The chain tensioner on the W113 engines is a mechanical/hydraulic unit. It is mounted directly below the thermostat housing. A piston protrudes into an oil pool in the chain gallery of the head, where it contacts the chain tensioning sprocket arm.
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An opening in the end of the piston draws oil into the hydraulic cylinder and a check valve prevents the oil from escaping. Normal engine operation and chain sprocket movements provide a pumping action which keeps the tensioner and chain tight by filling the piston and housing with engine oil.
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A spring inside the tensioner provides some tension, however the real work is done by the hydraulic pressure. This spring is also critical in the operation of the oil check valve of the tensioner. This check valve involves the ball, the cap and the spring.
A plastic or metal spacer is located in the tensioner spring and limits inward travel of the piston.
The "oil pool" is an area built into the chain gallery of the head which collects oil as it splashes inside the engine. The opening in the chain tensioner piston retrieves oil from this "oil pool". A 6mm socket head bolt is also located in this oil pool. This bolt must be in place or a severe exterior engine oil leak can result. The threaded hole for this bolt can emerge on the exterior of the block behind the water pump. If the bolt is left our during repairs, a mysterious oil leak may result.
The chain tensioner provides chain tension until the chain wears or stretches beyound the tensioners outer limit at which point the timing chain would need replacement. These tensioners are very reliable and durable and normally last the life of the engine. There are no seals invoved in the hydraulics. Very, very tight tolereance between the piston and its housing (cylinder) insure good seal and long life. Instances of tensioner failure on these engines is very rare.
An aluminum seal is located uder the "cap". Also large rubber "O" ring is seated in a groove at the tensioner/head parting surface. These two seals prevent oil from leaking but are not involved in the tensioner hydraulics.
Removal of the chain tensioner is accomplished by removing the thermostat housing and removal of the two nuts at the tensioner. If the car has factory AC the complex compressor brakcet must be removed. It is not necessary to remove the chain tensioner sprocket and arm in the chain gallery when removing the tensioner.
Joe Alexander
Blacklick, Ohio