Camshaft Bearing Question

[Kmort]

I've got a 1995 Mercruiser 4.3LX V6 and found out that I have a camshaft bearing gone bad making a rattle noise. Two guestions, what should I expect to pay to have this fixed and secondly, what could have caused it to go bad?

 

[[OBC]Patch]

Re: Camshaft Bearing Question

Couldn't guess at the cost, but low oil pressure could make it fail. make sure its the cam and not a lifter. Watch the valves running with the valve cover off.

 

[Bt Doctur]

Re: Camshaft Bearing Question

there are 4 or 5 cam bearings supporting the cam. how does 1 give you a rattle. cam is a solid piece of cast iron.

 

[Silvertip]

Re: Camshaft Bearing Question

What you may have is a loose/worn timing chain. Try to pinpoint the location of the noise. Is it RPM sensitive? Front of engine, back of engine, top of engine, one side or the other or both. Give us some help here.

 

[Kmort]

Re: Camshaft Bearing Question

I have scoped the engine everywhere and really haven't come up with the location other than at the timing chain cover plate and even there it's faint. I thought too possibly a timing chain but the noice is not RPM sensitive.

As for the oil pressure... it pretty much reads a constant 40psi. and on top of the rattle, there is an oil leak around the oil sensor.

 

[adeneo]

Re: Camshaft Bearing Question

How did you find out that it's a camshaft bearing?

There are 4 of them, and they rarely cause any trouble, but they will wear as any bearing will, excessive wear on just one bearing usually will not happen, as the other bearings will take up the slack, unless some debris got onto the bearing surface.
It is possible that one is spinning and making a noise, however I have never seen this myself as they are usually seated very well due to being pressed in.

To change them the cam has to be removed, this is done by removing the water pump, everything fitted to the crankshaft, and the timing cover, then unbolting three bolts at the top timing gear, removing the top timing gear and chain, then removing the cam holder plate, wich has two hex bolts and pulling the cam out. The pushrods and lifters must be removed prior to pulling out the cam.
A special tool is used to knock them out, this can only be done with the cam plug removed, wich is located behind the flywheel cover, so the engine must be separated from the flywheel cover, and most likely the flywheel has to be removed to make enough room at the back of the engine to get the tool in to knock out the bearing closest to the front of the engine.
It is possible to get the bearings out without removing the oil pan, but drop one down there and the pan will have to come off. In other words it's easier, and most likely necessary to lift out the engine before removing the bearings.

On the other hand it's much more likely that your problem is something else interely.
Try checking for timing chain stretch, bad lifters or pushrods, broken or worn valves or other valvetrain parts.
To check the cam you can remove the top timing gear and the lifters (making sure you put all the lifters and pushrods back exactly where they came from) and spin the camshaft by hand feeling for rough spots and play, a little in and out play is normal but there should not be any play sideways nor any rough spots or noises.

 

[Kmort]

Re: Camshaft Bearing Question

I had 3 mechanics listen to the engine and they have all isolated it to the same area. They have eliminated the timing chain because there isn't much indication by sound when scope is on it's cover and the fact the rattle is consistent regardless of RPM.

Granted (and they would agree), you can never know for sure until you get into the motor. The guy that I'm going to have do it said he is almost positive that it is what it is (bearings).

The only problem is I can't get an answer as to how much it's going to cost. I understand to a point that you can't get an exact price for something until you get into it, but I would at least think I could get some sort of range.

I really appreciate all you guys comments. I'm really learning from them which helps me understand when these mechanics talk to me.

 

[glennwolf]

Re: Camshaft Bearing Question

The price for cam bearings is usaully 15-20 for the bearing + Labor about 35-50. That is if you rmoved the motor and took it to the shop. If you have the shop do everything it will be 1500-2500.

 

[KJSmitty]

Re: Camshaft Bearing Question

I had 3 mechanics listen to the engine and they have all isolated it to the same area. They have eliminated the timing chain because there isn't much indication by sound when scope is on it's cover and the fact the rattle is consistent regardless of RPM.

How much noise are we talking here - a light tick or low knock etc?

I find it very difficult to believe you have a bearing knock that doesn't change with RPM etc. Unless you mean the sound or degree of sound doesn't change "YET" the frequency/rate does? IE does the tick/knock frequency get slower/faster in conjunction with RPM?
Has the sound gotten worse over time, has your oil pressure decreased at all over time? Have you considered taking an oil sample (sent to a lab) to see what particles may be present - maybe pointing to a possible source etc.

I have seen worn cam bearings cause low oil pressure yet never a specific "cam" knock.

But,,,, hard to contribute from my keyboard vise having a scope in my ear hanging over your engine.

Keep us posted - good luck

 

[Kmort]

Re: Camshaft Bearing Question

How much noise are we talking here - a light tick or low knock etc?

I find it very difficult to believe you have a bearing knock that doesn't change with RPM etc. Unless you mean the sound or degree of sound doesn't change "YET" the frequency/rate does? IE does the tick/knock frequency get slower/faster in conjunction with RPM?
Has the sound gotten worse over time, has your oil pressure decreased at all over time? Have you considered taking an oil sample (sent to a lab) to see what particles may be present - maybe pointing to a possible source etc.

I have seen worn cam bearings cause low oil pressure yet never a specific "cam" knock.

But,,,, hard to contribute from my keyboard vise having a scope in my ear hanging over your engine.

Keep us posted - good luck

Neither. It's a rattle. Like a loose nut bouncing around inside an engine might sound like. Yes, I took an oil sample and put it in a glass jar. Mechanic wanted to see it for "shininess" which he didn't find. As I've stated... the rattle is consistent under all conditions. In the beginning, it didn't do it the next morning until about 20 minutes of run time. Now it does it regardless.

 

[zbnutcase]

Re: Camshaft Bearing Question

And nobody here has mentioned the fact that the balance shaft rides on a needle bearing up front, which could be an issue

 

[Kmort]

Re: Camshaft Bearing Question

And nobody here has mentioned the fact that the balance shaft rides on a needle bearing up front, which could be an issue

This is interesting!!!

Since my last post I've had 2 more mechanics take a look and listen, and again STUMPED and countering everyone else's theory.

The one guy said since it still runs and performs good... "Don't fix it until it's broke", which at this point I tend to agree (or perhaps just want to). He said it's a lot easier for a mechanic to find something broken.

Since I'm not able to tear down an engine and put it backk together, I guess I'm just pretty well screwed since it would cost a small fortune to pay a mechanic to do so.

 

[John_S]

Re: Camshaft Bearing Question

He said it's a lot easier for a mechanic to find something broken.

Yea, I imagine that is true. .... and much more expensive for the owner.

 

[a70eliminator]

Re: Camshaft Bearing Question

Has the engine been run with the accessory belts off, cam bearing failure is rare, I would put money on it not being a cam bearing failure.

 

[Bt Doctur]

Re: Camshaft Bearing Question

loose balance shaft??

 

[Kmort]

Re: Camshaft Bearing Question

Has the engine been run with the accessory belts off, cam bearing failure is rare, I would put money on it not being a cam bearing failure.

NO, and you know I (and obivously the mechanics) never gave that a thought and you are right.

Thanks for the Post!

 

[fossill]

Re: Camshaft Bearing Question

Worn out cam bearings dont and can't rattle.

 

[Alpheus]

Re: Camshaft Bearing Question

Worn out cam bearings dont and can't rattle.

Agreed.

Your mechanics are falling under a very powerful spell known as the "Power Of Suggestion"...

You would not have a steady oil pressure and if one bearing would happen to go (I've never seen just one go) The cam shaft would snap. (Seen that many times)

 

[westportfish]

Re: Camshaft Bearing Question

Before you tear into the engine, cut the oil filter apart and check it for metal. If a cam, rod or main bearing was to fail there will be babbit and metal shavings in the filter. Cam bearings rarely fail and if they have it would require a new cam and lifters also.

 

[ENSIGN]

Re: Camshaft Bearing Question

Check the water shutters and make sure the rubber coating is not burnt off.