Normal Bolex 8mm motors wind from complete rundown to full wind about 11 1/2 full or 22 half turns of the winding key. If your motor won't wind, or runs only for a few seconds, the motor may be overwound.
Customer writes to say that, "the motor runs for a second or so, and then stops. It won’t wind more that a fraction of a turn and then stops”.
From the description, it sounds like the motor is overwound. Bolex states in writing that their motors "cannot be overwound", but in actuality, they can be overwound.
It takes a lot of force and if the camera has been used a lot, or there is excessive wear in the limiter gears, overwinding can happen.
Overwinding causes the winding limiter ( two slightly different gears that intermesh ) to “slip one over the other” from their factory setting. This causes a loss of the gear’s relative indexing and now the motor winds only a little.
Sometimes after an overwind the spring is still okay and just needs the limiter gears to be reset.
In other cases, the motor’s spring can be damaged (bent) when the initial overwinding slippage takes place. Rapid unwinding can permanently damage the flat spring. This can result in a permanent kink in the flat spring of the motor and the only fix is to replace the motor.