I need your help..

[Tripleblack51]

My '67 coupe started making this tapping noise a few months ago.
The tapping coincides with the speed of the engine.
After listening to it, a buddy suggested it was my water pump going bad.
So we spent one Saturday afterenoon replacing my water pump with a new one.
The new water pump looked great.. all spiffied up with chevy orange spray paint.
Guess what? The tapping persisted.
We observed that a belt needed adjustment because it was making contact with a hose. We made the adjustment.
Guess what? The tapping persisted.
We now move on to the bigger leagues.
Thinking it could be lifters, I took my car to my mechanic (a guy that specializes in old vettes only)
He kept the car for six weeks and:
Replaced:
All pushrods
All lifters
New Cam (Mellings 350 HP Stock)
New springs.
New alternator belt
Spark plug heat shields
New vacuum advance
New Left and right upper control arm bushings.
New regulator for driver's side vent window
Recharged my AC.
I just got my car back today and she ran great all the way home (about 15 miles) but...
Guess what.....you got it!!
The tapping noise came back!!!
What could be making this noise?
It seems to be coming from the front of the engine water pump/ fan area.
Please help!

Thanks,

Pedro

 

[Mikey1]

Have you checked that the seal around the lower fan shroud area is free....maybe it has moved a little and has contact to the fan.

Often enough simple things cause silly noises. Check for the more simple stuff first.

 

[WayneC]

Need a bit more information about the tap.

Can we assume the noise isn't there when the car is not moving? Otherwise I expect you could use a mechanic's stethescope and/or a rubber hose to localize the noise.

If the noise isn't there with the car not moving, then:
When you say the noise seems to coincide with engine speed... does that mean you've tried putting the car in neutral with the car moving along at speed and the noise slowed down in concert with the engine speed, not the vehicle speed, to be sure it's an engine-related noise rather than something like a stone or nail in a tire?

 

[Tom Bryant]

Well you have fixed most everything that could make a tapping noise. How about the exhaust packings where the front pipes bolt to the manifolds? If there is a slight leak there it will make a metalic sounding ticking noise that changes with rpm.

Tom

 

[IH2LOSE]

Need a bit more information about the tap.

Can we assume the noise isn't there when the car is not moving? Otherwise I expect you could use a mechanic's stethescope and/or a rubber hose to localize the noise.

If the noise isn't there with the car not moving, then:
When you say the noise seems to coincide with engine speed... does that mean you've tried putting the car in neutral with the car moving along at speed and the noise slowed down in concert with the engine speed, not the vehicle speed, to be sure it's an engine-related noise rather than something like a stone or nail in a tire?

Pedro Waynce C and other have some good information here.But I have a question When you brought it into the mecanic did you bring it in specificly for the tap problem and the listed repairs you had done wher done by him to correct/remove the tap ?

I would bring the car back in and have him fix what you paid him to fix. Best of luck and I will be staying tuned to the post to see if I can help once we find out if it there with the car standing still
Larry

 

[Tyler Townsley]

I once chased a 'tap' like this for several years on friends car. Car ran fine but had this lifter sounding tap on # 8 cyl. Replaced everything in the valve train except cam. Finally the friend felt it was time to rebuilt the motor. When it came apart we found a broken piston skirt. A one inch half moon shaped piece had broken off the skirt but the shape of the cyl and piston kept it from falling into the pan. It was loose so every time the piston started a down stroke it would 'tap'.

Tyler

 

[paul67]

Long shot. Fuel pump pushrod.

 

[3TT3V]

another long shot: leaking exhaust manifold gasket.

 

[vettepilot]

Long shot. Fuel pump pushrod.

I agree, that would be on my short list of things to check first before tearing the engine down.

Also,is the noise present at an idle, or only when driving.

Is this an automatic? If so, check for loose flexplate to converter bolts.
Whoops, I looked again, I see it's a 4 spd.
Are you certain the sound is from the front of the engine, I'm thinking maybe the throwout bearing is beginning to get rough.
Also, I noted the valve train replacements, but see no mention of the rocker arms. Did you replace those or at least check for ball pivot wear.
Did you check for loose (as in pulling out) rocker arm studs.
Have you checked the harmonic balancer for deterioration, and/ or loose bolts backing out.

Re-read your original posting on the post work ride home. No noise for approx. 15 miles, then it returned.
I would pull the rocker arm covers and check the height of all the rocker arm studs, sounds like one is pulling up causing the valve lash to increase.
Either that or you have a sticking or collapsed lifter.




vettepilot

 

[Roadfrog]

Another option....before you tear it down to find the elusive noise, just run the car till it breaks. You'll have to tear it down then anyway. This would be hard for me to do, but it's an option.....

 

[67HEAVEN]

Have you used a mechanic's stethoscope to zero in on the noise?

 

[rwd]

A piece of wooden dowel can also be used.

 

[brumbach]

Do you have a mechanical tach? Not sure of what sound you're hearing but my 65 was making a tapping sound similar to a valve out of adjustment. I discovered the tach cable connection to the distributor had worked loose. Once tightened, the noise went away. Hope yours will be as simple. Bill

 

[IH2LOSE]

Have you used a mechanic's stethoscope to zero in on the noise?

Alittle off this topic but bob can you share with us the story behind this photo.

 

[studiog]

Disconnect all the belts and run it for a few and see if the noise is gone. This would eliminate all pulleys, water pump, alternator, Power steer??? and fan noise which also might help you hear it better if it is still there.

 

[Tripleblack51]

Thank you all for your reponses, suggestions and help.

I was beside myself last night with this noise. I got up early this AM and called my mechanic.
I brought the car to him and he listened with a stethescope to determine where the sound was coming from.
He removed the AC compressor belt and started the car turning the ac on.
No noise!!
The noise that we heard previously was similar to this but and it was two lifters and my cam going out. I have no idea who worked on the car before I bought it.
What had happened was that my vintage AC was only at half charge and had not been working properly. This also was checked and no leaks were found.
The car had sat a lot without being driven.
My mechanic said that when you run the ac without a full charge, it can damage the compressor? The bearing in the compressor was making the racket.

While the ac was working great when I picked the car up Friday, I could not stand to listen to that racket.

I trust this guy as he has been in business for a long time working only on old vettes.
He told me that he would not have replaced eveything he did if it was not required. I believe him.

The guy that originally diagnosed the water pump is my C5 mechanic who is well respected and a good friend to boot. He was wrong.

Quite a few of my friends listened to the noise originally and no one guessed the ac compressor. Most of them thought it sounded like lifters.

Bottom line, my saga is over. The car sounds wonderful, much better than it did before the work. The resonance inside the car with the ac on is awesome, and the exhaust note is much deeper.

I am not a mechanic. I can do minor things like a tune-up, hoses, water pump, etc. But I've never had an engine apart and re-assembled it.

I do appreciate my on-line corvette family though.

Here's to you guys...

Thanks.



Pedro