Knocking sound only in neutral idle

[skydiveD30571]

Volvo Penta 5.0GL-H with SX-A outdrive.

I just finished making some idle adjustments and went out for a test drive. It now idles great in gear, right at 600rpm as the manual suggests. In neutral it idles slightly higher at 800rpm. Is this too high for neutral? The reason I ask is because I started having some issues on the way back to the dock.

I was running low on fuel so I decided to head back to the dock. This is when I first started noticing that shifting to forward and reverse was making a "clunk" louder than normal, and required a little more force than normal. I cannot say if it was doing it sooner in the day, but this is when I noticed it. I cruised back to the dock at various rpm's ranging from idle to WOT, maybe a 5 minute trip. Once in the cove I brought it back to neutral to wait on another boat leaving the dock.

Right then I noticed a knocking noise coming from the stern. I am not 100% sure if it was the drive or the engine, but I am led to believe it was the drive. Funny thing is it ONLY happens in neutral. Once I shift to either forward or reverse it is gone completely. Once on the dock and heading towards the truck, the driver popped it into reverse and then forward, and I could easily hear the "clunk" a couple hundred feet away. It has never had this issue before, or any issue with the lower unit for that matter.

I checked the lower unit oil before trailering to the lake and it was clean (clear and greenish color) and full. What would cause it to suddenly start shifting rough? What could cause a knocking noise and be isolated during neutral idle but not in gear? Is 800rpm neutral idle too high? Like I said it idles perfect in gear, and 800 doesn't seem like it would be high enough to damage gears when shifting. Thanks (again) for any input...it seems like everytime I fix something I get a brand new problem

 

[Don S]

Re: Knocking sound only in neutral idle

V8 engines don't normally drop 200 rpm when put into gear, 50-75 rpm is more typical.
If the knocking noise you here is more of a rattle than a hard knock, it may be from the back lash it the upper gears of the outdrive. It also indicates a rough running engine.
It sounds to me like you have some engine problems, a miss or something going on with your engine and you should get your idle down to around 700 or less in neutral.

 

[skydiveD30571]

Re: Knocking sound only in neutral idle

I used the word "knock" because it was rhythmic. If I wasn't low on gas I would have done some troubleshooting on the water, since all my issues occur there but never on muffs. I did notice when the engine first started the idle was about 6-700rpm, then rose to 800+ over the next 5-10 seconds. I read that this is a sign of a vacuum leak, but the vacuum gauge last week showed a steady normal reading. When I checked the vacuum it was on muffs, could it register different under load in the water?

 

[Don S]

Re: Knocking sound only in neutral idle

I did notice when the engine first started the idle was about 6-700rpm, then rose to 800+ over the next 5-10 seconds. I read that this is a sign of a vacuum leak, but the vacuum gauge last week showed a steady normal reading.

It could also mean your throttle cable is out of adjustment. When you bring the throttle back to neutral, the idle speed adjustment screw should be touching the stop on the carb. If not, adjust the cable end so there is light pressure to the idle position.

 

[skydiveD30571]

Re: Knocking sound only in neutral idle

It could also mean your throttle cable is out of adjustment. When you bring the throttle back to neutral, the idle speed adjustment screw should be touching the stop on the carb. If not, adjust the cable end so there is light pressure to the idle position.

I had this problem while idling on the driveway with the hose, so when it happened on the water the first thing I checked was that the cable wasn't pulling the throttle open. To my disappointment it was completely seated. I'm about to just bite the bullet and take it in to a mechanic, but I'd like to give it one last shot. What all would cause a 200rpm drop while shifting into gear? It has brand new plugs/wires/cap/rotor. Could following the manual and adjusting idle mixture WITH idle speed adjustment, instead of just idle speed adjustment, make a difference in that rpm drop?

However as of now i just want to make sure the knocking noise and loud shifting clunk hasn't caused other problems too.

 

[skydiveD30571]

Re: Knocking sound only in neutral idle

Friend marine mechanic said a steady vacuum reading of 17" proves nothing, and that 17 is a bit low (should be closer to 20-21"). Combined with increasing idle speed, he suspects a lean idle caused by a vacuum leak. I assumed a steady reading in the spec range proved against that. I guess I will check that next. He confirmed Don's thoughts, and mine, that 8-900rpm is too high to be shifting at, and that an engine issue is to blame and it needs corrected to save the gears.

As for the knocking noise, he threw out the idea of exhaust shutters but I'm fairly sure they don't exist on this engine since it was manufactured well past the date Volvo quit using them. Other than that, he agreed it'd be best to check it out before using it again. Damn I was really trying to learn this stuff and handle any issues on my own :facepalm:

 

[skydiveD30571]

Re: Knocking sound only in neutral idle

I isolated the knocking noise to the lower unit, and specifically at the area shown in the first picture.



I'm pretty certain this would be the u-joints correct? Also, listening to it out of the water its more of a "click click click click" instead of a noise. It has the same sound and rythym as this video, but definitely quieter.

http://s36.photobucket.com/albums/e3/mprentice1804/

When hearing this noise, the drive has been full down (in the water) and about 90% down (on the hose). I haven't checked to see if it changes with tilt. Last year was my first year of boat owning, and I did not know to not run the engine in full up trim position. I have since learned this lesson, but I'm thinking the u-joints are finally wearing down from the damage I probably did to them last year. Sound reasonable?

I also did some investigating into the high idle issue, and posted into the thread I have devoted to that.

 

[Don S]

Re: Knocking sound only in neutral idle

You need to pull the outdrive and check the ujoints, and see if there is water in the bellows.
Just an FYI, that is not a lower unit. While a slightly older model, this is the same parts.

 

[skydiveD30571]

Re: Knocking sound only in neutral idle

Thanks for that Don I never knew the difference. So to clarify, the noise is coming from the upper unit towards the transom. I am taking it in to have the drive pulled tomorrow since I keep it on a friend's land and do not own the tools necessary.

 

[skydiveD30571]

Re: Knocking sound only in neutral idle

Update: Mechanic pulled the drive and said theres a "spring" inside the bellows that helps it keep its shape? I've never heard or seen a diagram of this. He said it can dislodge by running with the drive up. Anyone familiar with something like this? The clicking noise was apparently coming from it since it was out of place. The u-joints/gimbal looked good, clean bellows, but alignment was off a little.

He also said the u-joints and gimbal bearing are both non-greasable. I've heard of u-joints that cant be greased, but gimbal bearings too? He said its common on newer drives. Since I have been studying the service manuals and plan to do my own maintenance, what does that mean as far as making sure the gimbal bearing stays in good shape?

 

[Don S]

Re: Knocking sound only in neutral idle

Update: Mechanic pulled the drive and said theres a "spring" inside the bellows that helps it keep its shape? I've never heard or seen a diagram of this. He said it can dislodge by running with the drive up. Anyone familiar with something like this? The clicking noise was apparently coming from it since it was out of place. The u-joints/gimbal looked good, clean bellows, but alignment was off a little.

Yes, it's all possible. NEVER start the engine with the drive in the full up position. Always trim the drive down to running position before starting.

 

[skydiveD30571]

Re: Knocking sound only in neutral idle

I have since learned this. Last year was my first year of boat ownership, including first year with an I/O, and most of what I used to do was wrong :facepalm: After reading this site and manuals, I think I have it down. Why isn't this "spring" shown on exploded views of the sx-a drive?

 

[skydiveD30571]

Re: Knocking sound only in neutral idle

The boat ran all saturday without the noise from the clip, but yesterday morning it started again and continued all day. Seeing as I shouldn't need to pull the drive every day to fix this clip, what can be done? Is it extremely necessary to have in there? Could it be weak and just need replaced with a stronger one?