LiftMaster K16-51219 4L420 Belt for Select SL3000 and Gate Operator Drive Assemblies
The LiftMaster K16-51219 is a 4L420 V-belt used in select LiftMaster gate operator drive assemblies. The belt transfers power between pulleys and can affect operator speed, smoothness, and torque transfer. A belt that is glazed, cracked, stretched, oil-contaminated, or improperly tensioned can slip under load and make the operator seem weak even when the motor is still good.
The 4L420 designation generally points to a 4L section belt with approximately 42 inch outside length, but LiftMaster fitment still depends on the operator design and pulley spacing. Supplier references point primarily to SL3000 and SL3000UL slide gate operator use, with some descriptions mentioning specific heavy-duty swing gate motor assemblies requiring the same 42 inch belt. Use the original part callout to avoid ordering the wrong belt length.
Compatible With
- Select LiftMaster SL3000 slide gate operator drive assemblies
- Select LiftMaster SL3000UL slide gate operator drive assemblies
- Specific heavy-duty swing gate motor assemblies requiring a 4L420 belt when confirmed by parts diagram
- Applications calling for LiftMaster K16-51219 or 16-51219
- Not automatically interchangeable with K16-50186 or other 4L420 LiftMaster belt listings unless the parts diagram allows it
Features & Specifications
| Manufacturer | LiftMaster |
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| Product Type | V-belt |
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| Part Number | K16-51219 |
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| Belt Size | 4L420 |
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| Approximate Belt Type | 4L fractional horsepower V-belt |
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| Application | Gate operator pulley drive system |
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| Known Model References | SL3000 / SL3000UL in supplier listings |
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| Notes | Confirm belt length, pulley alignment, and tensioning requirements |
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Also Known As / Related Part Numbers
- K16-51219
- 16-51219
- 4L420
- 4L420 belt
- LM-K16-51219
- SL3000 belt
- SL3000UL belt
Technician Note
Mechanical drive parts usually fail because of wear, misalignment, loose hardware, poor chain or belt tension, or a worn supporting shaft/bearing. Correct the cause of wear before installing the replacement part.
Before Ordering
- Confirm the operator parts diagram lists K16-51219 or 16-51219
- Check the old belt size printed on the belt if still readable
- Inspect pulley wear, pulley alignment, and belt tensioner condition
- Do not force a belt that is too short or too long onto the pulley system
Professional Advisory
Gate and barrier operators can move heavy equipment and may contain high-voltage circuits. Disconnect power according to the operator manual and use a qualified gate technician for electrical diagnosis, unsafe movement, or commercial operator service work.
Important Ordering Warnings
- Similar LiftMaster sprockets, belts, pulleys, and retaining clips are not always interchangeable
- Model suffixes and operator generations can change the correct service part
- Do not bypass entrapment protection, guards, covers, or safety devices during service
- If the drive assembly is badly worn, inspect the mating chain, belt, shaft, bearing, key, and hardware before returning the operator to service
Product Questions & Answers
What is K16-51219 used for?
K16-51219 is a LiftMaster replacement belt used in the drive or retaining assembly described on this product page. It should be matched to the operator parts diagram and original part number.
How do I know if this belt is the correct replacement?
Confirm the original part number, operator model, diagram location, and physical dimensions. For drive parts, also compare chain or belt size, bore, keyway, tooth count, pulley diameter, or retaining groove as applicable.
Can I replace this part based only on the product photo?
No. Many LiftMaster mechanical service parts look similar but differ by bore, keyway, tooth count, diameter, offset, belt profile, or operator generation.
What symptoms can point to a worn belt?
Common signs include rough movement, chain or belt slip, noise, vibration, worn teeth or grooves, loose fit on the shaft, damaged retaining hardware, or inconsistent gate travel.
What else should be checked during replacement?
Inspect the mating chain or belt, shaft, bearings, keys, set screws, guards, covers, and overall alignment. On powered gate equipment, use safe service procedures and a qualified technician when needed.
