I have a standard 1275 (22lb) flywheel and was wanting to lighten it to at least stock Cooper S (18lb).
It will installed in a MK2 Cooper S.
I have read where this can be an issue given the flywheel is cast.
Is this correct; or can it be lightened?

Yes, cast flywheel can be lightened, easiest way will be to face .200" off the non-clutch plate side and then make up 3 x .200" spacers to go under the straps, still using the original washers. Should also check that your diaphragm is set up properly. And, yes, flywheel will need to be re-balanced after lightening.

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Steve

Sure it can be done, I do it to both the 1 piece and 2 piece flywheels. Just don't touch the hub area.

For road use I face .200" off the outer face, down to 1/4" from the thick tapering bit near the hub.
Then I face another .120" off, just down to the 3 slots.
The straps need .200" thick machined spacers fitted to put them at original height.

Vizard's HTMYM book shows metal taken off the inside face too, below the ring gear- but I don't bother.
Stock Deluxe or Cooper S 2 piece flywheel, or Mini 1 piece is ~7.4kg. The Morris 1100S one is heavier.
Weight of mine after machining above is 6.0kg.
Other folks drill big holes around them too, but I don't bother for a road car.
If I'm changing the ring gear, I go for the 3/8" wide one as it's lighter.

After machining the flywheel MUST be balanced, as grey cast iron is not homogenous.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Dr Mini, do you have a picture of one you've lightened side-by-side with a standard 1100S?

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did I tell you that I won a trophy?

I have a standard 1098 one, not an 1100S.
I also have a lightened one I've just done, can take a pic, it used to be an 1100S one...
If anyone has a stock heavy 1100S one please one put a pic up, and I'll add mine.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Don't forget the back plate, good weight savings there too eh


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Great thanks for the info guys, appreciate it.

Nowhere near what you can get off the flywheel.

Flywheel weights-
1 piece stock = 7.4kg
1 piece DrMini lightened = 6.0kg
2 piece stock = 7.1kg
2 piece 1300 stock = ? bloody heavy!
2 piece DrMini lightened = 6.0kg

Backplate stock = 2.5kg
Backplate QH triangular = 2.0kg
DrMini triangular lightened = 2.0kg
Backplate 22G270 faced off to 7.5 thick = 1.9kg (was in miniDave’s 1293 but I took it out) too thin to trust... they are NOT steel.

I don't lighten backplates- it takes far too long milling the outer shape manually, maybe worth it if you have a CNC mill. I did a few triangular Mazda rotor shaped ones on a lathe where I worked last, that took a lot of setting up on a faceplate 3 times. Not worth it, takes too long.
IMO if you want a real light (and safe!) backplate go buy a steel one from UK.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I did, actually the whole assembly from Med. just giving options in case the dude didn't have 350 pounds plus postage to spend


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They're not steel, that's true. They're HSCI. I wouldn't go crazy lightening the other vatiety, but these ones can handle having more removed.





For the time v's results... It's more effective to buy an after market Flywheel and Backing Plate in any case.

22G270 S backplate is SG (spheroidal graphite) cast iron. Yes, stronger than grey iron, but not strong enough for a rally motor with an orange dot clutch when they are thinned down to 7.5mm thick, like this one was by somebody.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I think I have photos of the clutch bits Kev if you want them included here?

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Dave K.
1979 Moke Californian + 1981 'Coke' Moke

Yeah they probably won't like that much The I have a 22g270 in the blue mini in my Avatar, I took it down to 10mm and just milled out around the diaphram bosses and down to the edge of the friction face. You need to take off a lot of material before you see an substantial loss of weight. They're about 11.5-12.0mm thick through the friction face, all I really did was clean it up and then a bit. It was just what I had at the time, I wouldn't waste my time doing it again, I'd just buy an aftermarket one, they're lighter to start with, and if you want to be a real nut case you can still take meat off most of the ones available.. might be able to get another 50g off them

The one in my 1360 is a 22G270, it came out of a track car, it was milled out on a rotary table, in between the 3 lugs. After all that work by somebody it is only .5kg lighter, but it's all off the outside which is good.

I'll put some lightened flywheel & backplate pics here tomorrow.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

IMGP2692 by k_green1310, on Flickr
Left flywheel one of mine, middle one is stock, right one is a Lynx Engineering milled flywheel from the 60s.



IMGP2693 by k_green1310, on Flickr
Left backplate is stock (2.5kg), middle one is the over-lightened 22G270 (1.9kg), right one is a Quinton Hazell backplate (2.0kg).

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.