Flexible coupling

[sonny21566]

Hi Fellow members,

I have a Hunter 33, 08 model with 3YM30 Yanmar 29 hp engine. Is it advisable to install a flexible coupling between the gearbox and the prop shaft in order to cut the noise level and a bit forgiving on engine aligment with the prop shaft? Your advice and help is much appreciated.

Sonny

 

[Ed Schenck]

Coupler was recommended.

When I installed a 3YM30 to replace my 2QM20 it was recommended that I install a "shaft saver". Since I was doing the work myself I wanted to have some leeway on the alignment. Primarily because I had to design and build my own mounts. Now everyone comments on how smooth and quiet the engine is. It also somewhat protects the prop and tranny, kind of like a heavy duty shear pin.

 

[Scott B]

Ed, how does the shaft saver work. Looks interesting.

 

[Ed Schenck]

Not to be funny Scott but I don't want to know(how/if it works) if you catch my drift. As you can see in the picture the original coupler bolts to the "rubber" shaft saver. So there is some give if the prop were to engage something. Because it is not rigid the shaft can run true in the cutless bearing even if the alignment gets slightly off. I am not certain of the composition. Here is one mfg: http://www.clrmarine.com/462.html?m4:cat=All Categories/Engine Systems/Shaft Saver .

 

[chuckwayne]

We installed a PYI flex coupling on our 356 and it made a huge improvement in noise, vibration, and cutless wear-highly recommended! The PYI coupler is only 1 5/8" long, so it fit really well without pushing the prop back too far.

 

[Steve Dion]

Looks like a guibo on the Euro cars. They are essentially a u-joint! While this is not an issue when shifting, it dampens some of the vibration. Personally I think a good balanced prop will do the some thing. On the other hand if you prop hits something it "may" help cushion the blow!

Pushing the prop further aft will also help the prop walk a little.

"Drivetrain Guibo
A common wear item on BMWs over a period of time is the drivetrain guibo. The guibo serves as an interface between the transmission and the driveshaft. Since the guibo is primarily made from rubber, it acts as a damper when shifting and engaging into gears, so that the transfer of power to the driveshaft is smooth and dampened, instead of abrupt and harsh."

 

[Ken13559]

We installed a PYI flex coupling on our 356 and it made a huge improvement in noise, vibration, and cutless wear-highly recommended! The PYI coupler is only 1 5/8" long, so it fit really well without pushing the prop back too far.

I've 2GM20F on my H326. 1" shaft size. Do I suppose the PYI you got for your shaft would fit mine ? What's the partnumber/model you use ? Moving the shaft coupling flange back 1_5/8" leaves little room for the packing gland nut to move when you need to repack the gland. Am I right ?

 

[chuckwayne]

Hi Ken,
Although our 356 has a 3GM30 it is a 1" shaft, so the PYI coupling would work fine. Yes, it's crowded, so repacking the gland would probably mean unbolting the coupling-8 bolts. the improvement is well worth the hassle IMHO.

Steve, you're right about a well balanced prop also helping-we've got an autoprop and the 3 blades are exactly matched at the factory-found that out after the fact, because they will only sell you a spare blade if you send them one to balance to!

 

[sonny21566]

Hi Fellow members,
Thanks for the reply, in order for the flexible coupling to work, one must install a mounting plate with bearing attached to the hull holding the prop shaft in order for the coupling to work, or it will cause more movement than without. Please correct me if I am wrong on this. Your advice is much appreciated. sonny

 

[chuckwayne]

HI Sonny,
no, there's not that much flex in the coupling. All you have to do is unbolt the flange (4 bolts) slide the shaft back and bolt in the coupling. the worst part of the installation was reaching down into the shaft compartment and tightening the bolts-if you're short like me it was kind of a reach, not a lot of room for shoulders.

 

[sonny21566]

Hi Fellow members,
Have installed the coupling, everything works fine except that it gives a Harmonic sound above 2400rpm and above, any remedy to solve the wanted sound. Your advice is much appreciated. Sonny

 

[chuckwayne]

Hi Sonny,
I haven't experienced that....check and make sure all the hardware is in place and tight-it sounds like something is causing an out of balance condition that resonates above 2400

 

[sonny21566]

Hi Chuckwayne,

Do you have the same R&D flexible shaft coupling like mine or otherwise. I am sure it was is correctly installed, even with gear in neutral, with the shaft spinning it does give some harmonic sound. Could it be that the coupling comes with age or lost it flexibility. Can't think of anything else.

 

[Ken13559]

sonny, can you post pictures of your coupling ? I'm interested to install one but haven't figure out how to sequeeze it in the tight space there is. Thanks. If you can't post picture, could you email to me at trantor12020-sailnet at yahoo dot com ?

 

[chuckwayne]

HI Sonny, I've got the 4" yanmar flange version of the R&D coupling-it's probably the same one you've got. If you have a pic, post it-I won't be at the boat until next week (we haven't uncovered her yet)

 

[Ken13559]

my stern coupling area seems tight and with that little raise rim, I'm afraid the flange may hit it after its move aft by 1_5/8".

 

[chuckwayne]

measure carefully before you decide-our 356 is similar but clears fine