Noises coming from transom area/outdrive

[sms986]

I just bought an '89 Larson 21' with a GM 305 mercruiser in it. The block was cracked when I bought it, and I built a 350 to put in it's place. Just got the motor in and started yesterday. Engine runs great, but I hear a noise around 1500-2000 rpm coming from somewhere behind the engine. Best way to describe the noise is someone running over something hard with a lawnmower. It isn't a steady sound, it comes and goes, and I can feel the engine fighting the extra resistance when doing it. Outdrive was up. Putting the outdrive down made the noise no better or worse, but it did mane the noise occur at idle. I fired the 305 a few times before yanking it out, but I did not hear this noise before. Had the engine "aligned" when I got the engine in, and installed the outdrive myself. I'm guessing either the alignment was a pretty bad job or I messed something up. I have built many engines before, but this is my first outdrive. Any ideas?

 

[tpenfield]

I would pull the outdrive to get a look at the u-joints and the coupler, as best as you can see it.

 

[Rick Stephens]

Pull the top cap off the outdrive. You can look at the gears in the upper gear case.

Pull the outdrive and look at u-joints and gimbal bearing. (most likely cause of your noise)

In the future, don't run your motor, at all, with the drive trimmed up. This stresses the u-joints beyond normal operating range and also bangs the u-joint coupler against the bell housing. Noise with the drive trimmed up would be normal and indicative of the damage being done.

 

[wahlejim]

As others have said, remove the drive, I am assuming Alpha One? based on the year? Feed water through the bell housing with a cut off hose (washing machine hoses work nicely for this). Run the engine. It will tell you if the noise is coming from inside the boat or the outdrive.

 

[harringtondav]

. I have built many engines before, but this is my first outdrive. Any ideas?

Did you rebuild the outdrive? If so shimming the gear sets is critical

 

[sms986]

No, I have not dug into the outdrive at all. I only pulled it off to get the engine out and back in, then replaced the gaskets and put it back on. What I meant was the is the first time the engine I built wasn't being bolted up to a transmission. I am headed back south to work and won't be home for another month. I obviously didn't have time to pull and inspect the outdrive before I left. I just want to narrow it down as much as possible before I go back home so that I am ready to get to work. Thank you all for the input, and if anyone has any other ideas let me know.