Replacement of the rotor gear in a Sankyo sealed can motor

[Johan de Jong]

The Sankyo “sealed can / Telechron style” motors are known to be unreliable and hard to repair. They often stop working due to old dried out lubrication or a broken gear.

Earlier I did already find out how to open up this type of motor for service, see: Sankyo sealed can motor repair. This made it possible to properly lubricate the gears.

But a broken gear was still end of story. The gear that usually fails first is the tiny gear on the rotor axle. This is made of a brownish plastic that deteriorates over time and becomes very brittle. Triggered by this post I thought it might be possible to replace that gear. To execute on that idea I first waited for a broken motor where the gear was still intact, so I could determine its dimensions (and now I was onto it, did the same for a Tamura motor):

• Sankyo: module 0.16, 16 teeth, bore 1 mm, height 3 mm
• Tamura: module 0.2, 12 teeth, bore 1 mm, height 2 mm

Note that I determined these dimension from 50 Hz motors. I expect this gear is the same for the 60Hz version, but I’m not entirely sure about that.
I ordered a couple both of these gears from kkpmo.com and then had to wait for a motor with a broken gear. I did not have to wait for very long, as last week my Sankyo 401E stopped working.

The old gear had was easy to remove as it was so brittle. After the gear is removed the rotor can slide outwards far enough to insert the new gear. (The axle cannot be removed entirely as it has a section with a ribbed profile to hold the gear).



To make the new gear fit the axle I had to slightly increase the bore hole using a 1.0 mm drill. I first pushed in the rotor and then used a screw driver to move the gear a bit further up the axle. Here is the new gear in place:



The clock has been running happily for 24 hours now, and I’m pretty confident it will do so for a long time!

All and all this is quite an easy repair. Removing the seal is still the most work, but if you’re lucky that can go quickly as well. BTW: I don’t bother anymore about sealing the case anymore. The lid fits tight enough to not let any oil leak and it makes it much easier to open up again for service if needed.

[gschmidt958]

That's fantastic that you were able to specify and order a replacement gear. Congrats on getting it to work again!

Do you think that will work in general for any clock geartrain that has a broken gear?

Greg

[flipoclock]

I have yet to find the time (and patience I suppose) to actually crack open one of these without damaging it too much, but this is really good stuff, thanks for sharing it Johan!

[Johan de Jong]

Do you think that will work in general for any clock geartrain that has a broken gear?

Greg

In principle, yes.
I have successfully replaced gears in motors/gearboxes from Copal, Sankyo Intermatic, Kundo, an early Copal 101 and a few others.
Since the number of these motors in the world is limited, I feel it is better to fix a motor if I can than to replace it

[gschmidt958]

That is very encouraging, you are making me think that I (and others) should consider repairing their gear trains this way. Do you have any information on how to go about doing this? I imagine that a bunch of spec's would need to be determined. Size, number of teeth, depth of teeth, pitch, pressure angle, center hole diameter, etc. It seems like that might be tricky to get right. Perhaps maybe some of these are standard for Copal gears.

Thanks,
Greg

[Johan de Jong]

Determining the correct dimensions can be difficult indeed. But for most motors/gearboxes it is always the same gear that breaks and for these the dimensions have already be determined. See the links in my previous post.

In case you need to the dimensions of a different gear, here is how I would go about it:
The things you need to determine are:
- number of teeth
- module
- thickness
- bore diameter

The number of teeth you need to get exactly right (or the clock will not run at the right speed). What helps is to take a picture of the gear, enlarge it on a bigger screen and do the counting there. On one occasion there was too little left to count the teeth, so I had to use a workaround: determine the in and outgoing rpm of the gearbox, count the teeth on every gear in between and then calculate the missing parameter (see this post).

The module is a measure for the size of the teeth. You can determine it from the number of teeth and the outer diameter of the gear using an online tool like this one: https://www.technobotsonline.com/gea...alculator.html Sometimes this does not give a definite answer. Then I go to kkpmo.com and look through the different gear modules to find one with an outer diameter (OD) that is closest to what I need.

Thickness (or height or width it is sometimes called) can simply be measured by a caliper.

Bore diameter can best be determined from measuring the diameter of the axle using a caliper. If in doubt I order the small one and then make it fit using small drill bits (1.0mm, 1.1mm, 1.2mm, etc) or a needle file.

Nowadays I buy the gears at kkpmo.com. They deliver excellent quality for a fair price (I know I'm repeating this every time, but no, I don't have shares ). In the past I also sourced them from AliExpress and other sites on the internet. If you're lucky you can find one there and much cheaper, but it is very hard to find the correct size. 3D printing the gears is not yet an option at this scale.

[gschmidt958]

Thanks for the detailed info, I might try it! Based on another post, I wasn't sure about the reliability of a replacement gear, but I think in that case, it was an RC gear.

Greg

[Pitini]

I found the perfect tool to open these cans is a nice sharp corkscrew
.

[Johan de Jong]

A corkscrew as can opener, as illogical as it sounds I can see that could work! Thanks, I'll try that the next time.

[flipoclock]

If anything, it will be less dangerous than a knife (any knife), it sounds like a good tip, thanks!

[erbsele]

Hi Johan,
I will try the same procedure with replacing the gear. Do you remember which 1 mm drilling parameter you ordered from kkpmo? 1.0 M6 or 1.0 H6?
Thanks,
erbsele

[Johan de Jong]

Hi Erbsele,
I ordered the 1.0 M6. I was quite puzzled as well what to choose there. I wanted to be on the safe side and think M6 is the tight fit.
Great you are trying this as well, let me know if you succeed!

[Johan de Jong]

Now also replaced the gear in a Tamura motor (from a Loewe Opta Sweetclock 32009). Same procedure, except that on this one I could completely remove the rotor. The new gear (module 0.2, 12 teeth, bore 1 mm, height 2 mm) fits fine after minor filing of the bore hole with a needle file.



The motor is working again but rather noisy. This noise though has nothing to do with the gear replacement, but is caused by excessive lateral play on the rotor axle. If ever we find a solution for that problem...

[Jonas Sandstedt]

Hello,
I have a Sankyo model 401E which has not worked for a couple of years. I tried it recently, but the motor did not move, although there was some humming sound. After reading these posts, I used the sharp tip of a corkscrew to remove the white seal – it took only a few minutes. It did, however, an hour to remove the gears from the housing, but then it was easily established that the brownish rotor axis gear was broken. I ordered some replacement gears from kkpmo as suggested, and they arrived a little more than a week later. The gear fit exactly on the axis and everything seemed fine. But when the motor was mounted into place nothing happened when connected to the mains – not even a faint sound. When I measured over the windings I got infinite resistance, so I assume that the coil windings are broken somewhere – not the successful end of the day I had hoped for. I opened the sealing tape over the coil, in case the thin coil wire had loosened from one of the input leads, but it is difficult to establish since the coil wire is very thin and brakes at a heartbeat. I have tried to measure at different positions, but always get infinite resistance. Does anyone have any suggestions about what to do? Is there any known replacement coil that can be used?
Best regards Jonas

[Johan de Jong]

Hello Jonas and welcome to this forum!

Sorry to hear that coil failed on you after you have come that far. That is a real bummer! I never measured the resistance, but if you hold a screwdriver near the coil you can easily feel if it is working or not.

Replacements are hard to find online, but maybe someone else on the forum can provide you with one. Need to know the voltage though (220V or 110V).

Another option might be to rewind the coil with a new wire. I have heard about it but have never done it myself.