Bernette 334DS/334S (1999) Overlock Machine Service Manual (P/N 501 546 13 GB)

• Covers the Bernette 334DS and 334S overlock machines, including 2-needle/4-thread overlock with integrated safety seam, 1-needle/3-thread overlock, and 1-needle/2-thread overlock
• Official Bernette instruction manual, P/N 501 546 13 GB
• Clearly separates the two models: the 334S is not equipped with differential feed, while differential-feed sections marked with an asterisk apply to the 334DS
• Provides illustrated machine views, color-coded threading paths, stitch and fabric settings, owner-level maintenance, and a problem/cause/solution troubleshooting guide

Operation and Threading Configuration

The PDF identifies the working parts around the looper and needle area. Labeled views cover the upper and lower loopers, lower-looper threading device, upper and lower knives, stitch plate, presser-foot pressure regulator, tension dials, cutting-width adjustment, roll-hemming selector, thread guides, waste collector, and the swing-out presser foot.

Threading is broken out by path: upper looper (blue), lower looper (red), right-hand needle (green), and left-hand needle (yellow). Separate illustrations show the thread guide bar, tension-disc routing, needle threader, and the individual looper/needle paths. The 2-thread conversion attachment is also covered. For narrow 3–5 mm 2-thread work, the left needle is removed so the right needle remains in use; the wider 5–7 mm configuration uses the left needle. The same needle-position logic is explained for 3-thread overlocking.

The machine uses the 130/705 H needle system for both needles, with needle sizes 70–90 specified in the manual. The needle/thread/application table distinguishes settings for fine seams and roll hemming, general seams, neatening, stretch seams in knits, and decorative thread use. Trial-sewing pages show how stitch appearance changes when individual looper or needle tensions are too high or too low, making the guide useful for diagnosing an unbalanced seam instead of simply giving one generic tension number.

Setup and Specifications

Technical data lists stitch length from 0.8 to 4.0 mm. Seam width is 3–7 mm for 2- or 3-thread overlock and 5–7 mm for the 4-thread overlock safety seam. The cutting-width section goes further by relating knife position to the active needle: 3, 4, or 5 mm from the right-hand needle and 5, 6, or 7 mm from the left-hand needle. The manual lists sewing speed up to 1,500 s.p.m., with machine weight given as 7.5 kg for the 334DS and 7.4 kg for the 334S.

On the 334DS, the differential-feed section explains the front and rear feed dogs and gives the working range used to control fabric distortion: N–2 for preventing waving or fluting in knits and 0.7–N for reducing puckering. A fabric table ties specific differential settings to thick wool knits, cotton and synthetic jerseys, woven fabrics, fine nylon jersey, lining fabric, satin, and poplin. The manual also covers presser-foot pressure, including higher pressure for firm fabrics such as denim or tweed and lower pressure for lightweight fabrics such as chiffon, georgette, and batiste.

Practical settings are provided for 4-thread seams in thick knits, jerseys, and fine woven fabrics; narrow and wide 2/3-thread neatening; 3-thread stretch seams; 2-thread flatlock; and 3-thread decorative edging. Roll hemming has its own 2- and 3-thread settings, while the gathering section gives a 4-thread baseline using differential feed, stitch length, cutting width, and thread tension together. Tape insertion and seam-guide use are also illustrated.

Maintenance, Troubleshooting, and Repair Scope

Owner-level procedures cover needle replacement, presser-foot changes, lower-knife replacement, bulb replacement, cleaning, and lubrication. The moving upper knife is identified as a special-material part that normally does not require replacement; if it is damaged, the manual directs the owner to a Bernette dealer. For the lower knife, the manual specifies that the sharp edge of the replacement knife must sit in line with the stitch plate. Lamp ratings are listed as 15 W for 115 V machines and 10 W for 220/230/240 V machines.

Always disconnect the machine from the electricity supply before maintenance work or working around the needle, knife, or looper area.

Several repair pitfalls are made explicit. Needles must be pushed fully into the needle clamp with the flat side to the back; incorrect insertion is tied to thread breaks, skipped stitches, and needle breakage. Pulling the fabric while sewing is also listed as a cause of broken needles and distorted seams. A blunt or wrongly positioned lower knife appears in the troubleshooting table as a fault source, so knife position matters before a feed or seam problem is blamed on tension.

The troubleshooting table covers uneven fabric feed, thread breakage, needle breakage, skipped stitches, poor stitch formation, waviness in knits, puckering, and curling fabric edges, with causes linked back to the relevant adjustment pages.

Illustrated references include the view with looper cover open, upper-looper thread path, lower-looper thread path, cutting-width/knife-position view, differential-feed diagram, and lower-knife replacement view. There are no wiring diagrams or electrical schematics in this manual.

This is an instruction and maintenance manual, not an internal workshop repair manual. It does not provide motor teardown, internal timing procedures, electrical repair schematics, torque specifications, or specialist service-tool procedures. The safety section specifically states that repairs, especially electrical repairs, are to be carried out by service agencies. Buyers looking for internal repair data should therefore distinguish this publication from a full service manual.