Lift truck labor
You're setting yourself up for a fall if you take a nonchalant approach with lift chains and fork maintenance

by Paul V. Arnold

When it comes to the care and maintenance of lift trucks, chains and forks are often overlooked.hardware.

The tendency is to focus on the mechanical parts, the engine.  That’s where most look for wear and problems.  For the other parts, most think that if it’s not broken, if they don’t see a piece broken off, that it’s OK.  There’s danger in that mentality.

Forks and chains do not fail catastrophically very often, but certainly there is that risk.  If a chain breaks or a fork bends, the load will fall.  And that could mean injuries to yourself or co-workers and damage to expensive materials.

At the very least, unattended chain or fork problems can mean downtime for your vehicle.

To avoid such situations, operators and mechanics need to get close and personal with each truck’s lift chains and forks.  They need to examine and troubleshoot.  It’s a shared responsibility.  The operator is responsible for inspecting the truck before each shift.  That inspection should include a visual inspection of the chains and forks.  Certainly with every planned maintenance, a full inspection of the chains and forks should be part of a mechanic’s routine.

But what do you look for?  What problems require attention and repair? And what is the root cause of the damage?  It’s straightforward stuff, even if your chains and forks aren’t.

Chains can fail; here’s what to look for
There’s no such thing as average or standard chain life.  Lift truck manufacturers recommend chains be fully examined and lubricated every 50 to 250 operating hours, depending on the amount of use and the plant environment.  Trucks exposed to moisture, low temperatures and chemical solutions or vapors should be checked every 50 hours.

Check for chain elongation, edge wear, side wear, protruding or turning pins, cracked plates and strength failure.  Then lubricate them correctly.  Look for . . .

Elongation: It’s normal for chains to stretch over time.  However, heavy loads and underlubrication can speed this process.  When a section of chain has been stretched 3 percent (from, say, an original length of 12 inches to a current length of 12.36 inches), both chains should be tossed.

Use a wear gauge or tape measure to check elongation.  It’s important to measure the chain in the section that moves over the sheaves since that area receives the most wear.  Measuring chain near the clevis terminals can give a false reading.  Make your measurements from pin center to pin center.

Edge wear: Chain running back and forth over the sheave wears the link plate edges.  Replace chain if the height of the edges is worn 5 percent or more.  Determine percentage of wear by comparing the height of a worn link plate with that of a normal plate (one found in a portion of chain that doesn’t run over the sheave).

Side wear: A wear pattern on the pin heads and outside plates indicates poor alignment.  This can damage chain and sheaves as well as increase internal friction in the chain.  If you find wear in these areas, check chain alignment and clearance and then adjust.

Protruding or turning pins: Highly loaded chain operating with inadequate lubrication can create too much friction between the pin and link plates.  In extreme instances, the torque surpasses the press-fit force between the pins and outside plates, so pins rotate.  Over time, pins can twist out of a chain when operated in this condition.  Never attempt to weld or drive the pin back into place.  You can’t restore press-fit integrity once it is compromised.

Cracked plates: Plates will crack over time.  It’s normal because after repeated heavy loads, fatigue sets in, plates crack and, eventually, chains break.  Fatigue cracks are almost always found through pitch holes, perpendicular to the pitch line.  Cracked plates can also occur where chains are subject to sub-zero temperatures or chemical vapors.

Tight joints: Lift chain joints should flex freely.  Tight joints resist flexing and increase internal friction, resulting in wear and fatigue problems.  Bent pins or plates, rust in the joints and peened plated edges cause tight joints.  Heavy lubrication can free tight joints and combat rust problems.  Replace chains with bent or peened components.  Worn sheaves and very heavy loads can cause peening.  Correcting those problems can prevent future damage.

Strength failure: Lifting loads that exceed the truck’s design can cause enlarged pin holes and broken plates.  Don’t exceed the maximum load level for your lift truck.

Look for fork damage and wear
Many fork maladies are easy to spot.  Others require close inspection.  Red flags for fork problems include: surface cracks, worn tips, bent tips, tips at different heights, worn heels, worn blades, unusual wear and positioning lock damage.  If any of these areas are damaged, the forks need to be repaired and possibly replaced.

Forks are most often damaged by collisions, excessive heat, picking up loads heavier than the truck rating, picking up a load too far out on the forks, bending forks, welding on forks and drilling holes through forks.  Also, fork blades wear down because of contact and scraping.

Perform a caliper check to inspect the thickness of each blade since thickness has an impact on load capacity.

According to lift truck manufacturers, load capacity drops 20 percent when blades lose 10 percent.  This means the safety factor for a pair of forks also drops 20 percent.  Therefore, a 5,000-pound truck with forks that have been worn 10 percent can only safely handle a 4,000-pound load.

To check blade thickness:

1) Measure the shank of the fork with a wear caliper.  Since the shank gets little or no wear, it can be used for original thickness.

2) Place the adjusted caliper over the blade at any point between the end of the taper and the heel of the fork arm.

3) If the inside or lower jaws of the caliper pass over the flanks of the blade, the fork has been worn 10 percent and should be replaced.

Fork stop devices should be inspected.  Repair or replace if the fork retainers are removed, worn or broken.

This article appeared in the December 2000/January 2001 issue of MRO Today magazine.  Copyright, 2000.

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