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Current Replies for Shaft Size on 1986 Mk V
  Shaft Size on 1986 Mk V (dmoores)
Posted: 5:00:55 pm on 5/27/2011 Modified: Never
Hi all, I have searched the site but didn't find the information I seek. Can anyone tell me the shaft size and taper/no-taper for the shaft on the Mk V with the Yanmar 1GM engine?

If anyone knows the required diameter and pitch that would be handy too!  I'm fed up with my rattling/vibrating Gori: it has to go!

Dave Moores,  "Overime"
  Re: Shaft Size on 1986 Mk V (Tonyj)
Posted: 10:16:32 am on 5/28/2011 Modified: Never
Hi Dave:
My 1985 MkV has a 7/8" shaft, tapered, and I am using a 12 x 9 prop.
If you look in the "Black Arts" section of this site, you'll see that there are a few different diameter and pitch combinations in use on Mk V's.  You might want to measure your shaft diameter before getting another prop, there are supposedly a few 1" shafts out there.
You may be able to find a good used prop on E-Bay.
Good Luck,
Tony Jeske
Mk V #581
San Diego  
  Re: Shaft Size on 1986 Mk V (davidww1)
Posted: 11:08:21 am on 5/28/2011 Modified: Never
Leaving aside that most everyone dislikes Goris, if it's rattling and vibrating, there are probably more issues than the prop alone. The cutless bearing is probably the main culprit, but if it's really loose, it may have worn the shaft to the point that it should be replaced, too. Search the forum for many discussions of prop shafts and their ills.

David Weatherston
Towser, Toronto
C&C 27 Mk IV

  Re: Shaft Size on 1986 Mk V (Dick)
Posted: 1:58:41 pm on 5/28/2011 Modified: Never
Hi Dave,

The original owner of my 1984 MK-5 replaced his fixed pitch prop with the Gori when he had the boat. When I bought the boat from the second owner I was not able to get more than 2300 RPM on the engine. I checked back with the second owner and he confirmed that he too could not get the engine above 2300RPM.

I thought something was wrong with the engine and tried everything the experts suggested might be the problem. The list is to long to mention.

Finally, in desperation, I tampered (adjusted) the engine governor thingy, the one that is safety wired that we are not supposed to mess with. That did the trick and I now can get 3600 max RPM.

Just mentioning my experience as something you may have to consider when making the change from Gori to fixed pitch prop.

I have no noticable engine rattle or vibration with my Gori. Of course never ran it with a fixed prop so can't make a comparison in that regard.

Dick White

  Re: Shaft Size on 1986 Mk V (dmoores)
Posted: 2:35:16 pm on 5/28/2011 Modified: Never
Thanks one and all.  I'll certainly be checking ebay for a replacement prop(another brand of folder, as I race).  I believe the rattling/shaking is the Gori not fully opening, because if I go from reverse to forward with the boat still moving aft, the problem does not occur - presumably because this situation pushes the blades to open fully.  As well, depending on sea state and monoeuvering, the shaking sometimes smooths out after a few minutes and I can go to high revs with no problem.  Finally, I had the same problem with a Gori on my last boat and never could cure it!
  Re: Shaft Size on 1986 Mk V (dmoores)
Posted: 9:45:39 pm on 6/22/2011 Modified: Never
THE RESULT: a new Martec folder was fitted yesterday (cheapest I could get!)and all my problems are solved.  No more shaking/clattering/shaft rumble.  It is labelled as a 12 x 12 and drives boat really well.

My mechanic showed me where the limit-stops on the Gori get flattened over time and allow the blades to go over-centre.  Unless the wear is exactly symmetrical each blade takes a slightly different angle and that causes the vibration etc.
  Re: Shaft Size on 1986 Mk V (admin)
Posted: 1:46:50 pm on 6/22/2011 Modified: 1:47:28 pm on 6/22/2011
This is a new one on me, but makes eminent sense once you hear it. I've added your experience to the props page, both as a listing and to a section on vibration. Hope you approve.

- Admin