Thorens mainsprings, do I have to buy 2 new mainsprings?

[casey-eamonn]

Hi all
I m currently overhauling a Thorens 2 spring motor. While overhauling I found 1 original mainspring in reasonable condition, ie it s diameter was about 3 times the diameter of its drum, my usual yardstick for should do its job fine. The other mainspring was not so I ve replaced it with a new old stock mainspring.Unfortunately the motor is still struggling on pretty good records and has no hope on an average or below average record. Will a second new mainspring solve the issue ?

[soundgen]

Probably not ! There is some other problem . the criteria for spring suitability is to wind the motor up fully and then while the motor is unwinding try and stop the motor with your hand on the spring barrel . a spring problem will show itself as it is really easy to stop the motor unwinding . most often it is very hard to stop the unwinding which always suggests a smaller problem down the line usually the governor , small vagaries in the governor have a huge influence on the motor working properly

Also i don't really understand your " ie its diameter was about 3 times the diameter of its drum my usual yardstick " To get maximum torque from a spring in a barrel the barrel should be ½ full

[casey-eamonn]

Thanks for that.
I should said when I have taken the mainspring out of the drum that it is approximately 3 x diameter of the spring drum.
I ll certainly have a go at stopping the spring drum by hand after a full wind,never tried that before, thanks again for the input.

[edisonphonoworks]

Usually, it is best to replace both springs. I have made it a habit when spring repairs come in, I replace both springs, it ensures maximum power, and reliability. We don't always know what conditions the machine was stored it, or if the spring broke from over-winding or other factors.

[soundgen]

Usually, it is best to replace both springs. I have made it a habit when spring repairs come in, I replace both springs, it ensures maximum power, and reliability. We don't always know what conditions the machine was stored it, or if the spring broke from over-winding or other factors.

I've never ever replaced both springs in 40 years of repairing 100s of double spring motors ,and on only two occasions have gramophones come back to have another spring fitted in this time , and they came back within a week ! It's a fallacy that both springs need to be replaced in fact it's a con . after replacing the broken spring an explanation of why they break and how to avoid this stops it happening , 99.9% have never required a further repair in the last 40 years

[casey-eamonn]

Thanks for that guys.
To be honest I was talking specifically about Thorens motor s as I have found them to be consistently weaker than others.
They have a similar duration but can't get through the more worn records unlike most other motors.They just never seem to have the power of even later single spring HMV s (and others) with similar size mainspring s. That said I have never replaced both mainspring s because it never seemed necessary, except possibly this time.

[soundgen]

Thanks for that guys.
To be honest I was talking specifically about Thorens motor s as I have found them to be consistently weaker than others.
They have a similar duration but can't get through the more worn records unlike most other motors.They just never seem to have the power of even later single spring HMV s (and others) with similar size mainspring s. That said I have never replaced both mainspring s because it never seemed necessary, except possibly this time.

I have occasionally replaced both springs in gramophones at the insistence of the owner and guess what ? the motor still wouldn't work properly and I couldn't get it too either !

[gramophone-georg]

Usually, it is best to replace both springs. I have made it a habit when spring repairs come in, I replace both springs, it ensures maximum power, and reliability. We don't always know what conditions the machine was stored it, or if the spring broke from over-winding or other factors.

I've never ever replaced both springs in 40 years of repairing 100s of double spring motors ,and on only two occasions have gramophones come back to have another spring fitted in this time , and they came back within a week ! It's a fallacy that both springs need to be replaced in fact it's a con . after replacing the broken spring an explanation of why they break and how to avoid this stops it happening , 99.9% have never required a further repair in the last 40 years

I always replace all springs in a gramo motor if one is bad. That way I know it's done right- and I am apt to replace the governor springs whilst there... and 100% of mine have never required a further repair. I mean, come on... if you have the thing torn down THAT far, why on Earth wouldn't you just finish the job right?

If your car has one bad spark plug, do you just replace the one? Of course not.