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Old 11-06-2012, 01:55   #1
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Re-Powering 34ft Yacht

Hi Cruisers.
Thinking of replacing 20hp BUKH (20 yrs old and goes well) with New Yanmar 35hp Diesel in 34ft Yacht........can someone assist me, step-by step, on HOW and WHAT to do please...! cheers Harry
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Old 11-06-2012, 02:29   #2
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Re: Re-Powering 34ft Yacht

If this is a DIY project, then it is a big ask to get step by step instructions as there are many many variables.

The easier way is to throw cash at the problem - go to a Yanmar dealer and ask them to sell and install the engine for you.

However if you are serious about a DIY installation then here is a very brief outline. This is based on what I did some years back when I removed a Stuart Turner petrol engine and replaced it with Yanmar 2GM20.

Measure existing engine space and check if new engine will fit, if not, work out how to increase engine room space.

Check existing prop shaft to see if big enough for extra engine power.
Check existing prop aperture to see if big enough for larger prop.

Solve any problems encountered above.

Remove old engine, clean and paint engine space.
Replace prop shaft if required
Sit new engine in place on temporary blocks
Work out new engine beds
Build new engine beds
Toss out old controls, fuel lines, exhaust components, wiring, shaft seals, raw water seacock etc and buy new ones to suit new engine.
Fit new components.
Fit new engine to new bed
Connect engine to shaft
Double check everything
Bleed fuel system
FILL WITH OIL
With stop leaver pulled, and engine decompressed, turn it over by hand; if OK, turn over with starter motor.
You should now have oil pressure and raw water flow. Don't over do this part, you don't want exhaust to fill up with water.
Turn over with starter motor and engine compressed.
If still OK, check you are in neutral with closed throttle, release engine stop lever and try a engine start.

Now if you say all the above quickly, the task doesn't seem too huge but if you stop and think about every possible problem that might be encountered, maybe the old Bukh will start looking pretty good.
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Old 11-06-2012, 03:31   #3
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Re: Re-Powering 34ft Yacht

Harry,

Just thought, you have placed this thread under "Forum Tech Support and Site Help". This is usually for tech help around IT issues with the forum itself.

It might be better under "Const. Maint. Refit" or "Engines and Propulsion"; if you think so, then ask one of the mods to re-list it.

Just an idea!
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Old 12-06-2012, 06:13   #4
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Originally Posted by Wotname
Harry,

Just thought, you have placed this thread under "Forum Tech Support and Site Help". This is usually for tech help around IT issues with the forum itself.

It might be better under "Const. Maint. Refit" or "Engines and Propulsion"; if you think so, then ask one of the mods to re-list it.

Just an idea!
Thanks Wotname for the tips, and information and suggestions, they are gratefully appreciated. I guess my next step is to consult with Yanmar dealer then weigh up all the options etc... Cheers Harry
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Old 12-06-2012, 07:14   #5
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Re: Re-Powering 34ft Yacht

A search on the internet should bring up some articles/blogs from people who have done it themselves. It is not an easy job and having someone do it for you will be costly.
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Old 12-06-2012, 07:14   #6
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Re: Re-Powering 34ft Yacht

Be sure to check the exhaust size required by Yanmar against your current equipment--they usually demand an oversized exhaust hose, which will complicate the installation.

You will also need to look at the alignment of the prop shaft to the engine mounts--a new transmission and engine will mean that you may have to redo the mounts.
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Old 12-06-2012, 18:13   #7
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Re: Re-Powering 34ft Yacht

I am going through a repower myself. Being mechanically and technically inclined, I am having a mechanic perform the work; and I'm playing a role in technical guidance and have designed the necessary modifications and instructed my mechanic to follow and use them.

I chose to have a marine mechanic perform the work rather than myself; and not because I lack the time or energy, but wanted to free up myself to be able to focus on various aspects of it. It is a HUGE project (I'm converting from gas to Diesel and adapting an engine that is not typically used for my hull).

While your project is not as complex as mine, I would highly advise you to obtain technical assistance if this type of project is something you have not taken on yourself in the past. There are so many variables involved; and the absence of a highly experienced mechanic is going to be a huge disadvantage for you.
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Old 12-06-2012, 18:15   #8
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Re: Re-Powering 34ft Yacht

Quote:
Originally Posted by donradcliffe View Post
Be sure to check the exhaust size required by Yanmar against your current equipment--they usually demand an oversized exhaust hose, which will complicate the installation.

You will also need to look at the alignment of the prop shaft to the engine mounts--a new transmission and engine will mean that you may have to redo the mounts.
You will also need to recalculate prop size. A 20 hp engine is going to run more efficiently with a different sized prop than is a 35 hp engine.
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Old 13-06-2012, 01:54   #9
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Quote:
Originally Posted by DeepFrz
A search on the internet should bring up some articles/blogs from people who have done it themselves. It is not an easy job and having someone do it for you will be costly.
Thanks for the tip..! Cheers Harry
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Old 13-06-2012, 01:56   #10
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Quote:
Originally Posted by donradcliffe
Be sure to check the exhaust size required by Yanmar against your current equipment--they usually demand an oversized exhaust hose, which will complicate the installation.

You will also need to look at the alignment of the prop shaft to the engine mounts--a new transmission and engine will mean that you may have to redo the mounts.
Thanks Don for the advice..! Cheers Harry
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Old 13-06-2012, 04:30   #11
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Re: Re-Powering 34ft Yacht

if the bukh is solid mounted you'll have to give some thought to what a newer, flexible mounted yanmar will do to the stern gland, probably need to fit a universal or a new stern gland - I've been wondering about this myself...
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Old 14-06-2012, 02:46   #12
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Originally Posted by charliehows
if the bukh is solid mounted you'll have to give some thought to what a newer, flexible mounted yanmar will do to the stern gland, probably need to fit a universal or a new stern gland - I've been wondering about this myself...
Thanks Charlie, interesting point, will refer this one to the "experts" ......cheers Harry!
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Old 14-06-2012, 06:14   #13
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Re: Re-Powering 34ft Yacht

Before you buy your new engine I suggest that you spend some time with someone in the propeller business. Provide all the boat specs and possible engine specs and transmission ratios available. He will then be able to determine if the prop needed for the new engine / transmission combo will actually fit on your boat. It is no point buying a new engine if you have to make compromises by fitting an inefficient prop to accomodate the incorrect engine or transmission ratio.
Stanley
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