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MG Midget and Sprite Technical - Clutch combination conundrum

Hi

is it possible please to use a 1098cc clutch with a 948cc engine that has a smoothcase gearbox? And what components and modifications would that actually mean in terms of flywheel, gearbox housing, clutch cover, arm and release bearing as well as the larger diameter clutch.

Would I be better with a 9 Spring 948 clutch (and eventually the car is going sprinting)? And people who go for smoothcase modified with 1098 gear set (i.e. ratios the same as NLA MkII 948cc Sprite - Heathrow Transmissions do this conversion both with normal gears and straight cut) - what clutch and associated components do they fit?

My reason for asking is that I am trying to understand the range of possible options of what might be in my car without pulling the transmission - the previous owner when I picked the up the car said it had a 1100 clutch but he did not do the work and I knew even less to ask exactly what he meant. I also want to think through what might be sensible to do in the long term (apart from build and install a 1293cc engine with correct ribcase gearbox!).

I am thinking I might have to pull the transmission and fit a new clutch since the clutch pushrod was incorrect (a Mini one) and I may have a bent clutch fork. I just want to know what I might be getting into and what bits I might need. I also do not know what gearbox I have beyond it is smoothcase (hopefully MkII Sprite with close ratio gear set, but could be Minor etc) and cannot identify the clutch arm, gearbox housing or clutch diameter until I pull the transmission.

The clutch worked OK and gearbox too until on test run number 2 last Sunday it dumped all the clutch fluid and looks like the clutch slave has overthrown (I had just replaced a seized slave cylinder and corroded and worn Mini pushrod with a new 7/8 inch slave cylinder and the 'correct' length, ie, shorter, 948/1098cc item). Car has a Sebring Sprite pedalbox with a separate 7/8 inch clutch master cylinder, note this has no stop on the pedal or box itself.

I note some useful info: http://www.gerardsgarage.com/Garage/Tech/TO_Bearings/tobearings.htm

Cheers
Mike



M Wood

Mike,

The smoothcase has inferior syncromesh and is not as strong as it has plain rather than needle rollers for the gears so unless you want to retain originality its much better to go to a ribcase gearbox from a later spridget (not morris minor which has different ratios and has plain bearings for the gears). If you have to pull the engine its easy to change the box at the same time. If you are retaining the 948 engine you will need a later 1098 backplate, 1098 4 bolt flywheel and the later 1098 clutch and release bearing. You mention a bent fork you may need to renew this as well. You can retain the original slave cylinder.
Bob Beaumont

The 948 9 spring clutch requires a mighty push, very heavy in operation.
Alan Anstead is the one you should ask about clutch/flywheel combinations.
Rob
MG Moneypit

No need to ask me as Bob has explained it.
Alan
Alan Anstead

Thanks all, very helpful.

As a follow up, I have just discovered I have a 1275 ribcase gearbox (MkIV Sprite/MkIII midget) in the spare parts pile taht could be rebuilt. How easy is to fit this to the 948 engine, what bits do I need, as well as how desirable in terms of ratios? It would make any possible later upgrade to a 1275 easier.

Cheers
Mike
M Wood

Thick backplate. You may have to sculpt the oil pump body as the hole in the thick plate does not exactly align.
Early 1098 flywheel which has same pcd fixing holes for attaching to crankshaft?
1098 7.25 clutch. Usually cheaper from a Morris Minor Parts supplier.

Your rib-case will satisfy a conversion to 1098 / 1275 at a later date.
This method and parts is as described in the Special Tuning manual for the 948.
I also have a letter dated circa 1976, from BLMC, confirming the parts for the conversion.
Alan
Alan Anstead

Just to add to Alan's helpful advice, the ratios for all the ribcase Spridget boxes is the same as the Mk11 Sprite smoothcase.
Bob Beaumont

This thread was discussed between 09/09/2020 and 10/09/2020

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