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MG Midget and Sprite Technical - Diff torque figures

Could anyone help me out with the these torque figures?

1. Ring gear/crown wheel to the diff cage.
2. Bearing carriers to main casing.

Cheers,
Malc.
Malcolm Le Chevalier

Are they not in the haynes manual ...

im away from home fkr a few days... sorry i cant look them up

prop
Prop and the Blackhole Midget

My Haynes manual only gives the figures for the carrier retaining cap nuts at 65 lbf ft (8.99 kgf m) and the pinion drive flange nut at 140 lbf ft (19.4 kgf m)
David Billington

Does the attached taken from my manual contain the info you need?


Jim


J Smith

Indeed it does Jim. Perfect, thank you.

Prop, funnily enough I have had the car six years and still not bought a midget Haynes manual. I have a Spitfire one that does me for the engine and gearbox bits, then I just make up the rest as I go along!

Had a look in a B manual (assuming they would be pretty similar) and that didn't have them in.

Thanks
Malcolm
Malcolm Le Chevalier

What size are the crownwheel to carrier bolts?

I know the manual says 60 lb. ft., but unless they are 1/2" bolts that seems high?

Do the bolts a letter stamped on the head? R, S or T?

A 3/8" UNF T grade bolt should be a maximum of 35/40 lb. ft. and a 7/16" UNF T grade bolt a maximum of 50/55 lb. ft.

Richard
Richard Wale

They are 3/8" and appear to be marked W.

They were pretty tight, it needed a 2ft bar to undo.
Malcolm Le Chevalier

In fact, now you mention it, that is a lot. 1500 head studs are 3/8" and only done to 45 lb. ft.
Malcolm Le Chevalier

My BMC manual contains the same paragraph as Jim's.

Curiously, the MGB manual quotes the same figures. I can't remember if the bolts are the same size though.
Dave O'Neill 2

Been looking into this, it appears Grade 8 (equivalent to 10.9 in new money) torqued dry is typically quoted as 49 lb. ft. So maybe 60 is OK.

http://www.almabolt.com/pages/catalog/bolts/tighteningtorque.htm

and M10 x 1.5 grade 12.9 is 60+ lb.ft with a coarser thread
Malcolm Le Chevalier

W is correct marking, and is well in excess of T.
I have always used the book figure of 60, never any problems other than the time a T bolt slipped in unnoticed. It stretched a little but didn't break. And could be felt going soft. Replaced of course.
60 lb-ft is not unreasonable for a good grade of 3/8" bolt. Don't forget that standard HT head studs (dimple or 22) are torqued to 50 as well, and there are stronger ones than this available - Peter Burgess refers to ~70 lb-ft in a recent thread.
Paul Walbran

Paul,

I have looked, and cannot find any specifications for 'W' grade bolts - do you have a link to them please?

Richard
Richard Wale

I can confirm 60 works just nicely! Thanks folks.
Malcolm Le Chevalier

Richard
I did find it once, but can't remember where! IIRC it was progressing the alphabetic sequence. As most are aware, the bulk of the normal application higher tensile bolts were marked S, with special applications such as around the suspension and propshaft T. The data I saw carried on the sequence throught U,V then W.

Malcolm
Yes, it feels nice and solid at that doesn't it!
Paul Walbran

This thread was discussed between 28/07/2016 and 30/07/2016

MG Midget and Sprite Technical index

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