Gearbox

[claymanhotshot]

Hi, my roadster has an mgb engine but I dont think the gearbox is mgb. To put it in reverse I have to lift, move right, then forward. Am I right in thinking it is a marina gearbox? or what other gearbox could be compatable? I would one day like to change it to one with overdrive if I could.

[stevejgreen]

Re: Gearbox

MGB and Marina engines are very similar.
MGB has an electric fuel pump, Marina mechanical.
There are other differences but difficult to say without pictures.
MGB gearbox has an integral bell house. The Marina has a separate gearbox and bell housing.
The MGB clutch slave is bolted to the casing the Marina slave simply slips through a cast hole on the near side.
I cant remember the MGB gear shift but what you describe is standard Marina.

Overdrive gearboxes for Marina engined cars are limited to Dolomite overdrive, though there are other possibilities most of which are discussed on the forum.
You could also fit a back axle with a higher ratio to get a similar result.

My roadster is unusual as I have married a Ford Type 9 gearbox to a Marina bellhouse. A fairly easy mod and details are available at 5speedmarina.com.

[greggpearson]

Re: Gearbox

The small MG Midget I had (MkIII) had the Marina Gearbox and it was as you described, nice close ratio and movement though.
Gregg

[gaddbrose]

Re: Gearbox

Hi Gary. If you are interested, I have a spare engine and gearbox, complete with overdrive, sitting in my garage,and getting in the way. They were spare units for my daughters MGB.GT, but were never needed as the car has long gone. They will need some work, and their condition is not guaranteed, but they are available if wanted as I shall never use them in the Berli.
As a final comment, there are differences between the MGB and the Marina engines, the MGB haa a 5 bearing crankshaft as against the Marina 3. That made it a smoother , better balanced engine, and there will be others. contact me if interested, no. 01453 542135. Brian.

[lil_red_roadster]

Re: Gearbox

Sorry to have to correct you Brian but the Marina was, to my knowledge, NEVER fitted with a 3 brg B series engine. It was only ever fitted (in petrol 1.8 form) with the 18V engine which were all 5 bearing units. By contrast the MGB was initially fitted with a 3 bearing crank, only later moving a 5 bearing.

Peter Burgess, the renowned MGB tuner has even stated in print (Tuning the B Series) that early cranks from Marina 18v engines were the best balanced of all the B series crank types he'd encountered.

[stevejgreen]

Re: Gearbox

This started as a gearbox question and seems to have deviated.
The later Roadsters used Morris Marina donors so it is likely that his engine looks MGB but is infact Marina.

If Gary can find the engine identification plate up near the alternator we can be a bit more specific.
Engine numbers 18G and 18GA are three bearing MGB engines. These engines were phased out in the early/mid 60's, ten years before the Marina was introduced.
All other numbers 18GB,18GD,18GG,18GH,18GF,18GJ,18GK are five bearing MGB
All the Marina B series engines are 18V engines with five bearings.
MGB cranks were all forged but the Marina ones were cast. There is little to choose between the two. It is often thought that late model MGB's used cast cranks.

So Gary if you have a 18G??? its an MGB engine and probably gearbox but if its 18V??? its a Marina engine and probably gearbox.
I say probably because over the years MGB and Marina engines are pretty much identical. The most significant difference between them is the backplate, flywheel and clutch and it may be that a B Series has been rebuilt and moved from car to car.
So Gary assuming you actually have a Marina engine and gearbox you really only have the option of fitting a Dolomite Overdrive box or changing the back axle to a better ratio for modern road speeds.
That is unless you fancy fitting a Type 9.

[donsayers]

Re: Gearbox

Your gearbox sounds like a Marina one to me. Earlier versions of the 18v MGB engine had some differences to the front end as well as the crank and flywheel, the timing cover was different and hid a duplex timing chain, Marinas did not have this, the fan belt pulley was bigger too.

Later MGB engines and Marina engines were virtually identical.

The Marina gearbox is very variable in quality, some have simply appalling gearchanges, and the synchro on third is fragile. If you actually use the synch on first to engage first whilst you are moving you will eventually strip all the teeth off the reverse ring as well.

A good Marina gearbox will have a good shift but don't expect it to last if you use it with gusto.

[stevejgreen]

Re: Gearbox

This is where the forum lets us down because you cant edit previous posts.
I started writing this before Don posted so excuse the time warp...

Don is absolutely right but what I missed off my post was that 18V engines were used in an MGB post 1971 if I remember correctly. These had simplex timing chains fitted like the Marina and I guess the cast crankshaft.
All previous MGB 18G?? engines were duplex timing chains.
So it is possible though unlikely that Gary has a post 1971 18V MGB engine and gearbox.
Having said that, I would guess that many 18V engines, like mine, have been modified to fit a Duplex timing chain as it is a simple parts swop, the timing cover will accept the new wider gear so again there is no certainty as you cannot see inside.

But all this become irrelevant as I have just been reminded that on MGB gearboxes post '68 reverse was to the left and backwards the opposite of a Marina. Pre '68 MGB gearboxes were 3 speed.

So Gary, you inevitably have a Marina gearbox and all that Don says about them is absolutely valid.
Generally parts are readily available and in a recent copy of the Morris Marina Owners Club mag Understeer there is an article about rebuilding Marina gearboxes.

But....
I have just looked in the classified adverts on this site and there is a Dolomite overdrive gearbox for sale, though it might have gone by now!

[danny_nelson]

Re: Gearbox

I have an overdrive gearbox from a Marina based roadster available, complete with prop etc etc.
Danny.

[claymanhotshot]

Re: Gearbox

Hi, thanks everyone for their help, it is much appreciated. I haven't had chance to fully check out and see if the engine is mgb or marina. But will get to the bottom of it this week. The person I bought it from said the engine is mgb but others think it is marina.
Im assuming mgb and marina can take the same gearboxes?
So to fit a type 9 or a dolomite gearbox I will have to decide.
What gearbox is the one you speak of Danny?

[danny_nelson]

Re: Gearbox

Hi, It is a dolly box and it was mated to a MarinaTC 1800.

[Pierre_Smits]

Re: Gearbox

Danny: Do you still have the Marina 1800 engine available as well? if so, we maybe could work something out as my connecting rod came through the engine last weekend making a 6 cm hole on the side near the oil filter:-(
And the dolly box could replace my 4speed marina box...
let me know: marlinroadster [at] gmail [.] com
cheers Pierre

[claymanhotshot]

Re: Gearbox

My engine is marina! the number starts 18v.
So Danny I would be interested in the box. My marina is a swb so would your prop fit? And what condition is the gearbox? Thanks Gary

[stevejgreen]

Re: Gearbox

That's that one sorted now then. There are no significant internal differences between an MGB and Marina engines but many of the ancilleries like carbs, distributors, clutch etc vary, though in some circumstances parts can be swapped between the two.

Two sources of Dolomite gearbox, one with a prop, seems to answer all the problems.

All that remains is for someone to persuade Gary to join the Club and buy a complete set of TechTips, that includes several articles on Dolomite gearboxes as well as overheating issues.

[danny_nelson]

Re: Gearbox

Hi, send me an email after Wedensday please.
Danny.