964 Oil Pressure Q

[widebody911]

Recap: after a great track day a couple of weeks ago, my oil light was on at idle, and I had a gnarly chain noise. I took it to the shop, and it turns out one of the tensioners failed. I haven't seen the failed parts yet, and I don't the explanation mymechanic gave me well enough to relay it here. New tensioners made the noise go away, but the oil pressure is still low at idle: 8 psi cold, 4 psi hot. At speed, the pressure is fine.

He checked the relief pistons, said they dropped out fine. He said there was a 'booster spring' installed, and wanted to know if I did that, and if so, why. Wasn't me.

He says there's a bunch of possibilities as to why oil pressure is low, anything from a dislodged piston squirter to a deteriorating oil pump. Of course, they gotta go inside for that.

Any other ideas before they have to crack the case?

[Bill Verburg]

Thom, that doesn't sound good

[widebody911]

Originally posted by Bill Verburg
Thom, that doesn't sound good

Yeah, I know.

Oddly, the car was still running like a bat-out-of hell. I don't think it was my driving that did it in - I'm sure Jack drives his at least as hard as I do.

[ischmitz]

Hmmmm,

I have quite the opposite problem: When idling cold my oil pressure is around 2.5 to 3 bar and when really hot it drops to about 1.2 bar. So far so good. On the other hand no matter how cold the engine is I will never get the pressure above 4.5 bar when reving it. So I went ahead and swapped in new pistons and springs for both the oil pressure reliev valve and the safety valve. No change whatsoever.

If I duck my head low to about steering wheel level one might interpret the 4.5 bar as 4.8 Still it somehow nags me that the pressure gauge should peg with the engine cold and mine doesn't..... BTW: It's a 964 gauge and its the original sender.

Ingo

[ischmitz]

Thom,

here are a couple of pictures as to how the pressure fed tensioners on a 964 work. The oil feed bore is where the red arrow points to



The thing looks almost like a coil over strut. The spring is really weak and not sufficient to do any tensioning. That's the reason you need to use mechanical tensioners while you time the cams on a 964. The tensioner has a little check valve. When I took mine out during the rebuild I first thought one of them was frozen. Turns out it was full of oil. Once the check valve gave it pored all the oil out and the remaining spring pressure was next to nothing.

Here is a picture of the entire arangement. The triangular cap has oil galeries that feed the tensioner that itself acts directly onto the chain ramp.



Good luck with your repair. Let us know what the failure mode was. Did the tensioner get fozen collapsed or did it rupture. Curious.

Ingo

[Tinker]

Thom,

Am I correct in assuming that you checked the pressure with a mechanical gauge to confirm the sender is o.k.?

Tinker

[widebody911]

Originally posted by Tinker
Thom,

Am I correct in assuming that you checked the pressure with a mechanical gauge to confirm the sender is o.k.?

Tinker

Yes; these numbers come from the mechanical guage.

[addictionMS]

on the chain tensioner thing, consider sending them to JWE and them install their anti fail mod, I have it and it prevents the tensioner from collapsing so far as to let the chain skip a tooth.

You can also get the collar things but I have heard they can fail, and have actually seen acracked one.

Jim