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Old 8th Jul 2018, 9:30 pm   #1
Vintage_Man2012
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Default Old British Thomson Houston motor

Hi everyone,

I've ended up with this old BTH motor (single phase).

It does work, but I can see that it is full of crud and needs an overhaul - The problem is, I can't find any obvious way to disassemble it to clean it.

Can anyone on this forum shed some light on how to get it open?

Cheers
Paul
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Old 8th Jul 2018, 10:24 pm   #2
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Default Re: Old British Thomson Houston motor

Usually there are some, typically 2 or 4, through bolts from one end casting through the stator to the other end casting, where there may be tapped holes or nuts. Undo the bolts and take the end castings off, Be careful of the winding connections though, because the terminals may well be on one of the castings, usually the non-drive end. If there is a terminal box on the stator you may not have that problem. Also, if there is a centrifugal switch that will be on one of the end castings
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Old 8th Jul 2018, 10:29 pm   #3
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Default Re: Old British Thomson Houston motor

Yes this motor had 4 through bolts, I’ve removed them but it still doesn’t seem to want to pull apart.

Maybe I need to be a bit more forceful. I wondered if those holes on the side of the casing might have had something to do with it?

Paul
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Old 8th Jul 2018, 11:16 pm   #4
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Default Re: Old British Thomson Houston motor

The end caps may be a press-ish fit into the steel body housing the stator, especially since there's some rust - you may need to tap it about a bit with a soft hammer.

It looks like it once sat on rubber mounts around those circular things at the front (and, I presume, back). Or maybe you already removed the pedestal in preparation for taking it apart?

I have one of these which works, but whose case is unfortunately live. I only found that out when for safety's sake I thought I ought to earth it

(Edit to add - you might do just as well to just blow it out with an air line. I obtained a 1.5hp single phase motor very very cheap once because the centrifugal switch was bunged up with sawdust!).
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Old 8th Jul 2018, 11:28 pm   #5
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Default Re: Old British Thomson Houston motor

I'll dig a rubber mallet out and give it a few taps and see what happens.

If I had a compressor I would try and clean it with a blast of air but sadly it's on my wish list!

Paul
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Old 9th Jul 2018, 9:09 am   #6
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Default Re: Old British Thomson Houston motor

The castings should be a good snug fit to the stator, so add some intermetallic corrosion between the steel stator and the aluminium castings they could now be quite tight by now. Apply some thin oil to the joints and wait a few days may help. Don't forget that a couple of the through bolts refitted loosely (if they are long enough) may stop the thing falling apart if/when somat moves suddenly
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Old 9th Jul 2018, 10:09 am   #7
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Default Re: Old British Thomson Houston motor

Before going much further, scribe across the stator ends to casing, two marks one end single the other, don't use a centre punch as you may crack the alloy casing. These marks will help you to re assemble the motor so that you can spin the shaft by hand as you tighten up the 4 through bolts. Insert two bolts opposite to one another and tighten a bit a time. Be careful when the end shield do fall apart as the wires are very small and are easily broken. You have to wriggle around to get the through bolts to pass through the stator. Don't use compressed air to remove any dust etc you only blast it further in and most compressed air contains water unless fitted with a water trap, use a vacuum cleaner and a clean paint brush. Finally DON'T lay the stator on its windings on your bench, that's a sure way to ruin a good motor. Ted
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Old 9th Jul 2018, 11:37 am   #8
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Default Re: Old British Thomson Houston motor

It looks like it once had an "M" shaped bracket bolted to the stater in those 4 holes.
There also appears to be the remains of a spin drier brake on the output shaft.
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Old 9th Jul 2018, 11:52 am   #9
emeritus
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Default Re: Old British Thomson Houston motor

You could try putting it in the fridge or applying ice to the ends before attempting to dismantle it. I believe that light alloys have a greater coefficient of thermal expansion than iron and so would possibly be a force fit at the high temperatures we are currently experiencing. Cooling it down should make the alloy shrink more than the iron. When I used to do my own car maintenance, the piston and crank had to be heated to about 150°C in an oil bath to allow the gudgeon pin to be removed from the piston. At room temperature there was negative clearance and it was impossible to drive out. At 150°C the pin fell out under gravity.
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Old 9th Jul 2018, 12:11 pm   #10
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Default Re: Old British Thomson Houston motor

Hello,
These motors often have ball bearings at each end and if this is the case they are usually a light inteference fit on the shaft and in the bearing housing so you may need a bit of force to remove the end covers.
Yours, Richard
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Old 9th Jul 2018, 12:14 pm   #11
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Default Re: Old British Thomson Houston motor

If you have got a 3 jaw hub puller it should come apart easily.
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Old 9th Jul 2018, 1:13 pm   #12
Vintage_Man2012
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Default Re: Old British Thomson Houston motor

Thank you all for your comments, I will have a go later when I get home from work and try some of the methods mentioned. I have a 3-jaw race puller somewhere in the workshop, I'll have to dig it out.

From what I can gather, the end-caps should pull apart from the central body which is shown rusted?

The four holes contained the through bolts which I have removed, there was a bracket for mounting it, probably to a lathe or similar but I've already removed this as it was terribly rusted.

Thanks again for your help!

Paul
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Old 9th Jul 2018, 1:19 pm   #13
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Default Re: Old British Thomson Houston motor

A hammer and block of wood would be an alternative if a rubber mallet won't shift it.

Peter
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Old 9th Jul 2018, 1:59 pm   #14
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Default Re: Old British Thomson Houston motor

Faced with this problem I'd tap an old screwdriver into the gap twixt frame and end plate, gradually working my way round.
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Old 9th Jul 2018, 3:02 pm   #15
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Default Re: Old British Thomson Houston motor

Back again, using a hide faced mallet give the stator casing a good sharp rap and it will fall apart. As I said previously, be very careful as you remove the non drive end which has the centrifugal switch and wires attached to the stator winding. The switch is awkward to remove and they don't normally give much trouble. The centrifugal switch operating gear is attached to the rotor, providing the spring are OK leave well alone, it/they should be left dry, no oil which collects dust and jams things up.Usually the cheap motors have phosor bronze bushes in place of ball bearings, a few have a bearing at the drive end. If all else fails resort to Graham Station X above. Done the job many times. Ted
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Old 9th Jul 2018, 10:14 pm   #16
Vintage_Man2012
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Smile Re: Old British Thomson Houston motor

UPDATE:

Thanks to the good folks on this forum and your help and advice, tonight I managed to crack open the old BTH motor and give it a good clean.

I've reassembled it for now, mainly to protect it but in due course I will give it a paint job and replace the rusted dome nuts with some new brass ones.

I've attached some photos for anyone who's interested.

Again, my thanks to everyone who offered advice and help!

Paul
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