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Old 27-09-2021, 02:26   #1
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Rebuild or Replace

I am buying a 1993 Beneteau Oceanis. The original engine is a Perkins M-90 4.235. It has no reported issues until during the sea trial when it suddenly stopped. We just found out it threw a rod in the second cylinder. The owner is taking care of everything and the plan is to rebuild. Before we go through I am trying to get as much feedback and thoughts on rebuild versus replacing. If I do replace it, I would go with a Yanmar.
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Old 27-09-2021, 03:56   #2
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Re: Rebuild or Replace

Itís a good engine , itís not a complex rebuild better engine then then the yanmar
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Old 27-09-2021, 04:21   #3
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Re: Rebuild or Replace

Replacing with a different engine is a potential nightmare. Aside from fitting into the space, all the hoses, cables, electrical connections, through-hulls, exhaust, and even the engine mounts will be in the wrong places. Think carefully before going that route.
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Old 27-09-2021, 04:38   #4
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Re: Rebuild or Replace

Luckily it happened before you closed on the boat purchase!
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Old 27-09-2021, 09:21   #5
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Re: Rebuild or Replace

Your going to pay money for a 28 year old engine that has sketchy parts availability and a 'rebuild' that could mean just about anything short of an actual complete rebuild. Not a good idea.

Sounds like your buying somebodies trouble. A decent engine doesn't just up and throw a rod.

There are engines that will replace the old one without much trouble and you will sail away with a warranty and reliability. You can even reuse the old transmission if it is a decent model. It will fit the new engine.

Be smart. Negotiate the price of the vessel with the idea of installing a new engine.
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Old 27-09-2021, 20:39   #6
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Re: Rebuild or Replace

When an engine suddenly stops from a blown rod, there's almost always some other damage. Often the crank has cracks. Whatever the damaged rod hit to stop the engine has some damage. They're many things that need to be checked on a damaged engine.
The rebuild could be just putting a new rod and piston in the cylinder, or maybe sleeving the cylinder and nothing else. You need to know what's being done.
Usually I come down on the rebuild side rather than the cost of a new engine. But this one, unless I was doing the rebuild, I wouldn't accept without a long talk with the rebuilder. In my life I've rebuilt hundreds of engines, mostly marine diesels, a few gas racing engines and I started with aircraft radials.
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Old 28-09-2021, 11:02   #7
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Re: Rebuild or Replace

Quote:
Originally Posted by Lepke View Post
When an engine suddenly stops from a blown rod, there's almost always some other damage. Often the crank has cracks. Whatever the damaged rod hit to stop the engine has some damage. They're many things that need to be checked on a damaged engine.
The rebuild could be just putting a new rod and piston in the cylinder, or maybe sleeving the cylinder and nothing else. You need to know what's being done.
Usually I come down on the rebuild side rather than the cost of a new engine. But this one, unless I was doing the rebuild, I wouldn't accept without a long talk with the rebuilder. In my life I've rebuilt hundreds of engines, mostly marine diesels, a few gas racing engines and I started with aircraft radials.

+1 for this sage advice.
I'd go with a mechanical injection Beta if re powering rather than a common rail Yanmar but thats just my opinion.
Much easier to repair in remote places & far cheaper parts not that a new engine should need any for quite some time.
Welcome to the forum too!
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Old 28-09-2021, 13:03   #8
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Re: Rebuild or Replace

It's a 4.236, not 4.235.


An ancient engine, the design is older than I am. Just one evolutionary step ahead of a hot bulb engine or even a steam engine. Dead simple, naturally aspirated, and of legendary reliability. Many sailors love it, not few consider it the best sailboat engine ever made.


But not all. It has a number of drawbacks: noisy as hell, vibrates like crazy, spews oil, inefficient, more than double the weight per hp compared to Yanmar, sensitive to underloading and so to wet stacking (because of extremely low specific output).


For all these reasons, personally, I prefer Yanmar, the turbocharged but mechanically injected ones. Strongly. YMMV.
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Old 28-09-2021, 13:18   #9
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Re: Rebuild or Replace

I agree with the earlier sentiments, questioning how some kind of broken conrod cannot have done a lot of damage to the block, crankshaft, cylinder lining. I don't use my engine that much but when I do I am just so grateful that it is always ready to go and it just keeps going. Am not sure if this would be the outcome with a rebuild.

With regards to fitting a new engine, I read a post some time ago of someone who made a mock-up of the engine out of wood and cardboard, mimicking exactly where the engine supports would end up, exhaust connection, prop shaft, gear shift lever, etc. For sure a bit of work to do this accurately but in that way I imagine it is possible to 'prepare the ground' before hoisting in the real thing. And it should fit!
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Old 30-09-2021, 08:22   #10
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Re: Rebuild or Replace

All parts for the Perkins are still available, and are very affordable.

Not that you'd need them, a price comparison for an equivalent Yanmar engine (4JH4TE) part;

New perkins crank, 700.00 USD with bearings

New Yanmar crank, 2522.00 pounds without bearings

Given the weight difference, 1100 vs 500, something may have to be shifted to accomodate the change.

There will have to be quite a few modifications made to switch to such a different engine.

New engines are expensive.

If it were me, I'd probably rebuild.
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Old 30-09-2021, 08:50   #11
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Re: Rebuild or Replace

I have a perkins 4.236, its a 1978 build, and I had it completely rebuilt (1st time in its life) 3 years ago. Was running fine, but boat was new to me and being refit at the time.
Cons... HEAVY
Pros... Easy parts availability (this is the same engine as hundreds of thousands of tractors worldwide)
Heavy... Changing this for another engine will require re-balancing fore / aft
No glow plugs... doesn't need them, starts instantly even in cold weather
Simple... No electronics to fail
Durable... These can easily get 10000 hours between overhauls with regular maintenance)

These are great engines and incredibly reliable. I'd own another in a flash.
If you do decide to part with yours, please let me know.
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Old 30-09-2021, 10:40   #12
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Re: Rebuild or Replace

Many valid points- different horses for different courses. Not sure if put such a heavy engine back in what is a fairly light boat- youíd probably benefit performance wise under sail with a newer, lighter engine. You could make up weight differences with tankage (always handy) but then you lose any performance increase again.

For a heavy displacement boat those old Perkins 4-236ís were tanks. Loved em in every boat Iíve run that had them- they are easily to rebuild too. but they are damn heavy.

Fwiw You can buy a fully refurbished 4-236 from transatlantic diesel for $9500. Essentially a brand new (but yes, very old design) engine.
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Old 30-09-2021, 15:41   #13
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Re: Rebuild or Replace

Quote:
Originally Posted by laurenalanders View Post
I am buying a 1993 Beneteau Oceanis. The original engine is a Perkins M-90 4.235. It has no reported issues until during the sea trial when it suddenly stopped. We just found out it threw a rod in the second cylinder. The owner is taking care of everything and the plan is to rebuild. Before we go through I am trying to get as much feedback and thoughts on rebuild versus replacing. If I do replace it, I would go with a Yanmar.
Where I got hung up in this is where it is bolded. If you trust that the owner will be knowledgeable and prudent about where he sources the new bits that go into the engine, and remediating any collateral damage that occurred when it threw its rod, then that could work out just fine for you. But, as remarked up page, well taken care of engines are really extremely unlikely to throw a rod. Over revving will do it, sometimes, combined with over-heating, but someone who is sensitive to engines would notice the temperature gauge, will not over rev unless in some really extreme situation. So, if you decide you cannot trust the person, then you're back boat shopping. Or you take enough off the price to have it done, and try and find someone local to you that you think you can trust to do a proper job of the rebuild.

Just as a comment, we had a friend had an engine "rebuilt". It turned out it was not, it was just re-painted, and the present problem at the time fixed, and the whole deal did self-destruct. So there are dishonest engine rebuilders out there. Beware. Your solution will partly depend on your contacts.

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Old 30-09-2021, 16:11   #14
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Re: Rebuild or Replace

Quote:
Originally Posted by JPA Cate View Post
... If you trust that the owner will be knowledgeable and prudent about where he sources the new bits that go into the engine, and remediating any collateral damage that occurred when it threw its rod, then that could work out just fine for you...
The owner will be incentivized to do the job as cheaply as possible. The suggestion up thread that you work closely with the mechanic is a good one but he will still take his a direction from the owner who is paying him.

So I would consider a new engine. Figure out the price difference between a rebuild and a new engine and negotiate with the seller.

I replaced a Westerbeke with a Yanmar and the accommodation for the new motor was minimal (custom motor beds fabricated).

A good Perkins is fine. A patched up Perkins, not so much.
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Old 02-10-2021, 21:28   #15
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Re: Rebuild or Replace

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Originally Posted by HeinSdL View Post
I agree with the earlier sentiments, questioning how some kind of broken conrod cannot have done a lot of damage to the block, crankshaft, cylinder lining. I don't use my engine that much but when I do I am just so grateful that it is always ready to go and it just keeps going. Am not sure if this would be the outcome with a rebuild.

With regards to fitting a new engine, I read a post some time ago of someone who made a mock-up of the engine out of wood and cardboard, mimicking exactly where the engine supports would end up, exhaust connection, prop shaft, gear shift lever, etc. For sure a bit of work to do this accurately but in that way I imagine it is possible to 'prepare the ground' before hoisting in the real thing. And it should fit!

Building a mock-up of the new engine is very helpful for a good fit. Using factory engine drawings and specs, I built a precise mock-up with a pin hole at each end, in line with the shaft. A laser pointer was centered at the aft end of the stern tube and shot the beam directly up the center of the tube. The new engine beds and stainless mounting plates (holding the engine mock-up) were fabricated so that the laser beam passed through the two pin holes in the mock-up. This was done with the adjustable engine mounts all adjusted to their exact midway points in their adjustment range. The beds were first built to their approximate size and slope and then adjusted to final height and slope with layers of glass and epoxy. Final height and slope was achieved when the laser beam passed through both the fore and aft pin holes on the mock-up. It was very successful. When the engine was mounted, it needed zero adjustment of alignment and was at the midway point of the adjustment range on all four motor mounts. The old original beds were too tall and too far apart. So, they were first cut shorter and then thickened inward before the final buildup of the height and slope. Sounds complicated but it was actually pretty easy.
For a visual of the mock-up, see my ďrepowerĒ photo album on my profile.
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