Bernina 708 Broken Gear Replacement

A neighbour sent me an SMS and asked if I repaired sewing machines. It was broken, as in the bobbin gear was jammed. I freed that up then cleaned and serviced it for her (she and her husband are lovely people).
I noticed the zig-zag doing bizarre movements and took a close look under the top.

Very common problem on Berninas

Okay, ordered one from England, an eBay store. I won't mention which one because I don't want to be giving recommendations. Just search for Bernina 708 cam gear and you'll find it.

Replacing the gear

Searching for instructions led me to here. It's for a 730 sure, but both have cams right? His looked a bit complex, hence the delay. I was planning on making the tools at my dad's tomorrow then just out of curiosity unscrewed the (three) grub screws. The shaft started sliding out very easily!
I got it all the way out and lifted the gear out.
Putting the new one on was a matter of removing the screws holding the cam to the gear (two flat screws) and transferring it, then putting it into the machine and replacing the shaft.
I tightened up the grub screws and of course the zig-zag wouldn't work.
After half an hour of removing the gear and replacing it in a slightly different position, I realised what a waste of time this was. Regardless of what I did, the swing always started at the bottom of the needle's travel!

Setting the zig-zag timing

The hard bit was fixing the swing. Before doing this you should look at the cam and see how it works. The swing happens only in the ridge between the lower flat and the raised one and you can set it like this:
1. Loosen the two screws holding the worm gear

Unscrew both of these

2. Now the worm gear can move freely.
3. Make sure the zig-zag width is at maximum.
4. Move the hand wheel toward you until the needle is on its way up and has already passed through the needle plate.
5. Now move the cam until the flat is just about to start swinging and tighten one of the screws.
6. Check that the swing occurs only when the needle is above the plate. The swing must finish at the same needle height on the other side. You have to make sure the swing is the same on both sides. Once you do, tighten the other screw. You don't want the worm gear to move.
7. Check it again, then test by sewing at maximum zig-zag width.

Certainly a lot easier than expected. The replacement gear has an aluminium base, and the original was steel. Not sure if this will affect the machine but if the plastic is the same quality as the original you can expect it to last 40 years. Not bad!

Bernina Favorit 540 1958

This machine was, let's just say, a bargain.
It's a home industrial machine with built-in cams! It came with an 80 watt Sew Tric motor which was almost fouling the knee lift mechanism. Yes, it has a knee lift! Just about everything here makes this an exciting machine. It's Swiss, knee lift, industrial, full rotary hook and pattern cams in a single machine. Additionally, it can be connected to an external industrial motor or a treadle. Can you see why I'm excited about this? It  is exactly the same size as a Singer and the hinge holes are in exactly the same place, but the front is chunkier than a Singer and in my treadle cabinet the front flap wouldn't go back in place. A little disappointed but to be honest I might have been overwhelmed and had a stroke if it got any better.

 The 540, 640 740 and 840 are all designated as 'Favorit' by Bernina (as opposed to the 530 etc. which are all 'Record'). All of them have a full rotary hook (they go faster), patterns, etc.
They also all have a plastic (nylon) cam drive gear. They do break, so I checked mine carefully but it is intact at this time. They're a royal pain to put back (I have one waiting for the drive gear to arrive from England so will make a blog entry about it).
There are 12 patterns on the 540 and 640 and 20 patterns on the 740 and 840. All of them are basically a heavier, faster flat bed Record.
Mine was missing its knee lift (slightly annoying) and the foot controller (more annoying). Since the motor was kind of generic anyway I replaced it with an 85W Wernard, with new wiring and a Wernard foot controller. To me this is still rather under powered for this machine and I'd really like to get the cabinet inside and mount the 1/4 hp Singer motor to it. It will easily handle the power and I'd only be worried about low speed control.

The picture from the ad

After a good clean and oil (with tri-flow)

Someone asked me the difference between the 540 and 640, and the manual has a whole page dedicated to answering this:

This machine will be a keeper, I'm pretty sure. It's extremely smooth, has the flexibility of zig-zag, and tough enough for anyone. Can't wait to get her into production!