This information relates to most Singer 300 and 400 series sewing machines, and explains how to remove, refit and retime the machine after fitting the new top shaft bevel gear.
Lay the machine on its back and remove the bottom cover, slacken the belt tensioner.
Stand the machine on its base, take off the top cover and loosen the screws on the top shaft vertical gear.
A few options are available to allow access to the vertical gears adjustment screws...
1. To get to that screw you can get access via inserting a long screwdriver into the gap above the stitch length lever.
2. If the stitch length is a dial, remove - pull off the dial, you should be able to reach the gear screws without removing the stitch length adjuster unit
3. Remove the front front plastic panel, behind that there will be an inspection hole with a smaller metal cover to remove, held with 2 black screws
The top shaft will now drop leaving the gear easy to remove. Its a bit of a fiddle to get the loose gear out of the machine.
Replace with the new gear and make sure the single screw tightens onto the flat on the shaft. Also make sure there is no up and down play in the shaft.
Re-tighten the belt tensioner.
To time the machine remove needle plate and bobbin case, slacken the two grub screws on the underside pulley of the stitching mechanism. Once slack turn the needle bar to its highest position.Now turn the stitching mechanism by hand so the point on inner circumference is at 12.00 o'clock.
Insert a new needle and turn the needle to its lowest point in the normal direction of travel and continue until it rises again approximately 2mm.
At that point, the point on the stitching mechanism should be at the needle to catch the thread. Re-tighten the pulley screws and reassemble. (further information is available on re-timing a sewing machine in the knowledgeable)