LM27 engine beds

[guitarobin]

I recently bought Liberte, a LM 27 in Holland. I live in the UK and I am marinising a Kubota D905 to replace the Bukh DV20. My question is - are the engine beds sloping aft to give the downward rake angle or are the mounting feet placed higher at the rear and lower at the front. I am trying to fashion mounting brackets for the Kubota without having access to the boat in Holland.

[jandane]

I have never seen the Kubota, and my best guess is that the engine mounts on the engine are at samt height meaning that.the angle on propeller shaft is from sloping engine mounts. But why are you replacing the Bukh DV20?

[oceandancer]

Hi guitarobin,

The replacement engine must be parallel to the engine bed but maybe at a different height. I replaced my old volvo with a new Beta (Kubota). I had some feet made out of steel to adjust the height and got quite close but still needed to pack out the bed in order that the engine be mounted as low on the mounts as possible which is very important for minimising vibration. I used drilled iroko wooden blocks under each mount as this is a durable but very easily worked material and have found this to be very successful. It is easy to lift the engine in order to get the height right. You can do this single handed. Place two pieces of 100mmx 50mm timber across the locker tops with loops of 10mm rope over the timber and through the lifting eyes of the engine. Then use a small piece of broom handle though each loop as a spanish windlass. You can easily lift the engine about 25mm this way to change a mount or get the alignment right. When lifted sufficiently, tie off the broom handles to the sheet cleats. In your case you could crane the engine , complete with mounts onto the engine bed and suspend it as above to measure the height difference and make the iroko blocks accordingly.

I have lifted my engine several times this way without difficulty. If you are setting the longitudinal alignment you can shift the engine to port or starboard by levering the ends of the cross timbers.when all is about right support the engine by winding up the lower nuts of each mount, remove the timber and proceed to fine adjustment with a spanner. Your engine alignment should be checked at the gearbox flange with feeler gauges. Do the longitudinal alignment first and then proceed to fore and aft height adjustment. It takes time but the results are very worthwhile.
You need a good cushion to lay over the engine when checking the alignment as you need to lay on top - ouch!
Best of luck

Regards

Mick Legg

[pengwyn]

Hi guitarobin,

hopefully not too late,to be useful, I'd like to make some comments on engine beds for use with standard propellers (not saildrive). If you have to design an engine bed from scratch, you have to aim with the propeller shaft (comming from the gearbox which is attached to the motor) directly at the shaft seal / steve pipe. This has to be perfectly in line and the required position and angle of the motor and also the design of the required engine bed is defined by that. The propeller shaft has to be perfectly in line with the steve pipe - otherwise there will be a lot tear and wear resulting in noise, reduced lifetime, reduced efficiency and in worst case, water might enter the hull through the steve pipe.

Attempts to fix minor position errors by using a flexible coupling is btw not recommended (at least for for volvo-type shaft seals.) The engine bed should be designed to make the propeller shaft point perfectly towards the steve pipe. This will possibly not achievable instantly and to achive a perfect alignment after initial installation, you should allow fine tunig of the motor position (+- a few mm let/right and up and down). Also the motor fixations should be placed on rubber-bonded metal, which has to be selected according to the weight of the motor (please note: e.g. bukh is a little heavier at the flywheel side - i would expect the same in other motors). without rubber-bonded metal, all noise and vibrations will be coupled via engine bed directly into the hull - resulting in noisy boating. construction of the rubber-bonded metal (see catalogue), allow vertical adjustments, which is achieved by special bolts (or normal bolts) holding the motor. horizontal adjustments are achieved by slotted holes, which are used to fix the rubber-bonded metal to the engine bed. the rubber-bonded metal will be compressed a little under the load of the motor, which has to be taken into account while designing an motor bed. also you have to keep in mind, that the engine bed not only has to carry the load of the motor, but also has to take the thrust of the propeller and introduce it into the hull. the motor bed needs a very stable connection to the hull (I habe a engine bed, shapes like a tub, providing a large area for a stable connection to the hull and also serving as an 'extra bilge' for the motor. The thrust of the propeller also requires, that the rubber-bonded metal does not have to be too soft - otherwise the motor will be pushed a forward on its engine bed, while trying to accelerating your boat. A good source for such rubber-bonded metal or "schwingmetal" is: www.willbrandt.com/willbrandt/en/vibration_technology/products_schwingmetall.php (no friends /family of mine and no other connection. I'm just using "elbe90" rubber-bonded metal for a couple of years. which is very affordable eliminates vibration to a sufficient degree).

I also have some sketches and infos in various file formats (some unfortunately in german) about motor position, engine beds (bukh) which might be helpful in engine bed design / engine bed modification, as well as proper adjustment of the motor position and -angle. But I can't find any 'upload button' here. If someone is interested in such files, just send me an email.

regards

Pen Gwyn

[Charles]

I'm not sure why Pengwyn advises against flexible couplings. We have an Aquadrive flexible coupling, installed well before we bought the boat, presumably when the replacement engine was installed in 1991, and it has never given any trouble at all. The engineer carrying out the engine survey before we purchased was very pleased to see the Aquadrive in place. Have a look: www.aquadrive.com/

Charles

[jandane]

Charles.
To aquadrive or not to aquadrive....that's the question, and I think there are many opinions about it.
I had a Volvo MD11C in my LM27. It lost compression on the rearmost cylinder, and had some damages here and there. It was not fitted with aquadrive. It was, In my opinion, noisy and shaky especially compared to the Buck DV36 in my brother's LM30.
I decided to get a new engine and bought the Volvo D1-30 and together with this, a new gearbox, propeller with shaft and seal. The engine bed was changed to the new engine and in order to make it even better, I had a aqua drive installed as well.
I must say, I was disappointed. The noise was the same and the vibrations even worse. Volvo came with an expert and the aqua drive was removed, as Volvo is not recommending such a gadget on their installations. As the aqua drive is a bit flexible, their theory is, that the vibrations coming via the propeller and the shaft- and being absorbed by the gearbox and the engine mounts- now will stay in the shaft and destroy the shaft's seal, eventually causing a leak. When the aqua drive was removed, some vibrations disappeared. The alignment has been tested and it is more than perfect and within the limits and now, after 300hrs the vibrations have decreased

[oceandancer]

Hi All,

Just to join in the conversation, I have a Vetus Bullflex flexible shaft coupling and a conventional stuffing box an installation which I am very happy with and which is very smooth and vibration free. Whatever you have, correct alignment is essential. A flexible coupling like the Bullflex will accept up to 2 deg of misalignment but will not elliminate undue vibration caused by it.

One important point is that you must always ensure electrical connection across the coupling. I don't know how, but one year I forgot to put back the electrical link and very nearly lost the ironwork holding the bottom bearing due to rapid corrosion! This all happened within a single season so beware.

Happy Christmas to all

Mick

[pengwyn]

Hi Charles,

as Jandane already mentioned, the volvo guys do not recommend flexible coupling in combination with their shaft seals.

Another point is, to install everything that is actually required on board, but skip anything which is of no advantage or simply is 'masking' the origin of problems. flexible couplings in boats like LM 27 might just mask effects of misalignement or inapropriate engine bed or wrong (too soft/ too hard) or worn "schwingmetall"

(there is a whole universe of possible reasons for undesired vibrations on a boat - and I had had 'a lot of fun' with 2 inappropriately mounted gearwheels in a DV20, which are originally intended to eliminate vibration but have been reinstalled by murphy-bukh-service "experts" in a way, to enhance motor vibrations in my LM27).

So now my opinion is, If you have a strong and properly designed engine bed (not too flimsy, which might cause problems by acting as a resonator in combination with the hull) and If everything is properly aligned, every gearwheel and anything else in the right position and properly adjusted and the engine bed (in combination with rubber bonded metal) actively reduces vibration - I can not see any advantage of installing a flexible coupling on the relatively short propeller shaft of a LM27. The whole setup of motor,gearbox, shaft, propeller and motor bed has to be regarded as one unit, which has to be designed to introduce the thrust into the hull, while avoiding resonant structures and vibration.


(I have to admit, that initially and with all that desperate vibration issues, i already had bought a flexible coupling (vetus) - but before installation I decided (advised by an experienced skipper) to adress the 'basic issues' first, an try to stay to the "kiss-principle" ('kiss' now is my mantra to keep things reliable, when "improvements" tend become "ingenius miracles of outstanding complexity" ;-) ). Meanwhle the vibrations have decreased by many orders of magnituide and the still 'brand new' vetus coupling is for sale.

happy sailing in 2017

Pen Gwyn