Hornby M7 repair

[Alan-720285]

Due to erratic running I stripped my Hornby M7 for a clean and service and noticed the front driving wheels and therefore the great wheel were off centre of the chassis. It pulled to one side only by the magnets in the frame. It didn’t move to the other side as the wheel appears to have a boss on the inner face that holds it off. Two questions.

1. What are the magnets in the frame for?
2. Should both wheels have a boss/spacer to hold them central?

[Going Spare]

The chassis magnet was fitted to improve traction on steel rails but has no useful effect with modern nickel-silver rails.

Insulated wheels are needed on only one side, the side on which the pick-ups are fitted, as the electrical path through the loco is from one rail via the insulated wheels and pick-ups to one motor brush, returning from the other brush via the motor frame, chassis block, axles and non-insulated wheels to the other rail.

In your photograph, the wheels look a little too far apart - all wheels should be set at 14.5mm between the backs of their rims. If they are correctly spaced, gently lever the wormwheel back to the centre of the axle.

[Ruffnut Thorston]

The Boss/ Spacer is the back of the plastic insulation bush, as mentioned by GS above.

This is there to prevent the metal wheel touching the metal chassis, as these wheels are of the opposite polarity to the chassis block and the uninsulated wheels.

The uninsulated wheels and the chassis block are of the same polarity, so it doesn’t create a short circuit if they touch the chassis.

[Alan-720285]

Thank you for your replies they have given me a better understanding of the problem and I’ll check out the points you have made.

Regards

Alan