1862 General repair

bent axle? worn bearings?

Many Lionel gears are spur gears where the teeth roll in and roll out.  Sometimes noisy but usually reliable.  But the worm gears are sliding contact. They must be kept lubricated with a good grease.  I assume that the loose wheels are due to having to pull the wheels off the axle  to change the worm wheel.  With Locktite products these days, loose wheels can be fixed fairly easily.  If you have anymore trouble you might want to find a different repairman to fix it.   I believe that white grease that Lionel uses in some applications is a food grade lubricant.  That way if a child gets it into their mouth there should not be any problems. If you loco is lubricated with the white grease you might want to find a better grease for the worm wheel.  You could try one of the power tool repair stations and see what they use on their worm wheels. 

Thanks for getting back to me! As far as I know the axels were not bent. And the worm gear was highly lubricated. As a matter of fact I was picking out brass shavings from the grease from when the gear was being ground by the armature. I am going to try a different repairman, who I've already contacted. He mentioned about using an epoxy bond on the wheels. It's frustrating because when running, it's a beauty. For a simple, non-smoking, non-whistling engine, it's really nice but I'm so hesitant to try and run it because of this recurring problem. 

then the hole for the wheel  is out of whack, you may need to get new wheels, but still pressing on the gear the ends of axle can bend.

if the wheel is not sq  when pressed on , its going to bend the wheel and possibly the axle,

using a lathe is best for replacing  gears, and putting on wheels. and even better with wheel cups.

If the wheels are straight on the axles, and aren't loose enough to wiggle, I'd use Locktite or Gap Filling CA glue over epoxy. If they aren't straight, or are loose on the axles, I'd look to replace both the wheels and the axles.

Whatever is used, it will be important to clean away any grease, oil and dirt first.