Engine Noise Comes and Goes

[Avanti]

77 911S with stock 2.7 and CIS.

This noise sounds a bit like a fan belt chatter but its not that. Kind of a whirring sound. It happened all of a sudden one morning on start-up. Its always there when the engine is cold and when warm up through the revs. It can be heard at idle but sometimes just stops and the engine sounds normal. Then it may or may not be there at the next stop light when idling.

Can't pick up the noise on recording so I haven't posted a video.

The engine runs fine, idles smooth. Valves were adjusted a few hundred miles ago and all head bolts I could get to were tight, nothing broken.

My first thought is a timing chain tensioner has gone bad but can their noise come and go? When the noise goes away, its suddenly gone like someone flipped a switch.

How can I tell if I have oil pressure fed tensioners? The previous owner did quite a few upgrades/corrections on this car.

[zedsn]

You should have hoses with metal lines that go to your oil system coming out of the front chain covers if you have fed tensioners.

[Avanti]

Thanks. I have small oil hoses in the areas near the timing covers but it looks like they do not go into the timing covers. Could the hoses be for something else?

Anyone have a photo?

[timmy2]

Any play in the alternator pulley when cold?
Up/down, in/out with belt off.
Could be the bearings starting to go.

[Avanti]

Alternator ok. Fresh rebuild with new bearings. Also just replaced the belt as it was 20
Years old. Thought it could be brittle and making the noise. Wish it had been that easy.

[jlex]

Losing any coolant? Maybe bearings going bad in the water pump. Tensioner? Get under the hood when it's making noise to see if you can pinpoint the source.

[jlex]

Originally Posted by jlex

Losing any coolant? Maybe bearings going bad in the water pump. Tensioner? Get under the hood when it's making noise to see if you can pinpoint the source.

Ha.... I feel stupid.... thought I was posting to the BMW forum...

[timmy2]

Take the belt off the A/C if you have it?
Same with alternator/fan belt and run it to see if it goes away when cold.
Don't run it more than a minute or two like that.

New bearings fail faster than old ones these days.
Just eliminate the easy stuff first.

[Avanti]

I can do that, however, I spun the alternator when I changed the belt and the bearings were fine. However a test with the belt would be a 100% in diagnosis. But I've never had alternator bearings make noise and then not at all.

Do timing chains ever make noise intermittently as I described?

[75 911s]

My 75 had some odd intermittent noise. I pulled the cam covers and discovered solid tensioners. With thermal expansion, the chain would be slack at cold and tight at hot. If you don't know the history of the car, it's worth checking it out.

Drain the oil, pull the muffler, rear engine tin and cam covers and take a peek. You can do it without draining the oil if you tilt the rear up enough, but it's a pain and difficult to keep the new gaskets dry.

[Avanti]

Thanks Duane. After warm up would the noise come and go? And what I mean by come and go is not when idling it will come and go. You can be idling and it just goes awayand won't come back. Then drive some , come to a stop and it's there. Then it may go away or not. Going to try again to get it on video.

[75 911s]

The noise I had wasn't consistent enough to pin down in that manner. All I can tell you is that I didn't have Carrera (oil fed) tensioners, and I had done 3 or 4 valve adjustments and was still getting odd noises. So I figured one more thing I could do was to inspect my tensioners and make sure everything was on the up and up. Good thing I did because a PO's wrench had installed solid tensioners on mine. From what I've read, solid are terrible for a street car and can actually lead to the case being ruined from oscillating crank.

After all I read about the tensioners, I knew I would need to get in there and see what was going on. The ones you have need to be rebuilt every 40k miles (assuming you don't have solid tensioners which are fixed to one position). The rebuild kits are $32.00 each and you need a new wright racing gasket kit for the covers. The job is tricky and requires patience and finesse - but it's doable. It's way cheaper than "upgrading" to the Carrera kit which can run $550 used up to 1700 for the peace of mind kit. Assuming you can install yourself. The kicker is Carrera tensioners can still fail and they can leak at the cover seal. So they aren't all that much of an upgrade imho. people seem to go nuts over the Carrera tensioners, but I know at least two great engine builders that use the hydraulic style that are found on the older cars.

Not saying this is the noise, but probably worth checking them out as a long term maintenance item.

Here's my car. You can see the standard oil line. A fed tensioner line would have an additional small metal line leading down from the middle of this line to the middle of the timing covers.


A lot of info, that may or may not be tied to your sound - maybe it's something different. Perhaps an air leak? or exhaust leak?

[Avanti]

Duane,
Thanks for the photo. I have standard tensioners.

Your comment above in post #12 about standard tensioners being bad for a street car has me a bit concerned. I drive the car a few thousand miles a year so hoping if I "go in" and discover a bad tensioner I can just replace it with another standard one. Money needed for another project prevents a Carrerra tensioner upgrade right now but doable in 6 months.

The previous owner of my car was a PCA guy and gave me some extra parts including a couple of tensioners. Is there a process to test them out of the car? I see the kits for $31 and $42 (Porsche) so it only makes sense to rebuild them.

Could you elaborate more on what you mean by "The job is tricky and requires patience and finesse"? I've done a lot of engine repair but none on a 911. I assume I need the cam tool(s) for this job?

[zedsn]

Standard tensioners are fine. He was talking about solid tensioners that some people make. The key is to make sure your chain stays in the same spot when you compress and remove the old tensioner. You don't need cam tools. I used cable ties to keep my chain in place and made a metal piece to keep the tenisoner together once compressed for easy install. There are most likely right ups for tensioner removal and install.

[Avanti]

Zedsn, thank you. Seems like a relatively easy project. Will start digging in the forum.

An earlier recommendation to just check them seems prudent since I have no idea of their condition. The car sat for 18 years (indoors) and was revived two years ago. It still runs fine, just this pesky noise.