Engine replacement question

[johnchampion]

I am half way through changing from a ST petrol engine to a Yanmar 1GM10. The ST was on a rigid bed i.e. no flexible mountings whereas the Yanmar has flexible mounts and, I am told, a propensity to jump around a bit.
The stern tube is also of the rigid type with a normal packed gland and greaser on the inboard end and the gland is screwed onto the stern tube so is also rigid.
I am getting conflicting advice as to how to handle the possible/probable movement of the engine with the current set up of a rigid inboard bearing. Some say using a flexible coupling such as the Centaflex or Bullflex will solve the problem while others are adamant that it won't and I need to use a flexible inboard seal on the stern tube and do away with the present greaser and gland.
Any one have any experience or views on the best solution?

 

[Poignard]

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Any one have any experience or views on the best solution?

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Yes. I have a BUKH 10hp engine with flexible mounts, and a traditional type of inboard bearing and stuffing box, such as you describe. Drive is transmitted through a Centaflex coupling and the whole set up works very smoothly and quietly. If you want a picture of the set up I can email it to you.

 

[johnchampion]

Thanks - a picture would be most helpful

 

[KenMcCulloch]

Border Maid has a 1GM10 which replaced a ST petrol engine about 7 or 8 years ago under the previous owner. The stern tube has a conventional stuffing box and greaser, and there is a flexible coupling (R&D I think) at the gearbox. It seems to work OK. The engine does leap about a bit at idle speed but as soon as you put a few revs on it settles down quite nicely.

 

[Roach1948]

I had the same worries as you and I installed a Halyard Aquadrive unit that connected via a hot-dipped galvanised steel thrust bulkhead as shown

 

[Tranona]

I have also replaced a ST with a 1GM 10. Initially I removed the fixed stuffing box and used a seal on a flexible hose so that the shaft could move with the engine. This was unsuccessful as the shaft hit the tube.

Next iteration was an R&D coupling to take up the bounce of the engine and a short cutlass bearing in what was the housing for the original ST white metal bearing, bored out. Better, but the bearing eventually wore.

Current arrangement is a Bullflex coupling, a Volvo shaft seal and the cutlass in the old bearing housing (turned down on the outside to take the Volvo seal). Near to perfection as one can get. The shaft is fully supported at both ends and the Bullflex allows the engine to perform its gyrations. The Bullflex in theory allows up to 2 degrees misalignment, but I set mine up as near in line as possible using the traditional method of rotating the coupling until the gaps are equal using a feeler gauge. Time consuming but worthwhile. Also ensure that you use the Yanmar mounts in the correct position because I believe they have different resistance front and back.

If you do go down this route and have a rigid shaft, make sure you follow the Vetus instructions in respect of the centering ring (see p143 of the Vetus catalogue).

 

[johnchampion]

Thanks for the input guys. I did consider an Aquadrive (or Python drive) but felt the extra expense of the unit and the need to somehow construct a thrust bulkhead (although the one in Roach looks neat, do you have a bigger pic?) was probably overkill for a nine trusty horses engine.
The R&D although billed as a flexible coupling does not appear to me to be actually flexible, so I discounted that.
My current thought is that I shall try a Centaflex and retain the rigid gland to see if that works.
Tranona, I'm interested in your comment about the centring ring in the Bullflex as I confess I did not really understand quite what the catalogue was suggesting. I will have about 20" from the gland bearing to the flexible coupling which was about the distance they said to lose/not lose the ring for size but I couldn't make out the theory as far as rigid / non rigid bearings was concerned. I rang Vitesse who were very helpful but they suggested that it was to do with whether the engine was on fixed or flexible mounts which confused me even more which is why I thought I'd go with the Centaflex as it doesn't seem to get a technical write up anywhere so I couldn't get confused! (And it's cheaper, especially when you factor in the price of an extra coupling flange needed for the Bullflex). Can you shed more light on the centring ring business?
I borrowed a book yesterday for Yanmars and it mentioned what you say about the mounts in that there are front and back ones which I had not known - you've now reminded me to check where they are before I bolt everything down, which at the present speed of progress and indecision feels as though it may be the 2009 season and not the 2008 one - I must get a move on.

 

[Roach1948]

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(although the one in Roach looks neat, do you have a bigger pic?)

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Sorry my computer died over Christmas and I lost all my large format pics. The one here is taken from my blog and that is as big as it goes.

I think Halyard to a smaller unit now, that might be easier to fit. Most people have a seperate thrust bulkhead, but on my installation the thrust is taken to under the (new) engine beds. These beds extend will into the cabin and form part of the companionway steps. This is a far better solution to having a bulkhead mounted laterally across one set of frames which is what most people do. My thrust goes across four or five floors if I remember corrrectly. It does make for a very vibration free engine, speacially in a seaway.

 

[Tranona]

John

In the Vetus catalogue their Uniflex which is made by Centaflex is about the same price as the Bullflex and still needs an adaptor. It is also only available with metric bores and I guess your shaft is Imperial. I have not checked Centaflex itself as they might have a wider range of sizes. In my installation there was no room for a Centaflex anyway as it is longer.

With regard to the centering ring, I will find the explanation from the fitting instructions and send in a PM

 

[Seanick]

If I may add my ha'penny-worth.......It is quite important to get this bit right, as I have had to rectify poorly installed engines when the stern tube has rattled away at the stern post and created leaks. The original stuffing box or other seal mounted on a flexible pipe usually works. If you have minimal clearance between tube and shaft you may get shaft slap at tick over. Make sure all the mounts are settled evenly all round, as otherwise you will make things worse than they could be. You could try slightly stiffer mounts, or else Aqua and Python drives are well worth the time and expense. They preserve an older vessel from unpleasentness! I have not used Bullflex or centaflex couplings but would be interested to know your results. One advantage over Aqua/Python drive is that they don't mind getting wet.

 

[Spuddy]

I gather you are concerned about engine bouncing about on flexible mounts and so stressing the shaft and tube. In fact set ups like this are very common and work fine provided engine lined up correctly so that jitterbugging takes place around axis of rotation of shaft.

 

[Talulah]

Our original setup was the traditional engine, gearbox,R&D coupling, prop shaft. No issue under normal conditions. However, when motor sailing and healed over the engine is invariable tilted slightly sidedways on its mounts. You could almost feel the extra sideways force exerted on the prop shaft and cutlass bearing together with a grinding sensation. When we re-engined we put in an Aquadrive to purely do away with this problem. Not an issue if you rarely motor sail in heavier conditions but worth doing if you can.

 

[srp]

I changed from a Britt to a Yanmar in my old gaffer a few years ago and used an R and D coupling. I was always a bit concerned about the 'leaping about' but it seemed to be fine, and is still going ok with no problems (I sold it 2 years ago).
I've just put a Yanmar in my Corribee documented here - this uses an Aquadrive, as I thought that the grp structure of a small boat like this would struggle to absorb the vibration from a single cylinder diesel. The thrust bulkhead is a piece of cake - make a dummy out of 6mm ply and get a local blacksmith to weld one up for you, then send it off to be galvanised. The only likely problems are in the extra space an Aquadrive takes up.