Short rumble/groan/vibration during hole shot

[SilentJ20]

This seemed to be the best place to post this:

Ever since I bought my 1994 220BR (Alpha 1 Gen 2, 5.7L, high five prop) a few months ago, when I do a hard hole shot (in fwd gear, idle to WOT) I will usually get a short rumble/vibration at the beginning, then speed off as normal. It happens more noticeably when I have more weight behind the boat, like a 2-3 person tube. When pulling a significantly heavier tube (3 adults) it may last a couple seconds and seems to hesitate a little during the noise, then it stops and I accelerate. RPMs never rocket up like it's free-wheeling. It's not a hard, sharp grind, more of a softer sound. I don't think it's the coupler, as I hear those usually just let go all together. Could it be the rubber bushing in the prop? Cavitation of the prop (likely not, but options...), something else?

 

[scoflaw]

Well how long would you expect a 27 year old Alpha to last hammering on it?

Probably not the answer you were looking for but....

 

[SilentJ20]

Well how long would you expect a 27 year old Alpha to last hammering on it?

Probably not the answer you were looking for but....

That was actually more of a non-answer. I understand it's an older boat, but if taken care of, they tend to hold up. So that's what I'm trying to do. Figure out what is wrong and fix it. I knew I'd be getting my hands dirty (already have).

And ideas as to what is causing the sound and if it's a problem?

 

[Stee6043]

That was actually more of a non-answer. I understand it's an older boat, but if taken care of, they tend to hold up. So that's what I'm trying to do. Figure out what is wrong and fix it. I knew I'd be getting my hands dirty (already have).

And ideas as to what is causing the sound and if it's a problem?

I had a beauty of a Four Winns Liberator 211, my first boat, loved that thing. She had some hours on her (and a lot of rot I did not know about at the time). But I can recall a similar feel/noise on that boat the year I blew my Alpha One sky high. I did such a number on mine that I tore the bellows with some shrapnel from the u-joint. Made for quite a leak in the boat, one the bilge pump was only marginally keeping up with.

If you are capable of pulling the lower unit you may be able to see/feel some wear in there. Mine gave up the ghost at the u-joint which may or may not have ever been serviced.

 

[Thornton69]

Idle to WOT in the hole with a 5.7 in front of any alpha is pushing it toward it's limits. In a lighter boat you may be fine but adding a heavy drag behind it is rolling the dice a bit.
If the growl is internal in the outdrive, it would likely tear itself apart in short order under those circumstances. When was the last time you replaced the oil? It will give you a good indication of whether or not it is where the problem is.
The universal joint and gimbal bearing is a common spot that can cause it as well. Pulling the outdrive and checking their condition along with the engine alignment is also routine maintenance. I do it annually in the off season on our boat. They are both replaced with the bellows every 3 years preventively for us, but we put a lot more hours on than most in a season. Approaching 50 days and over 200 hrs so far this year.

 

[SilentJ20]

Idle to WOT in the hole with a 5.7 in front of any alpha is pushing it toward it's limits. In a lighter boat you may be fine but adding a heavy drag behind it is rolling the dice a bit.
If the growl is internal in the outdrive, it would likely tear itself apart in short order under those circumstances. When was the last time you replaced the oil? It will give you a good indication of whether or not it is where the problem is.
The universal joint and gimbal bearing is a common spot that can cause it as well. Pulling the outdrive and checking their condition along with the engine alignment is also routine maintenance. I do it annually in the off season on our boat. They are both replaced with the bellows every 3 years preventively for us, but we put a lot more hours on than most in a season. Approaching 50 days and over 200 hrs so far this year.

I will definitely ease up a bit on the hammer a bit. Guess that's one thing I needed to learn. Everything else about its performance is smooth without any slipping/noise.

Drive oil was replaced by previous owner just a year or two ago when previous owner replaced water impellor. I checked the level a bit ago along with letting a little weep out the bottom hole. Both locations were still blue with a slight darker complexion and no signs of water (water should sink towards the bottom, right?). Because it's new to me, I'll drain and replace the drive oil this off-season to better check for water, shavings, etc.

U-joints were just replaced by me (for another issue) made the sound before and after replacement. The gimbal bearing is smooth and tight (I plan on replacing it this off-season along with all bellows just because). Alignment was also good.

Just as an easy elimination of a component, I'll switch props before I go out again. I know the chances of it being a partially spun hub or cavitation are slim, but it's really easy to eliminate if changing the prop significantly changes or stops the noise.

Thanks for the advice.