I have looked at the motor shield for some years how, a matter of fact since the 5 pole high efficiency motor came out because with this motor there is little allowance for any movements and any abnormalities within the motor shield or the motor block as a whole could result in the motor either not running at all or it runs with excessive noise.
another observation I've made, the motor block in its early stages including all the analog motors and locos weren't always precise and more care would have taken place when the 5 pole motor was introduced and who knows they may have re machined them.

Anyhow the motor block was never a number 1 problem it happened occasionally or one could say on rare occasions.
When we talk about the motor shield there has been one change from the previous, it is much thinner because of the wider perm. magnet.

the brush shaft assembly with its tension spring is pressed by machine onto the brush plate and if it is pressed to hard the hole assembly no longer lays flat but it has lifted itself at the end of the brush plate by doing this it is no longer at a 90° angle in relation to the armature and therefore prevents it from running at its top speed and also created extra noise.

the armature shaft over time either by usage or being idle for too long can also create more noise. oiling of course is the obvious answer but it doesn't resolve the noise level completely by adding 2 4mm x 2mm x 1.5mm ball bearings on each side eliminates 2 problems a.) oiling and b.) noise level.

the ball bearing on the motor block can be replace directly by removing the plastic insert whereas the motor shield a 4mm hole has to be drilled precisely,

my sketches and illustration below shows you the state of the motor shield it could be in and the state or position it should be in.

my solution to the problem is to lift the brush shaft slightly higher, get a toothpick and put a fine drop of superglue on it and than place the toothpick between the brush shaft and the motor shield and press it down with a pair of pointed pliers, there has to be enough superglue to bind the 2 parts together. do not try to do this while the brushes are still inserted nor do it while the motor shield is still attached or screwed to the motor block with its armature sitting inside.

the middle section is a front view and the right hand side a side view and the top sketch shows you the gap between the shaft and the motor shield itself.


regards.,

John

Edited by moderator 12 August 2017 12:25:22(UTC)  | Reason: Made topic 'Sticky'