Orange part numbers and product names are Amazon affiliate links (we may earn a commission at no cost to you).

We found no Kubota statement that either engine has a timing belt. The B2650 evidence comes from the cab model’s workshop manual (B2650HSDC), and the B2650 operator manual lists the B2650HSD as D1305-E4. Earlier versions of this page named the L3901 engine D1803-M-DI. Kubota’s manuals name it D1803-CR-E4, so we corrected it.

Both schedules say “Adjust,” not “Replace every 100 hours.” We found no fixed hour or age limit for replacing the belt. Earlier versions said “about 1/2 inch of play” and that belts last 1,000–2,000 hours. The first does not match the manuals, and we found no source for the second.

Dealer pages do not say that one belt fits every configuration of the B2650 or L3901. The cab and ROPS B2650s have different numbers, and the Coleman L3901 list shows two belts. Match your serial number with your dealer or parts diagram. 16241-97013 replaces 14431-72530, 16241-97010 and 16241-97012 per Messick’s. Belt width and length were not published in the records we read, so earlier versions’ “3/8 x 37-1/2” and “1/2 x 42-1/2” sizes are removed. Earlier versions also said the B2650 belt fits the B2320, B2630, B2920 and B3030 and that the L3901 belt fits the L2600, L2850 and M-series. We did not verify those.

• Stop the engine and remove the key.
• Apply moderate thumb pressure to the belt between the pulleys and measure the deflection (7 to 9 mm; 98 N on the L3901).
• If the tension is wrong, loosen the alternator mounting bolts and use a lever between the alternator and engine block to pull the alternator outward until the deflection is within the limits, then tighten the bolts.
• Replace the fan belt if it is damaged.

These are the steps in both operator manuals. They are adjustment instructions, not a full removal procedure. We found no alternator pivot or adjusting bolt torque in either manual, and we did not find the belt removal steps. Use your model’s shop manual for those. Earlier versions gave a “30–60 minutes” time and dealer and parts price ranges. We found no source for them, so we removed them.

These are general signs, not Kubota-published criteria: squealing when cold or under load, a glazed or cracked surface, fraying at the edges, a charging warning light, or the engine running hot. Kubota’s own instruction is to replace the belt if it is damaged. If the engine overheats, see our overheating guide, which covers the manual’s fan belt spec as one item on its checklist.

• Fan belt width and length, and whether one belt fits every B2650 or L3901 configuration.
• The L3901HST belt, and how to choose between 15196-97010 and 15606-97020 on the 4WD.
• Alternator pivot and adjusting bolt torque, and a full belt removal procedure.
• A fixed replacement interval (the manuals say adjust at 100 hours and replace if damaged).
• Time, labor and price ranges from earlier versions, which we removed.