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MG Midget and Sprite Technical - Snail blower in reverse

When I bought our 1965 midget, the snail blower wasn't connected up, so as usual, good weather and nothing better to do, I thought that I'd have a go at it.

When I connected it up,(positive earth) it runs, but in the reverse direction, as it's trying to blow back down the ram air pipe. I've tried reversing the connections but no joy.

Is there any electrically minded person out there with any idea please, as I'm of the "if you cant see it, I cant fix it" type.

Graham

I believe that as the heater blower has a centrifugal type fan, it should suck in the correct direction regardless of the motor direction, (though one way will be much more efficient). Reversing the motor connections should reverse the motor direction.

I wonder if you have a blocked air passage, maybe the heater matrix itself is blocked with leaves, insects etc?

Jim
J Smith

It could have the wrong fan installed. They will physically swap, but the blade orientation is different.
Trevor Jessie

see my last post in the thread called 'Alternator or not?' for ideas, the two main ones have been covered for you by Jim and Trevor

IIRC there's also a John Twist video that covers this too
Nigel Atkins

Assuming the one I have is correct (it came with the car but I have yet to fit it), imagine the blade profile as a capital L. Looking end on, from the open end towards the motor, the L is reversed and the foot runs on the circumference and the vertical leg runs towards the spindle.
Does that make sense?
Graeme W

.... I am referring to the profile of the blade on the rotor, following on from Trevor's comment. Perhaps that wasn't clear.
Graeme W

I think a photo might help
Nigel Atkins

Take the motor apart: the carbon brushes are held against the commutator by little springs and the brushes wear asymmetrically. So after a few years they are too worn to make good contact in the 'correct' direction and the motor stops working but, when the springs have the opposite sideways force, the brushes are at a new angle and so contact is made and the motor runs. this is a very common problem with old electric motors so get a pair of new carbon brushes and your problem could be solved.
N.C. Nakorn

Take the motor apart: the carbon brushes are held against the commutator by little springs and the brushes wear asymmetrically. So after a few years they are too worn to make good contact in the 'correct' direction and the motor stops working but, when the springs have the opposite sideways force, the brushes are at a new angle and so contact is made and the motor runs. this is a very common problem with old electric motors so get a pair of new carbon brushes and your problem could be solved.
N.C. Nakorn

Can you just flip the fan over

Prop
Prop and the Blackhole Midget

Just see which way blows more. That's what I did.

I'm beginning to think it's rare to find one that's turning the right way.
Nick and Cherry Scoop

Mine didn't

it's on a shelf now

I just have the air pipe directed towards the heater inlet hole and it works

This happened because when I fitted the blade fuseboxes and the later pedal box the old fan didn't fit anyway

the heater still warms the car just from the directed air coming through

funny things Spridgets
bill l

Funny that Bill. Mine is on the shelf too because the po fitted a later pedal box which pushed everything over. I shortened the inlet to the box (this is the Mk 1 heater) but found I could fit the casing but not the fan. As long as I keep moving there is a fair old draft!
Graeme W

All this reminds me of a discovery last week.
THe engine was running hot in traffic so I switched on the manual electric fan (it's in addition to the standard fan). The engine got hotter.
It turns out the po had wired it to suck rather than blow so it fought against the mechanical fan rather than worked with it. Brilliant for assisting warm-up in winter; rubbish for cooling in summer.
Reverse the wires - sorted.
I could understand this to an extent if it were intentional, but the po told me how he had fitted the fan because he was worried about overheating!
Graeme W

Nigel suggested photo


Graeme W

I am sure that a centrifugal fan can't "blow" the wrong way. What ever the impeller design the rotating cage is going to spin the air which will move outwards and into the casing and thus through the tangential outlet. THe only difference the blade design makes is efficiency and pressure/flow profile.

It can sometimes be difficult to be sure which way the air is actually going. Did you drop a few small bits of paper into the air flow?

Is the flap valve in the pipework open?
Graeme W

that's a very arty photo, you could get a prize with that

don't drop paper as it could get 'sucked' inside, instead hold a long thin strip of paper close by - or if you're a smoker blow the smoke towards it and see what happens
Nigel Atkins

With all thne crud in there anyway, the odd bit of paper (ok, tiny bit of paper) probably wont make a great deal of difference. Although it's tempting, don't tear the corners of the pages in the Handbook - too heavy!
Graeme W

You're right - it can't blow the wrong way.

But one way is certainly stronger than the other, as your picture makes clear.
Nick and Cherry Scoop

This thread was discussed between 08/06/2014 and 09/06/2014

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.