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MG Midget and Sprite Technical - Lightening a flywheel

Hi guys,

I'm building a new engine and while I'm at it I thought; let's beef it up a "little".
Part of this project is a 7,5" clutch, because my old clutch cover had hair fractions in it (after 3 yrs).

As I have to put my flywheel in a lathe anyway is there someone out there who can give me some tips on how to skim some pounds off of it while I'm at it?

Thanks.

Alex
AG Matla

Look Mom,

No legs. Yes you to can now have a can of instant no legs in a can, just turn flywheel down on lathe, open pop tab on can, drink in one gulp, then rev engine to 6000 rpm, wait for explosion, and your legs will come right off at the Knee's

So try some of our other great product drinks like

Look mom, I lost an eye ball,
look Mom, I lost my testies
Look Mom, I tosted my buns in the fire

Ah its so much fun, get your can today!! only $19.95...sorry no refunds or CODs

Prop...as seen on tv...Prop
Prop***The End in 2012

Alex,

I've used a heavy duty 6.5" clutch on my 85bhp at the wheels 1420 and not had any problems with it over about 60k miles so maybe you should look into one. Fitting a 7.5" clutch removes the possibility of removing material outside the clutch cover as IIRC the cover is about the same diameter as the flywheel. If the 6.5" cover is used then there is a useful bit of material which can be removed outside the cover where it has the most effect to reduce the rotational inertia. If you search the archive you might find the info from the BMC special tuning dept about lightening or a link to it.
David Billington

David, I'll search for it, thanks.
And prop, just 6000 rpm?
And ofcourse I've seen the pictures of shattered flywheels.
But the mass-production of car parts means xtra security is embedded in the production process, wich means there is always a way to impove the standard.
Alex G Matla

Somewhere on-line is a scan of the original Sepcial Tuning diagram to show the lightening suggested for the 1275 flywheel. There is a link in the archives (which is where I found it) but i cant find it again quickly now:-(
Dean Smith ('73 RWA)

Alex,
Despite Prop's little rant, lightening the flywheel was a recognised means of getting a faster "blip" response on the A series engines - to the extent that BMC Special Tuning published recommended dimensions for lightening. I do have their drawing and can scan and post here if you cannot find it in the archives as David suggests.

I have a lightened flywheel in mine, and have done about 55,000 miles with this and so far it has remained in one piece just where it is supposed to be.

Guy
Guy Weller

Guy, if you could scan the drawing and mail it to me I will be for ever thankfull.
Alex G Matla

Alex,
I have just been looking for it! I have found one drawing, but I think that is for the 948cc engine. I do have one for a 1275 engine somewhere as well as that is what mine is. But I haven't found that one yet and need to keep looking! - Unless someone else can post that version?

I will post the one I have anyway, it may be of use to someone.

Guy
Guy Weller

Peter May did mine.
Brad (Sprite IV 1380)

There's an image attached to this thread

Shows bothe 948 and 1275 flywheels.

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&mode=archiveth&subject=97&subjectar=97&thread=2007082610324126995
Dean Smith ('73 RWA)

Dean, that image that Nick posted originally is the same as the one I have for the 948. But better than mine as it also has the 1275 dimensions.

Copied and attached here (acknowledgement and thanks to Nick Cherry-Scoop)


Guy Weller

Right, that's exactly what I needed. I'll link it here again.



Alex G Matla

Ok, I didn't see the last post by Guy, was making me some coffee........

Thanks everyone

Alex"busy day tomorrow on a lathe"Matla
Alex G Matla


guy, does lightening the flywheel not make for a lumpy tickover?
i can imagine this not being a problem for race tuned cars (foot to the floor most of the time!!)but not very nice for a road going vehicle.

i only ask as i recalled something about it from a good few years ago whilst reading up on tuning the 2L pinto engine for performance..


regards, john..
j b biggs

John,

I've got a 948 flywheel on my 1420 engine lightened as per the details mentioned and I never felt it was that much less smooth than the standard flywheel. I put about 60k road miles on it and never found it an issue. IIRC originally it was a bit easier to stall but one rapidly gets accustomed to it just like driving a different car. The engine response was noticeably better than the standard flywheel.
David Billington


ahhhh right david, many thanks for the reply.

regards, john.
j b biggs

http://s82.photobucket.com/albums/j279/foggythomas/?action=view¤t=1312a.jpg

Shaved a few pounds off. Shame it doesn't work on my waistline.
rob multi-sheds thomas

Rob,

If you were mounted between centres or clamped to a mill table then I'm sure it would work but be the stuff of horror films/books. BTW it looks like you can gets some more removed off that flywheel as you can do more than a straight chamfer.
David Billington

John,
Not from my experience. I do a lot of driving on twisty / hilly Lake District roads and rely on having plenty of torque, even at lower revs. My car pulls OK from about 1500, really comes on power at 3500 and runs so smoothly that it will run without snatching on a level road in 4th gear at 1000 rpm with my feet off the pedals.
Guy Weller

Alex

come to the ws my flywheel is out (the whole engine is)
it weighs in at 6KG (1KG less than Lijn her flywheel ;) )

At the same time you can look at my head with rimflow valves
always a nice present when you tear apart an engine you did not build yourselfs

Onno Könemann

good idea, will do that.
btw, I saw your engine today, had a quick glance at it already.
Alex G Matla

Gee, Prop, my flywheel was lightened to about 9 pounds or so (IIRC) and it hasn't reduced my dance height yet. I will admit that I ALWAYS stop looking at the tach when it goes north of 7000, however.
David "glad my tach does not have a telltale" Lieb
David Lieb

Sorry guys,

I was just having a laugh, but its still a scary thought...but yes vary doable And if done correctly, Im sure will be safe enough at least for the cat to ride shotgun.


Hey alex,

Here is a great idea, how about an aluminum fredinsia, I think the wiegh around 7-9 pounds, Instead of resurfacing you buy screw in inserts, which are cheap $25 USA

AND

with the exchange rate it will cost you around $200 uk money, Here in the USA, I imgine the machine work on a stock fly will easily cost you that much

http://www.bpnorthwest.com/.sc/ms/dd/ee/8079/Aluminum%20Flywheel%201275


Just a thought
prop....to short to play pro basket ball...Prop
Prop***The End in 2012

They are cheaper from ultrarev.com (NFI)
Trevor Jessie

Well guys, the bottom of the money-pit is coming in sight, so.....(and the wife is happy with the midget,but only as long as it drives)
And as I have acces to a lathe and capable of doing it myself, that the way its gonna happen.

Maybe I'll put some 1/4" thick explosion shielding over my tunnel...
Alex G Matla

Alex,

Hopefully you can get it balanced as well after machining. The last one I did didn't require any balancing at all as it was spot on but the guy that did it said that's unusual but does happen occasionally.
David Billington

Well, after a hard days work I am now left with a flywheel that weighs 6.1 kg, I started with 7.1 kg. I only trimmed the back side some and flattened the front side competely for the bigger clutch.
So onno, yours could lose another 400 gr according to the drawing and leaves me wondering what one has done with lijn's flywheel?

Alex "moderately satisfied" Matla
Alex G Matla

Thats great news alex, post some pic. Im sure we all want to see it., I know I do.

BTW...you probably already know this, but just incase, make sure you chamfer all your holes and round off any square edges, thats where spieder webs and cracks usally start and grow from on high stress parts

Prop
Prop***The End in 2012

Here is a "before" picture.



Alex G Matla

backside "before"


Alex G Matla

front side after


Alex G Matla

frontside after.


Alex G Matla

and at how mutch does it tip the scale?
Onno Könemann

Not bad alex, looks good, how is the balance?

Prop
Prop***The End in 2012

Onno it weighs 6.1 kg, as you can read a few posts up.
Balancing has yet to be done, first I will have to drill the holes and thread them for the bigger clutch.
And then i must chamfer those holes.......(thanks for remining me prop)
Alex G Matla

This thread was discussed between 02/03/2009 and 04/03/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.