new Beta Marine engine, prop shaft, flexible coupling questions

[greg harris]

had new beta marine 25 engine installed on my 1988 Ericson 35-III by a yard in New Jersey. The engine comes with a flexible coupling to fit the prop shaft to the engine and Beta says to use it. the quite experienced owner of the yard claims flexible couplings are for people who cant properly line up the engine to the prop shaft. So he left it off. Beta literature say to use it to reduce torsion vibrations and some literature says you should always use a flexible coupling when you have flexible engine mounts. Traveled 5 days under power and what a nice engine and vibration is very minimal.

but figure i should put the flexible coupling in as it is recommended by the manufacturer. The easiest way to do this is leave the engine mounted where it is and just let the prop shaft extend aft the extra width of the coupler which is maybe an inch. Any thoughts from anyone qualified to address this. i would have to relocate the line cutter on the shaft but that's no big deal.

any thoughts.??

thanks

greg harris

 

[Mort Fligelman]

Flexible Coupling

Greg: The more thoughts you have, and the more people you listen to the more confused you become....that said...this is my story!

Having to replace a severely butchered cutlass bearing meant pulling the shaft......don't ask what that entailed.....at any rate I was told by many people that the installation of a flexible coupling would eliminate vibration.......by keeping the alignment of the engine as it should be, and that the safety factor of hitting a floating log or other flotsam would keep from bending the shaft, as the coupling would go first, and less damage would occur....

The end result is that I have the coupling installed and of course with the new cutlass bearing the vibration is certainly less......is it better with than without....I really have no basis of comparison.....but I doubt it......

Confused....join the club......

But my feeling here is that since you have the unit......use it...it can't hurt......might help......

Interesting to see who will weigh in here and with what!

Good Luck

 

[greg harris]

thanks mort. the more i have read i think the issue is the length that the shaft extends beyond the cutlass bearing. I have read somewhere 1.5 times the diameter of the shaft I think.

thanks

greg

 

[Alan Gomes]

thanks mort. the more i have read i think the issue is the length that the shaft extends beyond the cutlass bearing. I have read somewhere 1.5 times the diameter of the shaft I think.

thanks

greg

Actually, it should *ideally* be 1 shaft diameter or less to prevent shaft whip. But sometimes the geometry doesn't always work out for that. On my previous boat, a C30, I replaced the shaft and made the overhang about 3/4". (It was 1" shaft.) That was the ideal. It's definitely more than that on my current E26-2 but I don't have any vibration issues so I'm not worried about it.

It sounds like you don't have any vibration right now, so you could just leave well enough alone. If you want to experiment, I assume the coupling is easily added just be removing the flange bolts and sliding back the shaft. So install it and see what happens. It couldn't hurt anything to try, "in the interest of science."

One other question: Did the people who installed the engine say that anything about your warranty is affected if you *don't* install the coupling they provided?

 

[Loren Beach]

Flexible Coupler notes

I sent this question over to my diesel mechanic friend and he writes back:

"Beta wants the flexible coupler installed for damage control. It does dampen out the engine movement between the engine and the rigid prop shaft caused by flexible engine mounts.
I have installed 6 flexible couplings during the past 2 years. All have reduced the vibration considerably."

He has over 40 years diesel experience and nowadays is the service/warranty guy in this area for Beta.

My personal guess is that the "damage control" referenced refers to harm to the transmission if the prop whacks something solid like a deadhead. (?)

Regards,
Loren

ps: I next asked my friend a followup question, and here it is, with his answer.

"Do you still do your usual close-tolerance alignment first and then put the coupler in?
I would wonder how you could even do an alignment with some give in the drive train."

His reply:
"Yes the alignment is done first but this is a static adjustment, as you have probably witnessed ,your engine jumps around quite a bit while running, the flex drive compensates for this. Just an added smoothness."

 

[Schoolboyheart]

I have a beta 14 on my 27 and i'll be the first to admit that i'm not an engine guy. Sea Marine in port townsend installed then engine and they used the flexible coupling. My guess is the guy at you're yard just likes the old way of doing things. Sort of like when macs came out i thought microsoft products were far superior. then i actually tried a mac and haven't had anything since. it's hard to make the switch but usually the new technology is worth it.

For what it's worth though on my old engine the prop shaft extended about 7 inches past the cutlass bearing for years with no abnormal wear. i'm not sure why it was like this. I had it cut down at one point and didn't notice any difference. so if your shaft only goes an extra inch further than now i wouldn't think it would cause any harm, but again i'm no mechanic.

Love my Beta though, what a difference! it's also nice to be able to buy oil filters at napa for $8 instead of $20 from yanmar!

 

[e38 owner]

flexable coupling

I was having many vibration issues. The boat had the alignment checked many times and they would not go away. New Cutless, rebuilt Martec, new pyi dry seal etc etc etc. I added a flexible coupling and the problem was solved. I think part of the problem was the shaft was to close to the strut you could not even get a prop puller in there and part of the vibration was due to that. The problem was on my santa cruz not the Ericson. The Ericson has always had a Drivesaver and the shaft extends 3" or so past the cutless It uses a 6" cutless as opposed to the more common 4". Never had any problems on the Ericson and the last cutless lasted 25 years. That being said the SC is a uldb and you can feel every vibration. The boat has a yanmar that has flexible mounts. I believe the beta is the same block as the Universal and uses a firmer mount so the engine does not move as far forward when put into gear. Finally the coupling I bought is designed to breakaway if you hit something. To me that is a lot better than a transmission. Last but not least I would assume the engine mfg has more experience and engineering than any boat yard. Thus do what they recommend and forget about it.

 

[greg harris]

I sent this question over to my diesel mechanic friend and he writes back:

"Beta wants the flexible coupler installed for damage control. It does dampen out the engine movement between the engine and the rigid prop shaft caused by flexible engine mounts.
I have installed 6 flexible couplings during the past 2 years. All have reduced the vibration considerably."

He has over 40 years diesel experience and nowadays is the service/warranty guy in this area for Beta.

My personal guess is that the "damage control" referenced refers to harm to the transmission if the prop whacks something solid like a deadhead. (?)

Regards,
Loren

ps: I next asked my friend a followup question, and here it is, with his answer.

"Do you still do your usual close-tolerance alignment first and then put the coupler in?
I would wonder how you could even do an alignment with some give in the drive train."

His reply:
"Yes the alignment is done first but this is a static adjustment, as you have probably witnessed ,your engine jumps around quite a bit while running, the flex drive compensates for this. Just an added smoothness."

Thanks Loren, Plan to install the coupling when i haul out in a month or so. And i guess i can either have the shaft extend beyond the cutlass bearing about 2 inches or else simply cut an inch from the engine side of the shaft. The beta marine provided flange does not have a Key slot just a large set screw that fit into the key slot on the shaft and several more similar in design to what i see on zincs that go on the prop shaft. I will check with the guy at the yard and make sure whatever i do is ok'ed by the pros.

thanks again.

greg harris

 

[tenders]

This is an interesting discussion but wow, under no condition would I wake a sleeping baby. How much less than "very minimal" are you expecting this engine to vibrate?

 

[Loren Beach]

Betamarine 25 report

We just enjoyed our first hour of motoring with our new-install Betamarine 25.
Sort of a shake down trip.

We do have the flex coupling "donut" and the whole engine is so much quieter than the old Universal that it seems amazing. Very very little vibration.

Now I have to sound-proof the axial flow air fan that pulls warm air out of the engine compartment! Before, we could hardly tell that this fan was operating. Now the sound is Really obnoxious. :0

All in all a great upgrade to the boat.

BTW, purpose of our trip was to enter a marina in a sheltered bay with less current, where a diver could scrub the eight months of slime off of the bottom.
Only 6.4 going there...... and 7.2 kts oming home. Same 2500 rpm.
Clean is Good.