Vilhuer

From '91 MY changes document

Bypass valve
The engines for 928 models to date had, in addition to the pressure relief valve, a safety valve which served to by-pass the oil cooler. This safety valve is being deleted in engines for Model Year 1991. The crankcase is no longer being machined at this point. Reconditioned engines with new crankcases will also be installed without a safety valve.

There was reason for the change. Maybe not related to this case but worth looking into perhaps.

Mike Frye

Understood, but I don't believe in coincidence. Any chance the two are related? I'm not saying one caused the other, but is it possible whatever caused one also caused the other?

Big Dave

The timing belt warning happened because of the disturbance caused when the tensioner broke free. It's not hard to see how the cam sprocket could change its rotational speed for a moment and transfer slack to the belt, triggering the warning. I'm not concerned about the belt.

I only turned the tensioner bolt a little. When I restarted to see if the belt light was still coming on, that's when the noise started. It became a moot point whether the warning light was solved, so I stopped attempts to adjust it further.

PorKen

It takes ~3 minutes of discontuity for the tensioner warning to light.

AO

I thought that was upon inital startup, but that after the first inital 3 min, it was instantaneous.

Big Dave

I agree....time for some research.

Mike Frye

I can test it right now.

EDIT: I just tested it. 3 minutes from startup. After that it's instant. As soon as the circuit opens, light goes on.


My only point (really just a question) was that I can't figure out the relationship, but my gut tells me that when two systems go bad simultaneously they have to be related somehow. The cam tensioners don't directly affect the cam, so a bad cam tensioner shouldn't directly affect the belt tension, should it?

Sorry for the hijack. This isn't helping with the work you're doing. I'm just trying to learn more about the systems involved.