Is there anyone running a Yanmar GM20 in an Atalanta 26

I already have a RCA Dolphin

12 hp two stroke twin fitted in the boat.

I would like to know if this is a good replacement  I have a Gm10 in bits  being a single it would be a little harsh and noisy  ..not sure which way to go

    About simon

    Boat: A5 ** Interest: My father purchased Diaphony in 1977, having just sold Our Lysander 17 called Grebe and with two adults and three kids and a dog it was decided that we needed a bigger boat.Having looked at a few boats my father stumbled across Diaphony A5 at Chichester marina on its trailer,after a while the owner finally clinched the deal with my Father in a pub at Dell Quay . After a year spent renovating A5 she was ready for launching at Chichester .The boat was sailed for the remainder of the 70s and early 80's having crossed the channel many times ,she was returned home for minor work and hasn't seen the water since. ** Location: bucks ** Country: GB

    9 thoughts on “Engine transplant

    1. Hello again this weeks blog concerns engine bearers
      with my new purchase of a Nanni diesel twin 14 hp@ 3500 rpm and weighing in at 94 kg
      What size Engine bearers and wood type would you recommend as I’m ordering them this week..

    2. I have now ordered my engine
      Nanni 250 HE with TMC40 gearbox similar to beta 14 after many hrs measuring,drawing plans I have now bitten the bullet.
      It does however mean that I will end up with a large box in the cockpit .not sure about the puny 3/4 ” shaft

    3. Having had a good measure up
      it seems fitting a replacement engine is not as easy as I thought..I have concluded that a Yanmar 2gm20 will not fit
      The problem is height it is higher than the saloon hatch doorway
      and would leave a small walkway either side of the Engine.What is needed is a TMC 60A. gear box with a 7 degree angle on the drive flange this will allow the engine to be almost horizontal .
      This gearbox will fit Kabota based engines ..
      Are there any Atalanta Owners with Diesel Twins (with heat exchanger) having spent the last week measuring and mocking up I am still going to end up with a raised cockpit.
      Any ideas would be most welcome..

      1. Hi Simon

        There are a lot of (Mark II) boats with diesel twins. On the Mark II boats all of these (and in fact all normally orientated Diesel engines) will require the floor to be raised above the tops of the keel boxes, typically but at least 90-100cm, typically finishing just a centimetre or two at most below the companionway threshold.

        So I think you will have to have a raised cockpit.

        The other way of ‘levelling’ the engine is to fit an Aquadrive coupling which can accept over 10 degrees (I think up to 15 or 16) ‘mis’alignment.
        On Helene the 1GM10 is kept relatively low in this way. You can see my installation in this post
        What the post doesn’t show is the ‘box’ which fits over the engine to accommodate the upstaged. That can be see in the attached photo.


      2. Simon,
        I fitted a vetus engine in A90 see photos in her log, drive was achieved by converting a car prop shaft (ford sierra I think) as Colin did Which he wrote about in one of the bulletins. The top of the engine cover is about level with the companion way I also raised the aft end of the cockpit to give as level an area as possible.


    4. I have a GM10, which I dont find unduly noisy and considerably quieter than the Yamaha 8HP outboard I had onmy previous boat – its robust and reliable and gives about 5 knots with a bit to spare. The GM10 seems hard to beat on value for money, but I am always v.nervous about that exhaust elbow – Johara’s rusted away two months after I bought her, causing water in the engine and the need for a new engine. If ever I buy another boat with a GM 10 I will check that exhaust elbow before parting with any money. The engine I would buy if I had the money is the Beta, Hiran has one, I think it is the Beta 14?

      1. Having looked at th GM 10 exhaust
        I can see why they are prone to break the inner tube that the exhaust gasses exit through is only welded at the exhaust flange, my suggestion is buy a stainless exhaust manifold get a competent welder in stainless to weld the opposite end to cyl head with 3x welds 12 oclock 4 oclock and 8 oc from inner tube to outer tube to support it the exhaust resonance is the reason it breaks then disappears in your water ex tank .job done..

    5. Hi Simon
      I don’t have the twin – I have a 1GM10. I understand your comments about smoothness – a twin would definitely be smoother – but I don’t find the engine is that noisy or rough. It has good (Yanmar) flexible mounts so no significant vibration in the boat. My engine compartment is lined with foil backed sound deadening foam which does make it quieter than it would otherwise be.

      Interested to hear of people’s experiences with GM20s.

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