This is a small departure from my more recent computer centric posts, but I thought it was worth posting, since most of the directions online are text only. I’ve changed belts on Singers with external motors before, but this was my first time changing an internal belt. This post should probably help anyone with a Singer 327/328, a 337/338, and a 347/348, since they’re all very similar machines. The basics should be the same for other Singers from the same era, and probably some other brands as well.
The first thing to do is to lay the machine on its side, taking it out of the cabinet or the bottom of the portable case if you have one. I like to lay mine on top of a folded towel. Look at the side with the hand wheel. On the 338, there are two large screws on the side panel. You will need to undo these. I also took off the top of my machine, but I think that was probably unnecessary.
Pretend you’re looking at a torn and tattered belt. I forgot to take before pictures, so you’re looking at my shiny new belt here. The next thing to undo is the chrome part in the center of the hand wheel (what you normally loosen before winding bobbins). You will have to first unscrew the tiny little stop screw, then unscrew the entire chrome piece until it comes out.
Now it’s time to take off the oil drip pan (if your machine has one, it’s the plastic piece that covers the bottom of the machine, generally attached with a single screw) and undo the bottom motor mount screw. On the 338, the screw for the motor mount is in a tight spot that you can only get to through the cutouts in the bottom side of the machine. The screw passes through two nylon washers, which are divided by the metal piece that actually attaches to the motor.
Here’s how I unscrewed it:
And here’s another peek, so you can see what I’m talking about. Nylon parts in old Singer sewing machines are always that white beige color.
Once it’s unscrewed, the entire motor mount will move freely up and down. You only have to nudge it a little towards the top of the machine, though, so before you get too crazy, go ahead and pull the hand wheel away from the body of the machine just enough to expose the top of the belt.
Remove the old belt (if you haven’t already) and place the new belt in the hand wheel groove. Push the wheel back into the base of the machine and loop the other end of the belt over the bolt like protrusion that sticks out of the motor. The second picture I posted above shows a correctly installed belt. You can go ahead and screw the hand wheel back on to secure it, but don’t put the side panel back on until after you reattach the bottom motor mount screw and its two nylon washers. The motor will be under tension from the belt, so this can be a little tricky. Try not to screw it in crooked. I put my left hand in through the open side panel and maneuvered the motor into position that way. Nylon parts get brittle with age and can break, so just be careful of the any white plastic pieces inside your machine.
Once the belt is securely in place, turn the hand wheel and make sure everything works. If you can’t get the chrome center part of the hand wheel to tighten correctly (the stop screw hits the washer underneath too soon before the chrome part is sufficiently secure), the in between metal washer that sat between the chrome disk and the hand wheel may have been put in the wrong way around. Flip it 180 degrees and try again. (It has two flanges that want to sit in cut outs facing into the hand wheel, but there’s nothing to show which way is correct.) If everything looks good, put the oil pan back on, put the machine back in an upright position, and try sewing.