Flexible coupling / engine torque question!

[Northeaster]

Hi Folks,

I am looling at replacing my solid original tranny-to-prop shaft coupler with either a drive-saver / R&D type "disk", or a flexible jaw type coupling like the lovejoy (see link below):

Lovejoy

The lovejoy jaw coupling, with a 1" shaft is rated for up to 18hp / 318 inch/lbs torque. My Yanmar 2gm is rated for approx 15 hp, and 25 ft/lbs torque, at the crankshaft!!! I have a 2.62 / 1 reduction tranny, so would that mean that I have 2.62 times 25ft/lbs = 65.5 ft/lbs of torque at the shaft???? If so, then multiplying by 12 to get inch/lbs would = 768inch/lbs, which would be almost double the rating on the Lovejoy unit.

Am I calculating correctly - just want to see if the Lovejoy would work!! It is only $57!
A retired commercial marine guy told me to get an SKF coupling, but I beleive that is the company name, and i can't find a model for sale locally.
He sid it was a rubber centered flexible coupling.

[senormechanico]

How much would it cost if your $57 coupling lets go when you're frantically hitting reverse to keep from t boning a boat, log, dock etc?


Steve B.

[Northeaster]

Senor - That's why I am asking about the torque specs. It is a "real" jaw type flexible coupling, which should tolerate a bit more mis-alignment than a drive-saver type disk, that doesn't help with any mis-alignment.
If Ican find one with higher torques specs, for a 1" shaft, I am willing to pay more!

Also, it states that it will continue to function, even if the rubber insert breaks.

[Ziggy]

Originally Posted by Northeaster

My Yanmar 2gm is rated for approx 15 hp, and 25 ft/lbs torque, at the crankshaft!!! I have a 2.62 / 1 reduction tranny, so would that mean that I have 2.62 times 25ft/lbs = 65.5 ft/lbs of torque at the shaft???? If so, then multiplying by 12 to get inch/lbs would = 768inch/lbs

Am I calculating correctly

I get 25 ft-lbs x 12 in/ft x 2.62 reduction = 786 inch-lbs. Seems the Lovejoy's a bit wimpy for your power train (that may explain the price).

[Northeaster]

Ziggy- thanks, just wanted to make sure i was calulating correctly!

[senormechanico]

" Also, it states that it will continue to function, even if the rubber insert breaks."

For the rated load, but in an emergency stop / reverse, you may well be exceeding that when it does break and at the worst possible time.

Steve B.