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Flexible shaft couplings #18706
03/08/21 10:26 AM
03/08/21 10:26 AM
Joined: Sep 2009
Posts: 13
Kincardine Ontario Lake Huron
Twilight Zone Offline OP
Member
Twilight Zone  Offline OP
Member
Joined: Sep 2009
Posts: 13
Kincardine Ontario Lake Huron
How many have installed a flexible shaft coupling? And did it make any difference.?
We are replacing our prop shaft and considering a shorter shaft by 1.25in to accommodate a flex coupling..(R&D Marine 910-002)..hoping to reduce vibration from the old Yanmar. Will also be replacing the cutlass bearing.

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Re: Flexible shaft couplings [Re: Twilight Zone] #18709
03/08/21 07:25 PM
03/08/21 07:25 PM
Joined: May 2007
Posts: 2,620
Portsmouth, RI
Rhapsody #348 Offline
Past J/30 Class President
Rhapsody #348  Offline
Past J/30 Class President
Joined: May 2007
Posts: 2,620
Portsmouth, RI
I installed one on Rhapsody (picture at this post). Proper shaft alignment is still needed. check this post. Make sure you bypass the coupling with an electrical ground jumper wire to prevent prop electrolysis.

Re: Flexible shaft couplings [Re: Rhapsody #348] #18710
03/09/21 10:56 AM
03/09/21 10:56 AM
Joined: Sep 2009
Posts: 13
Kincardine Ontario Lake Huron
Twilight Zone Offline OP
Member
Twilight Zone  Offline OP
Member
Joined: Sep 2009
Posts: 13
Kincardine Ontario Lake Huron
Good info. - thanks! Do you think the flex coupling helped reduce vibration - and noise transmission? That would be my only reason for installing one. The alignment has always been good, but the old shaft - 40 plus years old - was worn down at the cutlass bearing as well as the key sheared off at the transmission end last year damaging the shaft and coupling so we are replacing it all. The original 2QM15 is a noisy and unbalanced beast anyway so a flex coupling may just be a waste of money in my case. There was a note in the Yanmar service manual that claims a flex coupling must be installed if the engine is mounted with flexible mounts - which started me thinking that our installation should have had one. It has a steady throb at cruising speed (2200 rpm) that rattles the whole boat. Prop was serviced and balanced by Martek recently.

Re: Flexible shaft couplings [Re: Twilight Zone] #18711
03/09/21 10:59 AM
03/09/21 10:59 AM
Joined: May 2007
Posts: 2,620
Portsmouth, RI
Rhapsody #348 Offline
Past J/30 Class President
Rhapsody #348  Offline
Past J/30 Class President
Joined: May 2007
Posts: 2,620
Portsmouth, RI
It helped a little, but not much. A straight shaft, good engine mounts (one where the rubber isolators haven't degraded over the life of the boat) and precision alignment are more effective.

Welcome to the world of a 2 cylinder diesel engine. The 3YM30 on my J/109 is much smoother at all rpms.

Re: Flexible shaft couplings [Re: Twilight Zone] #18712
03/09/21 12:10 PM
03/09/21 12:10 PM
Joined: Sep 2009
Posts: 13
Kincardine Ontario Lake Huron
Twilight Zone Offline OP
Member
Twilight Zone  Offline OP
Member
Joined: Sep 2009
Posts: 13
Kincardine Ontario Lake Huron
Ah yes - buy a bigger boat! That thought has occurred to me more than once, but I can't seem to find a better boat for the money that offers the racing and cruising potential of the J30 - even though compromised on both scores. I will keep searching, but in the meantime I am stuck with messing around in an old boat.
Thanks for all the info you have shared and continue to provide - a truly valuable resource to this community.


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