3.0 L Mercruiser engine noise

[jaylamb]

Hhttp://www.youtube.com/watch?v=S2KIeB2WQmAey guys I have an engine noise on my motor, I checked the valve train by pulling the rocker cover and I adjusted the valves for good measure while I had it off.I thought it might even be a rod because when I rev the motor and put a load on it it seems to go away,I was getting set to drain the oil and pull the pan down to physically check the rods,however I decieded to do one more thing,I listened to the motor with a stethoscope the sound appears to be coming from the timing gear area from what I can hear.Another thing I did I remember my dad had a 50 Pontiac with a rod knock and he pulled plug wires one at a time( while it was running),when he did it to the bad one pulling the wire the noise quieted I tried it didn't make any difference,so again I doubt a rod is bad.My question is when the timing gear on these motors are going bad (its an 86) will it make a knock? I put a timing light on the motor didn't seem to jump around but thats usually true witha timing chain,I never had a bigger motor with gears as opposed to a chain.Again any ideas would be helpful Thanks. Iam adding a video of the motor running with the noise.

 

[Aloysius]

Re: 3.0 L Mercruiser engine noise

Fuel pump drive??

 

[anymanusa]

Re: 3.0 L Mercruiser engine noise

I hear piston slap is common in some of the chevy engines. I don't know if yours is a chebby though.

 

[jaylamb]

Re: 3.0 L Mercruiser engine noise

I posted a video link maybe hearing it will help

 

[jaylamb]

Re: 3.0 L Mercruiser engine noise

I hear piston slap is common in some of the chevy engines. I don't know if yours is a chebby though.

Yes its the G.M.iron duke.

 

[anymanusa]

Re: 3.0 L Mercruiser engine noise

try to isolate the location with a mechanics stethescope, or a long screwdriver and your ear.

Check compression in a cylinders if that leads nowhere.

 

[anymanusa]

Re: 3.0 L Mercruiser engine noise

If it is piston slap, revving the engine would splash a lot of oil on the cylinder walls and quite the noise for a bit.

 

[jaylamb]

Re: 3.0 L Mercruiser engine noise

try to isolate the location with a mechanics stethescope, or a long screwdriver and your ear.

Check compression in a cylinders if that leads nowhere.

I used a stethoscope sound is in front of engine around timing gear area,the video I posted on the first post I put the camera in this area and you can hear the noise louder there,I haven't checked commpresion http://www.youtube.com/watch?v=S2KIeB2WQmA

 

[jaylamb]

Re: 3.0 L Mercruiser engine noise

Is there any other way to diagnose the piston slap?

 

[anymanusa]

Re: 3.0 L Mercruiser engine noise

remove spark plugs in suspected cylinders and squirt liberal amount of oil in and then start up again, slap should subside for a bit. It very well could be coming from your timing set though, from what you say.

 

[Bt Doctur]

Re: 3.0 L Mercruiser engine noise

Check 3A-39
http://www.boatfix.com/merc/Servmanl/13/13A3R2.PDF

 

[jaylamb]

Re: 3.0 L Mercruiser engine noise

Thanks both of you,I have also read older post that deal with 3.0 L motors with noises so I have several idea's,I want to pop off the timing cover just got to figure how Iam going to support the motor when I remove the front.

 

[fishrdan]

Re: 3.0 L Mercruiser engine noise

It does sound internal to me, but I'd take off the water pump belt first and run the engine (for a minute or so), to make sure it's not anything belt driven. If you don't have a mechanics stethoscope you could also use a really long (18-24") screw driver and place the handle against your ear, tip against the engine. That or a piece of hose.

For supporting the engine, I used a scissor jack (from car) and a piece of wood under the oil pan. In the past, I've also used various pieces of wood (12x12", 2x4 etc) under the oil pan to block up the engine, after lifting it a bit with a cherry picker/engine hoist . It would be best to check the engine alignment after disturbing the engine and front mount, especially if the engine alignment hasn't been checked in a while.

 

[jaylamb]

Re: 3.0 L Mercruiser engine noise

Well I did what fiserdan suggested,ran it with the belt off,still there,I did notice something,today is cold out not freezing but I had a jacket,when I first started the motor for a couple of minutes I didn't hear the noise.I talked to the mechanic at the marina he doubts the timing gear is bad because the 3.0 is not know for that according to him,he thought a fuel pump rod but listening to the motor that area is quiet.I think I'm going to have to pull it to start taking off tin and visually checking the motor internally,thanks for you suggestions guys,take care.

 

[fishrdan]

Re: 3.0 L Mercruiser engine noise

No fuel pump rod in the 3.0, the pump arm rides right on the cam. Though, if the pump arm spring was bad the arm could be slapping on the cam I suppose.

You say it was quite when you started the engine up cold, when the oil is thick. Could be a a bearing problem, oil thins down when the engine warms up and doesn't cushion the bearings as good as the thick oil...

Here's something to try, remove the oil filter, cut the can off the filter and look for metal fragments. A few flecks is OK, but if you see a bunch,,, well......

Here's another thought, the cam has a thrust plate on the back side of the cam gear, it's held onto the block with a couple of screws. If the screws backed out they could be rubbing on the gear or allowing the cam/thrust plate to walk around, causing noise. Just speculation though...

 

[89cruisers]

Re: 3.0 L Mercruiser engine noise

Im having a very similar noise, you might have seen my post in your searching, had my cousin who is a GM mechanic come look at it, said it probably isnt a bad bearing becuase I used my bayliner for a good 2-3 hours with the noise at 3k+ rpms and a bearing would have broken. Very possible it is piston slap since our marine engines dont get as warm as car engines mostly and so the metal does not expand as much to quite it down like it does in car engines.

 

[6meter]

Re: 3.0 L Mercruiser engine noise

That is not a rod or main bearing. Sounds like its there only on deacceleration or no load. Flywheel cracked?

 

[Silvertip]

Re: 3.0 L Mercruiser engine noise

Piston slap and rod noise will both generally quit if the plug wire for that cylinder is pulled. Timing gears can and do go bad and when they do, they generally make a noise at idle and tend to go away as rpm picks up. If oil pressures is good at idle it is very likely not a rod or main bearing. Weak fuel pump return springs can indeed make a noise. I've seen engines rebuilt because of it only to have the noise still there when done. So make engine removal and disassembly the LAST resort rather than the first.