I just changed my Kenmore serger's needle and it stopped making the overlock stitch. I rethreaded the machine twice and make sure the position of the needles is correct but it didn't help

Overlocker Serger Vs Coverstitch Machine What the Difference...

Could be a timing issue.

How to fix timing on serger

Serger Timing Fixed

SiRUBA Overlock Timing between Needle and Looper

catscradle Fixing the timing on an overlocker serger

Laura Blog Do it yourself serger repair How to adjust serger timing

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.

Make sure you are threading the machine correctly. Make sure you are using serger thread that isn't old. Make sure you are undoing all the threads when it breaks and thread it from the beginning.

Make sure you have the right needles in their respective places. My Juki MO has two different size needles.

is it possible that the needles are in backwards?
it's very possible that the machine is out of time & would have to be taken to a sewing machine repair shop to be retimed

It sounds like the timing needs to be reset by a sewing machine repair tech.

First, change the needles making sure to use the el705 needle system. Second, make sure the subsidiary looper is engaged properly (plugging up the upper looper hole). Also make sure the needles are all the way up in the machine. This should do it or it may need to be adjusted but the Evolve is a very, very reliable machine. Hope this helps...

Unthread the needles, rethread the loopers properly, then rethread the needles. Make sure that all four threads are pulled securely into the tensions and retry.

The loopers must always be threaded before the needles or it will not chain.

• the factory default settings are 4,4,4,4 and M
• Change the needles
• use a can of air spray ( compressed air can sold in computer stores) to ensure there is no fabric or dust under the needle plate

Make sure the chain stitch thread is threaded exactly as it should be, make doubly sure the thread comes off the bobbin vertically and runs through all eyes smoothly. Any faults in the threading causes extra tension at the needle despite what the tension is set on.
If this is not the cause then the needle depth and the looper timing needs checking.
Rob