948 onto a midget gearbox?

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burgundyben
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948 onto a midget gearbox?

Post by burgundyben »

Hi

I bought an engineless 2dr 948, its got a midget gearbox fitted as it had a 1275. I've acquired a 948 engine, will it go on the midget gearbox?

Thanks
philthehill
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Re: 948 onto a midget gearbox?

Post by philthehill »

Virtually a straight fit.
You will need the 1098cc thicker rear engine plate though.
May be better if you used the 1098cc flywheel and clutch assy.
As it has had a 1275cc Midget gearbox fitted the clutch linkage should not need modification.

PSL184
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Re: 948 onto a midget gearbox?

Post by PSL184 »

Yes, but you will certainly need the 1098 backplate, flywheel and clutch assembly.
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burgundyben
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Re: 948 onto a midget gearbox?

Post by burgundyben »

I think I might sell the MG box and buy a 948 box.
PSL184
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Re: 948 onto a midget gearbox?

Post by PSL184 »

I wouldn't.....
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philthehill
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Re: 948 onto a midget gearbox?

Post by philthehill »

If you are prepared to use a bit of forethought, imagination and skill it is possible to mate the 948cc engine to the presumed (needs confirming) 1275cc Midget box without having to purchase a 1098cc/1275cc engine back plate and clutch assy by using the 948cc back plate, 948cc flywheel and clutch assy.
The 1275cc Midget box has a hydraulic clutch release mechanism and reversing light switch on the gear lever housing.
If it is a 1098cc Midget gearbox it will still have the hydraulic release mechanism but no reverse light switch.
The 1098cc/1275cc engine back plate is required when using the deeper 1098cc/1275cc clutch assys to give a bit more clearance in the gearbox bell housing.
The 1275cc Midget flywheel will not fit the 948cc Minor crankshaft but the 1098cc flywheel will so long as the flywheel was not removed from a 10cc prefixed engine as the bolt pcd(s) are different.
As above keep the gearbox and make it fit with a bit of fettling.

IslipMinor
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Re: 948 onto a midget gearbox?

Post by IslipMinor »

The ribcase gearbox is much stronger and has better synchromesh than the smooth case. The later smooth and all ribcase Spridget boxes have closer ratios and the later 1275 ones also have provision for a reversing light switch. All the Spridget boxes use a needle roller bearing for 2nd and 3rd gears on the mainshaft - the non-Spridget boxes use a phosphor bronze bush.

The best way to identify the A-Series inline gearbox is from the input or primary shaft part number that is stamped into the shaft and can be seen within the bellhousing area - the part numbers are in the table below:
[frame]Image[/frame]
The picture below shows the 1275 part number on a box that I sold on eBay recently after 'storing' it in our loft for 30+ years!
[frame]Image[/frame]

Since the 948 clutch is much thinner than the 1098/1275, I would have thought that using the standard thin 948 backplate might work?

The gearbox front cover also has a different height on the ribcase (1098/1275) boxes, so it might be necessary to look at what the best carbon thrust to use?

When I fitted a ribcase to our original 948 engine, I fitted a ribcase front cover to it, but it meant blocking up 2 holes in the gearbox and drilling/tapping 2 new ones to match the 1098 cover. Also used the 1098 release arm, to match the cover, as the pivot bush hole position is different to the 948. A lot of messing about, and I am not at all sure that it was necessary.

It would be good to get definitive options for the backplate and carbon thrust set up for a 1098 box on a 948/803 engine:

Use original 948/803 clutch - is there a simple combination of parts to use?
Use 1098 backplate, flywheel and clutch - would this simply make the 948 into a '1098' as far as the gearbox mounting is concerned?
Richard


philthehill
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Re: 948 onto a midget gearbox?

Post by philthehill »

When I did the conversion (many years ago now) I had to bend the clutch release arm and take some of the carbon out of the top edge of the carbon thrust to allow adequate movement of the clutch release arm.
As Richard says not a straightforward job but with a bit thought it can be done.
It is better with the engine and gearbox out as you may find that a bit of assembling and dis-assembly of the engine/gearbox is required as the working clearances and mechanism are/is determined.
Richard
Many thanks for the list of first motion shafts/part numbers as it has identified the shaft I use (22G172) for centralising clutch plates as being from a Sprite Mk 3/Midget Mk2. The shaft came out of a 1098cc ribbed gearbox that I had fitted to the Minor at one time and which I subsequently re-built. That gearbox was originally taken from a scrap 1098cc Minor which must have been fitted with the Sprite/Midget ribbed gearbox at some time. Very interesting.
Phil

bmcecosse
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Re: 948 onto a midget gearbox?

Post by bmcecosse »

How do you 'know' it's a Midget gearbox -and is it a 1275 Midget gearbox? I don't see a problem using the 948 engine as it comes - flywheel/clutch and backplate included. Just use a 948 carbon thrust and the gearbox won't know the difference...assuming it has already been converted to mechanical operation - has it?
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