Elna Supermatic

This machine is from the hoard I'm supposed to fix and sell (I'm doing the responsible thing and not selling during the lockdown). There are four Elnas from around that time and three are like this one.

I've sort of given away the ending there. It didn't look anywhere near that good before I did my thing.
After the cleaning and oiling, it was making this thumping noise. It took about twenty minutes to realise that this is an Elna and therefore has a drive rubber on the motor (see the post from a few years ago on the Lotus).
I removed the hand wheel and sure enough there was a rubber wheel. This one was longer than the Lotus one but very similar.
I had a couple of 50c rubber bumpers left so drilled one with a hole much smaller than the motor shaft. Removing the existing rubber was not easy. You have to drive a pin out while holding the motor still. I jammed a very large screwdriver against the rubber to give it a bit of resistance.

Drive rubbers in foreground. Original is black

The replacement must have a small hole because there is only the pressure of the shaft stopping it from spinning, so to make this work, the rubber needs to take a lot of effort to push onto the motor shaft and you should also minimise the effort needed to turn the machine over.
If you find that this doesn't work, get something higher, so it matches the original and that you can make a very small hole for the pin to go back.

One rubber bumper in place

It works beautifully for me. The way to avoid the problem is to use your machine every now and then.
Oh and here's the 1962 manual I scanned and made into a PDF. It's made to be printed double-sided A4. Original size was approximately US Legal, so if you scale it up it'll be about the same as the original.

Elna Lotus ZZ

I bought this a few months back. She said it sounded a bit like a thrashing machine but confident that I could fix it anyway I took it home.

Okay it really, really sounded like a thrashing machine. The reason was the rubber drive roller (also called friction wheel).
I looked for a replacement but they're all extremely expensive. Ridiculous for such a small and unsophisticated component. Cheapest I found was $A80.00 posted from the U.S. but I can't afford that, especially when the machine cost a lot less.
The problem with the rubber is that when people let their machines run dry (of oil) which they generally do, the motor is trying to turn the hand wheel (which won't move) so it spins without moving the machine, putting the rubber roller out of shape and wearing in one spot. I suspect it's also because the rubber simply hardens over time. This is also probably more likely where I now live, in sub-tropical Queensland.
After calculating about $AU150 for a replacement it occurred to me today that the rubber feet I bought for my 411G looked about the same shape.

original Elna rubber is the black one

Do they look the same size? They're almost identical! The biggest difference is that the rubber feet are brown and had no hole. A minute later one of the brown feet had an appropriately sized hole (careful with the drill, I had to hold it with my fingers) and after another minute and it was in the machine, which is now as quiet as a mouse. I hadn't heard one before so didn't realise how they should sound. It's really a pretty nice machine that stitches well. It's portable like the featherweight, but can make a zig-zag stitch.

I pushed the new roller on and replaced everything

Tell everyone you know who might have one of these, since it's a very common issue. With a one dollar part you can fix this problem really quickly.
The original only lasted 30 before giving trouble, so even if your replacement lasts only a year, I'll still be $50 better off, assuming I'm still around in 30 years.