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Bernina 731
An in-law's in-law has a Bernina 731 she says works but like a slipping transmission.
I found a post here from a few years ago, and I was wondering if anybody thought the problem is more likely: That's a great machine! The clutch on the handwheel is gummed up. To get a better grip on the clutch knob, you can push the machine back against a counter, with the handwheel facing you. Loosen the set screw. Twist the center knob off, as you push against the counter. Sometimes I use a rubber gripper -- like you'd use to open a tight jar. If that doesn't work, I use those big plumbers adjustable wrenches, with the gripper still in place so the handwheel doesn't get damaged. When you get the knob off, there's a ring underneath it with nubs on the inside and nubs on the outside. When you put it back on, the nubs on the inside need to bump outward. If you're brave, you can loosen the belt with the hex screw below the lower pulley. Pull the handwheel off and clean the gummy stuff off. A squirt of WD-40 won't hurt the shaft, and works very well. Then I squirt some WD-40 on a flannel rag and clean the center of the handwheel with that. Also clean the washer (if it has one) and back of the center knob. Put 2 drops of oil on the shaft and put it back together. Remember that the ring goes on with the center nubs bumped outward. If, when you screw the center knob back on (and tighten the set screw), it doesn't loosen like it should, remove it and turn the ring one position. Try again. This machine has either 2 or 3 nubs in the middle -- don't have one here in front of me. It's a matter of trial and error to get the ring in the right position. Tighten the belt -- most of these with the hex screw are spring loaded, so you can't go wrong. Some others have the big screws behind the lower pulley that are a pain to get to. I haven't seen the machine but it might show up at some point. It's apparently very heavy. Thanks for the great advice! |
The "slipping transmission" could just be a belt that needs adjustment. My comment above tells how to adjust the belt. Just loosen the hex screw, let the spring put it back into position, then tighten it again. Sometimes it takes a little more fine tuning. Sometimes the belt is so dried out, it needs to be replaced.
I love working on the old Berninas! There are 2 "nylon alloy" gears in that machine. One is the camstack gear and the other is the vertical shaft gear. They can both be replaced with after-market gears that are pretty good. You can visibly see a crack if it has one. Unless it's the camstack that's stuck with the crack at the bottom. |
There is a plastic gear in connection with the cam stack, the only thing you can do is check it. Lift the top up, move the stitch length lever to one of the stitch patterns, turn the hand wheel by hand and watch as it turns. Any cracks or damage show easily. The 741 has an external motor in the back, check the motor belt (possibly under a belt guard cover). I think it has an internal vertical belt connecting the parts on the under side. I'm not entirely sure on this point, since some of the flat beds are a bit different and I am more used to the freearm models. There might be a vertical turning rod of there's no belt. I think it's a slightly simpler version of the 740, with the same rotary hook and bobbin case. These are heavier and sturdier models made for more speed. In theory it should be pretty close to the machine in this blog. It looks like the only belt on this machine is the motor belt.
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The 741 is a flat bed, but the 731 is a free-arm. It's just the 730 with fewer stitches. And it has the oscillating hook. Here's a good picture and article. http://thinmansewing.blogspot.com/20...nel-shirt.html
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Oh sorry, I managed to mix this up with another post. The 731 should be very close to my 730, two drivebelts, for the motor and a timing belt. The occilating hook is nice, very even zigzaging on this model. All 730 and close numbers like 731 aren't exactly the same, but generally the cam gear function under the top cover is. The first thing to check is this gear (easy to do), and do a general clean and inspection of the gears, under the top of the machine, and under the top of the freearm. There is a cover on the side of the hand wheel that needs to come off for the drive belts. The clutch wheel is not a bad thing to check either, but not the most common issue.
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Thanks Mickey2 and quilted sunshine. From what I've learned, the 730, 731, and 732 were a series with 730 having the most fancy ("decorative") stitches, the 731 four of the deco stitches, and the 732 the fewest. I've downloaded a manual, too and when it gets dropped off next week I'll update. I have never used an Italian sewing machine (though this one is actually Swiss, like the Artista 180 that my sister gave me several years ago and I should stop being scared of.)
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The Artista is very fancy, all kinds of stitches and buttonholes. It has a wider zigzag and I don't known a fraction of the software options on it; emboridery and all. I think you are right about the 730, 731 732, practically the same machine, same buttonholer function. I have noticed some of the older models are made to be more portable, smaller and a bit lighter like the 700. The 700 series are very forgiving when it comes to thread and tension, very little fuss and the neatest stitching.
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