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MG Midget and Sprite Technical - Minor vs Midget engine

What are the key differences between the midget and Minor engines...

My assumption is the block is the same...but front/back plates are different ?
Dean Smith ('73 RWA)

Minor and Midget front and back plates are the same, the 1098 Minor engine is essentially the same as the 1098 Mk1 Midget / Mk2 Sprite engine and they all share the same weak bottom end (which is why BMC at the time soon opted for the stronger crank with the 2" main bearings).
Yes it should drop straight in, but it does beg the question....WHY?????

Mark.
Mark T. Boldry

Actually its an A+ 1275 block bored out to 1380....but with the right front/back plates for a Minor.

wine induced impulse ebay purchase. If I can use the front and back plates then even better !
Dean Smith ('73 RWA)

Minor backplate has the same outer shape but the early (10CG blocks) and 10MA minor engines used smaller crank flanges and their backplates will not fit over the flange of a 1275 A+ crank. Also, and more importantly, the oil pump cover moved outwards and expanded for the 1098 (10CC) later blocks and for all subsequent 1275 A and A+ blocks. For an A+, then, you need either a 10CC, a 1275A, an alloy aftermarket backplate or get the 10MA/10CG backplate ground out to fit the new engine. Not hard to do since you can bolt one to another (you've kept the A+ backplate, right?) and open them out like a template-y job-thing. The early backplates also need a hole reamed out for the top dowel pin between the top 2 bolts on the gearbox casing. I lathed several new correct-sized ones up. If the backplate and oil pump cover don't sit right then you'll leak oil. BTDT. I've got an alloy plate cut out to the right shape but with extra 'ears' at the top to provide a better engine steady bar location. You can also undersize the bolt holes for the starter mounting and then tap them for UNC bolts. Easier to remove and refit the starter.

Front plates. Essentially the same but later A-series have a stiffener where the alternator adjuster bolts through. Needs to be trimmed carefully if you use the better A+ timing cover system. WEEEEEELLLLL worth doing. Several spot welds to grind past. One extra timing cover bolt hole to be drilled and you'll need to countersink the front plate for the cs bolts at the bottom if you use the duplex timing chain.

Is this the 1380 off E-bay?
rob multi-sheds thomas

Timing cover conv. picture.


PS Oops. Just re-raed your last post. Yes, it is the Ebay one!


rob multi-sheds thomas

Yes it is.

I was lookin for bits to make a 1380 anyway. I have an unmolested Ital A+ engine complete. And some 73.5mm pistons.

I'll strip this one to check out the internals but hopefully this will actually save some time and money. I'd like to keep my current and mostly original 1275 intact if I can.

Details are sketchy on the cam and the spare big valve head. I'm assuming they're no good but who knows.

Any other bits to be aware of ?
Dean Smith ('73 RWA)

90 degree dizzy cap required.
Make sure it has the A+ timing chain tensioner. Fantastic at doing the job!
Water bypass hose in the head?
Oil filter ought to have the correct anti-drain valve in it. (Part number, anyone?)
TDC mark may be in the wrong place if they've not used the correct crank damper pulley. Check it with the head off and remark TDC.
Also, you might add a remote for the oil pressure sensor since it is an absolute bu66er to get to once the engine is in.
Make a breather port in the redundant fuel pump hole and T-piece it into the timing cover breather hole.

I've got pics if you ned them.

Rob
rob multi-sheds thomas

Rob - be grateful for anything you have.

if you prefer to mail then its dean at eatworms.org.uk.

How do you change an oil filter on an A+ without making a huge mess ?!...and actually does that mean there's no way to plug in an oil coller. (have to go and look at the one in the garage!)
Dean Smith ('73 RWA)

Dean - oil cooler is done with a sandwich plate between filter and block.
David Smith

Now I know who outbid me!

I've bought some stuff from the same guy before, some good, some not so good. He did seem to know about mechanicals though so I hope its a good one!

I'll have to keep looking now

John
John Collins

John - hopefully I might have a spare set of 73.5mm pistons now ;-)
Dean Smith ('73 RWA)

It lives!

I 'hosed' the oil pressure sensor via a remote pipe union (brass) that is bolted to the rear alternator mount. The dizzy is now a 45d4 model and the carb/manifold is standard MG Metro throughout. It doesn't foul the bonnet at all. Much quieter than the previous engine although rather sedate by comparison to the highly tuned unit. The Minor clutch has now bedded in a bit and only slips under extreme acceleration but will eventually get changed for the Hunter one when I can find one.
Oil filter is easier to get to. Not the correct type but will do the job just fine.


rob multi-sheds thomas

This thread was discussed between 19/06/2008 and 28/06/2008

MG Midget and Sprite Technical index

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