How Often Should the Conveyor Belt Tension Be Checked on a Caterpillar AP655F?
Operating a Caterpillar AP655F paver demands consistent material flow, and the conveyor belt tension is a critical factor in achieving that. A belt that is too loose can slip, causing material buildup and uneven paving, while an over-tightened belt places excessive strain on bearings and drive components. For most UK and European contractors running the AP655F, the recommended inspection interval is every 10 to 15 operating hours—essentially a daily check during heavy use. However, if the machine is handling abrasive materials like high-stone-content asphalt or working in hot weather (above 30°C), reducing this interval to every 8 hours is prudent. Regular checks prevent costly downtime and extend belt life, a point reinforced in the Caterpillar AP655F Conveyor Belt Maintenance: Essential Tips for Longevity article.
The visual signs of incorrect tension are unmistakable: a sagging belt under the hopper at idle, or a belt that creeps sideways during operation. Tension should be measured with the belt stationary and the conveyor empty, using a straight edge across the top run. The factory specification allows a mid-span deflection of 15–20 mm when moderate hand pressure is applied (roughly 5 kg force). If the belt moves more than 25 mm, it is too slack; less than 10 mm indicates over-tensioning. A simple tension gauge can be used, but experienced operators often rely on feel—the belt should sit snugly against the drive pulley without squealing under load.
It is also worth noting that new belts stretch during the first 50 hours; check and adjust at 5-hour intervals during break-in. Ignoring this can lead to belt edge fraying or even drive pulley slippage, which may damage the conveyor gearbox. The AP655F uses a spring-loaded idler system on the tail roller, making adjustments relatively straightforward, but precision matters.
What Tools Are Required for Adjusting the Conveyor Belt Tension on the AP655F?
Before diving into the adjustment procedure, gathering the correct tools saves time and prevents damage to components. The AP655F conveyor tension system is a manual screw-type adjuster with lock nuts, located at the tail roller end (accessible under the rear hopper guard). Here is the complete tool list:
- 37 mm combination wrench (for the main tensioning bolts)
- 24 mm spanner (for lock nuts on both sides)
- Straight edge (1 m length) and a steel ruler (mm scale)
- Torque wrench (range 40–100 Nm) for final tightening
- Penetrating oil (e.g., WD-40) if bolts are rusted or seized
- Personal protective equipment (PPE): gloves, safety glasses, and steel-toe boots
While the adjustment itself is a two-person job for safety (one to tension, one to check alignment), a single operator can manage with careful use of a mirror. It is essential to ensure the machine is off, the engine is stopped, and the conveyor is locked out before reaching under the hopper. The AP655F Caterpillar AP655F Screed Electrical System Troubleshooting Guide provides additional safety lockout steps if the electric screed is involved in the conveyor drive.
What Is the Step-by-Step Procedure for Adjusting Belt Tension on the AP655F?
The adjustment procedure follows a logical sequence to maintain belt tracking and even load distribution. Follow these steps precisely:
- Park and secure: Place the AP655F on level ground, engage the parking brake, and turn off the engine. Remove the ignition key and apply a lockout tag.
- Access the tail roller: Remove the rear hopper guard (three bolts, 30 minutes for a first-time operator). Clean any debris around the roller.
- Loosen lock nuts: Using the 24 mm spanner, loosen both lock nuts on the tensioning bolts (one per side). Do not remove them, just back them off 2–3 turns.
- Apply initial tension: Turn both tensioning bolts (37 mm wrench) clockwise equally—half a turn on each side. Rotate the belt by hand to check for even tension across the width.
- Measure deflection: Place the straight edge across the belt top run (mid-span between drive and tail roller). Apply moderate hand pressure (5 kg force) at the centre. Measure deflection in mm. Target: 15–20 mm.
- Fine-tune tracking: If the belt drifts to one side, tighten the bolt on that side by an additional 1/4 turn, then check again. The belt should centre itself.
- Torque lock nuts: Once deflection is correct, torque the lock nuts to 60 Nm (approx. 44 ft-lb). Do not overtighten—this can strip threads or damage the bearing housing.
- Final check: Run the conveyor for 1 minute without material. Listen for squealing or rubbing. Re-measure deflection. Readjust if necessary.
Always adjust both sides equally to maintain belt alignment. A common mistake is to tension only one side, which causes the belt to run off-centre and wear prematurely. For more details on diagnosing belt noise issues, see the Caterpillar AP655F Screed System Noise Diagnosis Guide (note: conveyor noise is distinct from screed noise, but similar diagnostic logic applies).
What Are the Common Causes of Belt Tension Loss on the AP655F?
Tension loss can frustrate even seasoned operators, but causes are usually predictable. Below is a severity table ranking common issues by their impact on conveyor performance and required intervention:
| Cause | Frequency | Severity (1–5) | Remedy | Estimated Cost (GBP) |
|---|---|---|---|---|
| Normal belt stretch (new belt, first 50 h) | Very common | 2 (low) | Re-tension per procedure above | £0 (labour) |
| Worn pulley or idler bearings | Moderate | 4 (high) | Replace bearings; inspect seals | £80–£150 |
| Debris build-up on roller surface | Common | 3 (medium) | Clean roller with scraper; inspect belt underside | £0 (labour) |
| Damaged belt edge (frayed or delaminated) | Moderate | 5 (critical) | Replace belt; check for sharp metal contaminants | £400–£800 |
| Loose tensioner bolts (vibration loosening) | Occasional | 2 (low) | Retighten to 60 Nm; use thread locker if repeated | £0 |
Debris build-up is the easiest to fix but also the most overlooked. During hot asphalt laying, fines and bitumen can accumulate on the tail roller, reducing effective belt grip and causing slip. A wire brush and scraper after each shift prevent this. For bearing wear, listen for a grinding noise when the conveyor runs empty—if present, replace both sides symmetrically.
How Does Temperature Affect Conveyor Belt Tension on the AP655F?
Thermal expansion and contraction significantly influence belt tension on the AP655F, especially in the UK’s variable climate. The belt material (typically rubber with fabric reinforcement) lengthens when hot and shortens when cold. During a summer paving job where ambient temperature is 25°C and the asphalt is 150°C, the belt can expand by up to 3% of its length (approximately 5–7 mm on a standard 8 m conveyor). This requires a deliberate over-tensioning at cold start to compensate—set deflection to 12 mm (tighter) when the belt is cold, rather than the standard 15–20 mm, so that at operating temperature it reaches the correct 15–20 mm.
Conversely, in winter (ambient 5°C), start with the belt at the looser end of the range (20 mm deflection). A cold belt contracts, and if it was set at 15 mm, it can become over-tightened after warm-up, risking bearing damage. Some operators use a thermocouple on the belt surface to monitor temperature. A practical tip: after a 30-minute warm-up run (no asphalt), re-check tension—this catches temperature-related drift. For more comfort-related operation tips, refer to the Caterpillar AP655F Operator Comfort: A Detailed Review (note: climate control in the cab also affects how quickly you can resume work after a break).
What Do Owners Say About Conveyor Belt Tension Maintenance on the AP655F?
Owner and operator feedback consistently highlights the simplicity of the AP655F’s tension system but also its sensitivity to neglect. A paving contractor operating three AP655Fs in the Midlands notes: “We tension belts every 10 hours, and it takes 20 minutes. Saves us £500 a year in belt replacement. The manual is clear, but you have to actually do it—no shortcuts.” Another operator from Scotland comments: “The spring-loaded adjuster is decent, but the lock nuts can seize if you skip oiling them. We use copper anti-seize on threads every 50 hours. One man can do it, but alignment needs a second set of eyes.”
A common frustration is that the tail roller guard removal is fiddly—three bolts that can rust if the machine sits for weeks. Several owners advise replacing these with stainless steel bolts (M12x40mm, readily available at hardware stores) and applying silicone spray before reassembly. The consensus: budget 30 minutes per adjustment, and keep a spare belt in stock (approx. £600 for a genuine Cat part). For more detailed belt maintenance beyond tension, see Caterpillar AP655F Conveyor Belt Maintenance: Essential Tips for Longevity.
One cautionary tale: an owner of a fleet in Yorkshire reported a belt snapping after ignoring a squealing sound for two days. The belt tracked off the tail roller and wrapped around the drive pulley, requiring a full replacement and a damaged conveyor frame repair—costing £3,200. Regular tension checks would have caught the loose lock nut. This underscores the value of the Caterpillar AP655F Transmission System Troubleshooting Guide for diagnosing drive-related faults.
Frequently Asked Questions About Caterpillar AP655F Conveyor Belt Tension
Q: Can I use a pneumatic tensioner for the AP655F conveyor belt?
A: No, the AP655F uses a manual screw-type adjuster only. Pneumatic tools can over-torque and damage the threads or bearing housings. Stick to a standard 37 mm hand wrench.
Q: How do I know if the belt is too tight during operation?
A: Signs include a high-pitched squealing from the drive pulley, excessive heat near the tail roller (touch test—if too hot to keep your hand on for 5 seconds), and unusual belt wear patterns (shiny or polished centre). Check deflection immediately.
Q: Does the conveyor belt tension affect screed performance?
A: Indirectly, yes. Uneven material flow due to a slipping belt can cause screed bounce or inconsistent mat texture. However, electrical issues are more common—see Caterpillar AP655F Screed Electrical System Troubleshooting Guide for screed-specific diagnostics.
Q: What is the maximum allowable belt stretch before replacement?
A: Cat specifies that when the tensioning bolts reach their maximum travel (usually 30 mm from full slack to full tight), the belt is too stretched. Measure the belt length from the manufacturer’s mark—if it exceeds original length by 10%, replace it.
Q: Can I adjust tension with the conveyor running?
A: Absolutely not. Always stop the engine, engage the parking brake, and lock out the conveyor. Reaching under the hopper with moving parts risks severe injury or death.
Q: How much does a replacement conveyor belt cost for the AP655F in the UK?
A: A genuine Caterpillar AP655F conveyor belt costs between £550 and £750 depending on the supplier. Aftermarket belts can be found for £300–£450, but verify fitment and rating for hot asphalt (typically 150°C continuous).