Morris Minor Owners Club

Will a 1275cc engine with backplate fit a 1098cc gearbox

Yes, if it's a 1275 MG engine and backplate........

If you are using the MG diaphram clutch then you need to modify the clutch linkage

The only small issue is that the top dowel pin, right at the top of the place where box meets backplate, is a slightly different size on the 1275. I can't for the life of me remember which is which. Chances are that the 1275 dowel is lathed down so that a 1098 box will fit a 1275 engine but if you do it the other way round you will need to drill the hole in the gearbox casting oversize.
Might make it a teensy bit more of a struggle to get the engine in the car if the box has stayed in. The dowels are the same size on both engines at the 'forwards' end where it slips into the block and are only different on the bit that stands proud of the backplate.




Go on, ask me how I discovered this...

Just swop the dowel..........

If you are using the MG diaphram clutch then you need to modify the clutch linkage

Mike,

I have seen this comment before, but don't really understand why it is required? We have a 1275 MG engine, with the Midget diaphragm clutch and are using the standard Minor clutch linkage. It works very well, and if from memory the suggestion is to lengthen an arm to reduce the pedal pressure, I would be very concerned as our clutch disengages quite close to the floor as it is. We do have 10mm sound deadening material, carpet and overmats, so maybe a little less pedal movement than original? The clutch is very easy to operate, so am not sure why it needs to be changed?

I found when fitting the standard 1098 clutch linkage to the MG1275 diaphram clutch that the result was a very sharp and heavy clutch action, OK for motorway driving but tireing in commuter traffic. I found that by lengthening the pedal lever on the relay shaft by 1in pedal movement and weight was restored to almost normal. An added refinement was to use a roller bearing thrust bearing.
Perhaps we could meet up some time to compare as I am fairly local, Reading.

Hi Mike,

Yes that would be interesting. I tried a roller bearing, but it did not work at all well in conjunction with the Toyota gearbox conversion. I had to remove the thrust plate from the clutch cover, so that the bearing engaged directly on to the fingers, but the support for the release arm is not as sturdy as the standard Minor setup, so I ended up with quite a lot of noise on disengagement and very quickly worn clutch fingers! Very soon reverted to the standard carbon thrust and no more problems.

I do wonder if some of the clutch disengagement movement could be lost as I cannot fit the rear restraint cable with the Toyota gearbox? It does have the head to bulkhead tie.

You did not mention the Toyota box. My system is for the 1098/1275 box

Mike,

The Toyota conversion uses the standard Minor clutch operating mechanism all the way through - pedal, linkage, cross-shaft, release arm and carbon thrust, everything.

It's the mounting for the release arm that is not as well-supported as the A-Series box, and so does not limit the sideways movement as well - hence the problem with the roller bearing squirming about on the plain fingers. If the carbon thrust moves about it doesn't cause any noticeable problem.

can u use the 1098 clutch

I would think so, but with a shallower carbon thrust as the 1098 clutch is much bigger and projects further out from the flywheel face. You would need to try the whole engine/clutch/gearbox assembly together before committing to installing the engine in the car. Do you have the Toyota conversion kit or are we talking about different things?

Standard 1098cc ribbed gearbox with 1275 cc MG engine to replace a 948cc set up.

1275 clutch face is smaller than 1098

The rocker box on the 1098cc has a breather pipe in it but the 1275cc MG engine is blank can I use the 1098cc breather system on the 1275cc so the engine still looks the same

can u use the 1098 clutch

On the question of clutches, the 1275 flywheel is different to the 1098, it uses a 6-bolt fixing to the flywheel, against 4 for the 1098, and the 1275 clutch cover bolt fixing pattern is different as well. Why not use the standard 1275 flywheel and clutch? The 1098 and 1275 clutch heights are different, but the same gearbox front cover part number is used for both the Midget 1098 and 1275, so the 1098 gearbox should fit OK. Make sure that you use the 1275 carbon thrust, which is deeper to compensate for the shallower clutch cover.

The 1098 and 1275 Midget boxes are both stronger than the Minor (different gear helix angles (1275) and both had needle roller bearings on the mainshaft gears) so the life of a Minor gearbox on the back of a 1275 engine might be a bit less than normal?

What carburettor and manifold are you going to use? The 1275 Midget engine is designed for a 'closed' crankcase ventilation system and uses a connection from the timing cover to a port on the carburettor(s). No other vent connections and nothing open to atmosphere, which is why the rocker cover vent was deleted, as it was on the later 1098 engines with the PCV and closed system.

The 1275 timing cover has an oil trap built into it, so that oil is not sucked into the engine along with the fumes!

None of the rocker cover vents had an oil trap, and were never used as part of an OE closed system. The feed from the rocker cover into the air cleaner is not a closed system - there was still an open vent from the tappet cover.

Since the later 1098 engines did not have a rocker cover vent, you could still be keeping the original appearance intact!

standard 1098 carb and air filter

The standard Minor HS2 and filter are much too small for even a standard Midget 1275 engine. I'm not sure that you could ever get the needle/mixture close to right?

You will need at least a single 1.5" SU to make it work at all. If you use the HIF type (HIF4 or 38 for standard, or HIF6 or 44 for modified) they come with the crankcase ventilation connection for the timing cover. Metros were fitted with them.

It will work with the smaller carb - but the power will be restricted to pretty much the 1098 output - since the carb on that engine is the limiting factor anyway! And yes - just keep the vent on the rocker cover - I can never understand why they eliminated it. You can't ever have too much breathing on a 1275 engine. Some put a 1" diameter breather into the rocker - for competition use.