TC Tensioner - Oil Pressure or Spring Pressure

[Richard Howard]

While checking timing chain wear on the transplanted 617.950 in my recently acquired 300SD W126, I noticed about 1/2" to 3/4" lateral movement in the chain just below the cam sprocket on the passenger side.

(With the marks at the cam sprocket perfectly aligned, the marks at the crankshaft showed it to be 2 degrees after TDC; so although some chain wear exists, it could be much worse.)

I don't yet have any detailed information on this engine and, based on what I saw, I now need to ask how the timing chain tensioner operates.

Question: Does the tensioner take up chain slack by use of engine oil pressure or does the long spring shown in a parts picture at the Fastlane site provide adequate pressure to compensate for slack? Do I possibly have a broken spring with this installed tensioner?

The engine ran well before the shutdown for a valve adjustment and a glowplug check/replacements.

Thanks for any info on this.

[theo3000]

The tension is supplied by spring pressure, and I believe the 2 degrees of stretch is normal. I don't know about the acceptable amount of deflection however.

[leathermang]

There are two different styles of tensioner....

Somewhere in the archives I posted a picture from the FSM...

One style uses a spring, a ratchet and engine oil pressure. That is why on start up some engines make more noise before the oil pressure has taken up the last bit of slack. It is discussed in the FSM....

Sounds like you need to open the top of the engine up and recheck the valve adjustments....

[fdanielson]

The tension mechanism is ratcheting and should not move back in once it has pushed out to take up slack. It may be worth your time to remove the tensioner, clean it up, and replace the spring. I did that as part of some other preventive maintenance since the spring is only a few dollars and an improperly functioning tensioner can lead to major problems.