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MG Midget and Sprite Technical - Wiper Wheel Box Differences

Hi folks,

I have done some searching on this, but would like some confirmation.

There is a difference in the wiper wheel boxes between early and late systems, right? The early wheel boxes have a smaller internal cog, which is then matched to the earlier square type motors?

Coupling a later round motor with earlier wheel boxes would cause the wipers to over-sweep onto the scuttle, right? (The later round motor having a larger linear throw to match the larger cogs on later wheel boxes, when coupled with the smaller cogs in early wheel boxes results in too much angular motion as the cog circumference is smaller).

Cheers,
Malc.
Malcolm

On later style, there is a number stamped on the crank disc which gives the angle of sweep. It's a useful modification to swap this with one with a greater sweep ( I think mine came from an Austin 1100) which gives a better overlap between the sweep of the blades and clears the screen better.

I don't think using the smaller wheelbox cogs will impact on this, but maybe it would give a faster travel to the wiper arm?

I think Daniel Stapleton's book explains all.
GuyW

ETA: Guy got there before me, I think the motor gear wheels differ a lot between square and round, might be info on mgb-stuff website.

Malc,
I think there might also be other differences perhaps(?), do the boxes have different length shafts(?), the bezels might be at different angle for the much earlier screen(?).

The gear wheel in the motors vary so, as you say.

I think the rack wires are the same and possibly across a range of BMC?BL cars(?).

Not certain but others can give details.
Nigel Atkins

Having not so long ago rebuilt systems for both my Frog and my '71 car, I am not sure, but think the rack wire for both would work with either type of wheelbox. The stroke of the cable would depend on the choice/ combination of motor and crank at the other end but for the same stroke, the smaller cogs would turn through more degrees.

The angle of the wheelbox spindle through the scuttle is determined by the inner spacers and outer chromed bezels. They are definitely interchangeable, but as pairs. There are at least two different angled sets.
GuyW

Clear as mud :-) Thanks Nigel and Guy.

The situation is this: a mostly 1964 car has been bodged together with a later round body motor with 125 degree gear inside the motor. (I know about swapping these, I did it with mine. I can't remember from what to what though).

But the wipers sweep more like 180+ degrees so shoot off down the scuttle and bonnet!

What Guy says "The stroke of the cable would depend on the choice/ combination of motor and crank at the other end but for the same stroke, the smaller cogs would turn through more degrees." agrees with what I was thinking.

Round bodied motors I think have a longer throw so have to be matched with big cog wheel boxes.

Square motors have a short throw to match with small wheel boxes.

Round motor (long throw) with early (1964) small wheel boxes = too much sweep. That is the conclusion I have come to anyway.

Their wheel boxes are knackered anyway. The wiper arms had been sort of "glued" on with epoxy by the PO... I say sort of as they hadn't mixed in the hardener so it hadn't set! This is the level I am dealing with... :-D

Rack part numbers are the same across all years, so at least that can be reused.
Malcolm

I think you've got it, mix and non-matching gearing.

What about moving the windscreen 4" to the left. :)

Round motors have 110 degree sweep which isn't really enough as I discovered, the driver's side wiper doesn't oversweep the middle bit where passenger's side stops, I think Guy uses 115(?) degree.

The square gear and shaft looks to be 150 degrees.
Nigel Atkins

Malc

Is 'your' 1964 car a MkII Sprite (or MkI Midget), i.e with a Frogeye type flat screen or the curved screen of a MkIII Sprite/MkII Midget? 1964 is a change over year IIRC.

If MkII Sprite can look up part numbers.

Mike
M Wood

Thanks Mike, but it is a curved screen car.
Malcolm

Does the owner want a square body motor Malc?
David Smith

Thanks for the offer David, I have advised they get new wiper wheel boxes as the old ones have no splines left on them anyway.

It's the path of least resistance.

Malc.

Malcolm

The gear inside the wiper motor can be changed to modify the sweep. This is easy to do if the motor is out of the car. AFAIK the wheels fit both types of motor.
Dominic Clancy

This thread was discussed between 13/10/2020 and 15/10/2020

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