C-Drive vs Linecutter



A few years ago Amel changed the spec for all C-Drives to 80-90 gear oil. I always used waterproof grease on the lip seals, but always used silicone grease on any O ring. A crop-dusting helicopter pilot once told me that O ring failure is a very important issue with helicopters and he and his friends insisted on Trident Silicone Grease, only found in dive shops and also on Amazon.


CW Bill Rouse
720 Winnie St
Galveston Island, TX 77550
+1(832) 380-4970

On Sun, Sep 8, 2019 at 3:33 PM SY STELLA <stella@...> wrote:
Hi All, 
Thanks to everyone for the guidance. 

I found a source for the Dowty/ Bonded Seal washers, and have renewed the O-ring.
Could not get the V bolt to align with 1 or 2 Dowty washers, and 3 was too many. So have resorted to mastic like others to complete the seal.  Not very happy with that solution, but it seems to be accepted method so we’ll see how it goes.

Now part way through replacing the bushing and lip seals, so will be able to fill the transmission with oil before wintering. A little tricky finding ‘silicon’ grease around here on a Sunday :-)

One final question on this little project. I remember having previously seen discussion about which oil to use. I have both 15W40 engine oil and 80W90 gear oil.  

Which should I use?

Many thanks
SY Stella 

Dean Gillies

Thanks Bill, 80W90 it will be.
I was intending to use Silicon grease on both the O ring and the lip seals (since they contain rubber). Are you suggesting using some other waterproof grease on the lip seals?  Most of the waterproof grease products I’ve seen appear to be either Lithium based, which isn’t good for rubber, or have unspecified base material (probably oil based, again not good for rubber). 

Best regards
SY Stella

John Clark

Tim, I agree with Bill.  Not sure of the core foundational construction of the c-drive but I would bet a dollar that for that drain port the seal is the o-ring. I would replace the o-ring and liberally goop the nut with sealant.    The most likely source of water in the oil is the shaft seals.... especially if they are old.  I change mine every haul out(2-3 years) as the previous owners coached me to do and have not had any issues.  

It is fairly simple to do just be patient, clean the area and don't force anything.  

I used the heavy weight oil last time with no problems.

My SM is an early model but has the late model c-drive (and TMD-22) thanks to previous owner repower at La Rochelle in it should be the same as yours.

Regards,. John
SV Annie  SM37
still floating in Brunswick GA

On Thu, Sep 5, 2019, 10:41 PM Tim Melbourne <tim@...> wrote:
Here's a related problem- either a crack or deep scratch along the surface that seats the V-plug O-ring (see attached photo).  
Last haul out my oil also came out milky, but the propshaft seals were 4 years past changeout date, so I can't know whether seawater got in under the O-ring via this crack or through the mainshaft seals. 
Anybody have an idea for a fix?   Fill it with epoxy and sand it fine?  Somehow put in a new seating?  
Previous owner said "Ignore it, it's been there since 2003." which I find unsettling. 

SM2K #306