Tapping Sound - Carrera 3.2

[C3larke]

Hi,

My 1985 Carrera 3.2 has been making a tapping sound for some time that is driving me crazy. The sound is somewhat intermittent, but is usually present at idle. The tapping remains fairly loud up to about 1500 rpm, then fades out and becomes inaudible by about 3500 rpm. Sometimes the tapping sound just fades away for a little bit and the engine idles as it should. I took a video of the engine running and making the sound in the hopes someone may be able to tell what it is. Any ideas on what could cause this?

https://www.youtube.com/watch?v=IpIiXIcQSo0&feature=youtu.be

Yesterday I got an automotive stethoscope and tried to isolate where the sound was coming from. I checked the timing chain covers and the oil feed into each tensioner. All I could hear was a steady whirring sound. At the valve covers I could hear varying levels of tapping valve noise in different locations. I decided to pull the intake valve covers while the engine was still hot to see if I could find any obvious problems. I found the rockers felt very loose with a lot of valve clearance. Moving the rockers back and forth sounded very much like the offending tapping sound. I returned the next morning after the engine had cooled and found the valve clearances had tightened back up and seemed to be within spec.

I rebuilt the engine completely about 1 year ago including new valves, guides, springs and seals. I am really hoping I do not need to drop it again to fix a valve/head problem. Could this be as simple as a bad valve adjustment, or is it something more serious?

I have also noticed the car makes a lot of oil smoke when I start it up. I'm not sure if this could be related to the tapping sound or not. Today I started the car after it had been sitting for 3-4 hours, and it smoked for a few minutes. It was thick enough I could see it wafting by when I stopped the car. Once it warmed up, the smoking stopped and it ran clean. It rarely smokes this badly, but is often a little smokey on startup. It seems like oil must be leaking through an exhaust valve into the manifold, then creating a lot of smoke upon start up until the car runs long enough to burn it out. I have not noticed any smoke except during the first minute or two(worst case) after startup. Could this be an issue with the oil tank emptying into the engine more than it should be, or am I looking at a ring or valve guide/seal issue?

Thanks very much for the help.

Chris

[dixbu]

Pulled stud perhaps.

[whiz05403]

When you rebuilt the engine did you have the rockers rebushed and refurbed? Might be a valve spring, were they all replaced or at least checked?

[sc_rufctr]

I just listened to the video.

That's loud and not good. I'm guessing you could have a stuck or sticky valve. I would bet one of them is binding up in the guide.

Were the valves and guides replaced during the rebuild?

With the valve covers off turn the engine by hand and listen for a thunk as each valve is releases as the cam passes over the rockers.
You may find one that sticks and then thunks as it releases. The good news it's an easy and relatively inexpensive fix.

FWIW... I doubt it's bearing related.

[arry911]

I have just listed to your video and I am sorry to say it sounds like mine when my camshaft went, blockage in oil feed pipe over #6 . I had to have a new camshaft and I was running 964 cams so not cheap !!! Does it turnover by hand without catching.

[hcoles]

^^^^^^ my 2 cents.
Doesn't sound good to me either. Your "ticking" sound sounds more than a worn valve guide which is a common problem. I rebuilt the top end 35k miles ago to fix my valve guides and the ticking I had went away at considerable cost (victim of slippery slope).

I suggest running the motor as little as possible while figuring out the cause. Others here will hopefully have additional detailed advice.

[C3larke]

Thanks for all the input.

I am going to pull the valve covers this morning and see if I can identify a problem.

dixbu: I will make sure all the nuts are still tight on the heads to rule out a pulled stud.

Whiz05403: I did not have the rockers refurbished when I did the rebuild. I think I measured the bushings and shafts to make sure they were in spec, but that was it. Is there a way to check on this now that everything is installed? There is definitely some play in the swivel foot or elephant foot on each of the adjusting screws. When I rotate the rockers back and forth by hand, I can see the ball move for most of the 0.004 valve clearance within the swivel. Could this cause noise? I always figured setting the clearance would take up any play in the swivel. Also, I only visually examined the portion of the rocker that runs on the camshaft. Could wear on this part of the rocker cause noise? I replaced all the valve springs as part of the rebuild. I have had the intake covers off before and confirmed that all of the intake valves are very hard to press open by hand. I will do the same check for the exhaust and also do a visual check with an inspection mirror to see if there are any signs of a broken spring.

sc_rufctr: I installed brand new valves, guides, springs and seals when I did the rebuild. Also did a 3 angle valve seat cut to get the seats cleaned up and in spec. I had multiple burned exhaust valves and had lost compression, prompting the rebuild. All that said, I did all of the work myself and may have missed something or screwed something up. I will check to make sure all the valves open and close freely when I get the covers off this morning. I also replaced all the bearings and had the crank polished as part of my rebuild and am very glad to hear it does not seem to be bearing related.

arry911: I will check all the cam lobes while I have the valve covers off. I assume I should see pitting or similar signs of wear if this is my problem. What specifically should I be looking for?

hcoles: I really hope this is not the valve guides as I just replaced them about a year ago. It is possible I screwed something up in the rebuild though. I was planning to drive the car for a ~120 mile trip later this afternoon, but I agree it would probably be prudent not to use the 911 until I get this resolved.

Thanks again for the help.

I'm heading out the the garage and will report back in a little bit.

Chris

[C3larke]

I checked the valves and tightened a couple of them up a little bit. I think they were all in spec, but I tried to get them all as tight as possible without going too tight. I found that I could push all the valves in using a screwdriver handle with a good grip on the cam tower. None of them felt soft and none of them felt sticky. I also looked at the springs using an inspection mirror and could not see any obvious problems.

I found that I could move all of the valves back and forth a little bit by gently levering the valve spring retainer with a screwdriver. This felt more like bending to me than play in the guides. The valves were all pretty rigid when I tried moving them by hand.

I buttoned up the covers and started it up. I was encouraged initially because the noise seemed quieter than I remembered. After a few minutes of driving the noise returned. I stopped by my local Porsche mechanic here in Santa Barbara and arranged to drop the car off Monday to get checked out. Their first impressions listening to the sound was timing chain slap or a broken valve spring. Hopefully that is all it is. In the meantime I will be driving my pickup.

I will post a follow up next week once my mechanic looks it over to let everyone know what the problem was.

[Kemo]

what was the final on this??? thanks!

[pampadori]

Post #8 was his last post.
What do you suspect was the cause? Was it an exhaust leak noise caused by broken lower head studs? perhaps a bad chain tensioner? We may never know.

[ClickClickBoom]

Motor was probably pulled and sent to MotorMeister.......

[OsoMoore]

Originally Posted by C3larke's Profile

C3larke C3larke is offline
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Last Activity: 12-29-2014 07:58 PM

Not a good sign.

[theiceman]

doesn't appear to be a member of the community , just comes here to get his problems fixed or has something to sell , you can ask him when something else breaks and he comes back for help ..

[Reiver]

Rod knock and rebuild time ...too much dinero? Ah, a mystery.

[sugarwood]

Originally Posted by Reiver

Rod knock and rebuild time ...too much dinero? Ah, a mystery.

Almost a natural haiku!

Rod knock and rebuild
Will need too much dinero?
Ah, a mystery.

[Reiver]

Originally Posted by sugarwood

Almost a natural haiku!

Rod knock and rebuild
Will need too much dinero?
Ah, a mystery.

Lol...I will now express myself by dance.....

[VFR750]

Just as a comment to the OP

My cam drive gear was loose on the crankshaft. Ticking sound was the gear knocking against the woodruff key. Woodruff key had significant wear from the hammering. Sound was most noticeable at idle, when warmed up

Repaired crankshaft. Sound went away.

[C3larke]

Sorry I never posted the outcome.

It turned out my valve guides were completely worn out. My mechanic pulled a valve spring and found the suspect valve was rattling loose in its guide. This was clearly the cause of the tapping noise and smoky starts.

I had redone the guides myself when I rebuilt the engine. I used phosphor bronze thinking it was a very hard material that would last a long time. I could have sworn I read phosphor bronze was an excellent material for my application, but it turns out I was wrong. Phosphor bronze has great heat transfer properties, but wears quickly and is therefore more suited to racing engines that are rebuilt often. Silicon bronze guides last a very long time and are well suited to street engines.

With the problem diagnosed, I had the car towed home, pulled the heads, and sent them out to get rebuilt. While I had the heads off, I also noticed the rocker arms seemed a bit loose on their shafts so I sent them in along with the heads. The heads were redone with silicon bronze guides, rockers were re-bushed and shafts polished. I also installed new valve adjusting screws for good measure.

The tapping sound is gone and I don't get any smoke on startup. I wasn't thrilled about having to redo the heads after all the work I did rebuilding the engine and transmission, but I think I got off easy all things considered.

Thanks again for all the help diagnosing this,

Chris