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MG Midget and Sprite Technical - Marina Gearbox

I've heard that it's possible to replace the 4 speed box in a 1977 1500 midget with a 5 speed Marina box. Is this true and how easy is it?
K Montgomery

Was there a 5-speed marina 'box?
Dave O'Neill2

You've heard wrong! And since I've not said it for a while, there are books with the stuff in.
Daniel Thirteen-Twelve

The Marina gearbox marries up to an A Series engine not the Triumph version fitted to the 1500cc unless I am mistaken?
Bob Turbo Midget England

The old school way over having an overdriven gear is by fitting a spitfire overdrive box. Nothing else from the era is a swap fit. Even then, you have to do a bit of bashing about to get it in the tunnel but, it does go in!
Bob T

What I am about to say may only add to the rumours and mis-information, but . . . .

Back in 1979, my 1500 Midget started to badly crunch gears when the gear lever was operated. I took the car to Graham Paddy in Beare Green, Dorking. He had it for two or three days in his workshop and - this is where my memory is foggy - he reported that a circlip on the mainshaft(?) had snapped which had resulted in the gears getting damaged by sliding along the shaft. He said he had a new Marina gearbox in stock and, by replacing the Marina's first motion shaft with that from my gearbox, the resultant Marina box would be a direct replacement for my Midget box.

Four days later, I came away from Beare Green, a happy boy. A working new 'Marina' gearbox had been fitted. And in the boot of the car I had a cardboard box of gears, shafts and housings. I vaguely recall Graham telling me that the 1300 Marina gearbox is identical to the 1500 Midget 'box in all aspects except one - namely the first motion shaft in an inch longer in the Marina 'box.

But, as I say, that was 33 years ago, and my memory is foggy, as were those early mornings in Beare Green, Surrey.

(PS. I have just unearthed the handwritten receipt from Graham, dated 29/8/79. On the receipt he lists " . . fit (original) 1st motion shaft to new (Marina) gearbox and refit to car . . . ").
Andy Hock

Interesting.

So could you put a Marina 1st motion shaft in 1500 box, and fit a Marina Engine to a 1500?

If so, the rear engine plates on an Autin/Morris Marina engine, and a Triumph 1500 engine, must be the same.
Lawrence Slater

Andy

That is exactly right, I have never done this but that is what I have always believed to be the case.

The reason why that is the case is obvious

BL or who ever were using A series cars with the familiar gearbox that we all know and love. Those all ceased production except the Marina so what to do for a gearbox with sync on first? The triumph gearbox fitted to the later Midgets was an Ideal candidate so they modified things to suit. We can now simply reverse that process.

I think???
Bob Turbo Midget England

>>Lawrence Slater writes>> the rear engine plates on an Autin/Morris Marina engine, and a Triumph 1500 engine, must be the same.

>>AH replies>> Possibly, but I'm not sure that the 'backwards compatibility' argument automatically holds true. I would need a few cups of strong coffee and, ideally, a selection of parts in front of me to be 100% sure. There is is the matter of bell housings to consider, too. I'm not sure if the Triumph bell housing is identical to the Austin/Marina's. Needs a lot of thought. And coffee.
Andy Hock

I fitted an overdrive gearbox in my 1500 Midget about 18 years ago. I bought the gearbox from someone in Milton Keynes who had intended it for a conversion, but never installed it. It was fully reconditioned and smartly painted. Cost me £60 IIRC. Bargain!

I always believed that the gearbox was from a Triumph- derived car of some sort - possibly a 1500TC saloon. But it had two oddities. First it had a huge heavy cast iron bell housing - even bigger and heavier than the 1500 Midget one. And secondly it had a longer input shaft.

I swapped in both the input shaft and the bellhousing from my standard 4 speed 1500 gearbox and it then fitted perfectly.

The gearbox and overdrive were exactly the same as a 1500 Spitfire one in every other respect, so maybe that gearbox was from a Marina. But it was definitely an overdrive box, not a 5 speed.

On another occasion, when prowling around a scrapyard, I remember seeing an in-line engine in what I seem to think was in either a marina or an Ital, though it may have been a Triumph saloon. But oddly it had what appeared to be a large external toothed ring gear on the front of the engine! Memory fades and I wish I had taken more notice as to what it was - if only because it was so strange! But in the dying years of BL they did do some odd things to some of their cars!
Guy

Guy,

The 1300 and 1500 FWD Triumph saloon had that arrangement with the starter on the front of the engine, I have the Haynes manual but never had the car. See image.


David Billington

I, too, did the overdrive conversion to my 1500 Midget, back in 1992. Total madness, really. Whilst it's good fun to 'flick the switch', any benefit (derived from the overdrive) to driving/economy is open to debate. (I bought a second hand Spitfire gearbox and overdrive and had them reconditioned prior to me fitting them along with various chassis mods).

To add to the general confusion of the Austin/Triumph/MG gearbox debate, the 1500 Spitfire gearbox has subtly different internal gear ratios compared to the internal gears of the 1500 Midget 'box - the gear cogs are not interchangeable. Either keep the box as a Spitfire version or an MG version.

Andy Hock

A couple of points...

Marinas didn't have overdrive.

The marina gearbox is essentially the same as the Midget 1500, as Andy pointed out. Hoewever, the bellhousings and backplates are different.
Dave O'Neill2

David B - yes that is the odd arrangement engine with the starter at the front that I remembered.

Andy - total madness-why? I found it a very good conversion and in many ways preferred it to my current type 9. The switched and non clutch overdrive was brilliant for driving around twisty lake district roads.

Dave - OK, so if Marina's never had overdrive gearbox couldn't have been a Marina one then. But I wonder what it was from. What about the 1.7 litre Ital then?
It was definitely a Triumph type box, identical other than the addition of the overdrive unit to the standard Midget 1500 box. And then this massive CI bellhousing which was far too big to fit to the Midget backplate. Plus the longer input shaft.
Guy

Yes that is I've always understood things - as Bob said.
Marina box was the essentially same as the Triumph Spit.
It is still a 4 speed though so no real advantage to putting it in a Midget.

If you want a proper 5 speed find a Ford Type 9 and a conversion plate - much smoother.
Bob T

Many thanks for all the information received so far. How much work is involved in changing the box for a Type 9 apart from the conversion plate. I presume the plate goes between the engine and bellhousing of the Type 9. Where would I source a conversion plate?
K Montgomery

Now let me just stir it up a bit.
Datsun/nissan made the A-series engine in licsense including (a modeded?) version of the ribcase.
They continued development on it and have made a 5 speed out of it.
It might have been in their saloon that came out just before the 1602 BMW (oft mistaken as inspiration for it) and is sucsesfull in historic racing in Japan (Indipendant suspetion all around)

How I always read it it might fit... but is only realy available in Japan.

Any more info?
Onno K

K Montgomery,

I not that up on the triumph engined midgets but have seen the conversion details and the adapter plate goes between the original bellhousing and the type 9 box.

I have an adapter plate here that goes between a FIAT bellhousing and a type 9 so allowing a FIAT twin cam engine to be fitted. Would be a nice conversion, easily a superior engine, shame not as plentiful as they used to be.
David Billington

Hmm just checked it out a bit further and the Datsun 310 series got an upgraded BMC A-series called the E-series (to confuse abit they later improved on this and called it the A-series)

This E-series is what BMC should have done with the A-series as it cured all oil leaks and gave about 60bhp from around 1 liter in their slowest single carb form!

But it still showed external resemblance to our BMC lump.
But it was never delivered with a 5 speed.
Only their later A series about 1,5 evolution cycles further (BL had not even thought of the A+) they gained 5 speeds in the 510.
But I doubt these fit without a different backplate.
Onno K

Does this help?
http://www.tooke.org.uk/convert.htm
Bob T

This thread was discussed between 21/05/2012 and 24/05/2012

MG Midget and Sprite Technical index

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