Try rethreading it using the order: 3, 4, 2, 1. If you are threading it in the wrong order it will give you problems. Afterwards, you will need to carefully adjust the tension controls. This can be done more easily using four different colored threads.

Looks like this is an old (possibly industrial) machine. Found this manual online:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwjYzYb_jPjKAhVNyWMKHRDpC9MQFgggMAA&url=http%3A%2F%2Fparts.singerco.com%2FIPsvcManuals%2F460_CLASS.pdf&usg=AFQjCNF9iAEEq7nMWMFRlVWITRGvhQciIw&cad=rja

You may want to contact a Singer dealer or the manufacturer support group.

The 335 has a two thread chain stitch (stitch type 401), and the overlock side (right needle side), is a three thread plain overlock. If you are describing the plain overlock as the problem, I would first suggest the following in re-threading:

1. Thread the upper looper
2. Thread the lower looper
3. Thread the needle last (important)

If the needle threaded, you cannot re-thread the lower looper without breaking the thread.
In order to thread the lower looper, the lower looper must pass by the needle thus picking up the needle thread. So, instead of threading the lower looper thread underneath the needle thread, the looper would be threaded on top and cannot sew without breaking the thread.
Make sure that the threads are bedded between the tension disks. Check this by stretching the thread fore and aft of the tension disks as well as visually noting that the threads are not accidentally threaded behind the disks. You can also loosen the tension disks when threading so as to allow the threads to bed deeply between the disks.
Please reply with your observations.

Serger needles are different from regular sewing machine needles, but like sewing machine needles, they are generic. That means that if you buy a serger needle, it should fit most sergers from any manufacturer.

My favorite manufacturer is Organ; they've been in business for a long time and manufacture for commercial and home machines and sergers and they're quite inexpensive.

It is, of course, possible to use overlock thread in a typical machine. Generally speaking, you only want to use overlock thread to overlock ("serge"). The reason for this if that while typical all-purpose or sewing machine thread has 3 strings wound together, overlock thread has only 2. When you are using 3, 4, or even 8 threads at a time with a serger, each strand doesn't necessarily have to be as strong as when you are sewing on a machine with only 2 threads. So, you physically could use the thread, yes, but it will not be near as strong, and you will probably have issues with breakage while sewing as well. The cost savings you think you may be saving by using overlock thread (which is, after all, considerably cheaper per yard), well soon be overrun with extra time sewing due to broken threads and overall less quality in your garment as it will be made weaker.

To use a 3 thread overlock, thread the overlooper; the underlooper and then use ONE of the needles. Removing the RIGHT needle will produce a 5mm or 1/4" seam. Removing the LEFT needle will produce a 3mm or 3/16" seam.

Follow the simple steps  :-
http://www.ehow.com/how_2301477_thread-singer-sewing-machine.html


Thanks.

With some sergers, but not many (singer 14u64 comes to mind), the top of the stitch will be an overedge that mates with the right needle thread, and the left needle thread will appear as a separate straight stitch. When you look at the underside of the stitch, the overedge will go all the way over to the left needle (the full width of the stitch). This is normal if you have this type of machine. Another stitch some sergers do (2/4 thread sergers) is a 2 thread chain thal looks like a lone straight stitch on both sides, and a 2 thread separate overedge.

As far as the threading of the takeup, it totally depends on your model. Always post your model number when you have questions as sergers vary greatly in design.