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MG MGB Technical - MGB / MGA Flywheel

Hi guys, anyone know what the difference is between an MGA flywheel and a 3 main MGB one?

I am clearing out some parts, and have a couple of early flywheels.

For info part numbers are 1H651 MGA, 12H713 MGB, and they both use the same ring gear, 1G2874..

Thanks

Colin
Colin Parkinson

If the drawings on the Moss website are at all accurate, the MGA seems to be solid, whereas the MGB is relieved at the back.

The clutch mounting may or may not be the same.
Dave O'Neill 2

Clutch mount is simplest. Same bolt pattern, but MGA has only two dowels, MGB has three.
Paul Walbran

Thanks Paul, that is the correct answer!

I did some more research last night and found that on the MGA Guru site.
Colin Parkinson

In addition to the clutch dowel number, the flywheel weights are different too.
MGA 1500 and MGA 1600 flywheels weigh 29.5 lb
MGA 1600 Mk II, MGB Mk I 3 bearing and MGB Mk I 5 bearing flywheels weigh 21 lb

Not that it's relevant to the question but it has always surprised me that the MGB Mk II flywheel is heavier than the MGA Mk II and the MGB Mk I flywheel. It has a larger diameter, so that no doubt contributes, but it does surprise me they went for a heavier flywheel for the MGB Mk II than the MGB Mk I.
I'm not sure of the figure but at a guess the MGB Mk II flywheel weighs about 3 or 4 lb more than the MGB Mk I flywheel.
T Aczel

But the extra weight is closer to the middle on the mk2.
The mk 2 ring gear is lighter and thinner, and I think the flywheel is thinner at the periphery (from memory, too late at night to check measure)
And of course it is a bit larger in diameter.
All of which makes the moment of inertia not a simple relationship to the extra weight.
Paul Walbran

"All of which makes the moment of inertia not a simple relationship to the extra weight."

Actually Paul, I agree with you completely. Looking at the MGA Mk II and the MGB 18V flywheels side by side, I thought the same: "how on earth do you compare the inertia of these two flywheels, when the distribution of the mass is so different."

I'm not sure you will agree, but I also thought the 18V flywheel would be a much simpler design to manufacture, needing less machining in its creation.
T Aczel

This thread was discussed between 10/08/2022 and 15/08/2022

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