1275 MG Midget engine and gearbox

[Murrayminor]

Hi all
Apologies in advance for the lengthy post and numerous questions that follow.

I have previously asked a question in relation to fitting different rear axles and gearboxes to my Morris Minor and obtained some very helpful responses, so I made the decision to fit a 5 speed ford "rocket" box behind my 1330 MG Midget engine.
I sourced a suitable box and had laid out a deposit on the box when I discovered a flaw in my plan.

My intention is to use my minor for Production Car Trials and also long distance classic car trials, so if I was to fit the ford gearbox it places me in the modified class and up against the proper modified trials cars and therefore would make the minor completely uncompetitive.

Rather than buy a suitable vehicle to run in the modified class I have made the decision to stay in class 3 (front engine, rear wheel drive).
So I have had to give up on the idea of the "Rocket" box and instead stick to the Midget gearbox.

The Midget box is slightly stronger than the 1098 box I currently have, so I pick a 1275 midget box up next week.

Questions I have before I pick the 1275 box up:

Do I need to run the 1275 Flywheel and clutch or use the 1098 flywheel and clutch? ( I have both a 1275 and 1098 flywheel at my disposal)
Will I need to modify the clutch to hydraulic and if so do I need a different release bearing and arm?
Can the mechanical clutch be made to work on the 1275 gearbox or not?
Is there anything else I can search for whilst I'm surrounded by Mg Midgets to assist in the fitting of the 1275 gearbox to the minor, I'm thinking brackets, mounts etc.

I believe from research the conversion is fairly straightforward but the clutch issue is mentioned a lot of times I just wanted a definitive answer.

My next question relates to the gearbox internals, my intention is to rebuild the 1275 gearbox and wondered if changing the Helical gears to straight cut is worth the effort?

Again from research the straight cut gears transfer the power more efficiently but are no stronger than helical gears, will the straight cut gears offer me any benefit bearing in mind the car will occasionally be driven on the road on the longer events (I'm thinking straight cut gear noise).

I'm going to collect the 1275 gearbox next Monday so I will no doubt have more questions when I return.

Thanks

Dermot.

[philthehill]

If you have a 1275cc Midget crankshaft you will need to use the 1275cc Midget flywheel and clutch assy.
The Minor mechanical clutch linkage can be used but makes the clutch very heavy. You can get over the heavy clutch somewhat by lengthening one of the relay shaft arms.

img150.jpg (133.63 KiB) Viewed 1430 times

You will need to use the 1098cc Minor clutch release arm with the 1275cc thrust bearing if you retain the mechanical linkage.
Use a poly or plastic bush in the chassis leg mount as the rubber bush will not last long.
Make sure that you have the correct gear lever for the 1275cc Midget gearbox. Also make sure that you obtain the 1275cc Midget clutch release lever as you may want to fit a hydraulic conversion at a later date.
I would suggest that you stick with the helical gears for now. A SC/CR Midget gearbox is very noisy.

It is most important to note that the weak point in the Minor transmission is the half-shafts. They will need to be upgraded to stronger ones.

[Murrayminor]

Phil

Thank you so much for your advice, and indeed the advice you provided regarding the rocket gearbox, which sadly I cannot now fit, I appreciate the time you took to find the correct information,thank you.

With regards to the above I will be visiting an MG Midget enthusiast who apparently has a number of gearboxes in his garage amongst other things so I will obtain the Midget gear lever and midget clutch release lever as pointed out by yourself.

I think I was going along the same line of thought with regards to the straight cut gears and the noise they emit, so for now I will stick with the helical gears.

I also see Peter May Engineering have some competition half shafts for sale, they are a not cheap but hopefully they will be plenty strong enough to take 70-80 bhp.

I will of course let you know how things progress.

in the meantime here is a taster of what my minor will be up to once built.

https://www.youtube.com/watch?v=d5wNLyMCe74

skip forward to 7:55 for the 4 wheel trials

Regards

Dermot.

[philthehill]

You will not regret installing stronger half-shafts even at that price.
Many thanks for the clip.
The Marlin is a very good car for trialing as can be seen in the clip. I have seen several being used in the Lands End Trial. Very similar to the Minor but has the advantage of the engine behind the front axle.
Phil

[Murrayminor]

Indeed the Marlin is quite a capable vehicle in trials, had I gone down the Rocket gearbox route I would have been competing against them, hence my reason to stay in class 3.

Weight distribution is an area I need to research, so the battery will live in the boot alongside the tyre compressor and tools, not to mention the spare wheels, which may find a home on a frame outside the car on the boot lid.

Yes the half shafts are expensive but hopefully they will give me peace of mind and one thing less to go wrong.

Regards

Dermot.

[philthehill]

The problem with the Minor is that the engine block is in front of the front axle which does not help with getting the weight down onto the rear wheels.
My battery and radiator where transferred to the boot especially to counter the rotational forces around the front axle.
Nic Mann put a length of railway line into the boot of his Minor to keep the back down.

[Murrayminor]

The problem with the Minor is that the engine block is in front of the front axle which does not help with getting the weight down onto the rear wheels.
My battery and radiator where transferred to the boot especially to counter the rotational forces around the front axle.
Nic Mann put a length of railway line into the boot of his Minor to keep the back down.

I was going to plate the boot floor over to add some weight to the rear and also fit a steel fuel tank guard plus the battery etc.
Nic Mann had a bit more power in his Minor from his V8 than I will have from my A series so I may not get away with a railway line.