Inconsistent noise when warm
 

My 86 911 has developed an inconsistent noise that only occurs when the engine is warm and even then only when the vehicle is reving at 2000 rpm's or more. Will also occur when down shifting. Suspected that it was the alternator bearings so I changed the alternator however noise returned. Suspect that it might be coming from exhaust system however the sound is hard to pinpoint. Thought it might also be valves or something in the heads however engine was completely rebuilt just 4000 KM ago. Again, the noise is not consistent and does not always occur even under teh conditions stated above. Not much info however any ideas where I could start to look as a process of elimination??

What's it sound like?

Chain tensioners failing sound like a rapid clack-clack-clack from the rear of the engine and will change with engine speed.

It is a rapid "clacking" sound. The sound is not consistent and will only occur when the engine is warm and revving above 2000 rpm. Even then, it will not always occur. The sound does increase with rpm increase. I was hoping for something that would be an easy fix however guess I will have to take it in to a shop.

If it smooths out a little with increasing RPM and frequency of the clack, I would say tensioners.

If you are a good DIY mechanic and have a few good tools, cam chain tensioner replacement is a simple procedure that you can do yourself.

I will have to pay closer attention to the noise and see if it reacts as you indicated. Given the few Km since the engine was rebuilt (top and bottom end) I had hoped it would be something else. Guess it is what it is. Other than the annoying noise, which only seems to bother me, will I damage anything by driving the vehicle for abit?? No highway trips obviously!

You can hope that it is the valves. Maybe the lock nuts were not tight enough and the valves loosened up a bit. 10000 miles is the adjustment schedule, IIRC.

I did not realize how fresh the engine rebuild was.

Tensioners were included in the job?

Just checking teh receipt for the rebuild job. Cost was $11,500 Canadian. Started with a broken head stud however car was quite smokey so had the valve guides, intake and exhaust valves as well as rings and bearings done. Some minor tranny work was done as well. They reference a chain guide on the receipt with the valve work. Just checked the mileage. The work was done 7000 KM ago. Had the car back for a valve adjustment 2500 KM after rebuild on mechanics request. Just started the car again and it only makes the noise when it is warm and even then it does not always make it. It is a clacking sound as you stated. I can phone the mechanic tomorrow however he is a 2 hour drive from my home so I cannot just pop in to let him listen to the vehicle when it is making the noise. There is a mechanic in town who whose whop works on european vehicles who just purchased an older 911. Could pay him a visit however I am hesitant to let just any mechanic start diagnosing teh problem and taking engine parts off.

If you feel comfortable, you could take the cam chain covers off yourself. Get Wayne Dempsey's 101 Projects book. You will take off some of the engine sheet metal shrouding but it is simple to take a look.

Can you post a video clip to YouTube or something that would have sound?

Also, use the search button. There are many threads about chain tensioners and how to replace/upgrade them. If it is tensioners, install the "Jerry Woods" mod. It is a piece of metal rod inserted into the Carrera pressure tensioner reservoir that prevents the piston from bottoming out in the event of lost oil pressure. It serves the same purpose as the collars on 930 tensioners which hopefully will keep your cam timing chain from skipping a tooth when the tensioner fails.

http://forums.pelicanparts.com/showthread.php?t=180710&highlight=carrera+tensione r+replacement

http://forums.pelicanparts.com/showthread.php?t=29888&highlight=carrera+tensioner +replacement

You will probably get more knowledgeable opinions in the Engine Rebuilding forum

I have both manuals, 101 Projects and the Bentley Service Manual. I will run the car tomorrow and try to take a video clip (with sound) if I can get the vehicle to make the sound again. I can post on youtube or email the clip to you, whichever is easier for you. Would the chain tensioner only make noise when the engine was warm or would it make the noise when the engine was cold as well?? Sorry for the silly question, I am new to this backyard garage mechanic thing however anxious to learn!

Tensioners are *usually* when cold.

I am not an expert by any means. Please consider posting a thread in the engine rebuild section because there are very knowledgable mechanics there like Steve@RennSport, Henry Schmidt, cnavarro, etc.

Thanks for your responses Flieger. You have given me some great ideas and good starting points.

I wish you well. Please keep us updated.SmileWavy