Odd Sound Coming from SC Engine

86 911 · 86 911's Garage

Hi all,

I have a '76 911 with a '78 3.0 engine and trans. Over the past few months I have been hearing an unusual sound coming from the engine. The sound is very similar to the sound that occurs when you hear the chain on your bicycle rub against the gear sprocket when your gears are out of alignment. It is kind of a raspy sound like someone is shaking pebbles in a tin can. I cannot place where the sound is coming from, so I thought I might get some ideas from you guys. This is when the sound occurs:

1) During the first 10 seconds of start up with the engine cold (trans in neutral).
2) When I shift the car into a high gear and it is under heavy load (e.g. going up a hill).

It is really starting to worry me. I went for a drive (only about 20 miles) and I was driving the car pretty aggressively and reaching high RPMs. As I finished my drive and drove down my street, there was a noticeable rattling sound coming from the engine. It was like the sound I described earlier but much much louder. The sound only occurred when I was in 3rd gear between 1500-2200 RPM and then it disappeared when I went above 2200 RPM.
I parked the car for a couple of hours and drove it for another 50-60 miles and the sound did not return. Should I be worried? I am thinking this is either a chain or a chain tensioner failing, but I do not know what they sound like when they are about to fail. How do they sound before they fail?

Thanks for any advice!

Oh Haha · 01-01-2012, 04:25 PM

Chain tensioner failure!! DO NOT DRIVE THE CAR UNTIL YOU FIX THE PROBLEM!!!!

This is a common problem so it's not the end of the world but you will need to read up on how to replace the bits.

tirwin · tirwin's Garage

Funny you have this problem. I got Wayne's 911 engine rebuilding book for Christmas and that's exactly the way the sound of the chain tensioner failure is described. I would agree with not driving until it. Do you have the upgraded carrera tensioners already? If not you need to add that to the repair list.

86 911 · 86 911's Garage

Hmm that is what I am suspecting. I do not have the upgraded tensioners on it and they are stock for all I know. I have done some research and the sound is definitley not a pinging sound, but rather a continuous rasp. It is hard to get a sound clip of it since it happens so randomly and it is barely noticeable over the already loud engine.

Oh Haha · 01-01-2012, 04:52 PM

Assume that it IS the tensioner(s) failing and plan to install the Carrera oil fed tensioner kit.

Don't mess around waiting to confirm the sound.

While the repair is DIY-able, if you aren't comfortable with opening up the chain boxes leave the job to a technician.

kodioneill · kodioneill's Garage

I would verify the tensioners but another source for the sound could be the alternator or the fan. Sometimes the alternator bearings wear out and the fan will rub the housing.

Tidybuoy · 11:37 AM

Just to throw in a wrench....my car has developed a rattle that has been a big concern. However, using my friend's set of ears (another Porsche owner), he feels like it sounds like an engine tin rattle. I then tightened all tin bolts and the sound switched to the other side of the car. I then jacked up the car and searched for the noise - it sounded like it was coming from the middle of the muffler & I could make it go away if I pushed up on the muffler real hard. I removed the muffler and there was nothing loose inside the muffler. I pushed up on all tin and nothing was loose.

Then, when I re-installed the muffler, I discovered that I could change the tone of the rattle from loud to soft by tightening/loosening the muffler straps. I can't make it go away but this tells me it is definately the muffler. The good news: it's the muffler, the bad news: I need to buy a new muffler.

Just throwing this situation in because my noise sounds like it could be coming from cam chains as well - but it's definately the muffler.

Vern

Flat6pac · 01-02-2012, 12:36 PM

The 2K RPM is the clue for the tensioner chain rattle at least with the Carrera fed tensioners it is.
Bruce

Alan Lindquist · 01-02-2012, 12:43 PM

This is not a mechanical problem any more. It's a gambling problem.

Don't drive the car. In fact, don't start the car. Start removing the muffler and the timing box covers and take photos and get trustworthy advice from the forum. You can always give up and get it towed if the project is beyond you but you'll KNOW what you're dealing with - FREE

or

Tow to mechanic now - $100
Chain Tension Inspection - ? (maybe $200?)
New chains and gears and tensioners and ramps - $ (not cheap, but you have to do it if necessary)

or

Catastrophic engine failure because it is the Chain Tension and you kept driving it while wondering - $6,000+

Are you the gambling sort? You have a hand to play.

RSTarga · 01-02-2012, 02:12 PM

STOP, have it towed to your shop!
I had a failure while driving and it ate just about all my valves, and a couple of pistons.

86 911 · 86 911's Garage

Thank you for the input. I'll see what I can do about checking it. I'm parked in a carport in an apartment complex (don't worry - very safe area) so I don't have the ability to do too much. I'll see what the procedure for taking off the chain covers entails but I'll most likely just tow the car to my mechanic (thank God for AAA unlimited towing!). I'll keep everyone posted.