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Savvy rental people understand that the performance of rental trenchers depends on keeping equipment in top operating condition. Customers expect the trenching machines they rent to work efficiently, without breakdowns on the job.

To ensure that efficiency and reliability, trencher users should devote special attention to the machine's digging components, to make sure the digging teeth are sharp and the chain tension is correct.

Most of the trenchers in rental stores have boom and chain digging assemblies that look much like a big chain saw attachment. Heat-treated, hard-surfaced teeth are mounted on a heavy-duty chain. During trenching, the digging chain moves over a system of sprockets and/or rollers. Teeth, chain and sprockets are integral components of these highly-specialized machines. Digging efficiency depends on using the correct chain and teeth for soil conditions and keeping digging components in good operating condition.

Some soils are easy to dig; others are extremely difficult. A trencher that's equipped to work in sand or loose soil may not perform effectively in sticky clay. A trencher set up to dig in rock won't be productive in sand or other soft conditions.

Digging chain is a roller-type design. During trenching, it revolves around the machine's sprockets and rollers much like the chain on a bicycle. Chain is rated by strength: heavier chains are recommended as digging conditions become more difficult. Digging teeth may be bolted onto the chain or carbide bits may be inserted in holders mounted on the chain.

The most popular digging teeth are cup teeth. The best cup teeth are heat-treated with tungsten-carbide hardfacing on cutting edges. During trenching, the shape of these teeth helps move soil fragments away from the walls of the trench. Cup teeth are used in soft and medium soils and some harder formations; and they are a good choice for sticky soils, but are not recommended for rocky conditions.

For rock and frozen ground, bits with carbide inserts are most effective. Bits of this type fit in holders mounted on the chain. Bits must rotate during trenching to help them wear evenly.

Many trenching projects are through areas containing a mixture of soils. Underground formations also change abruptly, and it isn't unusual for a trencher to work through several kinds of soils while digging a few hundred feet of trench. In such situations, many contractors like to use a combination of both cup teeth and carbide bits on the same chain. Tooth patterns vary with conditions.

Experience brings the knowledge of which teeth and chain to use in various conditions. If you are new to trenching, rely on the people at your trencher dealership for help. They know the equipment they sell and service, and they are familiar with digging conditions in your area. They know what works best and what doesn't.

Digging wears a trencher's chain, teeth and sprockets - no surprise there. So it is critical to inspect the digging teeth and chain carefully after each rental.

When a tooth's hardfacing is worn away, replace it immediately. Make sure carbide insert bits rotate freely in their holders. Turn bits to remove dirt or rock that could prevent the bit from turning. If they are stuck and can't be moved by hand, remove them with a hammer and special tool, and clean out the holder. Re-place tungsten insert bits before the inserts wear completely away. Contin-ued use of worn bits eventually will damage the bit holders on the chain - an unnecessary expense.

Always check the digging chain for wear and for correct tension. Not only do worn teeth not run smoothly, they also generate shock loads that can damage other components of the machine. Look for wear on chain roller links, too. Continued use of chain with worn links will allow sprocket teeth to wear completely through the roller sleeves and damage to the pins that hold chain links together will result.

Operating a trencher with an improperly tensioned chain limits the machine's performance. If the chain is too loose, it has a tendency to jump off its sprockets or rollers. A renter who loses the digging chain during a job is not a happy customer.

For instructions on proper chain adjustment, refer to the operator's manual provided by the manufacturer of each trencher model owned by your store. Models differ - don't use the same manual for all.

When the time comes to replace the chain or sprockets, they should be replaced as a complete set.

New sprockets will wear prematurely when operated with a worn chain and a new chain will wear prematurely when operated with worn sprockets. Also, spoil is more likely to be caught between sprocket teeth and chain rollers, stretching chain links and causing pitch length to increase. When the chain stretches, the distance between each pin becomes longer. When the chain's pitch (distance from the center of one chain pin to the center of the next pin) is lengthened by stretching, it no longer matches the pitch of the sprockets it runs on, creating a hammering effect. When a new chain is used on worn sprockets, the chain wears faster and can cause premature chain failure.

Finally, buy only good quality teeth, chains and sprockets that meet the specifications of your equipment. Low-cost bargain products don't save money if they can't withstand the tough stresses of trenching.