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FYI: Functioning of the timing chain tensioner


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I have this noise problem with my timing chain tensioner. Tommy and Karol were kind enough to reply to a question I posted earlier today about the 5mm ball (I wanted to know if there was a 5mm ball between the outer part of the piston and the screw plug. Bottom line is there is no ball there...the Real OEM's sketch No 11/38 is therefore misleading). Well, I took my piston apart and made a sketch of the chain tensioner arrangement to help me understand how it functions. Here are my findings:

- The piston assy pushes against the chain tensioner and takes up the slack in the timing chain. A spring pushes the piston.

- The piston fits in a bore that is machined into the timing chain cover. There is an oil pool casted into the timing chain cover. The top end of the piston bathes into that oil pool.

- The piston is made up of four (4) pieces that I will call: main body, head (that pushes against the chain tensioner), washer (with 2 notches and 2 holes) and 5mm ball (take note that the taper end of the spring must face the screw plug or else it will interfere with the 2 holes in the washer).

- Oil gets behind the piston: from the oil pool, through drilled passages in the head, past the 5mm ball and past the 2 holes in the washer.

- When you first install the piston, air is trapped behind the piston. There is a path for the air to escape from behind the piston through the top notch of the washer and slots machined into the piston's head (take note that the piston is symmetrical...that is. there is no up or down side since there are 2 notches in the flat, 2 holes in the flat and 2 slots in the piston's head). That explains why it must be bleeded as explained in the Repair Manual.

- As the chain wears, the spring pushes the piston. The piston pushes the chain tensioner. As the piston moves toward the chain tensioner, the ball unseats and oil is pulled behind the piston. There is therefore a liquid column of oil behind the piston that prevents collapse of the piston (and loosening of the chain tensioner) since the ball acts as a one way valve: it lets oil in (behind the piston) but not out. Also notice that there is no positive oil pressure from the oil pump acting on the piston.

Hope this will help those like me that did not understand the functioning of the chain tensioner.

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I did not fix my problem yet but what I hear is an intermittent clicking noise at idle and low RPM. With a stetoscope I can clearly pinpoint the noise to the part of the front engine cover that houses the piston. Go to this internet address for instructions on how to bleed the tensioner: http://www.thetiiregister.com./phpmyfaq/index.php?action=artikel&cat=220435&id=42&artlang=en&highlight=bleeding%20and%20adjuster

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Guest Anonymous

Practically speaking, the moving timing chain will never be as quiet as a similarly equipped timing belt and you may be attempting to cure the incureable. To the extent your noise is unusual, it may be a result of a worn (stretched) chain worn cam gear (and other gears -crank) and/or the guides and tension plate. The tension plate (upon which the piston pushes) is rubberized for obvious reasons. If the rubber is worn off - you now have rhythmic metal to metal contact that will provide a very nice rattle that can sound like war drums or an AC/DC concert parking lot. Use the stock two-row timing chain and double your driving sound! Run very light oil and even more.

A stethoscope is a good diagnostic tool, but hardly foolproof. The valve train is very noise even when it is new and properly setup. Things only get louder when there is wear, low oil pressure and/or improper adjustment added to the mix. Then, you have to factor in the fact that there is still another chain turning the oil pump. Since it is driven by the same crankshaft as the timing chain, one unusual chain sound can be easily mistaken for another.

If you do a search, you will find that many use a solid mechanical timing chain adjuster instead of the originally equipped hydraulic one. That is one way to take the slack out of the chain to potentially eliminate the chain or tensioner as a source of the noise. Again your noise may be normal.

As a final consideration, the alternator and water pump or more (fuel inj. pump if equipped) all make noise as do nearby unsecured bolts, nuts, screws and wires. These are all conveniently near the front timing cover of the engine. Not to be neglected, I have even seen loose spark plug insulators rattle against the head and masquerade as other potential problems.

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