FarmerJon,
I have spoken to my team leader today who is just about to sit his exam to be able to instruct others in the repair and maintenance of flameproof motors and equipment. He agrees that a grain store is a potential explosion area and any electrical equipment should be appropriate for the environment it is used in. In other words if you are using 'bog-standard' equipment in a grain store then you are quite literally 'playing with fire!'
Check the nameplate on your motors and see if they contain ANY of the following letters or symbols.
Ex, (the E will look like a reverse 3), EEx d, EEx de, EEx e, EEx p or any combination such as, EEx pe, etc.
If you see any of these then the motors are flameproof motors and you cannot do any work on them yourself. If they don't have any of these letters/symbols then they are not flameproof but you should contact a reputable rewinding company who will be only to happy to advise you on the suitability of the equipment you have. You will need special flameproof glands for any cabling that needs doing though the choice of cable is not so critical. The important factor here is that if anything should go wrong with one of the motors, eg. bearings seize causing a stall and overheating of the motor with possible internal short and explosion, then the reaction is contained INSIDE the motor and not allowed to escape into the surrounding area leading to a bigger explosion because of the dry and dusty conditions.
As I said in my previous post, I don't want to alarm you but I have been in the armature winding business for over 30 years and have seen the effects of a situation like this. The smallest damage to a flameproof motor can have dire consequences. Please get the professionals in. If you email me I can find a reputable company for you in your area that will advise you on the best course of action.