Auto_Werks 3.6

I recently noticed that my new to me 911 (964 3.6 conversion) is making a disconcerting noise when the engine is cool. I have spent quite a bit of time searching the archives, but I always turn up chain tensioner threads, and I really don’t think I have a chain problem.

The specifics: When the car first starts there are NO strange noises, just normal 911 valve sounds that are not worrisome. Then about 45 seconds or possibly more, (long enough to walk around behind the car, lift the hood and think to myself maybe the noise has vanished), I start to hear a knocking. It almost sounds like marbles and it is moving at the speed of the valve train / fuel injectors. The rhythm is not perfect though, it almost has a miss, but the engine is running smoothly. I have listened to the engine with a stethoscope, and can not isolate it. I can hear it very faintly in the center case, but I can’t locate the source. I will remove the heater fan tomorrow and see what I can hear from the front 2 driver’s side cylinders (I was poking around there today and noticed slightly louder in that area, but there was no easy way to get my scope in).

This noise gets progressively louder if you leave the car to idle for a few minutes, and then is completely gone by the time the oil temp comes up to the first mark… I have only had this car for a couple months, so I’m actually not sure if it has made this sound the whole time I have owned the car or not. I noticed it as I was waiting for the temp to come up after my first oil change.

To the best of my knowledge this engine has about 60k miles on it, and runs flawlessly. It uses no oil, and its STRONG compared to my old 3 liter car! The only thing I can think of is one valve that’s horribly out of adjustment, or a worn jug with a slapping piston .
Any other thoughts?

Thanks!!

LaughaC

Flux capacitor? Just kidding. You're trying the same things I would.
Until the sound location is isolated any guess is a shot n the dark.

Glad it goes away after warmed up. Maybe it's a sticky valve or a valve guide issue since that may not require engine removal.

Any fluctuations in oil pressure when the noise is happening? Is there a valve that opens the block-mounted oil cooler, and does this sound coincide with that phase of warmup?

Just thinking out loud while we wait for an expert's opinion...

Steve Weiner-Rennsport Systems

Hi:

A few questions, if I may:

1) Has this engine been rebuilt? Do you have any history on it?

2) Do you KNOW whether it has 60K on it for certain?

3) Have you used a stethoscope to listen to the chain covers while its making this noise? Listen to all 4 valve covers?

4) Have you disconnected spark plug connectors in each cylinder (top & bottom) to try isolating this to one cylinder?

5) What brand/viscosity oil do you use?

red67

valve adjustment sounds like what i'd summize with that too. when was the last valve adjustment? are some too 'tight'. loose 'tappity' sounding valves are easier to diagnoze than tight ones. but neither are ideal.

Auto_Werks 3.6

- The oil pressure is spot on, and no fluctuations while the noise is happening. I am using Mobil 1 15w50 which is what I always used in my old SC with great results.

As far as history goes, I don't have a lot. The car started as a '89 euro carrera, and was converted by a company called Ollman Tuning. It was taken apart and combined with a 964 to make an "RS america look". I bought this car from the previous owners widow with almost no documentation. I do have a letter from Ollman tuning stating that the engine was from a 964 with 60k kilometers when it was installed in my car. My odometer now reads 32,000 KM, so i am asuming that the engine probably has ~90k kilometers. As you know this information all actually means nothing, but its the best I can do. My guess is that the engine was never opend, or they would have made a big deal about going through it.

Steve, I have listened to upper and lower covers, but as I said, I have not been able to get to the front drivers side cylinder yet, possibly this afternoon. I also have not tried removing the spark plug wires... are you thinking this will stop the noise if it is indeed a piston slap, or small end bushing?

There are no knocking sounds coming from the timing covers. There is a slight "whirring" sound from that area, but it doesnt sound unnatural.

Steve Weiner-Rennsport Systems

Thanks for the info.

The timing cover sounds are normal, thats perfect.

If you have a loose rocker arm or valve adjustment, you will hear the tapping by placing the tip of the stethoscope (or screwdriver) along various points on the valve covers to find the offender(s).

If its something worse such as a rod bearing, this will change when the plug leads are pulled and that cylinder stops firing.

Please let me know what you find.

Auto_Werks 3.6

Well, it has only been three months , but its finally time for an update. I towed the car in to a local porsche specialist in Columbus, who believes the sound is indeed coming from a slapping timing chain / worn tensioners. He was able to hear it from behind the distributor (upper left), which is one place where I didn't wedge my scope in with great care.

I have pretty much mothballed the car until now, as my budget has been rather tight, but I would like to start making plans for repairing the car so that it is ready for spring. Therefore, I have several more questions.
1.) I feel that I should probably replace the chain ramps as well since they have probably been taking a beating. How much of a challenge is it to replace these parts with the engine still in the car?
2.) Is there a good resource that I can buy which will cover in detail the specifics of the 964 engine? I have a bently book from my old SC, but I don't know if any of this information is still useful (ie valve lash, cam timing etc etc.)

Thanks,

nineoneone

My car on real cool or cold days has a sound similar to what you describe. I found that the alternater was ticking on the shroud.........for what it's worth. After it warms up no more sound, only when cold.

Auto_Werks 3.6

Leonard, I had hoped for a similar situation, but I started the engine for a few seconds with the fan belt disconnected and the noise remained.

Thanks though

Mike Murphy

The good news for 911 owners is that I have yet to come across a thread where someone has reported a rod knock or piston slap that has turned out to be exactly that. The bad news is that it always seems to be related to the valvetrain!

Ryan, are you thinking about doing the work yourself? That might help with the cost and I don't believe it's all that difficult to do, aside from the possibly having to take apart the exhaust system to get at both timing chain covers...