street use. I would not recommend it.
Barney Gaylord

It's also not only the total weight, but the weight distribution. The flywheel moment of inertia is the sum of mass x radius^2, so mass at the rim is more important.
Art Pearse

I have the 20lb flywheel too, and it is a big improvement to the standard engined car. it's probably the biggest improvement for the lowest cost that you can do.

It does have the effect that all MGA owners who drive my car comment on the sharpness of the clutch - but that is compounded by the added grunt from the supercharger
dominic clancy

Thanks to all for your information. Clive
c allen

Extrapolating a wee bit as an engineer I always thought flywheel energy storage was much neglected . I am talking about ultra high speed, ultra strong flywheels ..not the puny load smother things ref. above. Given the bearing and material technology now available they are very efficient energy storers and give quick and huge response...they can be used as brakes to save wastage as well . There has been a slight move in the direction ( incl . in cars) and some good research is underway but.... a long way to go. ..but get out of the way if they crack up or escape from the bearings.
Neil Ferguson

There is certainly a lot of residual kinetic energy in a flywheel,certainly a lot more than I had realised.

Back when I was racing karts I was tuning up my villiers 9E 2-stroke engine in my garage, revving it up to about 10,000 rpm.
Suddenly the engine cut out and there was a strange loud ringing noise and something shot out of the open garage door. The key had sheared on the crankshaft and the 6 inch diameter flywheel dropped off, whipped out of the door, climbed up up the brick wall and went in through the open window of the house!

I rushed in to see where it had gone and couldnt find it at first, luckily it had dropped straight into a basket of clean washing and had tangled its self to a standstill.

Fortunately there was no one else at home but I got into trouble when I had to explain how the clean washing came to be covered in oily scorch marks!

Back to the MGA, does the reduced kinetic energy in a lightened flywheel cause the tick-over to become less smooth?

Colyn Firth

The 20 pound flywheel (as was standard on late production MGA 1600-MK-II and MGB through 1967) is enough to retain smooth idle, even with the slight upgrade fast street camshaft. A few pounds lighter flywheel may still retail smooth idle with a stock cam.

Rough idle is more associated with more radical cams that just don't like to idle at all. Full race engines like to idle at about 3000 rpm.
Barney Gaylord


You were saying there has been little development in using flywheels for energy storage. There has been a rail development here called the 'Parry People Mover' for small short distance rail journeys, see following:-

Sorry not MGA related.


Paul Dean

Paul: The Swiss had buses with Flywheel drive back in the 1950s:
dominic clancy

Common pratice in the aircooled VW world is to shed some flywheel weight.Don't remember now how much,but I had one with a lighter 'wheel and loved how quick it responded. The pressure plate in a MG engine is over the top too, put it on the original flywheel and they become quite the lump. If mine ever comes out again it won't be going back in.
gary starr

Dominic and Paul....Flywheels have been around a long long time and some great applications in the last century, incl. those you mention, but so far they have not universally taken off ..mainly because of overcoming alignment issues between wheels and their drives at ultra high speeds..... but to go back to history and the first application 'the potters wheel'...
'''Many modern scholars suggest that the first potter's wheel was developed in Mesopotamia. A stone potter's wheel found at the Mesopotamian city of Ur in modern-day Iraq has been dated to about 3129 BC"""
Iraq was the seat of urban civilisation back then..but now!
Neil Ferguson

This thread was discussed between 26/04/2013 and 28/04/2013

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