Are Centaflex coupling worth fitting

[TerryH]

I am having a new engine fitted this week and was planning to have a cenntaflex coupling fitted to relace the existing bronze coupling. Is it worth it or am I wasting my money?.

 

Thanks

[nbfiresprite]

I am having a new engine fitted this week and was planning to have a cenntaflex coupling fitted to relace the existing bronze coupling. Is it worth it or am I wasting my money?.

 

Thanks

 

Its worth every penny, R&D unit that it replaced was useless.

 

 

Firesprite

 

Middle Levels

[Smelly]

Its worth every penny, R&D unit that it replaced was useless.

 

 

Firesprite

 

Middle Levels

 

Why?

[nb Innisfree]

I am having a new engine fitted this week and was planning to have a cenntaflex coupling fitted to relace the existing bronze coupling. Is it worth it or am I wasting my money?.

 

Thanks

 

Better still an Aquadrive or Python Drive, more expensive and more fitting involved but an ideal solution IMO.

[Biggles]

My CentraFlex has made living with a solid mounted Lister so much better. Now the mugs on the hooks just rattle not gently instead of trying to jump off. I would imagine with a flex mounted engine and GB the results would be even better.

 

Biggles

[koukouvagia]

I am having a new engine fitted this week and was planning to have a cenntaflex coupling fitted to relace the existing bronze coupling. Is it worth it or am I wasting my money?.

 

Thanks

 

I fitted a Centaflex coupling mainly as a precaution against a possible engine misalignment occurring. (The Kelvin shaft has to be aligned perfectly because it moves backwards and forwards when changing from forward to reverse). I quickly noticed a dramatic reduction in both noise and vibration. I've had it running for over ten years with absolutely no problems. They are very simple to fit with clamp couplings.

[Tony Brooks]

I am having a new engine fitted this week and was planning to have a cenntaflex coupling fitted to relace the existing bronze coupling. Is it worth it or am I wasting my money?.

 

Thanks

 

Centaflex make a range of couplings and unless the specification says it will accept radial misalignment (AGM Series) there are better solutions. I go for Aquadrive but I think the AGM comes third after Pythondrive.

[Timleech]

Its worth every penny, R&D unit that it replaced was useless.

 

 

Firesprite

 

Middle Levels

 

 

 

Why?

 

R&D couplings aren't true flexible couplings but they are often used as such. They'll allow slight angular misalignment but don't allow free engine movement.

 

Tim

Edited April 19, 2010 by Timleech

[Speedwell]

We are pleased with our Centaflex. Greatly reduced noise, particilarly at low revs. Unfortunately it can't help the exhaust noise at high revs though . We could not use one of the other types as we have no thrust bearing.

Arthur

[colin stone]

Centaflex make a range of couplings and unless the specification says it will accept radial misalignment (AGM Series) there are better solutions. I go for Aquadrive but I think the AGM comes third after Pythondrive.

 

Disagree. Centaflex are superior to both AD and PD - cheaper, no metal to metal contact in the UJs as Centa use rubber donuts - hence more noise reduction. CF AGM in particular is brilliant and as I have a 8ft shaft, using a 5 inch diameter tube means that I do not need a support bearing, which would be needed with a solid shaft. Only disadvantage is that CF system may be a little larger that AD and PD.

[Gibbo]

Can someone explain to me why boats (well, the people that fit engines in them) go to all this trouble to line up the engine with a prop shaft, in every conceivable direction, and worry about engine mount movement, when a shaft with UJs at both ends would get rid of the problem. You know, like car manufacturers have successfully done.

 

What have I missed?

[RLWP]

Can someone explain to me why boats (well, the people that fit engines in them) go to all this trouble to line up the engine with a prop shaft, in every conceivable direction, and worry about engine mount movement, when a shaft with UJs at both ends would get rid of the problem. You know, like car manufacturers have successfully done.

 

What have I missed?

 

Dunno. We've got an Aquadrive

 

Richard

 

Like car manufacturers have done since- I'm guessing here - 1910

[Timleech]

Can someone explain to me why boats (well, the people that fit engines in them) go to all this trouble to line up the engine with a prop shaft, in every conceivable direction, and worry about engine mount movement, when a shaft with UJs at both ends would get rid of the problem. You know, like car manufacturers have successfully done.

 

What have I missed?

 

Yes it can work well, but:-

You do need two UJs, a lot of modern nb installations don't have room

UJs are not supposed to carry thrust, but they will do so if they're working through a small angle and if they're generously sized for the job

The snag with working them through a small angle is that the needles in the bearings don't circulate enough to keep the lubricant moving, which can lead to early failure.

If you run them through a large angle, apart from the thrust issue they are not a constant velocity joint so they can induce (torsional) vibration rather than cushioning it.

 

A cardan shaft with a pair of UJs can be very successful with the back cabin & engine room type of setup, I know people have done similar with a stern mounted engine but it doesn't lend itself so well.

 

Tim

Edited April 19, 2010 by Timleech

[RLWP]

I believe that rather than use two Hookes joints (which eliminates the torsional vibration problem) the Aquadrive and Python drive use Hardy Spicer joints - which also eliminates the torsional vibration problem.

 

From memory, ours is about eleven inches long.

 

Richard

 

Our boat has a cruiser stern

Edited April 19, 2010 by RLWP

[nb Innisfree]

Can someone explain to me why boats (well, the people that fit engines in them) go to all this trouble to line up the engine with a prop shaft, in every conceivable direction, and worry about engine mount movement, when a shaft with UJs at both ends would get rid of the problem. You know, like car manufacturers have successfully done.

 

What have I missed?

 

Seems a lot of fuss and bother to me when an Aquadrive or Python Drive with twin CV joints completely sidesteps any problems. Using anything less with a flexibly mounted engine is just a less than satisfactory solution.

 

IMO.

[Radio-Ga-Ga]

Yes it can work well, but:-

You do need two UJs, a lot of modern nb installations don't have room

UJs are not supposed to carry thrust, but they will do so if they're working through a small angle and if they're generously sized for the job

The snag with working them through a small angle is that the needles in the bearings don't circulate enough to keep the lubricant moving, which can lead to early failure.

If you run them through a large angle, apart from the thrust issue they are not a constant velocity joint so they can induce (torsional) vibration rather than cushioning it.

 

A cardan shaft with a pair of UJs can be very successful with the back cabin & engine room type of setup, I know people have done similar with a stern mounted engine but it doesn't lend itself so well.

 

Tim

The Aquadrive dosn't have UJs it has CV joints one fixed one sliding. Exactly the same as a modern FWD car driveshaft, all thrust is carried on err, the thrust bearing

[dor]

The Aquadrive dosn't have UJs it has CV joints one fixed one sliding. Exactly the same as a modern FWD car driveshaft, all thrust is carried on err, the thrust bearing

 

As does the Python Drive. All the thrust is taken directly to the hull via a thrust bearing. The flexible shaft then only has to transmit the rotation to the prop and allows to thengine to move in all directions, including fore and aft.

 

See March Waterways World for an article about one being fitted and sound meter readings before and after.

[Timleech]

The Aquadrive dosn't have UJs it has CV joints one fixed one sliding. Exactly the same as a modern FWD car driveshaft, all thrust is carried on err, the thrust bearing

 

Yes but Gibbo was asking why more people don't use UJs.

I was putting forward some pros and cons.

 

Tim

[Gibbo]

The snag with working them through a small angle is that the needles in the bearings don't circulate enough to keep the lubricant moving, which can lead to early failure.

If you run them through a large angle, apart from the thrust issue they are not a constant velocity joint so they can induce (torsional) vibration rather than cushioning it.

 

That's the answer I was looking for. I knew there'd be a reason for it.

 

Cheers.

[nb Innisfree]

Yes it can work well, but:-

You do need two UJs, a lot of modern nb installations don't have room

UJs are not supposed to carry thrust, but they will do so if they're working through a small angle and if they're generously sized for the job

The snag with working them through a small angle is that the needles in the bearings don't circulate enough to keep the lubricant moving, which can lead to early failure.

If you run them through a large angle, apart from the thrust issue they are not a constant velocity joint so they can induce (torsional) vibration rather than cushioning it.

 

A cardan shaft with a pair of UJs can be very successful with the back cabin & engine room type of setup, I know people have done similar with a stern mounted engine but it doesn't lend itself so well.

 

Tim

 

Same with an Aquadrive/Python which needs some offset to ensure adequate lubrication.

[RLWP]

That's the answer I was looking for. I knew there'd be a reason for it.

 

Cheers.

 

The torsional vibration bit is only true if you use one joint. With a single Hookes joint during a cycle of rotation the output shaft accelerates and decelerates because of the geometry of the joint. However, it's usual to have two joints phased so that the effects created at one end of the prop shaft are cancelled out by the joint at the other end. So the input and output shaft rotate at constant speed while the propshaft itself does the acceleration/deceleration cycle.

 

The lubricating the needles bit still stands.

 

Richard

[Gibbo]

The torsional vibration bit is only true if you use one joint. With a single Hookes joint during a cycle of rotation the output shaft accelerates and decelerates because of the geometry of the joint. However, it's usual to have two joints phased so that the effects created at one end of the prop shaft are cancelled out by the joint at the other end. So the input and output shaft rotate at constant speed while the propshaft itself does the acceleration/deceleration cycle.

 

The lubricating the needles bit still stands.

 

Richard

 

I pondered that bit before posting. I'm not so sure.

 

In the case of Lionheart there is a 12 foot long prop shaft (weighing about 100 pounds) between the two CV joints (yes CV joints) and I think accelerating and decelerating that (as it would with UJs) could cause vibration.

 

Having said that, with the prop being out of balance, the engine vibrating like a vibraty thing and all the cavitation I get I doubt I'd even notice.

[RLWP]

CV joints are OK, being Constant Velocity joints of course. So the propshaft isn't doing anything weird. Car propshafts, lorries, buses, they're all speeding up and slowing down every revolution, trapped by the geometry of the Hookes Joint. It's more pronounced as the angle of the joint changes.

 

Richard

 

You like equations, Wikipedia has them all layed out nicely. Including Euler angles (I used to know what they were once).

 

They have a jolly picture too:

 

Edited April 20, 2010 by RLWP

[WotEver]

(I used to know what they were once).

Wikipedia to your rescue

 

Although, having read it, I still don't know what they are. I knew I should have paid attention at school.

 

Tony

[RLWP]

 

Ah yes. Of course. Now I remember that I didn't understand this the first time...

 

Richard