Just put on Vetus K50's, will I need a Bullflex?

[SteveLyle]

#75 turns 20 this year.  Figured it was time to replace the motor mounts, so I got 4 K50's and spent a few hours this past Sunday crawling around the engine and banging my head on the aft cabin overhead.  I used Cap'n Al's "remove the old ones with a sawsall" technique, and it worked great.

I did not order a Bullflex coupler.  It seems that most (all?) skippers who have gone to the K50's also installed a Bullflex - Ron H. and Mike V. among them, and they seem very pleased.

Is there anybody who hasn't?  How happy are you?

Thanks,
Steve

[Ron Hill]

Steve : The two items have different PRIMARY functions.
New mounts - to soften the engine vibration transmitted to the hull.
Flexible Coupling - To eliminate future engine / shaft alignment.  

[SteveLyle]

Ron,

I know.  But from reading everything on the site, I didn't notice any cases of people who felt good about going to the K50's without also going to a Bullflex.  There were plenty of complaints about low rpm vibration without the Bullflex.  Coincidence?

Just curious.  I'll get launched in a couple of weeks and find out then.

Steve

[Roc]

Steve,
I have a flexible coupling (another type, not a Bullflex) and I highly recommend this upgrade.

[Mike Vaccaro]

While I make it a rule of thumb never to disagree with Ron Hill, I would argue the primary purpose of the flexible coupling is to reduce vibration.  It is still recommended that the engine be properly aligned for optimum performance.  At the speeds that the MX-25/35 engines turn, there is quite a bit of "slop" available for misalignment, which goes a long way to reduce vibration caused by the shaft in the log.  For a coupling like a Bullflex, the more misaligned the engine, the lower the RPM that the coupling can effectively deal with (i.e., inversely proportional).  If the engine is properly aligned, I've noticed almost NO vibration whatsoever in the shaft log when running at ANY engine speed.  I seem to recall that the maximum misalignment that the Bullflex is designed to deal with is 3 degrees at which point it's capable of operating at speeds of about 1800 RPM.  For specifics, I recommend that you check the tech data on the Vetus website (which is quite extensive).  

The secondary purpose of a coupling like a Bullflex is to "electrically" disconnect the shaft/prop/bearing/etc. from the engine--which helps prevent corrosion of the running gear.

One reason the soft mount/flexible coupling works so well is that the V-50's (or -75's for that matter) allow the engine to vibrate more freely, uncoupling this vibration from the engine bed (hull).  If you only install the mounts, you may find that some of that vibration is still transmitted to the hull via the shaft.  Since you've already completed the mount swap, why not motor for a while and make your own assessment of the improvement over stock mounts?  If you feel that your installation doesn't really deliver the damping you expected, you can go back and install the coupling at a future date.  

To check for shaft vibration, you can place your hand on top of the log with the engine operating at different speeds.  Obviously this requires emptying out the "aft storage locker" and lifting the access panel.  Also, it's necessary to use EXTREME caution any time you are working around operating running gear.  One slip and, well bad things can happen!  Alternatively, you can get a pretty good basic feel for things just by motoring and comparing the overall vibration from what you recall with your previous mounts...it's like the first drive after you put new shocks or struts in the car!  Although I changed the mounts and coupling simultaneously, it was immediately apparent that we scored a home run in the vibration department as soon as we started the engine.    

Something else to consider is your throttle technique.  Most small diesels without a large flywheel tend to vibrate at idle.  I don't recommend adjusting your idle stop above this vibration range, but I do recommend that you manually adjust the throttle to increase speed when it's not critical to turn the shaft at idle.  Each boat is a bit different, especially with a tach that gets is signal from an alternator, but on our boat, the tach reads 800 RPM at the idle stop, but I manually adjust to 1100-1200 when true idle is not required.  You can determine at what point your engine's "idle shakes" stop by simply observing it as the throttle is adjusted in neutral.  

One other thing to keep in mind is prop cavitation in reverse.  Most screws do not operate efficiently in reverse.  The cavitation causes shaft vibration that the flexible coupling will not damp out (since it's coming from the screw, not the engine).

Best of luck,

Mike

[Jeff Tancock]

I am one of the apparently silent ones that changed the engine mounts but did not change to a flexible coupling. The change was incredible. The old mounts used to shake and rattle everything. My feet would even get sore with the vibration. If someone were to give me a flexible coupling I would go ahead and put it on.....but even without it you will be very impressed.
I guess it is important to mention that I was very careful and persistent when I did my alignment!

[David Sanner]

I replaced my 16 year old mounts with Vetus K75 (without lifting
the engine) and I'm very happy with the noise and vibration reduction.

I also added some sound proofing behind the engine (I even made a
small panel that fits in the opening to bilge aft of the engine) but
the motor mounts made the real difference.

I haven't installed a flexible coupling because the vibration isn't
much worse under power than in neutral at the same RPM.

I've got decent alignment but I do notice a little movement
in the shaft log... I was thinking that might be from the
shaft not being completely true/straight and not the alignment.

I assume a little bit of movement / wiggle in the shaft log
is acceptable?

One of the reasons I went with the K75 is that I didn't want
to have to install a flexible coupling and figured the harder
K75 would work with a sold shaft.  So far so good.

[fulvio]

I replaced my 16 year old mounts with Vetus K75 (without lifting the engine) and I'm very happy with the noise and vibration reduction.

I am about to replace my mounts, as well, but how do you do it without lifting the engine?

I just checked last night, and the two aft supports are all in one piece with the transmission casing.

Thanks!

[SteveLyle]

Check the projects page for the "Changing Engine Mounts" topic.  Lot's of text there, but buried in it is a note from Capt. Al where he describes replacing the mounts one by one.  You remove the old mounts by cutting the stud off with a sawsall, then just unbolt the mount.  The studs can be removed from the new mounts, the new mount base placed, then the new stud threaded through the engine bracket from above.  Voila, no lifting the engine.

[Ron Hill]

To get the Vetus mounts apart you'll need a LARGE wrench and a very sturdy vice.  
On some of the Vetus mounts the vertical threaded rod was installed into the base using thread sealant (Locktite).  You'll really need some muscle!!!!  

[Jim Fitch]

Has anyone ever fitted a Bullflex to the M35?  I was looking at it last night and there isn't much room to play with back there.  If you have, do you still have enough clearance to get the packing nut off to replace packing?

Thanks

Jim

[Mike Vaccaro]

Don't be intimidated by the requirement to "lift" the engine.  Once the shaft is uncoupled from the transmission and the exhaust riser is disconnected, the engine only need be lifted high enough to slip the new mounts in place.  There may be sufficient room to do this without having to remove the exhaust riser from the engine.    

The M-25 only weighs about 225 pounds and is easily hoisted with a "come along" or a block and tackle.  You can either use the boom (with a halyard attached to support it) or simply lay a couple of appropriately sized 2 x 4's across the top of the hatch.  We used some old line to tie a bridle to the engine and then simply attached the come along to that.  Ron hill has a good article with pictures that illustrates the process.    

Cheers,

Mike

[Jeff Tancock]

Don't sweat lifting your engine. It was way easier than I thought it would be! I just wrapped the mainsail halyard around the boom and snugged it up for some extra support, then used my detachable boom vang (4:1) to tip up first the front then the back half of the engine. That way you change two mounts then drop the engine down to get reorganized to change out the other two. Piece of cake! You have to back off the top bolts of all mounts so that the engine can tip up of course.
The hard part was having to rat file out one of the bolt holes so that I could get the shaft alignment right.