quattrorunner

I realize it's impossable to diagnose from a post. It's even very difficult right in front of the subject at times. My symptoms are a "knock" @ 1300rpm to 1380 rpm or so. I hope I am hearing chain tensioner sounds or something else. The car has a touch less than 200000 on the clock. It's a 911sc 1979. any daring enough to take a guess? Thanks BA

emac

BA
A rod knock does not stop after a certain RPM, nor does it come and go. Its there and you know it. From the moment you start the engine until you shut her down you will hear the noise.


Ernie
81SC

Norske

I use a stethescope to locate noises like this. i agree with Ernie, a rod "knocks" throughout the RPM range and increases and decreases with engine RPM. If you are at the rear and rev the engine you can usullyy locatte the general area where the noise is and use the stethascope from thee.

Good Luck

Peter Zimmermann

BA: Actually, in a 911 engine a rod knock is almost always only heard in the 2800 - 3200 rpm range. Draining the oil and inspection of the sump area and drain plugs should be the first thing that you do. You haven't told us, is your car fitted with Carrera timing chain tensioners yet? If yes, were the 6 chain ramps replaced? Have you listened for the noise with the alternator belt removed? Pre-'82 alternators are very reliable, some can run long enough to have a bearing fail. Also, does the noise change with the clutch pedal pushed in or released?
Pete

emac

Peter
Thanks,, you taught me something today!


Ernie 81SC

quattrorunner

Peter, I'll drain the oil and check the drain plugs. Am I looking for metalic debris? It doesn't have the pressure fed tensioners. I know it's popular but was told very reciently that the older type is fine as long as I update some of the hardware such as ramps and such. Is this accurate? I will use a stethiscope again. The first time I didn't feel I had a good idea where it came from. It's a very small window of oppertunity to hear it. Now that I think about it, it makes sense to someone with no experience with the flat six maybe the sound is loose chain rattling more at a certain rpm?

Peter Zimmermann

Ernie: Thank you!

Quattro: Yes, you will be looking for metal debris. Drain the oil cold, it will come out slower, and there will be a better chance that nasty stuff gets left behind so that you can see it. 930 tensioners are OK, but I prefer the Carrera type. They are a legitimate update, created by Porsche, so, in my book, they are a good thing. Loose timing chains can certainly make noise in the rpm range that you're having difficulty with. If you proceed with tensioner/ramp replacement make sure that you adjust the valves and check the cam lobes for pitting. 200K miles, if all else is normal, can be a point in your engine's life when the cams might need replacement. It will be much cheaper to do while the tensioners are being updated. I had to do cams/rockers in my '82 at 192K miles. I did them because I have no broken head studs, oil consumption is a quart per 1200 (perfect), and the car runs like a watch. Every car is different, only you can know what's up with yours. Let us know what you find in the oil - hopefully nothing but oil!
Pete

quattrorunner

I never found anything in the oil, this is a long time later(1 year). The engine seems to be in good shape for its age, I don't here the sounds anymore, I don't know why. Latley, I have been using synthetic 15-50 and think I'll be switching back to dino oil as I leak worse than before now.

Mike Murphy

My 88 Carrera Targa has an interesting noise, and at first, I thought it was a couple valves. The sound is a little like a rod knock on just 1 cylinder. That is, until it heats up. Once hot, it sounds much more like a valve. How can I best troubleshoot this? I changed the oil recently and found a great deal of debris from the magnet on the tank, but not much from the engine magnet (maybe they just didn't clean the oil tank one?). In any event, the noise doesn't get any louder or software depending on engine RPM or engine load. Any suggestions?

911pcars

Try disconnecting the plug wire of the suspected cylinder. If the load is taken off the cylinder, the rod knock should be less - confirming it is indeed a rod bearing. If it's a main bearing knock, the sound will be constant.

Sherwood