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Old 22-11-2010, 17:35   #1
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Repower

I have a Perkins 4.236M normally aspirated diesel that is getting on and needs removing for a top overhaul (at least).
I am considering a repower with perhaps a Yanmar or equivalent - currently have 80HP.
Any idea or suggestions on a course of action would be appreciated.
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Old 22-11-2010, 20:47   #2
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If you decide to rebuild yourself, try here, Perkins 4.236 : Parts 4 Engines, Perkins Diesel Engine Overhaul Kits and Spares, Find your Perkins Engine Overhaul Kit and Spare parts here about thebest place I've found to get Perkins parts.
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Old 23-11-2010, 02:55   #3
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Quote:
Originally Posted by Underdog View Post
I have a Perkins 4.236M normally aspirated diesel that is getting on and needs removing for a top overhaul (at least).
I am considering a repower with perhaps a Yanmar or equivalent - currently have 80HP.
Any idea or suggestions on a course of action would be appreciated.
If you are in Sydney Australia Talk to Peter Noonan of Zenith Engineering in Brisbane - here is their web site - I have installed 3 of their Isuzu naturally aspirated engines - 1st class job. Home - Zenith Engineering
Richard
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Old 25-11-2010, 05:55   #4
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Originally Posted by Underdog View Post
I have a Perkins 4.236M normally aspirated diesel that is getting on and needs removing for a top overhaul (at least).
I am considering a repower with perhaps a Yanmar or equivalent - currently have 80HP.
Any idea or suggestions on a course of action would be appreciated.
We repowered our 12m steel yacht with a 75hp yanmar in Sept 09 . If you would like to know our exsperience you can pm me on byamee1@hotmail.com

www.byamee.com
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Old 25-11-2010, 06:51   #5
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I have just completed repower project on my 40' mono, replacing my
Perkins 4-286 with Yanmar 4hjt 75hp. Same issues with my 45 yr old Perkins as you. My decision to replace rather than rebuild was that the cost of a professional rebuild was $8-9k + whatever else they found was suspect: manifolds, etc, My Yanmar was $13.5k + custom exhaust ($900). In my work as an maintenance engineer working on production equipment that needed to operate reliably 24/7, I seldom recommended rebuilds if costs exceeded 50% of replacement prices. Additionally, in case of resale of my boat, the new engine will have more value than the rebuild.

I only have 8 hrs on new engine, but I'm very happy with result. Boat sits 3" higher in water, fuel consumption is improved, room in engine space way better, maintenqance access is much improved. My only disappointment is the only marginal improvement in quietness. I expected better, I'll still have to install acoustical insulation.
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Old 25-11-2010, 07:09   #6
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Be sure the Yanmar is what you really want.

We have a Yanmar 4JH3HTE in our boat. It is very quiet, very smooth, very compact and light, and starts when you just look at the key. So far so good.

But it is a massively complex piece of machinery with turbocharger, intercooler, etc. It is highly stressed producing 100bhp out of only 2000cc of displacement, the same specific output as my first BMW (running on gasoline). Redline is a stratospheric 3800 RPM and our cruising RPM is 2500 or more.

Is that what you really want?

I like the big Perkins myself -- extremely simple and robust, like marine engines should be IMHO. Last forever. Can be fixed by a monkey with a hammer. Yes, they are heavy, bulky, noisy, and less efficient (83 horsepower out of 4,000cc of displacment if I remember correctly).

It's an important decision.
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Old 25-11-2010, 07:51   #7
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if you are planning on being in thailand/malaysia a lot yanmar is the only way to go.all the locals use them so finding a decent mechanic is easier and parts are readily available.
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Old 25-11-2010, 10:08   #8
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good luck. i love my yanmar in my ericson and i love my perkins in my formosa. the good thing about old tractor engines(what we use) is they last FOREVER. if treated well and worked hard. parts CAN be found cheap and rebuild isnt necessarily as much as the manufacturer or boatyard says. i got my 4-108 for $2500 and i had it installed for the total of 3 loaves of bread and a year long cruise of the gulf of mexico. not a bad deal, all in all.... look hard you too can find good deals, if you are interested.
the thing i was advised against as i was repowering my formosa is the stringers will require mods if you go from perkins to yannie-- but yannie is so quiet an so smooth and so sweet and so--wow-- easy on fuel-- you may want to go that way. i was quoted 15k for a 3 cyl non turbo new yannie--PLUS install--dealer/distributor tome pricing-- a larger than 3gm would be more.

parts for yannie are easier to find than parts for the perkins in more remote places...
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Old 25-11-2010, 13:09   #9
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Thanks for all your comments and tips. The Yanmar engine I have looked at surprised me with the fuel burn figures. I had thought they would be more economical, but the 110HP (I can't find one between 75 and 110HP) uses about 15 lph according to the graphs from the company, when producing the quoted HP. I am also a little sceptical about the noise as these things rev a lot, compared to the old Perkins anyway.
Guess I will do a bit more digging, as I have a bit more time before I really am forced into this.
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Old 25-11-2010, 13:52   #10
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Thanks for all your comments and tips. The Yanmar engine I have looked at surprised me with the fuel burn figures. I had thought they would be more economical, but the 110HP (I can't find one between 75 and 110HP) uses about 15 lph according to the graphs from the company, when producing the quoted HP. I am also a little sceptical about the noise as these things rev a lot, compared to the old Perkins anyway.
Guess I will do a bit more digging, as I have a bit more time before I really am forced into this.
Fuel burn is similar for all diesel engines, as far as I know, on the basis of specific fuel consumption. I always heard 20hp for one hour on one UK gallon (about 5 us quarts) and 23hp in case it's turbocharged, as a rule of thumb.

Our 100hp 4JH3HTE burns about 6 liters per hour at our cruising RPM of 2500. According to the fuel curves it burns 23 liters per hour at fuel power and redline, but you don't use an engine that way, so it's theoretical.

A turbocharger and, better yet, turbo and intercooler, increases the inherent efficiency of the process so the Yanmar will certainly have better fuel consumption than the naturally aspirated Perkins, by perhaps 10% to 15% if we believe the rules of thumb.

The turbo will also make the engine quieter, as the turbine absorbs the exhaust pulses. So I have no complaints at all about fuel consumption or noise of my Yanmar.

The problem is that these advantages come at the cost of complexity.
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Old 25-11-2010, 15:20   #11
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When my boat was re-powered last it went from a 15hp Gray Marine gasoline to a 33hp Vettus M415 (Mitsubishi based Diesel) w/ prop re-size to a 16" three blade prop....some say it is too much engine, but those extra guts have saved this boat more than once and even helped in rescuing someone else. At 2200rpm it pushes the boat at 7knots using less than 3/4gal/hr...1/2gal/hr if I crank it down to 1800rpm/5 knots. My personal opinion on re-powering is...if you can afford a little bigger engine now, it might save your boat later.
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Old 25-11-2010, 15:26   #12
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Not clear why you'd want to replace your 80hp Perkins with new engine at higher hp. My 40' boat is full keel, 19,000 lbs and achieves theoretical hull speed 7.7kts at 45-50hp. With my non intercooled version of the Yanmar you spec'd out, it develops 75 hp. Actual measurements last week, I achieved hull speed at 2400-2600 rpm. There will be very few moments you'll need more than 75hp let alone 100 hp.

One thing only hinted at in the discussions above is that you need to look at your current prop and gear box ratio. My Perkins had 1:1 gears. I went with a larger prop (20x16 vs 18x12) and 2.57:1 gears to be able to cruise the Yanmar at lower rpms (1800-2000). That decision was not costly for me as I had the 2.57 Velvet Drive trans. If using your existing gear box is part of your decision, then you have some other things to think about re the Yanmar decision.
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Old 25-11-2010, 15:36   #13
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oh yeah--if your current engine is functioning well, dont worry about repower until you hear the rods knock or blow a hole in your block.......like my previous owner did to this boat.....oops......
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Old 25-11-2010, 15:51   #14
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If you put too big an engine in a displacement boat you end up having to run the engine at to low an rpm...over time that will cause serious problems with the engine.
The rated HP of my engine (VETUS M4.15) is 33hp at 3000rpm, 2200 rpm pushes the boat a bit beyond hull speed (7 knots, stern squatted down), 1800 rpm is the height of the power curve and most efficient fuel consumption for power output (5 knots).
The power of the engine should be balanced with the boat (I lean towards the more powerful of that), I have a 17,000lb 30' boat and would not like anything more, or less
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Old 25-11-2010, 16:06   #15
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Something people tend to overlook when repowering is the prop....the right or wrong prop can make a huge difference. With a 33hp engine and the prop I have it pushed into 40knot headwinds with 15' seas....a bigger engine and the wrong prop couldn't do that. When repowering tak a very very close look at your prop, with the type of boat you have you don't have to worry about the drag factor/
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