M104-timing chain tensioner confusion

[woodman]

Hi everyone. I hope someone can shed some light and clear up some confusion I have on this.
My understanding is that they are hydraulic. Yes /No?
Then, if that is correct, the only function of the spring is to maintain pressure on the guide and keep the chain taught until the oil pressure is built up and overcomes the spring.
Is this correct ?

 

[JC220]

Hi everyone. I hope someone can shed some light and clear up some confusion I have on this.
My understanding is that they are hydraulic. Yes /No?
Then, if that is correct, the only function of the spring is to maintain pressure on the guide and keep the chain taught until the oil pressure is built up and overcomes the spring.
Is this correct ?

Yes correct the tensioner element has a spring inside to keep a basic pre load on the timing system when the motor is off.

When it is running the engine oil pressure flows into the chain tensioner and keeps the chain tight during operation.

 

[gerryvz]

Building on what @JC220 says, the spring retains the adjustment that it reaches, via a ratcheting mechanism, and the mechanical spring tension once adjusted cannot get looser, only tighter.

This is why the M104 timing chain tensioner must be completely disassembled and "reset" when removed and re-installed, unlike the tensioners for the V-8 M117 and M119 models. It is a common mistake for those re-installing M104 tensioners not to reset them, and not doing this more likely than not will actually snap a camshaft.

 

[woodman]

Ok .. this is what I thought. I just did my chain and new guides. My old tensioner was not scored just a little polished. My new tensioner spring is 8mm longer.
My thought process is more spring tension more pressure on the new guides and chain.
If it is a ratchet and just to keep some pressure on the chain via the guide and the oil pressure actually controls the operating tension why would I want to install it? It seems to me that it would put more wear on the guide and excessive pressure on the chain and sprockets.
Is there a spec for free length of the spring?