Input please

I have a 1976 vette with about 120K miles on it.

Last year I had to do a fair amount of work on it (spring, shocks, rad
support bracket, new rad, new water pump.).

It seems to have been developing a problem and I am not sure what it
is.

I thought it started about the time I installed the new water pump,
but that could be nothing more than sheer coincidence. It was making a
sort of slight rubbing/banging/knocking noise, and I thought it was
some minor machining discrepency causing a slight rubbing of the water
and main pulleys. There was a rubbing sound that went away after a
bit.

Yesterday I had to replace a motor mount and tightened a bit of
exhaust on the manifold.

Today the noise is back. But now It sounds morelike a banging/knocking
sound. The frequency increases with engine RPM. If I bring the engine
up to a modest rpm and hold it there , it seems to go away. It seems
worse when I first start it.

Now I am obviously not expecting a thorough diagnostic from this
description, but I am not a very experienced mechanic. Does it sounds
like the symptoms of a main/crank bearing or something terminal of
that nature? If so, I'm afraid old Betsy is doomed because I do not
have the facilities nor the resources to get it repaired ......

FWIW, it still seems to run ok, oil pressure is normal, battery
charging, water temp, shifting etc.... I went around it with a crowbar
and using it on my ear as a poor man's stethoscope and was unable to
pinpoint the source of the problem (so far)... It definitely seems to
be coming from the bottom part of the front/engine somewhere.....

Thanks for any input.

On Jul 9, 11:29*am, " > wrote:
> I have a 1976 vette with about 120K miles on it.
>
> Last year I had to do a fair amount of work on it (spring, shocks, rad
> support bracket, new rad, new water pump.).
>
> It seems to have been developing a problem and I am not sure what it
> is.
>
> I thought it started about the time I installed the new water pump,
> but that could be nothing more than sheer coincidence. It was making a
> sort of slight rubbing/banging/knocking noise, and I thought it was
> some minor machining discrepency causing a slight rubbing of the water
> and main pulleys. There was a rubbing sound that went away after a
> bit.
>
> Yesterday I had to replace a motor mount and tightened a bit of
> exhaust on the manifold.
>
> Today the noise is back. But now It sounds morelike a banging/knocking
> sound. The frequency increases with engine RPM. If I bring the engine
> up to a modest rpm and hold it there , it seems to go away. It seems
> worse when I first start it.
>
> Now I am obviously not expecting a thorough diagnostic from this
> description, but I am not a very experienced mechanic. Does it sounds
> like the symptoms of a main/crank bearing or something terminal of
> that nature? If so, I'm afraid old Betsy is doomed because I do not
> have the facilities nor the resources to get it repaired ......
>
> FWIW, it still seems to run ok, oil pressure is normal, battery
> charging, water temp, shifting etc.... I went around it with a crowbar
> and using it on my ear as a poor man's stethoscope and was unable to
> pinpoint the source of the problem (so far)... It definitely seems to
> be coming from the bottom part of the front/engine somewhere.....
>
> Thanks for any input.

take a long screwdriver and place the tip on different parts of the
motor and the other end against your ear, and see where it's loudest.

On Jul 9, 11:38*am, m6onz5a > wrote:
> On Jul 9, 11:29*am, " > wrote:
>
>
>
> > I have a 1976 vette with about 120K miles on it.
>
> > Last year I had to do a fair amount of work on it (spring, shocks, rad
> > support bracket, new rad, new water pump.).
>
> > It seems to have been developing a problem and I am not sure what it
> > is.
>
> > I thought it started about the time I installed the new water pump,
> > but that could be nothing more than sheer coincidence. It was making a
> > sort of slight rubbing/banging/knocking noise, and I thought it was
> > some minor machining discrepency causing a slight rubbing of the water
> > and main pulleys. There was a rubbing sound that went away after a
> > bit.
>
> > Yesterday I had to replace a motor mount and tightened a bit of
> > exhaust on the manifold.
>
> > Today the noise is back. But now It sounds morelike a banging/knocking
> > sound. The frequency increases with engine RPM. If I bring the engine
> > up to a modest rpm and hold it there , it seems to go away. It seems
> > worse when I first start it.
>
> > Now I am obviously not expecting a thorough diagnostic from this
> > description, but I am not a very experienced mechanic. Does it sounds
> > like the symptoms of a main/crank bearing or something terminal of
> > that nature? If so, I'm afraid old Betsy is doomed because I do not
> > have the facilities nor the resources to get it repaired ......
>
> > FWIW, it still seems to run ok, oil pressure is normal, battery
> > charging, water temp, shifting etc.... I went around it with a crowbar
> > and using it on my ear as a poor man's stethoscope and was unable to
> > pinpoint the source of the problem (so far)... It definitely seems to
> > be coming from the bottom part of the front/engine somewhere.....
>
> > Thanks for any input.
>
> take a long screwdriver and place the tip on different parts of the
> motor *and the other end against your ear, and see where it's loudest.

I went around it with a crowbar
and using it on my ear as a poor man's stethoscope and was unable to
pinpoint the source of the problem (so far)... It definitely seems to
be coming from the bottom part of the front/engine somewhere.....

> wrote in message
...
>I have a 1976 vette with about 120K miles on it.
>
> Last year I had to do a fair amount of work on it (spring, shocks, rad
> support bracket, new rad, new water pump.).
>
> It seems to have been developing a problem and I am not sure what it
> is.
>
> I thought it started about the time I installed the new water pump,
> but that could be nothing more than sheer coincidence. It was making a
> sort of slight rubbing/banging/knocking noise, and I thought it was
> some minor machining discrepency causing a slight rubbing of the water
> and main pulleys. There was a rubbing sound that went away after a
> bit.
>
> Yesterday I had to replace a motor mount and tightened a bit of
> exhaust on the manifold.
>
> Today the noise is back. But now It sounds morelike a banging/knocking
> sound. The frequency increases with engine RPM. If I bring the engine
> up to a modest rpm and hold it there , it seems to go away. It seems
> worse when I first start it.
>
> Now I am obviously not expecting a thorough diagnostic from this
> description, but I am not a very experienced mechanic. Does it sounds
> like the symptoms of a main/crank bearing or something terminal of
> that nature? If so, I'm afraid old Betsy is doomed because I do not
> have the facilities nor the resources to get it repaired ......
>
> FWIW, it still seems to run ok, oil pressure is normal, battery
> charging, water temp, shifting etc.... I went around it with a crowbar
> and using it on my ear as a poor man's stethoscope and was unable to
> pinpoint the source of the problem (so far)... It definitely seems to
> be coming from the bottom part of the front/engine somewhere.....
>
> Thanks for any input.

Had a 56 T Bird and similar noise at lower front of engine. Turned out to be
the vibration pulley on front of crankshaft. WW

" wrote:
>
> On Jul 9, 11:38 am, m6onz5a > wrote:
> > On Jul 9, 11:29 am, " > wrote:
> >
> >
> >
> > > I have a 1976 vette with about 120K miles on it.
> >
> > > Last year I had to do a fair amount of work on it (spring, shocks, rad
> > > support bracket, new rad, new water pump.).
> >
> > > It seems to have been developing a problem and I am not sure what it
> > > is.
> >
> > > I thought it started about the time I installed the new water pump,
> > > but that could be nothing more than sheer coincidence. It was making a
> > > sort of slight rubbing/banging/knocking noise, and I thought it was
> > > some minor machining discrepency causing a slight rubbing of the water
> > > and main pulleys. There was a rubbing sound that went away after a
> > > bit.
> >
> > > Yesterday I had to replace a motor mount and tightened a bit of
> > > exhaust on the manifold.
> >
> > > Today the noise is back. But now It sounds morelike a banging/knocking
> > > sound. The frequency increases with engine RPM. If I bring the engine
> > > up to a modest rpm and hold it there , it seems to go away. It seems
> > > worse when I first start it.
> >
> > > Now I am obviously not expecting a thorough diagnostic from this
> > > description, but I am not a very experienced mechanic. Does it sounds
> > > like the symptoms of a main/crank bearing or something terminal of
> > > that nature? If so, I'm afraid old Betsy is doomed because I do not
> > > have the facilities nor the resources to get it repaired ......
> >
> > > FWIW, it still seems to run ok, oil pressure is normal, battery
> > > charging, water temp, shifting etc.... I went around it with a crowbar
> > > and using it on my ear as a poor man's stethoscope and was unable to
> > > pinpoint the source of the problem (so far)... It definitely seems to
> > > be coming from the bottom part of the front/engine somewhere.....
> >
> > > Thanks for any input.
> >
> > take a long screwdriver and place the tip on different parts of the
> > motor and the other end against your ear, and see where it's loudest.
>
> I went around it with a crowbar
> and using it on my ear as a poor man's stethoscope and was unable to
> pinpoint the source of the problem (so far)... It definitely seems to
> be coming from the bottom part of the front/engine somewhere.....

Does the vibration damper (crankshaft pulley) look like it is running
true? or does it wobble? Rubber does tend to fall apart after 35 years
and they can knock when that happens.

-jim

On Jul 9, 1:26*pm, jim <"sjedgingN0Sp"@m@mwt,net> wrote:
> " wrote:
>
> > On Jul 9, 11:38 am, m6onz5a > wrote:
> > > On Jul 9, 11:29 am, " > wrote:
>
> > > > I have a 1976 vette with about 120K miles on it.
>
> > > > Last year I had to do a fair amount of work on it (spring, shocks, rad
> > > > support bracket, new rad, new water pump.).
>
> > > > It seems to have been developing a problem and I am not sure what it
> > > > is.
>
> > > > I thought it started about the time I installed the new water pump,
> > > > but that could be nothing more than sheer coincidence. It was making a
> > > > sort of slight rubbing/banging/knocking noise, and I thought it was
> > > > some minor machining discrepency causing a slight rubbing of the water
> > > > and main pulleys. There was a rubbing sound that went away after a
> > > > bit.
>
> > > > Yesterday I had to replace a motor mount and tightened a bit of
> > > > exhaust on the manifold.
>
> > > > Today the noise is back. But now It sounds morelike a banging/knocking
> > > > sound. The frequency increases with engine RPM. If I bring the engine
> > > > up to a modest rpm and hold it there , it seems to go away. It seems
> > > > worse when I first start it.
>
> > > > Now I am obviously not expecting a thorough diagnostic from this
> > > > description, but I am not a very experienced mechanic. Does it sounds
> > > > like the symptoms of a main/crank bearing or something terminal of
> > > > that nature? If so, I'm afraid old Betsy is doomed because I do not
> > > > have the facilities nor the resources to get it repaired ......
>
> > > > FWIW, it still seems to run ok, oil pressure is normal, battery
> > > > charging, water temp, shifting etc.... I went around it with a crowbar
> > > > and using it on my ear as a poor man's stethoscope and was unable to
> > > > pinpoint the source of the problem (so far)... It definitely seems to
> > > > be coming from the bottom part of the front/engine somewhere.....
>
> > > > Thanks for any input.
>
> > > take a long screwdriver and place the tip on different parts of the
> > > motor *and the other end against your ear, and see where it's loudest.
>
> > I went around it with a crowbar
> > and using it on my ear as a poor man's stethoscope and was unable to
> > pinpoint the source of the problem (so far)... It definitely seems to
> > be coming from the bottom part of the front/engine somewhere.....
>
> Does the vibration damper (crankshaft pulley) look like it is running
> true? or does it wobble? Rubber does tend to fall apart after 35 years
> and they can knock when that happens.
>
> -jim

hmm - looking at it when running it does not *seem* to run off center,
but it does seem like the area where the noise is located (at least
generally at least). I will have to try that swimming pool hose trick
to see if I can further narrow it down (without lopping something off
in all the turning and whirling things in that area....) I wonder if
it would be made worse by disconnecting the a/c drive belt? I did that
since the A/c is not working and I only use it for scooting around
with the top out. That make it pull more to one side and like you say
- a 35 year old piece of rubber ...... maybe there is hope yet .....

Is that what the service manual would call a torsional damper? I have
the factory service manuals here to help me along with things, but
like I say, I am not a horribly experienced mechanic....

thanks

" wrote:

>
> hmm - looking at it when running it does not *seem* to run off center,
> but it does seem like the area where the noise is located (at least
> generally at least). I will have to try that swimming pool hose trick
> to see if I can further narrow it down (without lopping something off
> in all the turning and whirling things in that area....) I wonder if
> it would be made worse by disconnecting the a/c drive belt? I did that
> since the A/c is not working and I only use it for scooting around
> with the top out. That make it pull more to one side and like you say
> - a 35 year old piece of rubber ...... maybe there is hope yet .....
>
> Is that what the service manual would call a torsional damper? I have
> the factory service manuals here to help me along with things, but
> like I say, I am not a horribly experienced mechanic....

It is also called a harmonic balancer. You could get one new or used on
Ebay if that turns out to be the problem. If it is making noise you
should be able to see it wobble.


tinyurl.com/25ozvvd

-jim




>
> thanks

In article
>,
" > wrote:

> I have a 1976 vette with about 120K miles on it.
>
> Last year I had to do a fair amount of work on it (spring, shocks, rad
> support bracket, new rad, new water pump.).
>
> It seems to have been developing a problem and I am not sure what it
> is.
>
> I thought it started about the time I installed the new water pump,
> but that could be nothing more than sheer coincidence. It was making a
> sort of slight rubbing/banging/knocking noise, and I thought it was
> some minor machining discrepency causing a slight rubbing of the water
> and main pulleys. There was a rubbing sound that went away after a
> bit.
>
> Yesterday I had to replace a motor mount and tightened a bit of
> exhaust on the manifold.
>
> Today the noise is back. But now It sounds morelike a banging/knocking
> sound. The frequency increases with engine RPM. If I bring the engine
> up to a modest rpm and hold it there , it seems to go away. It seems
> worse when I first start it.
>
> Now I am obviously not expecting a thorough diagnostic from this
> description, but I am not a very experienced mechanic. Does it sounds
> like the symptoms of a main/crank bearing or something terminal of
> that nature? If so, I'm afraid old Betsy is doomed because I do not
> have the facilities nor the resources to get it repaired ......
>
> FWIW, it still seems to run ok, oil pressure is normal, battery
> charging, water temp, shifting etc.... I went around it with a crowbar
> and using it on my ear as a poor man's stethoscope and was unable to
> pinpoint the source of the problem (so far)... It definitely seems to
> be coming from the bottom part of the front/engine somewhere.....
>
> Thanks for any input.

Have a listen at the fuel pump.

On Jul 9, 1:26*pm, jim <"sjedgingN0Sp"@m@mwt,net> wrote:

> Does the vibration damper (crankshaft pulley) look like it is running
> true? or does it wobble? Rubber does tend to fall apart after 35 years
> and they can knock when that happens.
>
> -jim

On a that year engine, the vibration damper, (harmonic balancer), and
the crankshaft pulley are two separate pieces.

Never had one make a "knocking" sound on a small block Chevy. Never
had one come apart. The outer part of the balancer will "spin",
throwing the timing mark off, or, if on a 400 small block, it will
make the engine vibrate.

Even if the outer ring slid all the way back, it won't make a knocking
noise. It will make a "scraping" sound. (hits the "tin" timing chain
cover) If the rubber is that bad, the ring would come of. Usually the
rubber dry rots or gets soft from people putting the balancer in the
parts washer. The solvent softens the rubber.

A "knocking" sound, coming from the bottom, and going away at constant
RPM is a rod bearing, possibly a wrist pin.

On Jul 9, 4:08*pm, aarcuda69062 > wrote:

> Have a listen at the fuel pump.

They make a "tapping" sound when the diaphragm gets bad, and will be
on the passenger side, lower front of the block. Think on that year
the alternator is above it.