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Old 04-06-2020, 11:20   #1
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Seized engine (Yanmar SB12) - repair or replace ?

I've been looking at an old 1979 "project", 27ft sailing Colvic lots of work to update but the key issue is the engine, very old and apparently seized. The boat has been on the dry for 4 years and suggestion is that's why it's seized. Visually the engine is standing in rain water and rusty as heck, my questions are as follows:
- As the engine is old and looks "distressed" is it worth putting all the effort in to try and save it i.e. good money after bad ?
- Are reasonably priced parts readily available for a Yanmar SB12 compared to other more common engines ?
- If I were to replace it with a "cheap" second hand what would be recommended - make, model, HP ?
- If you change an engine I imagine there are a whole host of additional consequences e.g. electrics, mounting locations, coupling configurations, hoses, all more expense. Are my concerns valid ?
Has anybody swapped an engine or this particular engine out before and if so what did you replace it with and what were the implications, what did you put in and would you do it again ?
I'm mechanically minded but no real engine experience, I'm really keen to take on this project but pragmatic enough to realise my heart may be ruling my head, should I just be looking at spending more on a boat that's good to go. Would very much appreciate any feedback apologies for all the questions, would be great if you could respond to any one of them.
Regards
Gary
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Old 04-06-2020, 11:31   #2
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Re: Seized engine (Yanmar SB12) - repair or replace ?

To start with This is a free boat or every single every thing else is in outstanding condition? If not walk away, the number of nearly free sub 30’ boats in good shape is huge.
If parts are available, I would overhaul, first it’s easy but mostly everything else fits this engine, it’s all the accessories that will drive you nuts and have you spending a fortune on if someone gave you a free other motor.

But I’d bet there is a much better boat out there close by for the same or less money with a good running motor.
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Old 04-06-2020, 11:41   #3
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Pull the motor and rebuild it. Parts are readily available and you will learn a lot by rebuilding it yourself.
Send the head out for rebuild .....do the rest yourself. You can do it.
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Old 04-06-2020, 11:51   #4
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Listen to a64pilot. Rebuilding is easiest and cheaper than new. Maybe cheaper than another used engine.
My experience with used engines is often they have new paint on the outside and near end of life parts on the inside. People removed them for a reason.
A different brand/model engine may require engine bed changes, different plumbing, electrical, alignment.

Yanmars are common. Any rebuilder can get parts. Another option is find the land version (car, tractor, industrial) and maybe there's a short block available. The difference between land engines and marine is usually marine engines have more hp because of bigger injectors. Marine engines have better cooling.
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Old 04-06-2020, 16:49   #5
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Re: Seized engine (Yanmar SB12) - repair or replace ?

After having rebuilt the younger brother (YSE8) of your SB12, I strongly suggest you price the basic parts of the SB12 from your local Yanmar agent before proceeding.

You may be shocked! For example, here are some YSE8 prices - one main bearing $50, the other $500 (yes five hundred). A conrod about $500 (yes five hundred).

However many of the parts are available aftermarket from south east Asia as they are common to many other Yanmar commercial engines (pumps, rice planters etc).

I managed to get a new sleeve, new piston and ring set, head gasket, valves etc from after market sources that were way way less than the offical Yanmar agent. A second hand conrod for $50 etc.

Surprisingly the fuel injector pump parts were quite cheap from Yanmar and the injector pump can be rebuilt in the field despite what others say!

The engine itself is extremely easy to strip and rebuild.

There are many good reasons to rebuild the existing engine but do check part pricing and availability before you start! Price everything first and work backwards after you strip the engine and find what is needs replacing. Most likely you will end up with a new sleeve, piston, rings, bearings, valves and exhaust mixing elbow. They are a rugged engine.
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Old 04-06-2020, 17:22   #6
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Look for a free boat with a decent engine. You'll be light years ahead.
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Old 04-06-2020, 18:45   #7
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Having rebuilt a Yanmar 2GMF myself, my advice is, do not bother rebuilding anything older than a Yanmar 2GM20F.

As stated above, Some parts are cheap, others are expensive. If the engine has not been in production for 30-40 years, why bother?

A small Yanmar, 10-15 years old can be had for $2,000. Rebuild that if you need to. Rand new, it will be around $5-6,000 if you get lucky. You can probably reuse your transmission.

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Old 04-06-2020, 19:44   #8
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Dont even think of rebuilding a raw water cooled engine.
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Old 04-06-2020, 21:28   #9
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Quote:
Originally Posted by kmacdonald View Post
Dont even think of rebuilding a raw water cooled engine.
I'd completely disagree with this,
Only reason not to rebuild is if the castings are rotten from corrosion because the owners never replaced the anodes.
Our 40 year old raw water cooled yanmar was completely stripped a few years ago ( maybe 4 ) & it has virtually no internal corrosion. I fully expect it to be able to last another 40 years as long as the anodes are replaced when necessary.

I'd agree with what Wotname says. Price it up 1st.

I sell aftermarket parts for those old Yanmar singles locally so you might say I'm biased but I freely tell people I'd only buy a kubota based engine if getting a replacement engine.

Don't know where in the world you are but Colvic, I'm guessing UK.

If you are in the USA & can get a free better boat yea go for it but those motors are not hard to rebuild IF you are mechanically inclined.
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Old 05-06-2020, 00:57   #10
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Wow I've never used this or any boat forum before but what a fantastic response. Really appreciate the feedback from all, different opinions are valuable. Overall I think I should look again for at least a boat with working engine that I can work on anyway. I'm in the UK (London) and haven't seen any free boats but will keep looking for cheap project with working engine which will probably reduce my risk of failure and hidden cost in the short term.

Anyone else with an opinion please do post it's really useful to me.

FYI one of the challenges for me is the cost of storing/mooring the boat and this was in a super cheap yacht club, to expand my search I may look for something smaller with a trailer so I can get it to the club.

Many thanks
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Old 05-06-2020, 01:43   #11
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Yes I know yr problem with UK mooring. Thats the trouble with overcrowded countries, you have to be rich to be a yachty. Sadly NZ is working towards overcrowding.
Anyway if you decide to work on rebuilding that SB12 you can get a lot of tips here, including a workshop manual.
Atoll from Cornwall knows a good dealer for those old engines. You can search for him on CF
FWIW it doesn't look that rusty to me but I'd much prefer a 3 cylinder Kubota 20hp in terms of noise, vibration & power.
The old Yammer definitely can be resuscitated tho.
It's a lot of work to change engines only you can decide whats right for your circumstances.
That's why it's hard to answer your questions with a hard & fast answer.
How much time do you want to spend on rebuilding? How important is a pound ( currency ) to you?
I spent a LOT of time finding cheap parts & finding work arounds to escape the Yanmar mafia.
So, as usual, it's a time & money equation.
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Old 05-06-2020, 01:49   #12
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Hi Gary.
Unless the boat has a whole lot else going for it, I would look for something that you could use from the get go, instead of spending the next year putting time and money into a major project. There are plenty cheap usable boats out there that just need a good clean, some cosmetic work and possibly the outboard needs servicing. If you're starting out, why not go small, go now and later move on to something more substantial.


Also there are affordable moorings at clubs on the east coast in tidal estuaries, where you can leave the boat. Towing the boat back and forth, as well as loading, takes up a lot of the day. I'd look for a bilge keeler that can dry out when left in an estuary. Keep it simple.
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Old 05-06-2020, 02:29   #13
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Hi Gary, how do you know the engine is locked up? It appears that there is a manual start feature on that engine, is the hand crank on board? If it won't turn, see if you can pull the injectors and put some penetrating oil into the cylinders.....maybe the rings are stuck to the cylinder wall. It can live again!
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Old 05-06-2020, 02:35   #14
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Re: Seized engine (Yanmar SB12) - repair or replace ?

All good points above, but the real question is how 'siezed' the engine actually is.

The pictures show an average/not-so-bad-looking-somewhat-neglected engine; if the price is right, you may find that the engine is operational with as little as a breaker bar to loosen it's initial recalcitrance to rotate.

Doesn't seem you're looking to circumnavigate yet; a less-than-perfect engine is quite acceptable, perhaps even desirable (for its educational value) at this point in your sailing-life trajectory...
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Old 05-06-2020, 02:38   #15
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Re: Seized engine (Yanmar SB12) - repair or replace ?

Good lord, the 'crowd logic' this forum sometimes reveals is startling...
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