Flexible driver coupling - Aqua Drive?

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warrenmarkus1

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Hi,
My single cylinder VP 2001 in my Seamaster does move around a fair bit even with new engine mounts, and at certain engine (low) speeds causes a lot of vibration. Hence I am thinking of installing an aqua drive type unit, which consists of a couple of CV joints and a thrust bearing. As aqua drives are quite expensive and a little long for my engine/stuffing box installation, I was wondering if anyone has built their own and can offer any advice?
thanks
 
I built my own out of two used Mini CV joints.An engineer turned all the bits I needed.For the thrust bearing i used an off the shelf double row bearing.At the time it turned out at approx half the cost of a new one as there was a lot of lathe time involved.
With labour at UK levels it may not be worth it unless you can do your own turning.I can do a sketch from memory if it helps.
 
I sketch would be great as I was thinking along the same lines. I am especially interested in how you fitted the thrust bearing - machined a groove in the prop shaft on the stuffing box end?
Did it give an improvement?
My prop shaft has splines which I was going to match with an outboard (wheel) lohbro(?) joint and find a suitable mating inboard joint that accepts the splines on which to fit a flange to bolt onto the gearbox drive flange. This would give a very short assembly with enough articulation. I was planning to fit the thrust bearing at the of the prop shaft before it went into the first joint, via a mini bulkhead glassed into the hull to take the load.
 
I'll have to think a bit because it's been a few years.I'll try and do it tomorrow.
I had a Yanmar 1GM10 that shaked quite a lot and the prop shaft was hitting the stern tube.The difference was amazing.At least as effective as the real thing.
 
If it's a small engine and the shafts are approximately in line then I don't think it needs a separate thrust bearing. At least that is what my Yanmar agent/engineer said - the engine incorporates a thrust bearing.

I made a simple flexible coupling exactly like a very short car-type shaft. In fact I discovered that a LandRover male sliding joint was an exact fit for a Volvo female, and the result was an adjustable shaft about 10" long with a traditional hardy- spicer at each end, which simply bolted onto the gearbox flange and a split coupling on the end of the prop shaft.
After final adjustment I welded up the sliding joint.
 
We once got round this by bolting the engine onto angle iron, longer than the engine, then mounted the angle iron onto flexible feet further apart fore and aft. This will reduce vibration, you can also put extra flexible mounts, e.g. three a side.
 
[ QUOTE ]

I made a simple flexible coupling exactly like a very short car-type shaft. In fact I discovered that a LandRover male sliding joint was an exact fit for a Volvo female, and the result was an adjustable shaft about 10" long with a traditional hardy- spicer at each end, which simply bolted onto the gearbox flange and a split coupling on the end of the prop shaft.
After final adjustment I welded up the sliding joint.

[/ QUOTE ]

How many hours has it done, what H.P?
 
Yanmar 1GM10, not many hours yet, so could be described as still experimental.
There is a traditional stuffing box, with a bronze bush at the propeller end, and another bronze bush inboard just before the drive flange. No thrust bearing at this stage, the shaft is free to slide.
The double jointed connecting shaft therefore allows the engine to wobble as much as it likes. Alignment is not important - in fact a hardy-spicer joint can transmit power continuously at an angle of up to 15 degrees.
There is no need for constant velocity joints if two are used - correctly aligned and used in pairs the joints behave exactly as on a rear wheel drive car, and any non-constancy cancels out.

I grew up with a family boat which had a large Perkins engine. The drive was transmitted in the same way. As far as I know it was standard practice 40 years ago.
 
Sorry to contrdadict Cliff but a thrust bearing is vital. The CV joints will collapse under the strain.
Have a look at Centa-flex couplings, the type without the thrust bearing. They do a remarkable job of removing vibration. I fitted one and it transformed the boat!
 
As above, Hardy Spicers don't like end thrust, and neither does a two row bearing. I'd plump for the damping down the engine movement option, or buy the GKN aquadrive.
 
coupling122.jpg


I apologise for the drawing I did it in ten minutes so it's a bit askew.I forgot to draw a spacer that should go between the bearing and the flange on the shaft side
The double row bearing (should be sealed)is perfectly adequate if properly sized and the thrust won't ever be too much anyway given the HP.
As I said before,the coupling I built worked flawlessly for at least 5 years.I then sold the boat.
A word of warning,it's a lot of work.I'd buy the real thing now.
 
Thanks for the sketch.
My proposal is slightly different to yours in that I would keep the gearbox CV joint and flange, but reverse the next joint, so that the splined shaft becomes the driveshaft. My prop shaft would then fit into this joint. The trust bearing would fit onto the prop shaft between the joint and the stuffing box. I think the thrust bearing is necessary to take the force exerted by the prop, but also reduce axial movement of the shaft.
Yes it is tempting to buy off the shelf, but they are slightly too long (min length 10"), and around £800 each. So for the materials cost of a around £100, it seems worthwhile to have a go. And at this price even if they only last a few years , I will still be quids in!!
 
My engine sits on 4 volvo engine mounts which bolt down onto the I bar engine bed. Their is not much room to fit a sub frame which is what I think you have done.
Being an old single cylinder engine with a heavy flywheel it moves around a lot at low speeds.
 
If you're determined to go down this route, have a look at the drive-shafts and CV joints used on later aircooled VW busses.
(e.g. driveshaft + 2 CV joints £110 Just Kampers).

You'd need to get the shaft shortened, and re-drill the gearbox & propshaft flanges to suit the bolt pattern of the joints, and I agree you'd need a thrust bearing (the intermediate shaft needs to 'float'). I believe angular contact ball bearings have a reasonable thrust rating.

Given the 'custom' scene around aircooled VWs, I'm sure that there must be places that will produce custom 'driveshafts', or at least know the ins and outs of shortening them reliably.

Bear in mind that if this lot comes adrift, not only will you lose drive, but chances are you'll have a length of broken shaft flailing around under engine power - sod's law dictates this will happen when your pushing the engine revs to get out of a dodgy situation.....

Not for the faint hearted.

Andy
 
If you use Mini joints and do without one flange you'll have a coupling that measures less than 22cm wich is what mine was.
Get the biggest thrust bearing you can fit and you'll be ok.I got my CVs from a scrapyard and had no problems.They don't usally wear in the center only on the edges .Since the coupling will never be to far from straight any old CV joint in good conditon will do.
The intermedate shaft must be welded professionaly on a lathe to maintain accuracy.
 
I made my own about 10 years ago using a couple of Centaflex "Doughnuts"

http://www.centa.info/?show=products&c=mx&nr=32

and a cheap flanged bearing unit from RS

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0747541

The thrust is taken by a tiny cone-pointed grub screw which just digs into the prop shaft a tiny bit. Amazingly, it has never moved in all the time we've had it fitted.

It seems to work fine. The difference in structure-borne vibration and noise was considerable (but don't expect miracles)! The main advantage was that the vibration didn't keep bending the front of the propshaft and stern tube. The front stuffing box was bolted to a plywood bulkhead glassed into the hull and it had started cracking where it was bonded. The two rubber joints I fitted run visibly misaligned and have done for the last 10 years (although that's not as many hours as you might think - the boat doesn't get much use)!

It's a 12HP single cylinder diesel.

I have drawings and a few photos if you're interested.
 
I like the your idea.If necessary the thrust could be transfered to a couple of collars fitted to the shaft on both sides of the flange bearing.
 
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