Flexible Shaft Coupling

[Mike and Theresa Vaccaro]

Hi Folks,

Am considering the installation of a flexible shaft coupling.  Have found two that seem to fit the bill:  Federal and Vetus.  Was curious if anyone can provide part numbers for the couplings that they have installed on their M-25XP engines.

Thank you very much,

Mike Vaccaro
"Spirit" '88 Hull 563

[Jim Moore]

Lots of others have recommended to me the Vetus Bullflex #2.  That is the one I am going to order soon.

[Mike and Theresa Vaccaro]

Dear Ron,

Am in the process of installing a Vetus Bullflex as well as new engine mounts.  Lot's of lessons learned, and will post the results as soon as the job is done.

Cheers,

Mike Vaccaro
"Spirit" '88 Hull 563

[Mike and Theresa Vaccaro]

Dear Ron,

Finished installing the coupling today along with the new motor mounts.  Total time for the job:  3 days!  Not quite so simple on a boat that was neglected...one motor mount was corroded so badly that I had to remove the aluminum cast bracket from the block, drill out the old bolt, the corroded aluminum, and then turn and press a stainless bushing to repair the casting.  

Our shaft coupling was original and badly corroded.  Fortunately, the length of the Vetus Bullflex allows the shaft to be cut adjacent to the end of the stock coupling.  It's possible to use a cut-off tool, but due to the tight quarters, I used a plain, old-fashioned hack saw blade.  Took some time to saw through the bronze, but the cut was square due to the proximity of the face of the old coupling.  Finished the end with a mill bastard file and then 220 grit carborendum paper lubricated with cutting oil.  Worked like a champ.  Just for curiosity, I tried a steering wheel puller to remove the old shaft from the coupling.  No dice.  Also no dice with hammering.  The only way to free the shaft, was to cut the steel coupling on both sides and break it off the shaft.  This would be possible in the boat, but difficult to say the least.  

Although the Bullflex accomodates up to 2 degrees of misalignment, the folks at Vetus recommend a standard alignment prior to snugging it up.  In other words, the "flex" in the coupling should be used to minimize vibration translated to the shaft, not as a "universal" joint to accomodate a misaligned engine.  

Had to remove the exhaust riser to allow the engine to be lifted.  This isn't required for simply changing motor mounts, but due to the size of the Bullflex coupling, it's the only way to gain access to slip it on the shaft.  It should be noted that the Bullflex does not use a keyway, so no machining is necessary.  I'm not a fan of mixing dissimilar metals in a salt environment, so we simply slid our bronze shaft a bit to move the wear points.  Bronze is structurally just fine for the low torque application in our boats and using a stainless shaft with a bronze propeller results in a better "battery" than an all bronze assembly.

Please note that no grease should be used in assembly of the bullflex with the shaft.  It is a simple compression sleeve succured with four hex head (8mm) bolts.  If you loosen the bolts, it will slip over a clean 1" shaft easily.  Also note that you shouldn't install the studs until you've aligned the engine--makes it easy to turn the coupling to check alignment.  You can slip the coupling aft, then insert the studs, slide it forward and bolt it up.  Hardest part of the job was finding a small enough torque wrench to secure the nuts.  

Unfortunately, removal and inspection of the riser showed that it was time to replace it.  I suspect it was original, based on it's conditon (it was made of black iron, not stainless).  Additionally, our boat did not have the hump hose modification, so next week, I'll have a new riser fabricated and have already ordered a hump hose from Catalina.  Fortunately, the muffler is still in good shape!  

Overall the job is not inherently difficult, but if the boat has been in a corrosive environment without much maintenance, it can prove to be more complicated than you might expect!  If you've never aligned an engine, and are changing to other than stock mounts, be prepared to spend some time to do the job right.  Additionally, if you wish to swap to a dripless bellows type shaft seal, it's possible to do so in the water when the shaft has been cut and pulled back from the engine.  Guess I'm old fashioned and like the idea of being able to repair a stuffing box with an old sock, if required, so I simply changed the stuffing when it was possible to slide the nut off the shaft.  Just a quick pitch, but the best tool in the world to loosen a lock nut is a dull chisel and a hammer, fits all size nuts and never fails or breaks.  Teflon impregnated stuffing shouldn't drip, if properly adjusted.  The chisel/hammer technique works fine to secure the nut as well.

When I get the job finished, I'll post a step-by-step techniqe for swapping the stock coupling with a "Bullflex."  Readers should also note that if the shaft will accomodate another 1" of aft movement, then it's also possible to use a "driversaver" type rubber coupling using between the stock coupling (i.e., you don't have to remove it from the shaft) and the transmission.  This will go a long way toward damping vibration as well as moving the wear points on the shaft.  It requires a standard, accurate engine alignment.  I guess it bears repeating, but the "Bullfex" still requires you to align the engine!  Overall, the total tab for parts is just a shade over 7 boat units.    

Cheers,

Mike Vaccaro
"Spirit" '88 Hull 563

[Mike and Theresa Vaccaro]

Quick Update:  Reinstalled new exhaust riser/hump hose today and ran the engine for the first time since modification.  Without our SEAPOWER alternator connected (hard mounted to the forward end of the stringers and the adjacent sole immediately forward of the engine)there is no vibration whatesoever at ANY RPM, including idle.  Unfortunately, with the belts connected to the SEAPOWER unit, some vibration is translated to the cabin sole, although less then prior to the modification.  Since most boats don't have a generator hard-mounted adjacent to the engine, I'd have to say that the new mounts and coupling make a world of difference.  Almost enough to make you want to spend a lot of money on a separate, self-contained genset!  Having 120v AC is under power is still too handy to retire the SEAPOWER, in spite of the vibration.  Will post detailed notes on the coupler modification in the next couple of weeks.

Mike Vaccaro
"Spirit" '88 Hull 563

[SeaFever]

Hi Mike,

This was a great post from 2003! How are the motor mounts and coupling working out? I wanted to check as I will be doing the same replacing my A4 with the M25 soon. BTW, which motor mounts did you use? K75s, K50s or a mix? Did you end up posting your step by step replacement technique for the bull-flex?

Thanks,

Mahendra

[Ron Hill]

Mahendra : I've replaced my mounts with all K50 and then changed to rear K75s and front K50s.  You could use all K75 which I've also done.  The "all K50s" are a bit too soft. 
You need to join our C34IA.  A thought

[Mike Vaccaro]

They are.  The photo shows the condition of the coupling after six years of service.  Regular greasing of the running gear is important to avoid signficant corrosion issues.    

I concur with Ron, 4 K50's are probably a bit soft.  Recommend 75's on the aft end and 50's in front for M-25XP.  There is a step by step in the Tech Notes--you can access that section of the site if you're a C34 Association Member.  You might also think about shaft replacement, cutlass bearing and packing.  You will need a torque wrench and a metric bit to properly secure the compression fitting.  The coupling comes with instructions, be sure to follow them--you DON'T grease the shaft when you install it, it must be dry.  It can be greased after everything is together or treated with Boeing T-9 or an equivalent product.  

Cheers,

Vac