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MG MGB Technical - lightened flywheel

Can anyone offer advice on lightening the flywheel, ie, is there any noticable gain, how much whight to remove and is it a must that the crankshaft be balanced afterwards, thank you in advance for any input, Vin
Vin Rafter

Vin, there will be no more BHP, but the motor will respond faster and the whole car has less inertia, so a tad more acceleration.
You should only need to rebalance the flywheel, and only if you suspect there were cavities in the areas cut away.
Others can advise on how much and where to cut.
Art Pearse

I had 4 lb cut evenly off the back of my flywheel. The engine is much happier to rev now and I've noticed no ill effects. As Art says, the engine is internally balanced so only the flywheel needs to be balanced after being lightened (if even then).

I recommend it!
Rob Edwards

For the time and effort youll put into getting the original flywheel lightened you should perhaps consider buying an aftermarket aluminium product designed specifically for what you are after- more response and a lighter drivetrain unless there is a reason why you must keep the drivetrain "original".

Lightened original spec flywheels have a tendency to eventually warp. Once that happens youll have to lift the engine again and buy an aftermarket one anyway or source an original and get it machined all over again.

Why risk doing it all twice thats double the cost of buying a well designed properly balanced aftermarket part that will last.

Worth thinking about. Good luck!
JS Ahlund

Vin I run a light F/wheel and it does make the engine more responsive to the throttle, but it will require a few more revs to get it moving under load. Not a bad feeling though. You can be lucky and not need to balance the F/wheel after machining but I would get it balanced as even a couple of grams is not good. Even if you get a new alloy one it comes unbalanced. I have a Fedanza on my car (only weighs 4kg) and when it was balanced it needed two drill holes 5/8" dia and 1/4" deep. I have never bothered to work out how much but its a fair bit. I did mine during a complete rebuild and had the whole engine balanced. One of the best things I have done. Denis
Denis4

I haven't had the problem with warping that JS mentions but I've only put about 10k miles on it since I had it done. Perhaps down the road I may begin having issues. That said, Moss get $530 for any alloy flywheel; there's a Fidanza on eBay right now with a BIN of $315; I paid the machine shop $75 to lighten mine. Unlike Denis, I don't really notice the need to give it much additional revs starting from a stop, but then my lightened flywheel is about 8kg compared to his 4kg (and compared to about 10.5kg stock)....
Rob Edwards

I must add that as well as the alloy flywheel I fitted Pouter rods and forged pistons that were just on half the weight of the OE parts so this all would have added to my lack of flywheel momentum. So what Rob said would be right. Denis
Denis4

I am running the Moss alloy 9 lb flywheel with steeel insert - makes the engine pretty responsive to the loud pedal! No problem getting moving.
Mike
Mike Ellsmore

Vin-
In terms of acceleration the effect of a lightened flywheel is minimal, the difference diminishing as you engage higher and higher gears. The real purpose of a lightened flywheel to permit lightening-fast gear changes while racing. Of course, this means faster wear of the baulk rings (synchro rings), but in racing this is a small matter as victory is all that counts.

The crankshaft and the flywheel should always be balanced separately.
Stephen Strange

"In terms of acceleration the effect of a lightened flywheel is minimal"

In terms of effect on acceleration of the engine in 2006 at the Goodwood Festival of Speed there was a Renault F1 playing the national anthem:

http://www.youtube.com/watch?v=MGEqlNU30Tg
PaulH Solihull

I have never had any lightened flywheel warp, but of course I've only been at this for 40 years, so my experience is limited.....

Lightening a stock flywheel is a fraction the price of buying an alloy wheel and just as effective unless you want to get really light (which requires fancy machining like 'windowing') in which case alloy is better. I use both.
Bill Spohn

This thread was discussed between 14/03/2013 and 18/03/2013

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