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470 Drive unit noise

A

aussie_trev

New member
"Hi all, my boat is fitted wit

"Hi all, my boat is fitted with twin 470 engines and stern drives. On a recent trip one unit developed a knocking noise, with a reduction in revs the noise intervals slowed and likewise with an increase in revs the knocking noise increased. I feel this may be in the drive unit would like some ideas? Would this be a typical noise from a failing uni joint? In neutral there is no noise.
Thanks Trev."
 
"Well,.....
Everything But th

"Well,.....
Everything But the Propshaft is turning in Neutral,......
Have you checked the Prop,..??...

The U-joints tend to get Quieter, or Nosier as you turn the wheel, or trim the drive....."
 
Thanks for your imput. Props a

Thanks for your imput. Props are both new. The noise appears to be generated with the boat under load. I believe the noise is from the flywheel back. I have not as yet check rotating the wheel or adjusting the trim.
Trev
 
Check the props. I'd be wi

Check the props. I'd be willing to wager there is either something fouling one or there is a ding in one of them.
 
Had the same problem last year

Had the same problem last year with my 3.7 mercrusiers. (same as 470)After much investigating I found the gimbal bearing was the culprit. Fixed myself but took some work
 
"Hi all, I have used the boat

"Hi all, I have used the boat agian after adjusting the cable for the forward/reverse selection. Motor runs perfect in reverse but clunks in forward, this makes me confident that the problem is in the lower gearbox. I can not fix the problem by adjusting the cable I therefore feel the only option is to remove the lower leg and check the gearbox."
 
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