I have a knocking noise that gets louder as the engine gets warmer and louder with the rpms. It's not noticeable at idle or if letting off the gas during crusing. I was told by he previous owner that about 3 weeks ago, new connecting rod bearings were done so I hope that it's nothing from the bottom. Any way to tell with out pulling it all apart?

A mechanics stethoscope may be all you need to isolate the noise. They are cheap.

[This message has been edited by Gall757 (edited 08-04-2012).]

K I went out and bought a stethoscope. I can hear it from the front left(when standing from the rear and looking forward). So how do I differentiat between a rocker or lifter noise? I wasn't able to get underneath as I was buy myself and have no way of working the throttle. Any chance that the bottom end could transfer noise up and make it sound like the top end?

Just for grins, make sure that the bolts that hold the torque converter to the flexplate are tight.
If they're loose, it can make a loud clatter that sounds like a rod bearing.

quote Originally posted by Tweeder: I can hear it from the front left(when standing from the rear and looking forward). So how do I differentiat between a rocker or lifter noise?... Any chance that the bottom end could transfer noise up and make it sound like the top end?

To differentiate, you would really need to pull the valve cover.

As far as noise traveling, if you use the stethescope, it is a pretty good indicator on an engine where the noise is coming from. You will definately be able to tell if it were bottom end.

good luck,

Tony

quote Originally posted by Tony Kania: To differentiate, you would really need to pull the valve cover. As far as noise traveling, if you use the stethescope, it is a pretty good indicator on an engine where the noise is coming from. You will definately be able to tell if it were bottom end. good luck, Tony

I got the cover off and nothing looks broken. Where to goto next?

[This message has been edited by Tweeder (edited 08-05-2012).]

I have my doubts about how well the bottom end was put back together? Why did the PO do the rod bearings? No one goes, "Gee, I think I should change my rod bearings, they must be due for a change." I would be concerned the PO did it right and measured the journals to get the right bearings and checked if the journals were worn, scratched, out of round etc, . I hope it's not a bottom end problem for your sake. Does it make the noise under load or when you let off the gas?
edit: Duke or V6?

And what Raydar said, check the TQ bolts, I had that happen to a Caprice I owned. Had the whole front of the engine off ready to pull the motor out and went to loosen the TQ. Nuts were loose. Tightened them and had to put the rest of the engine back together but the knock was gone..lol

[This message has been edited by TONY_C (edited 08-05-2012).]

quote Originally posted by TONY_C: I have my doubts about how well the bottom end was put back together? Why did the PO do the rod bearings? No one goes, "Gee, I think I should change my rod bearings, they must be due for a change." I would be concerned the PO did it right and measured the journals to get the right bearings and checked if the journals were worn, scratched, out of round etc, . I hope it's not a bottom end problem for your sake. Does it make the noise under load or when you let off the gas? edit: Duke or V6? And what Raydar said, check the TQ bolts, I had that happen to a Caprice I owned. Had the whole front of the engine off ready to pull the motor out and went to loosen the TQ. Nuts were loose. Tightened them and had to put the rest of the engine back together but the knock was gone..lol

The mechanic told him that it needed con bearings and that the top end would need looking after, possible lifters. Hopefully it was done right but I don't know. It's a v6. I put the stethoscope on the back left and that's where it was the loudest. I couldn't get underneath as I was by myself. The noise is there only after it gets warm and after a certain rpm. As I drive it, and let off the gas it goes away until I give it gas again. It's loud once it gets going like its right behind my head.

------------------
86 GT Convertable 3800

A cracked manifold perhaps?

Tony

quote Originally posted by Tony Kania: A cracked manifold perhaps? Tony

I've had exhaust leaks before and it don't sound like that.

quote Originally posted by Tweeder: I've had exhaust leaks before and it don't sound like that.

Just a shot. It was difficult to hear over the internets.

Tony

quote Originally posted by Tony Kania: Just a shot. It was difficult to hear over the internets. Tony

For sure thanks for the idear though.

It would be more likely for a lifter to make noise upon startup and then get quieter as the oil heats up whereas the bearing will make noise as the oil thins and the clearance gets bigger.

quote Originally posted by TONY_C: It would be more likely for a lifter to make noise upon startup and then get quieter as the oil heats up whereas the bearing will make noise as the oil thins and the clearance gets bigger.

So pull the pan and wiggle all con rods?

Kill the cylinders 1 at a time, and listen for a change in the noise. If it is a connecting rod that is making the noise, the knock will get quieter or go away when that cylinder is dead. An easy way to do this is to get 6 short pieces of vacuum hose. With the engine off, pull a plug wire off the dist cap and install a piece over the terminal and place the wire over the hose. Do this for all cylinders. The spark will jump the gap and the engine should run fine. Take a 12 volt test light attached to a good ground. Start the engine and touch each piece of hose 1 at a time with the probe end, this will kill the cylinder. As you go along, make a mental note of the knocking noise. If you hear a significant change in a single cylinder, you found the culprit and you have a rod knock. If there is no change, your problem lies elsewhere.

Check out this link: http://troubleshootmyvehicl...r_balance_test_1.php It's a cylinder balance test for a ford, but it shows how to kill cylinders so it works to find a knock too.

[This message has been edited by seajai (edited 08-06-2012).]

quote Originally posted by seajai: Kill the cylinders 1 at a time, and listen for a change in the noise. If it is a connecting rod that is making the noise, the knock will get quieter or go away when that cylinder is dead. An easy way to do this is to get 6 short pieces of vacuum hose. With the engine off, pull a plug wire off the dist cap and install a piece over the terminal and place the wire over the hose. Do this for all cylinders. The spark will jump the gap and the engine should run fine. Take a 12 volt test light attached to a good ground. Start the engine and touch each piece of hose 1 at a time with the probe end, this will kill the cylinder. As you go along, make a mental note of the knocking noise. If you hear a significant change in a single cylinder, you found the culprit and you have a rod knock. If there is no change, your problem lies elsewhere. Check out this link: http://troubleshootmyvehicl...r_balance_test_1.php It's a cylinder balance test for a ford, but it shows how to kill cylinders so it works to find a knock too.

Alrighty will giver a try.

------------------
86 GT Convertable 3800

That is an awesome way to kill the cylinders! Well I certaintly won't be getting shocks anymore when I try and unplug them one by one

quote Originally posted by Tweeder: I've had exhaust leaks before and it don't sound like that.

not an exhaust leak
when the Fiero manifolds come loose, or break a bolt - they slap against the head after each exhaust pulse.
it makes a ticking noise which gets worse as the manifold heats up
gets louder based on throttle. when you let off the gas, and coast - the exhaust pulses are light.

quote Originally posted by Pyrthian: when the Fiero manifolds come loose, or break a bolt - they slap against the head after each exhaust pulse. it makes a ticking noise which gets worse as the manifold heats up

I have a broken/missing exhaust manifold bolt on my '86 GT and it behaves in the opposite manner. When first started, the engine has a relatively loud "toofing" sound from one exhaust port, but as the engine warms up the toofing sound disappears.

For the time being could I disconnect the Injector and take off the plug wire and use it with 5 cylinders? Just trying to get it by for the next two months max intill it gets parked for the winter and the 3800sc swap can begin over th winter.

------------------
86 GT Convertable 3800

What did you find? Do you have a bad rod bearing? I would think a piston in a dead hole rattling around on a loose rod bearing wouldn't live long before coming apart. Plus you would end up with an excessive amount of oil building up in the cylinder without the ignition flame to burn it, especially if the oil rings are worn a bit.

[This message has been edited by seajai (edited 08-23-2012).]

quote Originally posted by seajai: What did you find? Do you have a bad rod bearing? I would think a piston in a dead hole rattling around on a loose rod bearing wouldn't live long before coming apart. Plus you would end up with an excessive amount of oil building up in the cylinder without the ignition flame to burn it, especially if the oil rings are worn a bit.

Yeah the mechanic says its from the bottom end. Guess the po put new bearings in to keep it quiet but they now are failing.

------------------
86 GT Convertable 3800

What about dropping the pan and removing that piston completely from the bottom and run on five that way?

------------------
86 GT Convertable 3800

Pistons only come out the top. You would have to take the cylinder head off. You could try and jamb another bearing in the rod and see what happens. Other than that, there really isn't any way to limp the engine along, especially for a month or two. Realistically, replacing the engine or parking the car til you can are the only options.

[This message has been edited by seajai (edited 08-25-2012).]

quote Originally posted by seajai: Pistons only come out the top. You would have to take the cylinder head off. You could try and jamb another bearing in the rod and see what happens. Other than that, there really isn't any way to limp the engine along, especially for a month or two. Realistically, replacing the engine or parking the car til you can are the only options.

Yeah the bearings is what the po replaced a couple weeks before I bought the car and the more I drive the louder it gets. I could try that again but the last ones only lasted about a month?

------------------
86 GT Convertable 3800

It would be horribly unbalanced if you just removed the piston.

------------------
Turbo 3800 E85 F23 5spd spec5
11.54@132.7

Pulled the pan and it's a connecting rod bearing. I will replace it and
hope it lasts another month and a half intill it gets parked and the
3800sc gets swapped in.

------------------
86 GT Convertable 3800

Anyone use epoxy or cold weld to fasten the bearing to the rod end to keep it from spinning? (semi-serious)

------------------
Turbo 3800 E85 F23 5spd spec5
11.54@132.7

quote Originally posted by Justinbart: Anyone use epoxy or cold weld to fasten the bearing to the rod end to keep it from spinning? (semi-serious)

How would you keep it out of the oil passages?

------------------
86 GT Convertable 3800

[This message has been edited by Tweeder (edited 08-31-2012).]

The odds of replacing rod bearings, especially ones making noise, and having them last at all are slim to none. The noise you are hearing is the rod slamming against the crank and it will damage the crank and rod becomes “out of round”. Once bearings go, the only way to fix them is a full rebuild.

quote Originally posted by Tweeder: Pulled the pan and it's a connecting rod bearing. I will replace it and hope it lasts another month and a half intill it gets parked and the 3800sc gets swapped in.

Examine the rod, end cap, and crank journal. If you see any damage, just replacing the bearing won't work, and the new one will be bad soon.
Something you can do until you have time to rebuild (and don't laugh, I did it, and it lasted 20,000 miles), is to put a piece of aluminum foil between the end cap and new bearing to shim it and compensate for the wear. This may buy you some time until you have a chance to do the rebuild.

Tweeder, if the rod bearings have enough clearence to knock, then you should see it on your oil pressure guage as the oil warms up.

With this type of knock and good oil pressure would lead me to think you have coolant on a piston or excessive wristpin to piston clearance. Just my to two cents, hope it helps....

I am able to wiggle the con rod at the crank and see and hear it move. I also can see and hear movement at the piston wrist pin.

------------------
86 GT Convertable 3800

I used a single layer of aluminum foil. After assembling without the foil, I tried to move the rod, and it felt just a tiny bit looser than the other rods. After putting in the foil, it felt the same as the other rods.
Edit: BTW, I used a micrometer on the foil, and it measured one thousandth of an inch.

[This message has been edited by TopNotch (edited 08-31-2012).]

Just got'er back together no more knocky knock. The bearing had spun was the problem. I tightened it down and there was no play so I didn't add the foil as a shim...we'll see how long it'll last.

------------------
86 GT Convertable 3800

No dice a few klms later and it started getting louder. So I pulled the pan and its loose again but not as bad as before. I'll try the foil shim trick, if not then I guess the swap will be getting done sooner.

------------------
86 GT Convertable 3800

Nada, I shimmed it and it still wiggled, so I really shimmed it(3-4) pieces and it's still loose. Looks like the only way would be to grind the cap to decrease the distance. Forget that, guess the swaps gonna happen sooner than I wanted.

------------------
86 GT Convertable 3800