Replacing Vetus Coupling Bolts


We had 1 of 4 bolts that clamp the Vetus coupler together shear a while back and are replacing all 4 along with the 4 rubber bushings which are intact but showing wear, distortion, and cracking.  The Yanmar was easy to slide back on the frame but there is not space between the C drive flange and the Vetus nor the transmission flange and the transmission to insert an original length bolt.  The Vetus bushings replacements ($25USD/4) are a regular, say 5 year replacement item in our opinion BUT is seems that to replace the bolt as it was originally would involve removing the flange of the C drive. Earlier, Danny (with a Volvo engine) posted that by using a bolt with both ends threaded the bolt could be replaced without removing the flange from the C drive or the flange from the transmission.  Are we missing something or do you need to use bolts with both ends threaded and nuts on each end?

Bob, KAIMI SM 429 


Hi Eric,
Yes, we are SM hull 429 and the shaft is 35mm.  However it widens within a half inch of leaving the C drive to 60mm which is the diameter that the Vetus housing goes on.  Hopefully that information is helpful to you.  When I receive the replacement rubber bushings I will post the replacement procedure with some photos as well.
Bob, KAIMI SM 429


Hi Everyone--
I am following up on the Vetus Coupling related bolt and bushing replacement project.  In the process I received clarification on previous postings, new information on the Amel modified Vetus coupling and other email information--I will try to include this information in this posting.  Hopefully this will be helpful to anyone who needs to service the coupling for a broken bolt that holds the 2 halves of the coupling together and connects the transmission flange to the drive shaft. KAIMI is a 2004 Super Maramu with the Yanmar 4JH-3HTE and ZF-25 but I believe that most of this information pertains to other Super Maramus.

BACKGROUND--I had one of the 4 bolts that hold the Vetus coupling together shear and felt that I had a small amount of vibration.  I obtained some replacement bolts and nyloc nuts that could be used for an emergency repair and operated the engine (albeit at reduced rpm--less than 2000 rpm) until I arrived at location with supporting mechanical and parts services (tied up and plugged in at the Peveza marina).  I dove on my prop to make sure it was clean and that we could have a good test after the repair.

BUSHING INSPECTION OR REPAIR ONLY (no broken bolt)--just remove the nuts from the bolts that hold the Vetus coupler together, then separate the coupler and slip the rubber bushings off to inspect them.  Bushing replacements are inexpensive--$25USD--using Vetus kit K018.  Reassemble.  In my opinion, an inspection is worth doing every 5 years or if you think you have excess vibration.  My bushings were elongated and cracking and probably allowed excessive flexing that broke a bolt. 

PROCEDURE if a bolt has sheared--First, remove the nuts from the remaining bolts.  Then move the engine back--it only needs to go back about 3 inches.  The Yanmar is bolted to the frame with 5 bolts.  The frame is mounted to the fiberglass supports below the engine with the motor mounts.  Because of this design, if the engine is correctly aligned, you can shift the engine back without needing to do a re-alignment adjustment of the engine mounts. It also does not require disassembly or realignment of the C drive.   In order to shift the engine back it is necessary remove the bolts that support the intercooler/grab bar to the frame.  The caliper for the shaft brake also needs to be removed.  Apparently on some SMs there is a crossbar behind the v-belt pulleys that has to be removed, but on our model the support was curved and allowed the engine to be slid back with no problems.  Make sure that exhaust, fuel and electrical connections are not strained when you slide the engine but for us nothing else needed to be loosened or disassembled.

Inspect the engine mounts.  If one is broken then you will need to re-align the engine.  If the Vetus coupling needs to be replaced note that Amel uses a modified Vetus coupling. Our engine mounts and the coupling were fine.

When we shifted the engine back we took some weight off it.  This was achieved by placing a 4x4 timber above the engine between the 2 cockpit benches.  By sliding the timber back to the open hatch it was in a good position to connect a block and tackle to the 2 Yanmar lifting eyes without doing anything to the hatch.  When it came time to slide the engine back we just heaved on it with 2 guys standing in the engine room so it is debatable whether you need to lift the engine from above with that arrangement.  Danny noted using a piece of timber to lever and slide the engine back.

Sliding the engine back parts the 2 halves of the coupling.  The rubber bushings can be removed, inspected and replaced.  The heads of the bolts need to be hack sawed or cut off so that they can be removed.  New bolts should be strong steel like tool quality number 8 steel (NOT Inox) with threads on both ends and 8 matching steel nylocs.  Insert the bolts from the "inside" of the split coupling and screw the front nylok nuts on.  You can hold the bolts with a Channelloc or Vice-Grip using a cloth to protect the threads.  By making the replacement bolts about 9 cm long you are able to make the front nuts flush to the thread end and have an extension to the aft of the bolt that allows you to hold the bolt when tightening front and rear nylocs.  You can see this in the link to the  Dropbox photos.  We also used thread locker to assure that the nuts did not move--about half the threads on a nyloc are metal, so the Loc-tite will help to secure them. Slide the engine back while guiding the bolts through the transmission flange holes and then rebolt the engine and then tighten the remaining 4 nylocs.  By leaving a consistent amount of thread the bolt ends can periodically be visually checked without breaking the loc-tite.

Test the engine under various RPMs and conditions with a good load on the engine and monitor for vibration or noises.  Existing or future vibration or noise could indicate an alignment problem with the engine or C drive, a fouled prop or damaged bushings.  We now carry 4 double ended bolts, 8 nylocs and the Vetus K018 bushing kit as spares.

Dropbox photos include the Vetus K018 "flexible rubber coupling" kit, the old worn, distorted, and cracking rubber, the coupling housing and hub, lifting strap through 2 Yanmar lifting eyes, the engine to frame holes, double ended 9cm replacement bolts, and the reassembled bolts.  

Special thanks to Danny for posting this idea originally and responding to my emails with clarifications.


Alan Leslie

Great information Bob !

Thanks for all your detail.

Elyse SM437