Drive knocking

[bpritchett]

Had new to me 1985 Carver Mariner 36 out today for fourth time. Noticed loud knocking sound when in forward only on both drives. Each drive had same sound independently. Also when above idle the knocking disappears. Sounds like coming from in the salon area. No burnt smell or smoke or anything abnormal. After running for 10 minutes or so it somewhat stopped but occasionally would reoccur? Any thoughts would be appreciated. BTW it’s sunny and finally above 60 def in Indiana!

[Viper]

I'm assuming you're referring to an inboard application. Do you have Walter V-drives? They are separate from the engine and connected by a short shaft with u-joints. Could be a number of things; u-joints if applicable, V-drive, reduction gear on the engine side, an engine miss, loose props, bad alignment, running gear issues, etc. Have you checked fluid levels?

[bud37]

To add , one question, what rpm are you idling at in gear now ?

[SanJuanDreamer]

I would ask you have someone drive and you listen to hear where its coming from...
or...you drive and have mechanic listen....

[Viper]

Source of the post To add , one question, what rpm are you idling at in gear now ?

+1

[bpritchett]

RPM at idle(according to tach) looks like 400-500 rpm. Once it goes above 700 the knocking does stop.
Thanks for the suggestions.

[bud37]

Yup, kinda what I was thinking, they will do that at that low an idle,quite well known..there may be other reasons but ...try to get your idle in gear up to at least 650-700 RPM, hopefully that will calm everything down......check your particular spec,..

Actually if all is set right and engine tuning is on spec , there should not be much difference in idle rpm in or out of gear tied to the dock........good luck with it.....

[Viper]

Source of the post RPM at idle(according to tach) looks like 400-500 rpm.....

That'll do it if the tachs are accurate