Occasional Clacking noise when engine warm

[thaxtela]

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. Engine was rebuilt, top and bottom end approx. 7000 KM ago. Valves were adjusted 2500 KM after rebuild as per emchanics request. Again, the noise is not consistent and does not always occur even under the conditions stated above. Possibility of chain tensioner was suggested however the noise, when it does occur, is only when the engine is warm and revving above 2000 rpm. Not much info however any ideas where I could start to look as a process of elimination??

[88911coupe]

Interesting...I was hearing a similar clacking sound when Idling and the engine fully warmed up. I assumed it was loose valve guides and the need for a valve adjustment. My car is apart for a rebuild and I'm hoping the problem is solved. BTW, it would dissappear with very slight idle increase.

[thaxtela]

I am planning to have the valves adjusted again. Hoping this solves this problem as well. Thanks for the reply.

[Aurel]

I would also check that your headstud bolts and exhaust bolts are all thight. Leaks there would also cause a clacking noise.

Aurel

[911 tweaks]

+1 on the head & exhaust studs tight. Has the heads been re-torqued since the rebuild? I believe they should be done after ~1-2k miles.
Aurel had a somewhat similar sound from his exhaust flanges that mate up to the exhaust ports on the heads not being flat.
Good luck here and please report back what you find.
Bobi

[thaxtela]

Thanks guys. I will check the headstuds and exhaust bolts this afternoon. Will let you guys know.

[thaxtela]

Checked all bolts I could find on the exhaust system and all were tight. Have not checked the head studs yet. I do know that they were retourqued after 2500 km from the time it was rebuilt. Doesn't mean that they have not become loose. The sound was prsent again this morning and was evident within a few minutres of start-up. After the car cooled for about 5 hours the sound was not present. Leaning more towards thinking its the chain tensioner however this is an uneducated guess. Would the sound be consistent if it was the chain tensioner or would it come and go?? Everyday is a new adventure with a 20 year old vehicle isn't it!

[Aurel]

Record the sound and post it here. That will help us give a diagnostic. Most digital cameras will do it. You can post on youtube and link here.

Aurel

[Aurel]

Record the sound and post it here. That will help us give a diagnostic. Most digital cameras will do it. You can post on youtube and link here.

Aurel

[thaxtela]

Took distributor cap off last evening, cleaned contact points and reattached all spark plug wires. Re-attached distributor and ran the car until warm...no clacking sound was evident. Started the car this morning and took for a quick run...still no clacking sound. I know its too optimistic to think the problem has left however will run the car today and see if sound returns. If it does, will record as suggested and post. Would a loose distributor cap and/or loose speak plug wire cause engine to make clacking noise?? Probably a silly question from a guy still new to this garage tinkering mode.

[Flieger]

Certainly, it could be spark knock or a couple of intermittantly inoperative cylinders.

[thaxtela]

Ran the quite a bit today and no noise. However a noticable power increase. Perhaps I lucked out and the problem was in the manner in which the distributor was sitting and a loose spark plug lead or two. Will run the car again tomorrow and hope for the best.

[thaxtela]

Well, I knew it was to good to be true. the clacking noise has returned this evening. I removed the distributor cap and rotor again to look at the distributor shaft. The shaft has some movement, mostly up and down (approx 1/8 of an inch) and slight movement side to side. Is this normal?? I have searched the previous post however cannot find any indication how much movement is normal. The old rotor showed burn marks and wear on the right side of contact bar. The contact points in the distributor cap also show uneven wear, almost small gouges. Thanks in advance for your patience and assistance as I muddle through this problem.

[Flieger]

I would be most concerned about the side-to-side play. Steve Weiner @ RennSport is a good guy to contact about distributors. Maybe PM him and let us know what the correct specification is.

Steve@Rennsport is his username

[Flieger]

Henry Schmidt is good, too:

[thaxtela]

Thanks Flieger. I have sent a PM to Henry Schmidt. Will also send one to Steve.

[Porshaah]

Thaxtela

Could be the early signs of a main/rod bearing starting to spin. Draw some oil out of the crankcase and see if there are any sparklies in it.

Bill
90C2

[thaxtela]

Thanks for the advice guys. Have weakened and taken the car to a mechanic to diagnose the problem. He suspects a chain tensioner wo will start there. Will keep you guys posted.

[thaxtela]

Car fixed. Nasty little chhain tensioner was teh problem all along. Thanks to everyone who responded to my panic and offered suggestions.