For the engineers - torsional vibration? - long winded! - Help!!

[dur]

those mounts look very very high !

Ok maybe I should try and add another block. I'm not keen on having to lift the engine again though. The forward ones are higher than the after ones so maybe I will see if I can do those without disturbing too much. If nothing else it would alter the amount of deflection I suppose.

Another pic of the mounts. I like to think the bearers are beefy enough...

 

[Pye_End]

That aft mount looks a bit wonky, or is it just some odd effect of the photograph?

 

[dur]

That aft mount looks a bit wonky, or is it just some odd effect of the photograph?

You might be right - I'll check it out tomorrow hopefully.

 

[Pye_End]

Ok maybe I should try and add another block. I'm not keen on having to lift the engine again though.

Should be able to take each of the front mounts off in turn and block them up without needing to lift the engine. Just undo the lower support nut on the mount, then the two plate bolts/coach screws. The engine may well stay supported by the other 3 without any additional propping. The recommended position should be in the installation manual, and this does look a bit high.

 

[cryan]

As mentioned before. You must find out exactly where the knocking originates. Use a stethoscope and methodically work around the area until you pinpoint the component where the knock is emitting from. Until you do this you should adjust nothing as you will just end up chasing ghosts. There are far too many variables at play and until you reach a definitive origin you can't possibly assess the cause and trying will become expensive.

 

[dur]

Should be able to take each of the front mounts off in turn and block them up without needing to lift the engine. Just undo the lower support nut on the mount, then the two plate bolts/coach screws. The engine may well stay supported by the other 3 without any additional propping. The recommended position should be in the installation manual, and this does look a bit high.

That will be a job for the weekend. I will see if I can get a piece of 12 mm ply under them. Will need some longer coach screws which is not a problem.

 

[JumbleDuck]

As mentioned before. You must find out exactly where the knocking originates. Use a stethoscope and methodically work around the area until you pinpoint the component where the knock is emitting from.

Could be tricky, if it's the propeller.

 

[CreakyDecks]

those mounts look very very high !

If you look at the photo on page 8 of this manual they are pretty much the same height.

http://www.betamarine.co.uk/downloads/operators_manuals/1590-1025-HEKC-SOM-0314.pdf

 

[macnorton]

I think that is what I mean by torsional vibration - essentially the shaft speed is varying slightly or hesitating slightly with each engine revolution.

Ok--I did understand that but possible ways to reduce it would be to fit a heavy flywheel or/and a better box to engine coupling!

 

[Pye_End]

If you look at the photo on page 8 of this manual they are pretty much the same height.

http://www.betamarine.co.uk/downloads/operators_manuals/1590-1025-HEKC-SOM-0314.pdf

More information on the mount here: http://www.betamarine.co.uk/downloa...a25_HE_Drawings/Beta25_HE_TMC40_100_06495.pdf

 

[30boat]

There is something very wrong with the way the engine is resting on its mounts.It should be as low as possible,ideally with no thread showing under the bottom nuts.On my installation(beta 20) the engine flanges rest directly on the cups.I do have am Aquadrive which allows it but yours are way too high and the rear mount appears to be pushed latterally and backwards.You need packing pieces under the mounts before anything else.Use the nuts for very small adjustments only.

 

[cryan]

Could be tricky, if it's the propeller.

If propeller it will be loudest at the hull penetration. You can also narrow the search as noise from prop will be considerably less frequency than noise from engine as prop moving much slower.

 

[dur]

There is something very wrong with the way the engine is resting on its mounts.It should be as low as possible,ideally with no thread showing under the bottom nuts.On my installation(beta 20) the engine flanges rest directly on the cups.I do have am Aquadrive which allows it but yours are way too high and the rear mount appears to be pushed latterally and backwards.You need packing pieces under the mounts before anything else.Use the nuts for very small adjustments only.

I think mine could be a bit high but as Creaky Decks and Pye End pointed out the installation manual and drawings show something quite similar. The photo even shows the mount leaned slightly to cope with the angle between bearer and the engine - just as mine appears to be.

As it is a case of trying all the easy things first I will give it a go. It could be that if the engine movement is restricted as much as possible that will alter the frequency of whatever is happening with the prop shaft (if it is). I would put hard rubber mounts on if it was the only way of getting rid of the knocking.

(I know you are not suggesting it but I like the idea of an Aquadrive . However it sounds like another £500.00 plus making an oak floor to take the thrust plus there is only 10 or 15" to fit it into. And I wouldn't do it without first getting rid of the knock. Perhaps I don't like the idea really!)

 

[dur]

Could be tricky, if it's the propeller.

I have ordered a stethoscope with a swivel coupling - it'll be fine

 

[Jcorstorphine]

When I first marinised my Ford 1.6 diesel engine with an R & D drive plate and a Hurth gearbox, the rattles and clunks from the new gearbox were very loud. I was advised to fit a mass ring in order to increase the weight of the automotive flywheel as this would reduce the torsional vibration casued by the engine running at about 800 RPM

I fitted a 20 mm thick mass ring on top of the R & D drive plate and the problems with the gearbox rattles and clanks went away, I was also able to redcuce the RPM tickover to about 650 which gave a very good crawling speed onto our berth.

 

[dur]

When I first marinised my Ford 1.6 diesel engine with an R & D drive plate and a Hurth gearbox, the rattles and clunks from the new gearbox were very loud. I was advised to fit a mass ring in order to increase the weight of the automotive flywheel as this would reduce the torsional vibration casued by the engine running at about 800 RPM

I fitted a 20 mm thick mass ring on top of the R & D drive plate and the problems with the gearbox rattles and clanks went away, I was also able to redcuce the RPM tickover to about 650 which gave a very good crawling speed onto our berth.

Well if the engine mounts don't help and the tests still say prop, I might be back to ask a few more details. One of the problems could be getting it past Beta from a Warranty point of view, not to mention where to get, how to fit etc.

 

[30boat]

Well if the engine mounts don't help and the tests still say prop, I might be back to ask a few more details. One of the problems could be getting it past Beta from a Warranty point of view, not to mention where to get, how to fit etc.

The reason why I recommended placing packing pieces under the mounts is that having the engine near the top of the studs allows for greatly amplified movement.Not only due the engines own vibration but also due to the thrust of the prop.The deflection of the mounts fore and aft is greatly increased and is most likely throwing everything out of true and even putting severe stresses on the shaft,coupling and gearbox output bearing.If you contain the engine the stresses willl me manageable.I strongly suggest that you put things right in that area before investigating further unless ,of course,that that's the cause of your troubles.

 

[JumbleDuck]

I have ordered a stethoscope with a swivel coupling - it'll be fine

Don't try it till you've knocked it.

 

[Jcorstorphine]

Agree about height of engine mounts, BUT ?

The reason why I recommended placing packing pieces under the mounts is that having the engine near the top of the studs allows for greatly amplified movement.Not only due the engines own vibration but also due to the thrust of the prop.The deflection of the mounts fore and aft is greatly increased and is most likely throwing everything out of true and even putting severe stresses on the shaft,coupling and gearbox output bearing.If you contain the engine the stresses willl me manageable.I strongly suggest that you put things right in that area before investigating further unless ,of course,that that's the cause of your troubles.

I would agree with “30boat” as the engine is too high on the mounts as I had the same issue and had to fit packing pieces to steady the engine. However in my case there was no thrust on the engine as I had fitted a massive thrust bearing and two flexible joints forming a “cardan shaft” so the only force on the engine was the torque produced by the rotation of the propeller.

Despite all this effort to isolate the engine, I still had the problems with rattles and clanks from the gearbox and the solution was the mass ring.

I would be surprised if Beta had not sorted out any torsional vibration issues, however Volvo had a lot of problems with their 2000 series engines which resulted in damaged gearbox splines basically due to torsional vibration but denied any liability.

http://www.ybw.com/forums/showthread.php?14988-VP-2003-spline-problem.

Going back to your engine, there is a BETA spares document which lists a number of options of drive plates and spacers. Here is a link and if you go to page 37 you will see some options.

http://www.betamarine.co.uk/downloads/spare_parts_guidelines/B10_to_B25_Spares_List.pdf

Let us know how you get on.

 

[dur]

The reason why I recommended placing packing pieces under the mounts is that having the engine near the top of the studs allows for greatly amplified movement.Not only due the engines own vibration but also due to the thrust of the prop.The deflection of the mounts fore and aft is greatly increased and is most likely throwing everything out of true and even putting severe stresses on the shaft,coupling and gearbox output bearing.If you contain the engine the stresses willl me manageable.I strongly suggest that you put things right in that area before investigating further unless ,of course,that that's the cause of your troubles.

Yes I get that completely. I have been to the boat tonight and I took out the coach bolts from the slightly suspect looking mount (back left) partly to draw around it for making some spacers but also to see what it did. I was thinking that if it was under tension because it had an unfair angle on it it would try to move when released. But in fact I could lift the engine slightly and then it would sit back from exactly where it had lifted. In fact it doesn't look particularly odd when you see it in front of you. There is obviously a slight angle on that bit of the bearer but nothing to speak of.

I also felt each of the mounting feet when running in gear and clattering. They were all moving freely with no bumps or sharp movements which might suggest the bottom of the stud was hitting the bearer.

I then used the ensign staff as a listening stick. No undue noise from gearbox, stuffing gland and maybe just a bit from the shaft log. Then I put it on the nut which secures the one of the inboard ends of A bracket that holds the end of the shaft (which are just bolted through the middle of a plank). The knock was really loud and distinct. No doubt in my mind at all that that is where it is coming from. Doesn't do it going astern. I need to check that the prop is not moving forward and hitting the cutless bearing but it would have to be moving about 10 mm and there is no sign of it doing that from inside.

So what next. I could fiddle around and try another prop but suspect that will just come back to the same place again - needing some sort of torsional damping.