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MG Midget and Sprite Technical - Wiper motor - Frogeye

Yesterday I rebuilt my non-working Frogeye wiper motor. I'm quite pleased with myself, given the cost of reconditioned exchange ones from the usual suspects at over £200+!!

The reason it wasn't working was the field coil had shorted and melted so I stripped it down, counting the number of turns of copper wire and then hand wound a coil with new copper wire.I also replaced the wire from the brushes to the copper sweeper on the gear housing that functions as the mysterious self park mechanism. Why mysterious? - well it always seems magical to me that the wipers will continue to operate after the power has been switched off! Spooky!

All seems to work fine though I am yet to locate the 3 outer tube sections for the cable rack. They will be there somewhere, lurking in a box in the depths.

One thing I hadn't noticed before is that the wiper motor position differes from the later cars. On my '71 car it is between the blanked off LHD pedal box position and the wing. On the Frogeye it is inboard of the blanking plate. This means that the rack cable turns through a sharper angle as it goes through the bulkhead grommet and I now wonder if that might put more strain on the whole wiper operation?
GuyW

I'm impressed Guy! Sounds quite laborious. Fortunately, I found mine worked so just cleaned and re-greased it.
Bill Bretherton

Guy,

Good going, even I might baulk at rewinding the field coil. Regarding the mystery of how it works when I rewired my Sprite from scratch the wiper was the only thing I got wrong and then worked out that the frogeye motor is permanently supplied with 12V and the dash switch connects the motor to earth as does the park switch to allow it to carry on running until it reaches the park position. IIRC later motors are different.
David Billington

Not really laborious Bill. I had a reel of the right guage copper wire in stock and winding it only took about half an hour including soldering the ends!

I didn't think much about it at the time, but when I was rebuilding the shell. I found the top of the n/side footwell had splits in it, between what I now appreciate were the wiper mounting holes. I welded up the splits and thought that was sufficient. But maybe this is a known fault? With the stress from the sharply turned wiper rack is that what caused the fractures? Maybe I should have added some extra reinforcing under the panel when I repaired it. Bit late now I think!

Ah David! I had worked out that it is switched to earth, but don't destroy the magic!
GuyW

Yes it is tight through the bulkhead grommet but it seems to work ok. The trick is to assemble the wiper rack, including the wheelboxes loosely in the car together with the motor. The wheelboxes and the clamps to hold the rack tubes can be adjusted so it all works smoothly before finally tightening it all up. I have found in the past that this has not happened and a strain is put on the rack tubes and the wipers do not operate smoothly. I have seen a crack in the bulkhead when this happens. Its best to do this before the dash is fitted so you can get to everything easily.
Bob Beaumont

Yes Bob, that is how I have set them up in the past to get the line of least resistance for the rack tubes. But my point is that by moving the wiper motor position further out, as in the later cars, the angle through the bulkhead is much flatter and reduced quite considerably when compare to the line that it takes with the Frogeye arrangement.

It implies to me that a problem had been identified, possibly with fracturing occuring with the footwell panel top as had happened with my shell.
GuyW

Hi Guy I never seen a crack in the footwell top. It could imply the rack has not been installed correctly or perhaps the wiper mounting rubbers had become hard?? I guess no harm in changing though. May need a longer rack cable.
Bob Beaumont

Very possibly Bob. When l said l had followed your alignment method in the past, l didn't mean on this car, but on others. This one could well have been badly fitted. The footwell top wasn't just cracked, it was also rippled but with no evidence of this being caused by impact accident damage. So l think it was just the wiper motor. They are quite torquey and with quite a lot of leverage on the 3 mounting pegs.
GuyW

Cool Job, Guy. Do you have to use lacquered wire to rewind the coil? Did you happen to take a photo?

Charley
C R Huff

Sorry Charley, I didn't photo the coil before I reassembled it. And yes, the copper wire is pre-coated.

Some years ago I rewound the coil on my spot welder which was a much harder job as the wires needed to be wound very neatly and packed down in layers to get the right number of turns to fit in a tight space. On this much smaller coil there was more space and plenty of clearance for the rotating armature. I would not have attempted to wind an armature though!
GuyW

Thanks Guy,

I was kind of wondering if you had ever done an armature. I've got a generator on a Triumph motorcycle that has, I believe, a shorted armature.

Charley
C R Huff

Charley, if I had one to do I would probably give it a go as there is nothing to loose. To me, the problem with winding an armature is making good connections to the commutator, and also keeping the thing in balance.

There are firms who rewind electric motors. Presumably they would do a triumph one?
GuyW

It's the almost inconsequential things that trip me up!

I ordered some new mounting rubbers for the wiper motor - the old ones being no longer of this world.

The rubbers are small donut things with a deep groove around their equator and are supposed to fit half below and half above the footwell top plate. But how on earth does one install them like that? They just look too fat to get anywhere near squashing down through their mounting holes.
What's the trick with these?
GuyW

similar fashion to a grommet; rubber grease or washing up liquid, and a couple of old blunt screwdrivers.
David Smith

I wonder if you could use the windscreen rubber technique?

Wrap a couple of turns of string around the groove, feed the free end through the hole in the panel and pull the string to try and feed the rubber through the hole, while applying pressure to the rubber.

You may need long arms, assuming the 'screen is already fitted.
Dave O'Neill 2

Ok, l will persist. As long as it is achievable. The ratio of overall external size to hole diameter is much greater than a normal grommet though. The string idea may work - and the screen is not yet fitted!

I half expected the advice to be that you don't fit them like that, and they are supposed to be sliced through the groove with a razor blade and fitted in 2 parts.
GuyW

Well, just to confirm, those wiper mounting rubbers do go in with a bit more forcefull pesuasion than I had tried yesterday. Screwdrivers, rubber lube and string!
Oh, and windscreen wouldn't have mattered because is easier anyway to work through the LHD pedal box blanking plate hole. Thanks for the help (again!)
GuyW

Place them in a cup of hot water until you are ready to install. They will soften up enough to make installing easier. Note I said easier.
J Bubela

This thread was discussed between 23/02/2018 and 04/03/2018

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