Motor Has a Faint Tapping Noise

rickbtbird

Registered User
This started last week. On my 90, I can faintly here what sounds like a single valve noise coming from around the rocker covered on the driver's side. I put a stethoscope up to the rear of the rocker cover and it's more noticeable. If it's indeed valve noise what's the possibilities?
  • Broken Spring
  • Bent Rod
  • Defective/Dirty Lifter
What's the other possibilities?
  • Dipstick issue
  • Exhaust Manifold
  • Fuel Injector noise
Two years ago I removed and reinstalled (with new gaskets and seals) the intire fuel-injector, air system excluding the intake manifold so I know that's real new. The exhaust manifolds were reworked with ported ones three years ago. If you have any experiences like the valve noise I discribe please let me know what your root cause was.

Also, I'm a bit confused about the valve stem-to-rocker arm clearance. The book says it's .088 to .189. Then it says the Rocker arm fulcrum bolts have a two step torque sequence. So with that said, how is the clearance maintained? Do you measure it and adjust it after you torque the fulcrum bolt or do you use different size push rods to get the required clearance?
 
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I did an investigation today on the source of the problem. I've noticed that the sound is louder coming from under the car and when I open the hood it almost non existance. I purchased one of those $4.00 automotive stethoscopes a few weeks back. I check the engine bay and put the probe on different parts of the motor.
Engine Bay:
  • Driver's side valve cover front - soft taping
  • Driver's side valve cover rear - noticable tapping
  • Driver's side exhaust manifold rear - loud tapping
  • Dipstick Tube - loud tapping

Got under the car
  • Oil Pan - Noticable tapping
  • Exhaust Down Tube - loud tapping
  • Dipstick Tube - Loud tapping

So I'm not 100% sure where it's coming from. Can someone suggest some check points with the stethoscope or do I have to start removing parts?
 
Someone mentioned in another post to pull the dipstick and see if there is any kind of rubbing marks on it.. like a polished area. That would be the simplest thing to check for and rule out.
 
I'm not discounting the dipstick but I'm leaning towards the exhaust, here's why. If the sound gets louder on the exhaust and the dipstick it must have something to do with the exhaust rather then the dipstick because they're both loud and the dipstick tube is bolted to the exhaust manifold.

With that said I really think my next step would be removing the IC tube and check the torque on the exhaust manifold bolts. Also I had these manifolds put on special because they were ported. Since I didn't do the job, I don't know how they were torque on. Since I’ll have to remove the bolts on the dipstick tube checking the tube should be an easy next step.
 
Oh well, to me its alot easier just to pull out the dip stick and look at the end of it and rule that out first (not the tube as it is no where near the crank shaft), than removing all the IC tubes etc etc first.
 
Oh well, to me its alot easier just to pull out the dip stick and look at the end of it and rule that out first (not the tube as it is no where near the crank shaft), than removing all the IC tubes etc etc first.

If I pull out the dipstick the noise remains. Sorry if I didn't mention that eariler.
 
maybe?

Dunno
crank bearing's???

Heat is another factor that accelerates bearing wear and may lead to failure if the bearings get hot enough. Bearings are primarily cooled by oil flow between the bearing and journal. Anything that disrupts or reduces the flow of oil not only raises bearing temperatures but also increases the risk of scoring or wiping the bearing. Conditions that can reduce oil flow and cause the bearings to run hot include a worn oil pump, restricted oil pickup screen, internal oil leaks, a low oil level in the crankcase, aerated oil (oil level too high), fuel diluted oil from excessive blowby or coolant contaminated oil from internal coolant leaks.

Temperatures in excess of 620 degrees can melt away the lead in copper/lead bearings and those with babbitt overlays. Because copper doesn’t melt until 1,980 degrees, burned copper/lead bearings will typically have a copper appearance instead of the normal dull gray appearance.

Misalignment is another condition that can accelerate bearing wear. If the center main bearings are worn more than the ones towards either end of the crankshaft, the crankshaft may be bent or the main bores may be out of alignment.
 
I'll ask this. When I listen to the exhaust on the passenger’s side and there's no tapping noise but when I listen to the exhaust on the driver's side and I hear the tapping noise, wouldn’t that discount a crank bearing?
 
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