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MG Midget and Sprite Technical - Need a conrod are they the same as mini?

Hi guys,

I mentioned earlier my block needed sleeving. Well I've got that done and now have all the bits to build it except one of the rods is too loose a fit on the gudgeon pin (wrist pin in US?) so I need a new rod. The rod has AEG145 F&P63 on it. No.3 rod.

So can I use a Mini rod or is this just a Sprite/midget rod. I looked in my Vizard book but couldn't see any mention of AEG145.

I thought if it was the same as a Mini I should be able to chase something up locally if not I'd have to go further a field.
Greg H

That number was on the bearing cap. Just noticed that on the rod itself it has AEG 521.
Greg H

Greg

What you have there is an early 1275 Midget or Cooper S rod.

Non-Midget or 'S' 1275 rods - i.e. Mini, Allegro, Marina, etc., are different as the crank journal is a larger diameter.

You could also use a later Midget rod AEG625
Dave O'Neill 2

Yep only 1275 midget or cooper/cooper s rods fit
Onno Könemann

Ok thanks guys. Know what I'm looking for. Am I correct in assuming it will have to be a no.3 rod because of the offsets? Or can you flip a no.2 rod? Is the AEG625 rod the same weight as the AEG521 i.e. can I just put one in my engine?

Now 'Cooper S' rod sounds easier to find than a Midget where I live but a whole lot dearer. I may end up sourcing from the UK.

Looking at the fit of my rods on pistons and I'm not sure if no.1 and no.4 have been correctly aligned. When I centre the rod in the piston the gudgeon is offset a long way. When assembled does the rod sit in the centre of piston on 1 and 4 or offset? See pic


Greg H

If the rod is center in the piston depends on the place of the bore (there is room for deviation here)
Center the pin as best you can and it will be fine

Cooper and midget rods are not the same weight and are different strengths ( en24 and en21 or something like that)
The cooper rod is way overbuild but the midget one still is as well even though it is of lesser grade material
Onno Könemann

regarding weights: don't assume everything is the same, instead have the internal engine components balanced, it is not all that expensive and you'll be glad you did. I had a 1275 that had been rebuilt with a mix/match of various parts that ran OK, but when I had to take it apart for another reason and sprang for a balance it revved so sweetly that I became an advocate for spending the extra $100.


Norm
Norm Kerr

This is particularly bad with later A+ rods - I had occasion to weigh a batch of Mini A+ rods once - their variance in weight was in excess of 50 grams between the heaviest and lightest
James Bilsland

James
I presume those where the ones with the big counterbalance weight on the cap?
Onno Könemann

If you have access to mini rods 521s.. then go all the same

yes there is a differance in wieght that is noticable

with the mini you can have them lightened and still retain alot of the strength... is my understanding

but definatly cut the tabs off the bottom... just a waste... good for several grams x 4
Prop

Onno

The counterbalance rods are pre +, these were the latest type that look like Midget rods, but have a larger big end

James
James Bilsland

Umm there is another book with stuff in about rods, it even has photos. I think you will find the number on the rod is the casting number rather than the part number.

Some early 1275 Spridgets will have Cooper S rods in them, even if they don't have the EN 40 crank.
Daniel Thirteen-Twelve

Wow,

I didnt know there was a book that had ALL that info. I wonder if it would have lot of other info

LOL

Prop
Prop

It's a good book but while the current edition does have a lot of other info you have to get the original edition for a nice photo of what an anti-rollbar connected to a drop link looks like when it's the correct width.


Daniel Thirteen-Twelve

Well my rod weights are ok with piston 1032g to 1036g. I think 4g is pretty good. 0.1411 ounces for those that haven't moved with the times. I think I have found someone that has some rods so will take my scales with me. My rod is 2nd from right in pic.

The crank is an EN16T so I assume not the good one?

Now the block is cleaned up I can see that the cam bearings are a bit average so will have to replace them too. I should have got in done when it was at the machine shop but was being a tight ar*e and hoping not to. A little foolish I know.
Greg H

the good crank is a EN40B ...

Theres one for sale in the BBS classifieds ...150 pounds in the UK.



EN40B Crank shaft(needs grind) £150.00
1275 Midget conrods (std) £100.00
3.9:1 diff.£80.00
Works shape light weight hard top (to fit 1275 car)needs tlc £75


For further details please call me (dont E mail)
Contact: TONY GRIFFITHS Contact by email
HALESOWEN West Midlands United Kingdom
Tel: 01562 710455/07515 704554
Prop

Hap Waldrop of ACME speed shop
http://www.acmespeedshop.com/contact.html
says that he's seen both kinds break in the field, and few of either, so he doesn't feel that the EN40B is necessary unless one is going racing.

Note that BMC even dropped the tuftriding of the "weaker" EN16 on the '74 1275s, and I've not heard of any greater incidence of those breaking in the field than any of the others (Terry Horler points this out and makes the same comment in his book).

Norm
Norm Kerr

If you are going racing and spend all your time at 7500rpm i would prefer the EN40
For any other use the EN16 is fine
Onno Könemann

I had a EN16T crank last for about 6 seasons (with rebuilds) in a full race (MGCC and FISC championship winning) 1380. Rev limiter (for MGCC) was set at 8200rpm.

It did break eventually (all metal parts will ultimately fail given sufficient engine mileage/revolutions) albeit I caught it and switched off before it took the rest of the engine. I now have an EN40B crank fitted... I would however have no concerns with running another EN16T in a race car.

(although if the budget is unlimited then of course a new steel crank and rods are the way to go)

JB
James Bilsland

<<(although if the budget is unlimited then of course a new steel crank and rods are the way to go)>>

Do you mean a forging or a billet?
Dave O'Neill 2

Forgings are supposed to be better than billets, but frankly I've never had the money for either... :)

I know a man in Solihull who had a nice EN40B crank though...
James Bilsland

This thread was discussed between 23/03/2011 and 25/03/2011

MG Midget and Sprite Technical index

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