Engine noise diagnosis help Please - apparent valvetrain

[KobaltBlau]

Hello All,

I thought I might enlist your help with a noise I have on a stock 81 3.0SC engine (US).

It sounds like a lound valve "lifter", a sharp click. I realize 911s don't have lifters per se but it sounds like what would be described as "lifter noise". If I use a stethoscope on the valve covers I hear a similar noise coming from each properly adjusted valve, but this is much louder.

It happens more when the engine is hot, it doesn't really happen when cool.

More strangely, the car can be idling hot and the noise will come and go. It is easy to make the noise happen when the engine is hot by revving the engine up, then letting it fall back to idle. Once back at idle I will here a loud repetitive clicking for a while (perhaps 15 seconds) then it will stop and the engine will sound perfect. Sometimes it starts on its own, though. I can't hear it much when the engine is off idle, but I think that is because there are plenty of other noises at that rpm.

This noise seems to be coming from the cylinder #1 intake valve area.

I had this noise, and was due for a valve adjustment so I figured something was probably just out of adjustment. I did the valve adjustment and each cylinder including #1 took a consistent adjustment, which I double checked on all cylinders. I also checked all of the rocker shafts for tightness and position. no problems that I could find.

The engine ran very strongly up to redline both before and after the adjustment, with no issues at higher rpm.

I have also done a leak down test on the #1 cylinder which is very low at 2-3%, all appears to be past the rings by the listening to exh/intake/oil tank method.

Does anyone have any ideas on what this could be? I'd be happy to answer any questions!

Thanks in advance!

[Nine9six]

Right off hand I'd say possibly you have an exhaust leak. Many exhaust leaks have been misdiagnosed as valve train issues.

[thabaer]

My exhaust leaks have always been louder when I prod the gas off of an idle. The last one I fixed was quiet when the engine was cold and became louder as the exhaust plumbing heated up.

[KobaltBlau]

Thanks!

Couple of things that I think make that unlikely:

1. Exhaust leaks seem to be louder when there would be higher pressure in the primaries, like accelerating under load. Idle is not really one of those times.

2. The noise has a _very_ distinct loud click, not a sharp pfft like an exhaust noise.

3. The noise is louder from the top of the engine, as I mentioned the stethoscope test indicates the #1 intake rocker area. the #1 exhaust area does not seem to have the noise with the stethoscope test.

Keep 'em coming, please!

Appreciated,

[Jeff Alton]

How is the oil pressure?

[Scott R]

Possible broken chain ramp in the drivers side compartment? My timing compartment meltdown sounded like valve clatter, I think It was transmitting noise through the cams and into the heads, and everywhere else for that matter.

[KobaltBlau]

Originally posted by catca
How is the oil pressure?

oil pressure is great, runs like a champ! no issues detectable in the gauges or the way the car drives.

Originally posted by Scott R
Possible broken chain ramp in the drivers side compartment? My timing compartment meltdown sounded like valve clatter, I think It was transmitting noise through the cams and into the heads, and everywhere else for that matter.

That's an interesting thought, though when I put my stethoscope on the chain housing I don't hear the noise as much, just the chain whizzing around. but as you said, maybe it is transmitting through the cam, the noise sure doesn't seem to be originating in the chain housing, but who knows...

[hobieboy]

If you suspect its the intake valve, have you tried opening up the valve cover & take a look if there's anything obvious? Very simple job without even the need to drain the oil.

[KobaltBlau]

have been planning to do that, but I want to know what to look for. I just had it open 5 days ago for the valve adjustment and everything seemed fine, tight rocker shaft, I set correct valve clearance (was only a little off, consistent with other cylinders). There's not that much in there but I must have missed something, or the noise isn't coming from where it sounds like it is...

The noise was the same before and after that valve adjustment I just did last weekend.

[Grady Clay]

Andy,

I ran this by Greg yesterday afternoon. He suggested pursuing the broken valve spring idea more. That could give the come-&-go of the tapping as the spring parts rotate around. The inner spring is very difficult to see but you might make a wire tool to get between the outer coils and see if the inner spring wiggles.

Best,
Grady

[Scott R]

Originally posted by Grady Clay
Andy,

I ran this by Greg yesterday afternoon. He suggested pursuing the broken valve spring idea more. That could give the come-&-go of the tapping as the spring parts rotate around. The inner spring is very difficult to see but you might make a wire tool to get between the outer coils and see if the inner spring wiggles.

Best,
Grady

And Greg has been %100 dead on with all of my P-cars over the years, that's something to check for sure.

[syncroid]

My bet is that you have a broken valve spring.

[KobaltBlau]

Very good info Grady.

yes, maybe the inner spring only is broken, could the engine still run to 6000 without problems? maybe so.

I think I will take the upper valve cover off tonight and see if I can see anything in there.

[KobaltBlau]

What kind of disassembly does replacing a broken valve spring require?

[syncroid]

If it is an upper broken valve spring you will need to remove the upper valve cover. You should remove the bottom one as well. You will drop the keepers more then once if its your first time. I recommend also a magnet on a telescoping stick. You will need compressed air, the appropriate adaptors to keep the cylinder under pressure, the tool to compress the valve spring, and the patience to not want to kill something when you drop the keepers for the umptienth time.
Muahahahaha Have fun.

[hobieboy]

if you can rev to & stay to 6000 rpm I doubt you have a broken valve spring... maybe its not intake valves?

In fact, I just broke "something" in my intake valve "assembly" on cylinder 6 on the track 2 days ago - the spring & hat were way too high suggesting valve retainer is gone. The engine won't even idle right & sounds like its about the fall apart completely

[Scott R]

Originally posted by syncroid
If it is an upper broken valve spring you will need to remove the upper valve cover. You should remove the bottom one as well. You will drop the keepers more then once if its your first time. I recommend also a magnet on a telescoping stick. You will need compressed air, the appropriate adaptors to keep the cylinder under pressure, the tool to compress the valve spring, and the patience to not want to kill something when you drop the keepers for the umptienth time.
Muahahahaha Have fun.

I fill the cylinder through the spark plug hole, with rope. It keeps the valve in place while I work on it, learned that working for GM.

[wswilburn]

When I had a broken outer spring on my 82 SC, it would rev just fine until 6300 RPM, then act like the rev limiter was kicking in. In fact, I thought it was the rev limiter until I had the engine out for resealing.

Edit: changed 'inner spring' to 'outer spring'

[Early_S_Man]

Andy,

Could be that an intake rocker arm has worked loose ...

[ianc]

How about just worn rocker arm bushings?

ianc