Air in lower unit?

[C17LoadSmasher]

Hey all...<br /><br />It could be just me hearing things.. but, here goes. I decided to change the lower unit gear oil today. I went and got the pump and the proper oil and went about draining it and then pumped it back full until it was to the top of the vent like I am supposed to, etc. Well, I also was going to change the motor oil today, so I went to a nearby lake to fire it up and cruise around for about 10 minutes or so to get it up to normal operating temperature, and then I would drain the oil. Well I fired it up, and it could be me, but it sounded funny. This is after I changed the lower unit oil. I figured it could just be that it sounded different (was a shallow water slip) so I took it off the trailer and ran it around for a few minutes and it didn't seem to make any abnormal noises. I should note however, that several weeks ago, the bilge got filled with water when one of the cooling drain hoses popped off and pumped raw water into the bilge. I don't know if this might have anything to do with it? Could air in the lower unit cause the noise? Any suggestions would be a tremendous help. Thanks a lot.

 

[Trent]

Re: Air in lower unit?

I think you have no worries...You just heard that "Puff the magic dragon" fly over your head!

 

[Walt T]

Re: Air in lower unit?

You should check the U joints, its possible water got in there if it got high enough. That would cause strange noises

 

[geriksen]

Re: Air in lower unit?

You probably need a gimbal bearing. when the water got high in the boat it entered the u-joint bellow from inside the boat. This washed the grease out of the gimbal bearing. If the sound changes toen when you turn the wheel left and right (bingo)<br />You may also need u-joints as the previous poster suggested. Those however make aknocking sound when they start to go out. If you are hearing a roaring sound it is the gimbal bearing.

 

[C17LoadSmasher]

Re: Air in lower unit?

How would it enter from inside the boat? Wouldn't the U-joint or gimbal bearing bellow(s) be watertight as well? The water didn't get REAL high, it made it up to the bottom of the oil pan, maybe an inch or so higher. Just out of curiosity, that all sounds expensive, eh?<br /><br />--Chris

 

[geriksen]

Re: Air in lower unit?

There is a vent hole on the inner transom plate. It is just above the crankshaft level. If you drive the boat or pull it up a boat ramp the amount of water you had in there is enough for it to go in there. You will probably spend between $300 and $1,000<br />The sooner you do it the less it will cost. If the u-joints are not making noise and you get it to a shop quickly they can grease them and they will not have to be replaced. Pulling the drive and replacing the gimbal bearing should be about $300 or a little less.

 

[C17LoadSmasher]

Re: Air in lower unit?

Is there some sort of way to check for all that w/o having to tear it down or something? It happened on a Saturday a while back, we noticed no noise or anything abnormal that day, or the next day (we took it out for about 4 hours that Sunday). Only after I changed the lower unit oil that I noticed a noise. As far as the water, once we noticed it, we had shut down the engine and let the bilge pump do its duty after we reattached the line, and only after it was about 4" below the engine did we start it back up in order to make sure the pump was getting the full juice. It was dry in there in about 8-10 minutes.

 

[geriksen]

Re: Air in lower unit?

You could pull the top plug on the drive and stick something in it to verify that the drive is full. (lower the drive first) You did fill it from the bottom until it came out the top right? If the lube is there at the top run it in water again. If the noise chages when you turn the steering wheel it is the gimbal bearing.

 

[C17LoadSmasher]

Re: Air in lower unit?

Yeah, I filled it from bottom to top. I'll check it later when it gets somewhat warmer.. a little chilly in SC today.

 

[C17LoadSmasher]

Re: Air in lower unit?

Everything is good. I swear I still hear the noise when in the water though. No change regardless of where the steering wheel is turned. I might change the oil again tomorrow just to make myself feel better.

 

[geriksen]

Re: Air in lower unit?

I still think it is the gimbal bearing. If it is like a roaring sound that you can hear inside and outside the boat, that is it.

 

[flashback]

Re: Air in lower unit?

sounds like the majority says you have water in the shaft bellows,gimbal,ujoints,,,,,,ok. grease the gimbal and try it again,,,,still sounds funny,,,,,,take the outdrive off and grease the u-joints........as a matter a fact, considering how easy it is to remove the outdrive, i would probably grease the u-joints and the gimbal just to make sure. it can't hurt.............

 

[C17LoadSmasher]

Re: Air in lower unit?

Yeah I was thinking the same way, however, how much does the outdrive weigh? I don't have anything to take that baby off with, well to be more accurate, anything to hold it, etc. If it weighs maybe a hundred pounds or something, no big deal, but anything more than that and I don't know. And, when I go to put it back on, don't I have to realign the outdrive with the engine? I don't have the tools for that.<br /><br />--Chris

 

[Bondo]

Re: Air in lower unit?

I'm not very big,+ i can pop one off and carry it to the garage.... Might be 100lbs...

 

[AdmiralQ]

Re: Air in lower unit?

Just got done removing my outdrive, greasing u-joints, replacing u-joint bellows. Weight is not really an issue, the drive weights maybe 75-100 lbs. I was able to walk around the yard and garage with the drive, it's more unwieldly than heavy. As long as you don't pull the engine or mess around with the engine mounts, you don't have to realign the drive with the engine. Just have another person there to help you reinstalling the drive, one to hold the drive, and one to get the u-joints and shaft into the transom assembly. You'll probably have to take a big screwdriver and rotate the shaft a bit to get the splines to line up, but it's really pretty easy of a job. If you don't already have one, get a shop manual for your engine/drive combo. It will walk you right through pulling and reinstalling the drive. It pays for itself many times over the first time you use it.

 

[geriksen]

Re: Air in lower unit?

You can do it youself with a manual. Put the drive in forward gear, lower the tounge of the trailer and lower the drive untill the skeg is on the ground, un bolt it and pull it off. do not pry it off with a screwdriver. wiggle it and it will come off. Once you have it off look for rust. Turn the gimbal bearing by hand and you will likely find your noise. Greasing it will not fix it. It will have to be replaced. (Special tool required) Have a shop do that. Put a new gasket kit on when you re-install the drive.

 

[magster65]

Re: Air in lower unit?

I've noticed that if there is a problem with the u-joints, turning your steering from hard port to hard starboard will cause a rumbling or vibrating (so will over trimming the leg). A mercruiser has to be in forward gear to remove the drive. I find that if I remove the nuts, lift the leg up, put a small piece of wood under the drive it helps to crack the seal on the gasket. When reinstalling I usually use a good smear of grease on the gasket to help seal everything up again. You can handle the job! Happy Yachting!<br />

 

[C17LoadSmasher]

Re: Air in lower unit?

Thanks for the help and information! This forum never disappoints when it comes to that. Another note, I do have a shop manual on order, should be here this week. I plan on pulling the outdrive as soon as it gets here. I will keep you all posted. <br /><br />--Chris

 

[geriksen]

Re: Air in lower unit?

I use the wood trick too. I forgot to mention it.<br />Good call

 

[C17LoadSmasher]

Re: Air in lower unit?

Since the manual hasn't shown up in the mail yet, I decided to investigate and see what I could find by poking around. I hooked the engine up to the muffs and fired it up. First time she fired. It didn't sound abnormal really, just sorta like a noise/vibration within the boat itself. When you stood outside the boat, you couldn't tell there was anything wrong. At higher RPMs it wasn't there. I turned the wheel side to side, no change in noise. I put it in gear (idle) and turned it side to side, no change. I double-checked the lower unit oil - full, and still that nice shade of green (instead of that nasty azz black that I changed out last week). On another whim, I went and checked the plugs (the three that I could get to.) They all looked like this one:

<br /><br />That doesn't look inherently bad to me. I do notice that there is some rust on the hex-head part of the plug. Oh- when the engine was running, I had tried to listen to see where the noise might have been coming from, it wasn't really an audible noise, it did seem like it was coming from the rear of motor, near where the output shaft is. Should I go ahead and pull the outdrive anyways? I found several step-by-step procedures (http://www.mercstuff.com), or should I wait for the manual to show up? I'm somewhat close to bringing it to the dealer and see if they can hear anything, or if they think it's normal. But I am sure the dealer can find SOMETHING wrong if they want the $$.<br /><br />--Chris