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S&S Swan Maintenance - S&S 41/Options for Borg Warner Gear Box replacement?
02 May 2017 - 22:54
Join Date: 02 February 2013
Posts: 25

S&S 41/Options for Borg Warner Gear Box replacement?

Dear Professor, fellow members,

a few years back I made the decision to completely overhaul my Perkins Prima 50hp on Maje, our S&S41, and the engine, despite its known weaknesses/areas for improvements is still performing its duty well and is in prestine condition. Unfortunately, I can't say the same about the Borg-Warner gear box (ratio 2.1:1, combination with a Max Prop 3 blades 17" with 22 pitch) which noise while changing gear or at low speed (noise ceases at higher speed) starts to concern me. Can you suggest any good gear box replacement fit for the Prima (equivalent to the Volvo MD22L) any related advise and potential watch outs for this type of set up?

Many thanks in advance for your insights!



03 May 2017 - 16:57
Join Date: 02 January 2008
Posts: 1547

Dear Matt

Here some thoughts, for sure there are many other options.

The standard reduction gear for the Prima M50 engine was Hurth HBW10, but it appears that the Velvet Drive from the original engine was retained when the new engine was installed.

The mentioned Hurth gear is not manufactured any more. A corresponding model is ZF12M, available with the same reduction 2.1:1. There are, however, two important differences compared to the Velvet Drive - the ZF12M is over 200 mm shorter, and has 72 mm shaft drop. You must consider how this can be compensated. 
If the engine can move aft as well as up the mentioned distances the replacement should go smoothly, but otherwise the shaft length, stern tube, and shaft strut will require modifications.
The direction of shaft rotation also needs to be checked, surprisingly this information is not stated in the ZF12M brochure. In case it changes, the Max-Prop can be reset for this.
If the changes required by the ZF12M are too difficult you could consider having the Velvet Drive rebuilt, or installing a reconditioned unit.
Kind regards

04 May 2017 - 16:15
Join Date: 02 February 2013
Posts: 25

Thank you for your answer and advice Professor!

I'll investigate further. It does not seem there is much room to bring the engine further aft unfortunately.



05 May 2017 - 12:11
Join Date: 15 April 2011
Posts: 395

Hi Matt,

I was able to replace my velvet drive with a rebuilt model for $1200.  The company, TransAtlantic Diesel, specializes in Perkins engines and related gear such as transmissions.  The are located in North Carolina in the U.S. so I don't know if this is convenient for you.  If not, there may be other companies that provide the same service.

Good Luck.


Chris  43/003 Mabel's Casse Tete 

08 May 2017 - 14:38
Join Date: 02 February 2013
Posts: 25

Hi Chris, thanks a lot for joing the discussion and for advising!

I guess that might indeed be among the best options, as it seems (i haven't heard yet of many other alternatives).

I'll have to look in Europe though as the boat is in the mediterranean and I am in the UK.

many thanks for your input!



08 May 2017 - 19:41
Join Date: 15 April 2011
Posts: 395

Dear Matt,

You're welcome and good luck.  One final comment, the velvet drive is extremely heavy and I find moving the new one back on board a daunting task.  When I removed a Hurth transmisson from a previous boat, 85 hp diesel, the weight and size was manageable by myself!


09 May 2017 - 08:41
Join Date: 02 February 2013
Posts: 25

I know, the potential weight loss was - among others - one clear benefit of changing/upgrading the borg warner!

Thank you again, and with best regards


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