I've had 2 sergers. One was an old Singer UltraLock 14u64A. I sold it last week. The one I have now is a Janome built Kenmore model that's still in production. The Singer was quieter and likely more robust.
They're really easy to work on and clean. Just make sure you take pictures as you disassemble. Remove -all- the plastic panels you need to to get a good look and oil what you see moving, just like a sewing machine. Sergers are almost more important to disassemble to clean, they seem to suck a lot more in, likely because of the small bits that are cut off, unlike a sewing machine. Outwardly, this machine didn't look too bad... but once the panels were off... oi.
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Make sure that the loopers aren't rubbing on each other, they should almost touch, but not quite. That's one of the few adjustments, other than tensioner rebuilds that I've had to do on sergers.
Here's a good site (takes a long time to load!) on serger tensions:
http://www.fiberosity.com/?p=96
Basically though (assuming it's threaded right and the threads are completely into the tension disks):
- You want the 2 looper threads to lock at the edge of the fabric.
- If the edge of the fabric curls to the top, or the top threads stand off the fabric, or the bottom looper thread is curled over to the top, typically the top tension needs to be lowered.
- If the fabric curls to the bottom, or the bottom threads stand off the fabric, or the top looper threads are curled over to the bottom, the bottom thread tension needs to be lowered.
- If either looper thread "loops" instead of locking at the edge of the fabric, tighten its tension.
- If the needle threads are too loose, they will loop on the top, or be pulled down for an unbalanced looking stitch on the backside. You should only see a little pin prick of the needle thread on the bottom If they're too tight, you'll see looper thread on the top of the stitch at the needle holes.
I hope that makes sense. I've never tried to type this one out before. It makes sense in my head, but on "paper"??? I don't know.
Singer's Sewing with an Overlock book is excellent, and usually dirt cheap. I love the photos in it.