***Knocking sound from outdrive*** NOT gimbal, helping my nephew

[Lukelona]

Hello, helping my nephew fix his boat. It's a 1993 stingray 609 with 4.3 mercruiser/alpha gen 2 drive.
Recently while flushing engine it started making a knocking sound from outdrive.
Today I pulled the drive and ran it without and it didn't make the noise. So it's definitely in the drive I believe.
It happens at higher rpms in N and in drive it will make the noise either way.
It starts around 2k RPM. Sounds like it's coming from upper half of outdrive, the gimbal bearing is new and still perfect, the u-joints look good and only one has very minimal play on it. I took the top cover off and visually inspected the gears coming from driveshaft and they look good, no broken teeth etc. Also the bearing under that cover (don't know the name) feels good also.

This outdrive is exceptionally clean, no corrosion and seems to have been well maintained.
I also checked drain plug magnet for metal and only found normal very little shavings.
I'm stumped how to proceed diagnosing it.
Any help would be great, thanks

 

[Scott Danforth]

the u-joints look good and only one has very minimal play on it.

There should be no play as in zero. you found the issue. I would still replace the gimbal bearing while your in there.

 

[tpenfield]

^^^^ +1 I replaced a set of u-joints that were grinding, but to the touch they felt perfect. So, if you can actually feel some play then replace them and see how the drive sounds.

 

[Lukelona]

There should be no play as in zero. you found the issue. I would still replace the gimbal bearing while your in there.

it's very very little bit. Almost can't notice it. But I understand if it shouldn't have any it should be replaced anyway. But it doesn't seem like that would make this heck of a noise that it does. It's a loud knock.
Also, this is running with drive down, but it's possible he ran it before with drive up on the water hose.
Would that very little play in ujoint make that loud of a knock?
It doesn't make the noise at all at idle, if you rev it up some it will start making noise. Also is kinda delayed when it starts knocking. It takes a second to make the noise.
I'd hate to replace ujoints and reinstall just to find it still making noise.

This is very strange. lol
Any other possibilities?

 

[alldodge]

Was your drive all the way down when running or close to all the way?
If yes, check your engine/coupler alignment, and give a good look at your coupler splines

 

[tpenfield]

You could try a mechanics stethoscope to better isolate the source of the noise.

 

[thumpar]

If the ujoints have zerks grease them up real good and see if the sound changes at all.

 

[Lukelona]

Was your drive all the way down when running or close to all the way?
If yes, check your engine/coupler alignment, and give a good look at your coupler splines

it was down when I listened to it, but like I said this is my nephews boat and he may have started it with drive up. He can't remember if he did or not.

Engine alignment would cause vibration right? The boat does have a vibration issue also, but that wouldn't cause a knock correct?

 

[Lukelona]

You could try a mechanics stethoscope to better isolate the source of the noise.

I've thought of this too lol
But it seem like the noise is right at top of outdrive. Honestly didn't sound like it was as far back as the ujoints.
The only thing that could make noise in top of drive is the gears and ujoint right? The gears look good so maybe it is ujoint?

 

[Bondo]

the u-joints look good and only one has very minimal play on it.

Ayuh,..... U-joints are worn out, Before ya can feel Any play,....

I'm bettin' changin' 'em both will cure the knock,....

'n tell the kid to only run it with the drive down, or nearly so,....

 

[Lukelona]

Ayuh,..... U-joints are worn out, Before ya can feel Any play,....

I'm bettin' changin' 'em both will cure the knock,....

'n tell the kid to only run it with the drive down, or nearly so,....

Ok, I'll change them and put it back together to try it. I hope that's all it is!
If you guys can think of anything else I could even check, let me know...

What's the easiest way to change the joints?
Only way I've done them is on my trucks with a hammer and block of wood lol
That doesn't sound careful enough for the outdrive!

 

[alldodge]

I use big C-clamp and a socket, but have also used a hammer and socket. They do make the U joint tool

 

[thumpar]

Autozone has the u-joint tool in their loan a tool program. You have to put down a deposit but it is returned when you return the tool so it doesn't cost anything.

 

[Rick Stephens]

And Autozone would have the crosses in stock as well.

 

[Lukelona]

Ok. I'll probably rent it, it don't cost anything so I'd rather that then fight with a c clamp lol
Although now I remember seeing my dad use one to do them also.

Your saying AutoZone will have the ujoints?
Do you just try to match them up? Or they have them for marine applications?

 

[Rick Stephens]

Read this thread.
http://forums.iboats.com/forum/engi...outdrives/244162-u-joint-part-number?t=238091

 

[Lukelona]

Ok, I'm unsure is that Spicer part number they listed to fit mercruiser alpha one gen 2?
It's a lot cheaper buying from auto store rather than mercury!

 

[Rick Stephens]

Gen2 and Alpha 1 are same crosses. So yeah.

 

[Lukelona]

Great thanks! I'll throw some new joints in it, and hopefully the knock stops.
Any ideas of what else to check would be great thanks so much guys!

 

[Rick Stephens]

Pop the top on the outdrive. Take a peek. Can't hurt and you can make sure the gears aren't eating themselves.