Alpha one knocking noise diagnosis

[ba5e]

I noticed last season a very quiet knocking every now and then from my 1990 gen 1 alpha one drive, this season when taking the boat out, if I turn to starboard the is a very pronounced knocking at almost all rev ranges. It gets louder with higher revs too.

I pulled the drive, oil is clean, bellows intact, universal joints tidy with no play, however the entire joint assembly has maybe 1mm play into the top housing. The engine had sunk a bit since last alignment 2 years ago so I have raised it maybe 2-3mm and alignment is true now.

I'm pulling off the top cover to inspect the shaft tomorrow but does anyone have any knowledge of similar symptoms? Drive has done maybe 350hours in its life.

 

[Bt Doctur]

When you are running it the drive IS ALL THE WAY DOWN? That damage is typical running above the trim limit

 

[Bondo]

however the entire joint assembly has maybe 1mm play into the top housing.

Ayuh,.... My guess is, That's the knockin' noise,.....

 

[Bt Doctur]

In other words your loose .0393 or 3 /64 ths. Should be "0" movement.replace the U joints

 

[ba5e]

In other words your loose .0393 or 3 /64 ths. Should be "0" movement.replace the U joints

There is no play from the u joints, the play is on the shaft going into the 90? bevel gears at the top.

Is it it easy to shim it out or will I need specialist rebuild tools?

I have not dropped the lower half of the leg but maybe its worth having a look down there too?

 

[Fun Times]

There is no play from the u joints, the play is on the shaft going into the 90? bevel gears at the top.

Is it it easy to shim it out or will I need specialist rebuild tools?

I have not dropped the lower half of the leg but maybe its worth having a look down there too?

Does the drive input shaft retainer nut appear to be loose while noticing the in and out play?

If any shimming is required then yes some special tools are needed to shim it all out properly.

Also it's possible the pinion nut & washer to the drive gear and bearing assembly are loose and depending on design you have, it could just need torqued down or rolling preload needs to be set.

Whatever the case may be, you'll have to read all of Mercruiser service manual number 6 section 3A before digging into it so you are/can be prepared.
http://www.boatinfo.no/lib/mercruise...iser6.html#/40

 

[flipbro]

Do you mean 1mm of play in and out or if you turn it back and forth? If its when turning that is normal. Back lash

 

[ba5e]

OK I have after realignment the knocking seems to have gone for the most part (especially when turning) but at certain rpms there is an aweful noise even in idle. Could this be flappers? I also see now that my corsa exhaust system the starboard solenoid is not operating its full throw. No difference between the noise with the exhaust in either position.

Video:
https://youtu.be/cSxmMiJy8Xs

 

[ba5e]

Does the drive input shaft retainer nut appear to be loose while noticing the in and out play?

If any shimming is required then yes some special tools are needed to shim it all out properly.

Also it's possible the pinion nut & washer to the drive gear and bearing assembly are loose and depending on design you have, it could just need torqued down or rolling preload needs to be set.

Whatever the case may be, you'll have to read all of Mercruiser service manual number 6 section 3A before digging into it so you are/can be prepared.
http://www.boatinfo.no/lib/mercruise...iser6.html#/40

To answer your question about the nut, no it was tight. I had a good look In the top of the drive and it looked like new

So I'm still left with this noise at certain revs and I really hope it was not the drive! If after listening to the video it could still be the drive, I could swap it for my other drive to rule out drive and drive coupler (could get same noise on other engine).

 

[ba5e]

Do you mean 1mm of play in and out or if you turn it back and forth? If its when turning that is normal. Back lash

Hi, no it was lateral play 'after' the universal joints and up to the first bevel gear.

 

[Bondo]

OK I have after realignment the knocking seems to have gone for the most part (especially when turning) but at certain rpms there is an aweful noise even in idle. Could this be flappers? I also see now that my corsa exhaust system the starboard solenoid is not operating its full throw. No difference between the noise with the exhaust in either position.

Video:
https://youtu.be/cSxmMiJy8Xs

Ayuh,... Pretty much sounds like loose tin rattlin',....

Flywheel cover plate,..??

 

[Bt Doctur]

I agree with bondo, flywheel dust cover (if a tin one) is cracked and vibrating

 

[ba5e]

I agree with bondo, flywheel dust cover (if a tin one) is cracked and vibrating

Goodness, did not think of that! I suppose it's engine out again then for a repair, or can I get at it with the exhausts off and drive?

When you say tin, I believe mine is steel, I'll take some better pics soon. What types (materials) of cover are there and what could cause this type of damage?

 

[Bondo]

Goodness, did not think of that! I suppose it's engine out again then for a repair, or can I get at it with the exhausts off and drive?

When you say tin, I believe mine is steel, I'll take some better pics soon. What types (materials) of cover are there and what could cause this type of damage?

Ayuh,.... I have crawled into bilges, 'n removed that tin plate, to get a socket onto a starter bolt before,....
1/4-20 bolts I think, 7/16" wrench,...
It depends on how much "Boat" is in yer way,....

Their made of tin(stamped steel), or plastic,....

Anytime I've got one in my hand, I cut off the finger that gets in the way of some starter bolts,.......

 

[achris]

:lol: I have this vision of you ACTUALLY in underneath and engine with a little socket and handle removing the cover.... :lol:

 

[ba5e]

Brilliant! I'll be crawling in there on Saturday