2.7 engine noise

[pat9146]

I had my 2.7 engine rebuilt. There is a noise coming from the engine. The mechanic says "they have diagnosed the mechanical noise from the engine and have deducted that the overlap from the performance grind cams is allowing the compression from the engine to contribute to the mechanical noise noted." He says when they "change the idle speed the noise is diminished." I can still hear the noise. I have read "How to Rebuild & Modify Porsche 911 Engines 1965-1989 and see nothing in there refering to the cams. Could this be a bad diagnosis? If so what could be causing the noise? The noise is not a rattling sound.
I just want to make sure it is nothing serious and can it be fixed so there is no noise.
I would appreciate any help with this.

[greg bradbury]

What does the noise sound like to you, can you describe it to us?
I take it you have installed a new cam. The cam supplier would have a good idea if the cam should cause excess tappet noise. Usually tappet noise is worse at idle and then diminishes as the revs rise.
It's hard to say with a new engine what it should sound like. In general I would say that the 911 engine is a pretty noisy engine at the best of times. Tappet noise, cam chain whurring, pistons slapping around when cold all go to make a pretty noisy tune.
I have just completed my engine rebuild and it sounds noiser in the cam chain whurring department. I figure this is normal as I have new ramps and now oil fed tensioner so things are going to be tighter there anyway. I'm hoping it will quieten down as the miles increase.

So just drive it for a while as see if it gets better after a few 1000 miles or so. Also things may improve after the first tappet adjustment.

Regards,
Greg

[pat9146]

Hi Greg,

Thanks for your response. I am hoping it is nothing more than a valve adjustment. It sounds like you hit the nail on the head. Once the idle speed is increased it seems to be harder to detect. The cams were reground. I had one flaking so it was hard welded and reground. It sounds like something a tappet would make. That was my first thought but since I am not a mechanic I thought I would seek a second opinion based upon what they wrote.

Best regards,

Pat

[2.7RACER]

Gentlemen,
The Porsche 911 2.7 liter engine does not have "tappet noise".
The overhead cam design does not use tappets as found in a typical single cam push rod design engine.
The engine uses one cam per side for a total of two cams.
These cams open the valves through a rocker arm arrangement that has a very small gap (.004") between the rocker and the end of the valve stem to make certain the valves are fully closed under all temperature conditions.
This gap does make a very slight noise. The noise is more discernible if the gap is excessive. A single ticking noise or multiple ticking noise depending upon the adjustments.
It is normal after a rebuild to readjust the valve/rocker arm gap after the engine has run 500 to 1000 miles.
The newer Porsches have done away with this gap by using an oil pressurized (hydraulic) component in place of the swivel foot found on 964 and older engines.
I would suggest you listen to other Porsche engines of a similar vintage as yours to understand what are normal sounds.
Air cooled motors by their very nature are significantly noisier than conventional water cooled motors. All part of the Porsche experience.

[pat9146]

Hi Doug,

Thank you very much for your information. I have not had my valves adjusted yet. I feel better that it is not something that is major. Thanks again for your input.

Best regards

Pat