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Low RPM motor noise

T

the_last_hour

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"Several times, I've notic

"Several times, I've noticed a noise that is only noticable at low RPM's. (350 cu) It only comes out of the port engine. It sounds like a chain, but it is not constant, it is more of a surging sound or droning. One of my passengers said it was knocking, but I would think of knocking as a constant, this is more rythmic like a heartbeat. When I started it the other day, I heard it immediately when cold and as soon as the choke started to open and the rpms went up it went away. I've also noticed it on a trip when we returned at the end of the day and that motor was 2 quarts low on oil. I've run the boat 150 hours since the first time I've heard it with no issues. This engine has always burned oil since day one, and it is less than 2 years old. I can't identify where it is coming from, it sounds centered on the intake manifold."
 
"One more comment, some diesel

"One more comment, some diesel trucks have a rattle to them, when they are at idle, it reminds me of that sound.
Steve"
 
"Knowing it is the port engine

"Knowing it is the port engine, which runs your gear in reverse and adding the fact that it has done it since new, I would suspect you are hearing the normal low speed rattle common with many marine gears.

Does it go away by 1000 rpms?

Check it closer and try to determine if it is coming from that area."
 
Might it be the plate in the f

Might it be the plate in the flywheel that connects to the tranny? (Can't for thelife of me recall what it's called!)

Jeff
 
"Well, I think I had the same

"Well, I think I had the same noise and I replaced the DAMPNER PLate, not very expensive and pretty easy to do.<center><table border=1><tr><td>http://www.marineengine.com/discus/icons/attachment_icon.gif""" align=left alt=""image/bmp"">dampner plate
[url=""][b]Dampner.bmp[/b][/url] (53.0 k)</td></tr></table></center>

The springs in mine were so loose they could be pushed out with ones fingers. At high RPM the noise goes away because of centrifugal force..."
 
"I have a 454 with the same no

"I have a 454 with the same noise. Where is this damper plate located, do I have to pull the motor to get to it. My boat is a tollycraft aft cabin, not alot of room to work."
 
"It is inside the bell housing

"It is inside the bell housing. If you can get the gear off, you can do this with the motor in place. You just have to remember to support the back of the motor before you pull the gear."
 
"Rick is correct. The damper p

"Rick is correct. The damper plate is bolted on your engine flywheel, that big mother that the starter engages !!!
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You will have to remove your transmission, (unbolt it, move it),} to get at the flywheel and remove and put on the new plate.

In my case I have twin 350cu in and V-drives so I have enough room to undo the transmission and just move it out of the way. It was about a two hour fix.

JOHN....With little room to work it will undoubtedley take you longer .......unless you can find some leprechaun sized mechanic.
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"
 
"My experience calls for dampn

"My experience calls for dampner noise only in gear at low idle. That seems to bring out any wear in the spring area as noise. But in Steve's case, I'm thinking lifter noise. He mentioned low oil, and going away when warmed up. Best case a sticky lifter, worse case, perhaps a worn cam lobe. I'd first do a rocker arm adjustment, assuming this is an older engine that is adjustable."
 
"Thanks Diver dave, keep in mi

"Thanks Diver dave, keep in mind that this has happened in "Neutral" and in gear. The most recent time was in neutral with full oil, but the engine was cold, and maybe oil had not gotten to the top of the engine yet. The sound is definately the same with both situations. I believe it is related to oil. The engine is 1.5 years old, but has had a rough childhood, i still can't figure out why it burns so much oil, and the oil seems to get dirty much faster than its twin sister. What is a rocker arm adjustment, and how do you perform one?
Steve"
 
"Steve:

the rocker arm adju

"Steve:

the rocker arm adjustment is where you set the valve lash. some of the newer versions of engines have fixed rocker arms and require a different method to set valve lash.

two easy ways to determine what you have: 1) call local dealer, provide serial number and ask, 2) remove rocker cover and look. The adjustable ones ride on a "half ball washer" on their studs. the nut above the washer provides the adjustment. Look in any engien service manual and you can see all kinds of variations. If you need a pic or two, ask, and I can post/send some

The dirty oil may be an indicator of the problem in your troublesome engine - have you ever had an oil analysis done? given the age of your engines, you may want to consider it."
 
"I'm not sure how many acc

"I'm not sure how many accesories on your motor are belt driven, but you may want to run the engine with the belts removed to further isolate the problem."
 
"Excessive blow-by from worn p

"Excessive blow-by from worn piston rings will darken the oil faster and account for your oil consumption.

Is your oil pressure good? (if not high enough, suspect main or rod bearings as the noise)
You mentioned a rough childhood... has this engine every had water ingestion?

Lifters will make a methodical click click click, btw."
 
"MistaHays, I've got good

"MistaHays, I've got good oil pressure, 40-60 psi, typically will match the other motor exactly. Yes the motor has had water ingestion twice, I had a dieseling problem that was due to bad carb adjustment, but it hydrolocked twice before we figured out the culprit. The hydrolocks happened a year ago."
 
that hydro issue tends to rust

that hydro issue tends to rust cylinder walls = wear out your piston rings = oil consumption.

Still not sure about the noise.
 
"I found the explanation below

"I found the explanation below relative to rattle in the transmission of a BMW. It seems to explain the low RPM rattle we all encounter in our boats. I find that when I need a tune-up the rattle is worse and almost non existant when the engines are purring like a kitten.

Chuck Hanson

A piston engine's power delivery is not seamless like an electric motor. A piston engine makes pulses of power very rapidly. How often? In the M3, (3 X rpm) per minute. Now realize that any drivetrain component (transmission or differential) has a certain amount of looseness or slack in it - it must, or being too tight would create a lot more friction. So when the power pulse engages the transmission, it is causing the rotational power going through the unit to take up that slack. This effectively causes components to touch that were not pressed together a moment before. Between each power pulse, those components de-couple. Press any two hard objects together, whether it be a tea cup and saucer or a hammer and nail, and you notice that noise is made. Repeat the contact-release-contact cycle quickly and it makes a staccato sound - a rattle."
 
"Chuck;

that's the basi

"Chuck;

that's the basics; here's some of the "rest of the story". That pulsing is mitigated by two items. the first is that big heavy flywheel. It helps to maintain the rotational inertial to minimize those pulses. the other item is that wonderful, usually spring loaded, damper or drive plate. the typical one has three or six springs in it to absorb that 'slack' if it occurs (of course, they get to absorb the initial engagement when you engage the gear, too). the pulses are spaced based on rpm; which is why most of us only hear that rattle at a low idle. once i get over 750 rpm, mine quiet right down."
 
There is a third item to be me

There is a third item to be mentioned....the torsional vibration damper mounted at the front of the crankshaft
 
"Bob...very interesting. I kno

"Bob...very interesting. I know what one is and where it is located but I have never heard of one failing, or creating any noise.

Have you had any experience with that component failing or about to fail??"
 
Harmonic balancers "torsio

Harmonic balancers "torsional vibration damper" tend to fall apart when the rubber between the two cast pieces comes apart or allows the outer ring to rotate. I've replaced a couple on cars... or replaced with an aftermarket on something that's turning north of 7k RPMs. Doubt that is the source of your noice.

But frankly... if you have a rattle at low to mid RPM... just keep an eye on temp and oil pressure and it will likely get louder and become obvious in time.
 
"My mariner neighbor had a sim

"My mariner neighbor had a similar sound last spring. He found that the engine was running a little rough and after adjusting the fuel/air mixture screws on the carb, the noise stopped. Before ripping into the tranny, try doing a tuneup and carb adjustment. Since the engines are bolted down to the stringers it is hard to see any shaking from a poorly tuned engine.

Erich"
 
"Right on, Erich! Many a pers

"Right on, Erich! Many a person has discovered that a bad idle (more on this in a moment) can cause that damper plate to rattle like crazy.

Been adjusting carbs for half a century, yet I also have trouble getting a nice, smooth idle in a marine application. Why? With few exceptions, marine engines are hard mounted--they don't conveniently shake like crazy when the idle is off. In fact, that lump of iron can have a couple of cylinders off (from crossed plug wires) and still LOOK like it's idling just fine. (Don't ask!)

So be sure to get a tune up BEFORE ripping the trans out.

Jeff"
 
"Ummm... and if you start twis

"Ummm... and if you start twisting mixture screws, make sure you know where the original settings were in the first place."
 
"Jeff,

If someone (like

"Jeff,

If someone (like Steve or maybe me in the spring) wanted to use a vacuum gauge to set the carburetor mixture screws instead of doing it by RPM or rough idle, where can you connect the gauge? I understand that this is probably the best method to set the mixture screws. I don't see any extra fitting on the Rochester Q-Jet. Is there a plug on the manifold that can be removed and used for this purpose?
Also as Mista suggests, you should start the procedure by turning the screws all the way in with the engine shut off while counting the number of turns in order to get a benchmark of where you started. Then back them out to that setting before starting engine and making further adjustments.

Thanks,
Erich"
 
the older cast iron intakes ha

the older cast iron intakes have a pipe plug that can be used.

the quick and dirty spot is the supply fitting for the vacuum break (aka choke pull-off).
 
"Right. Just don't be a m

"Right. Just don't be a moron like me and use the PCV hose! Why? When you hook it back up, the "vacuum leak" it deliberately creates changes the idle mixture rather significantly.

I too used the choke pull off fitting but, there is none with the new Edelbrocks. That means drilling and tapping a hole in the manifold somewhere. Another item for the To Do List.

Jeff"
 
Jeff:

you might wann try D

Jeff:

you might wann try D & T the adapter (wedge plate) between the manifold and the carb. Another option area is the carb itself - the power brake signal boss used to be pretty obvious on the 'back' of the throttle plate area on the main casting. 1/8" NPT should be more than adequate
 
"The vacuum break fitting soun

"The vacuum break fitting sounds like a good spot to attach the gauge.

Thanks,
Erich"
 
"The 1409 Edelbrock has castin

"The 1409 Edelbrock has casting in the front for a non-timed (lower) and timed (upper) vacuum fittings. You have to take the carb off, drill and tap it (non-timed port). This will give you a place to take current and future vacuum tests. I put the 1409 on a qjet intake and luckily it already had a 3/8" plug in the manifold right behind the carb. Installed a barb fitting with a cover. Nice test port!!"
 
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