Whirring sound at low rpm from Alpha gen 2 on 5.0 carbed mercruiser.

[telstar1]

This is driving me a bit bananas.Distinct whirring sound from drive at say under 1200 rpm. In gear or out. No metal on drive magnetic plugs. No excessive gear noise at cruise ie when you lean over transom and listen. Steering side to side makes no difference. Take drive off and run engine theres no noise. I replaced gimbal bearing,rebuilt pump,took lid off upper drive all teeth look fine. Noise seems to come from upper drive. Been doing it for awhile seems to be worse lately. I did a self rebuild on upper drive about 400 hours ago and its been whirring a bit ever since.louder lately. I was very careful in shimming it but of course I could have got it wrong. Odd theres been no repercussions if its wrong tho...I dont know anyone else local with an alpha so Ive nothing to compare to but it seems to me it should not whirr.I can hear it from say 10 feet away from boat or more.All input appreciated.

 

[AShipShow]

Did you correctly set the rolling torque preload on the bearing stackup when you rebuilt the topend?

 

[AShipShow]

Did you correctly set the rolling torque preload on the bearing stackup when you rebuilt the topend?

"whirring" kinda sounds like bearings...but could be lots of other stuff.

 

[telstar1]

I carefully did the preloads as directed. Have not disassembled to check. Thats next I guess.

 

[achris]

Were all bearings new? And if so, what brand?

 

[Rick Stephens]

Years back I had a whirring noise after setting pre-load . I immediately pulled it back out to find it had moved and gotten loose. I didn't have the bearing pack compressed enough. MadProps is right - pull it and check it again. Beats trashing a drive.

 

[telstar1]

They were new mercruiser bearings and gears.Ill be checking preload.

 

[achris]

You also need to have used the Merc special tools to have set the gear teeth clearance.

Chris......

 

[telstar1]

Yes I have them well sort of. I built a set of setup tools for an alpha 1 years ago. For the gen 2 I used these tools,checked the setting before I disassembled the factory setup(bearings were fine a tooth came off) and used the same reading for the new gears. This came out to be within a thou of original shimming and I figured it was good. Not absolutely positive about this of course.In 4 years and 500 hours theres been no metal in oil and gears appear fine however I do have a whirring sound...

 

[telstar1]

Theres an expression among some in the equipment business"wait for something definite to happen then well know what to fix"Well I now know what to fix. An event occurred in drive today. Pretty sure its a tooth came off upper gears.It still works but with a tick tick noise.Shut it down shortly thereafter. Interestingly this was accompanied by a bang which was the drive oil reservoir disintegrating. Guess it had a rapid heat and pressure buildup. Never heard of that before....
New Alpha drive on order.Ill fix up the old one for a spare..maybe.

 

[harringtondav]

Ouch. Spiral bevel gears are tough. Tooth breakage doesn't happen with proper shim settings (cone point and backlash) and bearing preload. Impact or lack of lube are the main causes. I'd invest in a set of Gen II shimming tools before changing bearings, etc on you new Gen II.

Also the top cover bearing preload is just as critical. Not enough preload, or worse, no preload can cause the upper driveshaft/gear to walk away from the mesh. Then perfect shimming is out the window. Tooth tip loading will break gear teeth.

 

[Rick Stephens]

↑ What he said.