Help and advice requested


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Simon Currin
Simon Currin
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Any help or advice most welcome on our annoyingly intermittent propulsion problem.

On Shimshal we have a 75hp Yanmar J4HTE which runs beautifully smoothly and slips in and out of gear with no trouble at all. For at least 99% of the time the prop draft spins smoothly when motoring with no hint of judder or vibration. We have an Aquadrive CVB15 which is a constant velocity joint to diminish vibration and take care of minor engine misalignment. That drives a 3 bladed folding prop through a Sleipner Stern tube and cutlass bearing. There is some wear in the cutlass bearing with about 1.5mm of movement in the vertical plane.

Here is the problem. Very occasionally when slipping from neutral into slow ahead a thudding can be heard. As revs are slightly increased a vibration develops which is most prominent between the Aquadrive and gearbox. So long as revs are kept low that vibration will continue but when increased to 1500 rpm it disappears completely and does not return when revs are dropped back. This only occurs occasionally and most of the time it is completely smooth at all revs.

Last winter we changed the prop thinking it was the cause but to no effect. I now think it is the Aquadrive that’s at fault but there is nothing on the internet to point to Aquadrive failure. I have recorded a 1minute video of the vibration happening that can be viewed on this link: https://vimeo.com/291519307

Advice most welcome.
edited by simoncurrin on 9/24/2018
Bill Balme
Bill Balme
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That's a nasty wiggle as you increase the revs! I would suspect cause to be related to the worn cutlass bearing (1.5mm seems like a lot to me - no expert) and possibly exacerbated by some soft engine mounts (when were they last replaced)?

We had a similar sort of vibration some time ago - but it was during motoring in a following sea as we crested a wave. Everyone thought it was the prop, but in the end was traced to poor engine alignment. I gather your Aquadrive takes care of that - but presumably if it's well out of whack, alignment might also be an issue...

Bill Balme
s/v Toodle-oo!

Simon Currin
Simon Currin
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Thanks Bill I’m hoping it us dome resonance caused by the cutlass bearing which will be replaced soon.

I had quite s few responses on Facebook which I will copy across to here when they dry up.
Simon Currin
Simon Currin
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Sadly the transmission vibration continues (see video https://vimeo.com/291519307 ) although thankfully it is very intermittent. Thus far the prop has been replaced as well as the aquadrive and the worn cultless bearing. At least we now know what it is not! When we get to Baddeck I’m hoping to find a proper marine engineer to check alignment and mounts as Bill previously suggested. The guys in Lewisporte seemed to thing they were all ok but I don’t know what they did to deduce that. How do you check them?
Dick
Dick
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Simon Currin - 6/20/2019
Sadly the transmission vibration continues (see video https://vimeo.com/291519307 ) although thankfully it is very intermittent. Thus far the prop has been replaced as well as the aquadrive and the worn cultless bearing. At least we now know what it is not! When we get to Baddeck I’m hoping to find a proper marine engineer to check alignment and mounts as Bill previously suggested. The guys in Lewisporte seemed to thing they were all ok but I don’t know what they did to deduce that. How do you check them?

Hi all,
One of my strategies for going to wonderful, but isolated and remote, cruising destinations is to gather what I call “gurus” for consults in areas where my expertise is sorely lacking or areas where my efforts have brought no joy. I am willing to pay for the time these gurus spend helping me sort out an issue. They do not get consulted often, maybe once very couple of years, but when I have needed their help, it has proved invaluable.
I sent this problem to a mechanic/engineer (and general boat maintenance/repair expert) and he gave me permission to share his response, copied below. I thought might be of general interest to the Forum readers in part, as he may be correct, but also as an example of thinking and trouble-shooting problems that are complex and elusive.
My best, Dick Stevenson, s/v Alchemy
Hi Dick, I wonder if anyone has checked the travel of the shift linkage / shift lever? I have had several engines act in a similar manner ( minus the Aquadrive ). They tended to “buck” fore and aft as the clutch engaged and slipped/disengaged rapidly, primarily during acceleration. The problem would ease as the boat speed came up and the engine load lessened or if the cone clutch seated itself more firmly . Additionally, if the helmsman had separate shift/throttle levers a forceful shove on the shift lever would usually solve the immediate problem by squeezing that last bit of travel out of the cable. I have pushed the lever with my thumb while the engine was bucking and had it instantly correct itself. The longer term fix of this problem is to ensure proper shift lever travel for full engagement. And hope that the slippage hasn’t worn the clutch too badly ( probably hasn’t). In this instance the term “ easing into forward from neutral” makes my antennae twitch a little. The torsional movement athwartships would be more of a fore and aft motion , I suspect, if there were no Aquadrive doing it’s job in a perfect way of preventing thrust transmission. Since it is so robust and firmly attached to the hull the only motion available to the engine is to twist, as the torque of rotation loads and unloads in concert with the clutch slipping. Also, it sounds like they’ve replaced everything but the toilet seat in an effort to make this go away. Not to mention that when the problem “fixes” itself it stays fixed even when RPM is reduced. My guess is, that is because the the clutch has seated and is held in place by the spiral shaft of the cone. I’d be happy to take a call but feel free to forward my comments and let the owner try the simple process of pushing the shift lever while the engine is bucking.

GO

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