Change in engine/outdrive noise... possibilities?

[stephentyler20]

Boat is a 21' cuddy with a 1988 Mercruiser 5.0Litre (305 cid, 200hp), and an Alpha 1 Sterndrive.

Problem:

The boat sat for about 3 weeks. When I started it up again, I immediately noticed an unusual sound, emanating (I THINK) from either the sterndrive (underwater), or more likely the space between the engine and the sterndrive.

Basically, it sounds like a helicopter or airplane propeller, but slower, and it's not that loud but it is noticeable. It seems to be correlating directly with the spinning of the driveshaft, and is audible whether in gear (r or f) or in neutral. The boat operates 100% normally, however, temp is fine, oil pressure normal, and cruises/planes no problem. The only issues I've had this summer have been 1. Extensive fouling - I then removed the boat, detailed the hull and drive, and it ran fine; 2. Overheating - replaced the water pump and thermostat, problem solved. Also a bad water hose was replaced.

This problem began about 2-3 weeks after replacing the t-stat and water pump. The only other thing I noticed was that my water intake grate was missing on one side, with the other side barely hanging on. I'm not sure if this is related at all, but I don't think so.

Also, I pulled the boat recently for the fall layup, and ran it on the muffs. The sounds is still audible, although it gets drowned out by the out-of-water exhaust noise.

Any tips on where to start looking here? I want to say the problem is between the engine and the drive, but that also happens to be the hardest area to get to/work on/visualize. Any diganostic tips? Much appreciated!

 

[Haut Medoc]

Re: Change in engine/outdrive noise... possibilities?

Pull the drive & look at the ujoints for rust.
A bellows inspection is in order as well....
There should be no water in the bellows at all......

 

[stephentyler20]

Re: Change in engine/outdrive noise... possibilities?

If the U-joints are rusted, is the only solution to replace the U-joints, or will some grease do?

 

[Lou C]

Re: Change in engine/outdrive noise... possibilities?

You are going to need to pull the drive off and check the u-joints, gimble bearing and the driveshaft itself for rust. If it's rusted where it comes out of the upper gear housing it will tear up that seal and cause the drive to leak gear oil in the bilge. If there is any water in the bellows plan on a bellows replacement and maybe having to replace the ujoints, and gimble. Grease alone won't cut it! The ujoints should look like these on my old Cobra, not rusted.

 

[stephentyler20]

Re: Change in engine/outdrive noise... possibilities?

I see! So is that noise characteristic of a badly rusted u-joint?

I would be pulling the drive anyway for the winter layup (just a personal preference, I like replacing those seals every year), so I will check again. I know from last season, however, that the U-joints were indeed fairly rusted. They do NOT look as clean as the U-joint in your picture!

One more thing... tomorrow I'm planning what might be my last boat outing of the season. I'm actually trailering up to a nearby lake to cruise around a bit. Since I'm normally in salt water, I like to think of it as sort of a end-of-season clean out, letting the clean fresh water clean out the cooling system a bit.

Anyway, before I go, I will definitely do a quick gear lube drain and refill... Is there anything I should check for at that point?

By the way, I did have oil in the bilge the last couple weeks, that I only recently was able to clean up, but I'm not sure whether that's from the drive or the engine... I changed the engine oil before that, and I know I spilled a good amount of oil when changing the filter, because it was so hard to reach (I kept it out of the ocean at least, sucked it up into a pan later on).

 

[chiefalen]

Re: Change in engine/outdrive noise... possibilities?

Any of the bolts on the drive loose? The ones holding the transom mount on?

What i am hoping did not happen is that the transom mount or the motor dropped 1/2 inch or more.

88'- 20 year old boat. Transom rotten a bit, or the rear motor mount?

I didn't say this happened but when you pull the drive every year do you use a alignment bar?

 

[PhrozeN_FisH]

Re: Change in engine/outdrive noise... possibilities?

I think you are headed in the right direction by looking at the gimbal bearing and u-joints. You will usually notice a u-joint noise more when turning. The gimbal bearing noise is more of a rumble deep in the transom area. Once the drive is removed you can rotate the gimbal bearing for any roughness by reaching through the U-joint bellows. If you have any water in the U-joint bellows inspect it thouroughly for any tears, cuts or dry rot. Also inspect the exhaust bellows and water hose. If found, it may be a good time to replace all of them. While you are in that area also inspect the driveshaft and coupler splines for wear. Be sure to lube the coupler and splines and use a new outdrive mounting gasket set when re-installing.

 

[stephentyler20]

Update on this evolving problem...

Update on this evolving problem...

So today I decided to grease up all the zirks on the sterndrive, and also change the gear lube oil...

Yikes. I pulled the oil plug, and out came WATER. There was a small amount of pure water, followed by a mixture of oil and water that became increasingly more oil as the drive changed. At best, the oil was light green/muddy. One more thing... I checked the magnetic oil plug on the drive for metal shavings... I didn't see any, but I found what I believe is a small piece of gasket (about 1cm long, and a thin strip).

So at the very least, I know now there's a problem (which is why I last-minute canceled my trip to the lake... argh). My buddy, who is a boat mechanic and has helped me fix a lot of things, thinks it could be a bad driveshaft seal in the drive.

I also noticed there was more oil in the bilge today... Not a lot, but its definitely stern drive oil, as the engine oil is still at normal level.

So with this new information, now what should I be thinking? Could a bad driveshaft seal in the drive cause the noise, the water in the oil, AND the oil leak into the bilge? Perhaps this is a compound problem?

 

[chiefalen]

Re: Change in engine/outdrive noise... possibilities?

Reseal time.

Just for fun you have fishing line wrapped around under your prop on the shaft?

Messed up the seal?

 

[stephentyler20]

Re: Change in engine/outdrive noise... possibilities?

Reseal for sure, following a pressure test to figure out which seal is blown... I haven't pulled the prop yet, but I will and check for fishing line.