Knocking noice on 93 Caddy's 4.9 L,Touring sedan

[Azik]

Hello Folks,

I need some advise from you guys? My car 93 Deville Touring Sedan, recently I noticed some knocking or clunking noice coming out from engine.

It's got 153 K' mileage, what might be this kind of noice? Are these 4.9 L Engines are good or?

Do I have to take it to the dealership or? Can you please, advise me on these matters.

Thanks for everybody.

Azik.

[adallak]

4.9 has known main bearing knock when the engine is cold. You can hear it coming from serpentine belt area. It goes away as soon as the motor at operational temps. Is this what concerns you? It is harmless. If you were a little bit more specific we perhaps could point other problems.

[Scotty]

The 4.9 is a great engine, it can have a number one main bearing knock that gets much worse when the engine is hot and the oil is thinned out, say in heavy traffic and after a long drive. You may be able to minimize that noise by using a little heavier Delvac/Rotella 15W40 oil. However, you need to be more specific about this knock, it could also be detonation, try to describe it better.

This is a description of the #1 Main Bearing Knock in the 4.9 posted in 2002 by bbobynski:

It is difficult to diagnose noises from several thousand miles

away but I will hazard a guess from your description that you are

hearing the front main bearing thump. First off, other than

being an annoyance, there is absolutely nothing wrong and nothing

bad will ever happen to the engine because of this.

If you look at the 4.9 accessory drive you will see that the

serpentine belt wraps around the bottom half of the crank

pulley. This is necessitated by the location of the accessories

and the belt routing required to reach all the pulleys. The

rather unfortunate result of this arrangement, however, is that

the resultant load vector from the belt tension pulls the crank

upward. The gas pressure loads on the pistons acting on the

rods and crank journals tends to push the crank downward. The

belt pulls the crank up and each time #1 or #2 fires it pushes it

down. Up...down...up...down...thump...thump...thump...

The nose of the crank moving up and down (in reaction to the

accessory belt load and the cylinder firing loads) within the

small clearance of the front main bearing is what is making the

noise. As the clearance changes minutely with temperature and

the oil viscosity changes with temperature the noise will change

slightly and come and go. Nothing will ever come of the noise.

The engine will run forever. It is annoying, however.

I have never heard or the thrust bearing on the crank causing any

kind of noise. There are no alternating forces in the engine to

push the crank back and forth to cause a noise in that fashion.

The thrust bearing serves the purpose of absorbing thrust created

by the torque converter ( and the throw out bearing reaction

force in a manual transmission car) but I have never heard of a

single problem related to the thrust bearing in a 4.1/4.5/4.9.

Those engines are bulletproof in that respect. The thrust

bearing idea sounds like something someone came up with to

explain the noise and it turned into an "urban legend" type of

thing. That is not the problem.

If the noise becomes too annoying, go to a Cadillac dealer and

have th front main bearing replaced. I believe there is a

service bearing that is several ten-thousands over size that was

released to retify the main bearing thump in complaint cars.

This is not a difficult repair.

The particular engine in your car, Bruce, was probably borderline

for this noise and as the miles accumulated and the bearing wore

a few "tenths" it allowed it to move enough to start thumping.

If you want to verify the diagnosis, release the tension on the

accessory belt when the engine is thumping by holding the

tensioner off with a breaker bar. Or remove the belt and start

the engine if it is at the temperature range that you would

expect to hear the thump. One way to do it is to get your tools

ready and do a trial run then warm the engine up until the thump

is evident. You might have to put it in drive and hold the brake

and torque the engine gently against the torque converter to put

some load into it. If you have one person do this while the

other goes under the hood and releases the accessory belt tension

with the breaker bar on the tensioner you can turn the noise on

and off at will.

With a transverse engine going up or down a steep incline doesn't

do anything to move the crank one way or another. If the thrust

bearing idea was true you should be able to initiate the noise by

weaving left-right-left-right violently with the steering wheel

thus sliding the crank back and forth in the engine. Good luck...

When the main bearing thump phenomenon was recognized and

investigated many years ago we were curious as to any inpact on

the crank or engine durability. To investigate this we severely

opened up (only) the front main bearing clearance to about .003

inch. The normal clearance is about .0008 to .0015. Sure

enough, this created a rather severe main bearing thump so we

knew we could creat the situation. This engine then ran a full

300 hour endurance test without incident. There is absolutely no

durability nor reliability issue with the main bearing thump. It

is purely an annoyance.

You'll notice the Northstar accessory drive is designed such that

the belt tension load vector pulls the crank to one side rather

than up. This is to avoid the same phenomenon.

Hope this helps......

[Scotty]

Man I love that post! Bbobynski's post is so good it brings tears to my eyes.... This is one that we need to keep in his gems folder, great post bbobyski

I especially love this comment;

This engine then ran a full 300 hour endurance test without incident. There is absolutely no durability nor reliability issue with the main bearing thump. It is purely an annoyance.

Endurance test for 300 hours = 12.50 days! Does the engine stop at all? Is the oil changed during this test or just feed it gas and oil and watch for malfunctions like over-heating or a rod through the crankcase? What RPM is the engine run at during the test and is it constant or varying? This is done on a dyno?

[Scotty]

Thanks Guru that testing is incredible and rigorous! I cannot believe that the NS can endure this >>> On a Northstar engine, that test will run for 300 hours with the engine at WOT, the RPM varying from 6200 to 4400 back and forth constantly. <<< I would love to see that happening.

Have you ever seen any catastrophic failures during any of this testing? What happens at the end of the testing, does the team take the engine apart and inspect it and measure tolerances? Thanks, Mike

[Azik]

Hello Guys!

The knocking noice is still there and radiator start leaking with antifreeze.

Water pump was causing all these problems as I was told by ICE Certified Mechanic. They charge me for 500 $ to change the water pump and belt.

I have to take it on Friday and leave it at body shop for a whole day.

Is that normal price for this kind of repair services?

What might be causing such kind of problems, I mean water pump malfunction?

I had to drive my car for a long trip 600 ml. last week, that trip trigger the problem? What do you think?

Thanks again for your suggestions and comments.

[adallak]

Hello Guys!

The knocking noice is still there and radiator start leaking with antifreeze.

Water pump was causing all these problems as I was told by ICE Certified Mechanic. They charge me for 500 $ to change the water pump and belt.

I have to take it on Friday and leave it at body shop for a whole day.

Is that normal price for this kind of repair services?

What might be causing such kind of problems, I mean water pump malfunction?

I had to drive my car for a long trip 600 ml. last week, that trip trigger the problem? What do you think?

Thanks again for your suggestions and comments. 

The radiator has plastic tanks and they develop cracks. I have replaced the tanks myself following Guru's advice. I would address all cooling related issues at once. I do not know what kind of noise a failed water pump would make. $500 sounds too much to me.

[adallak]

The knocking noice is still there and radiator start leaking with antifreeze.

Water pump was causing all these problems as I was told by ICE Certified Mechanic. They charge me for 500 $ to change the water pump and belt.

Why does he think the water pump is bad? Does it leak or what? I personally would replace only the belt. It is just a $30 part at any store and a 15 minutes job. See if it makes difference. Make sure the belt tensioner moves freely. As` i told before 4.9 makes knocking noise coming from belt area for a couple of minutes until the motor warms up.

Where exactly the radiator leaks from?

[Azik]

Where exactly the radiator leaks from?

It's leaking from the upper right corner next to the battery and lights.

It start leaking with this knocking noice and getting wet on the ground a liitle bit with antifreez fluid. This mechanik just heard this noice and look at it...then he said water pump malfunction... What cause this problem?

[adallak]

It's leaking from the upper right corner next to the battery and lights.

It start leaking with this knocking noice and getting wet on the ground a liitle bit with antifreez fluid. This mechanik just heard this noice and look at it...then he said water pump malfunction...  What cause this problem?

Looks like one of the tanks leaks (if it is not the cap). I would replace BOTH tanks, since it's a lot cheaper than new OEM radiator. I still do not think this leak has something to do with the knock, unless the coolant is sprayed on the belt somehow. If your serprntine belt is old and does not look good, replacing it is not a bad idea. Again, check out the belt tensioner. A bad tensioner/belt can make funny noises. Start the engine and watch and listen to the area.

[Scotty]

Have you ever seen any catastrophic failures during any of this testing?  What happens at the end of the testing, does the team take the engine apart and inspect it and measure tolerances?  Thanks, Mike

At end of test the engine is quantified for performance, torn down, measured carefully, inspected and reviewed in detail by all the concerned engineers in a group, together.

Catostrophic failures....heck no....well....maybe....occasionally......LOL

The official answer is no. During the validation testing of the engine, once the design and development is complete the engines ususally run like clockwork. Sometimes we "learn something" during development testing and parts end up on the floor. When the engine is at 6400 and making over 300 HP it tends to dissassemble itself in a hurry if something, even minor, fails. During any engine development program there are several phases of development starting with the early mule engines thru the final testing of actual production engines. The endurance testing starts during the mule phase to test certain parts and parameters so sometimes there is a failure of prototype or non-production intent pieces. Not often...but it does happen. If a failure of any sort occurs during the final validation testing of production intent engines it gets a LOT of attention...really quick....and the failure is analysed and corrective action taken either as a design change, part quality change, etc...

There are some great dyno test stories....LOL LOL When you have many engines running wide open all the time and running absolute endurance limit testing there are bound to be some failures and some resulting great anecdotes....don't ask.

I am curious, what minor failures could cause serious damage at that RPM. Could a coil failing do it?

You know I recently appraised the New York Hotel and they produced their own electricity with 5, 400 cu in Ford engines converted to natural gas running at 3,500 RPM. I thought that kind of speed and duration was excessive and dangerous for an engine. However, I am beginning to see that engines are more able to operate at high levels for long periods of times than I previously thought. Thats interesting stuff bbobynski, when I come back again, I want to get a job like yours!