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Discussion Starter #1
I figured this was a good of place as any to start a last ditch effort to salvage my Yanmar YSM 12. 1980. It ran great through late Feb 2012 but has not started since. I now rely on my 7.5 kicker motor which eats plenty more gas than the diesel. If you don't know, this engine is a single cylinder with decompression chamber lever, fuel injected and fires via compression (no glow plugs). The fuel is good, filters were changed in Jan, fuel system bled in Jan, batteries are fully charged, and power at the starter tests 12.7 V with multimeter. Starter was just rebuilt to include solenoid. When I hit the start button it spins slowly. With the compression closed it spins even slower. It seems it used to spin much faster when starting. The teeth on the flywheel are good and the bendix is engaging properly. I can hand crank it some, but not nearly fast enough to get it going. Today, I did notice a black wire (small 12 guage) to one of my batteries start smoking during the start. It looks like the previous owners have by-passed most of the original engine controls but it obviously ran great like this for many years. I can't find any information about slow spinning engines during start up other than electrical which maybe is the problem. I redid all the positive cables and the connections are looking good. I haven't worked with the grounding system as much but it does test 12.7 on the multimeter from the solenoid + to the - on the starter bolts. Is their a way I can bypass everything to see if the flywheel is perhaps hung up....causing resistance? Also, I don't have the $$$ right now to take it in so everythings pretty much on me. I'm in Pensacola, Florida and the diesel repair rate is $90hr. I am free to any advice. Also, while I am using the old motor it has now been two months since this one has ran. I have the water intake closed since it did not start in Feb but is their anything else I should do (thinking winterization) since it sounds like this motor may be sitting off for the next few months.
 

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Don't despair! See my post in the "yanmar crank thread" that I posted a few minutes ago.

If you have a smoking black wire, that is because there's too much amperage going through it. i.e. it's too small. This is also quite likely why it's spinning too slow. The resistance of this wire is limiting the ability of the starter to spin quickly. This wire needs to be MUCH bigger to be safe and it will spin faster as well.

Try hitting the start button (lever at full throttle) while spraying WD40 continuously into the air intake as I described in my other post. If it's spinning slowly it'll likely still compress enough to fire, and if it fire's I'll start. If it starts with WD40 and continues to run after you stop spraying then everything is fine with you engine except your starter wiring. The WD40 starting test can teach you a lot about what's wrong.

Happy cranking and let us know how it turns out!

MedSailor
 

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waves from across the pond ...Hey there Sailingking, I am on Escambia Bay East bank, I have a ysm12 too! Fighting with mine since the day I got it, but it is still a labor of love. First it was the "golden" water pump, jimmy rigged it to work for now, next. I have all the fuel lines and filter assemblies in my hand, trying to clean out the black gunk. This will be followed by either removing the fuel tank or figuring out a way to pump and flush the old nasty diesel out of it. My YSM12 is mounted in a 1980 AMF Paceship, how about you?
 

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You might want to check the voltage at the starter while cranking.. probably well below 12.7 volts you're getting now. - a smoking wire is a pretty obvious place to start.

Knowing what boat might help someone familiar with that model to suggest wiring mods or updates. For example in many cases the long run from the batteries to the panel to the engine can cause unacceptable voltage drops.. adding a solenoid/relay to the system to take battery power direct (short run) to the starter can make a huge difference.
 

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Sailingking, I only just saw your post. I hope I am not too late to help. Now, no one can do a decent job of troubleshooting without references. So here is a Yanmar YSM 12 parts and specifications manual. There are a bunch of variations of this motor, but I doubt there are many differences electrically.

Faster is probably right. It sounds like you have 12.7V unloaded at the starter. I'd check the voltage across the starter while starting. I'd also look at the difference in voltage at the batteries while starting (i.e. while loaded). If the batteries are shot, that loaded voltage while starting will drop way down at both points. If you have wiring problems, it will drop at the starter but not at the batteries.

Now, I'm going to make a guess. Look at page 11-2 in the manual. It shows a wire from the starter back to your battery's negative terminal. If my guess is correct, that wire is your problem. Since the little black wire is smoking, I am wondering if it is trying to carry the current that should be carried by the big, low-resistance wire from your starter back to your battery.

Also, the manual notes that the total resistance of wires 1, 2, and 3 can be no more than 0.002 ohms. That means the red wire from the positive terminal of your battery to your battery switch, the red wire from the battery switch to the starter solenoid, and the black wire from the starter back to the negative terminal of your battery must all be huge, at least as big as the wires on your car battery. If they are not you have the wrong wires.

Since you need all the power consumed by the starter and none by the wiring, you want no big voltage drops along the wiring while you are starting. In other words, almost all the loaded voltage drop should be across the starter.

In case my guess is wrong, I want also to present some general techniques.

1) Make sure each wire is good with no corrosion and no internal breaks. Take it out and measure its resistance. If you see a milliohm or two, it is OK. Any big thick wires with more than that should be replaced. All wire ends need connectors.

2) Examine the connection posts (or whatever) and the connectors at the ends of the wire. There should no dirt, oil, or corrosion. When you connect them at a connection post (or whatever kind of connection it is), all connections should be clean and tight.

3) If you still can't find the problem, measure voltages from connector to to connector while starting to see where the problem lies. Start with the battery to your switch, across the switch, from the switch to the solenoid, and starter to battery. All voltage measurements while starting should remain small (except across the starter). If you find a big one, you have found your problem.

Hope this helps!

Tom
 

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Basically it can one of three reasons: weak battery, bad starter, or bad wiring. Based on what you've said, it sounds like the last. No way a 12 guage wire can carry the starting current.
 

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Basically it can one of three reasons: weak battery, bad starter, or bad wiring. Based on what you've said, it sounds like the last. No way a 12 guage wire can carry the starting current.
Nice summary! There's the occasional simple physical component that goes bad too -- the battery switch, for instance -- but it is far rarer than those three.
 

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Discussion Starter #8
Thanks everyone for the great advice. The latest update is....."It Starts!!!" The problem in this situation was the negative cable had been severed nearly in half under the battery bank. DaCap06 & MedSailor nailed it. Unfortunately, It was the last of the major wiring I pulled out to inspect and replace. It looked good on both ends but not until i pulled everything out to check did I find this issue. I had been in some big waves and the crashing must have caused the 3 battery bank bracket to come loose and slowly chop away at this wire over night while anchored in some pretty big surf. This was the last time it had started. Coupled with the starter coming loose and breaking it was multi phased issue as the starter had to be rebuilt...but all along the wiring had failed too. Amazingly, as JimCals said all the smaller wiring was still carrying the load on the negative end allowing for the starter to spin....but not fast. It actually appeared about 3 different 12 guage wires on the negative end were carrying the load....and one was smoking once the new starter was installed (tell tell sign). Amazing they could even carry that much load. Over the past two months I have become an expert at keeping the batteries maxed with no motor running (solar system and generator along with switching to all LED Navigation lights). Now that she runs again....and suprisingly well for sitting so long I've got to get the ship cleaned up. As before, the engine revs much higher with no load and probably only hits 2800rpm or so with the prop in gear which is still good for right at 4mph. It does seem like the max rpm drops as the engine warms up...I ran it about 4 hours today. I probably need a new impeller to maximize my cooling effect and the mixing elbow clogged in the past....probably will clog in the future. I've heard some forums where they do something to fix this clogging issue. Thanks so much for everyones help as we're up and running again!
 

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Fantastic! :D:D:D There's nothing like the sound of the ba$ard finally springing to life after a long bout of engine work.

Working in medicine, especially the last couple of years where I was treating really sick people in the hospital I have to say that the multi-factoral problem, ie where two separate things fail at the same time, is a problem exponentially more difficult to solve than your standard issue. Kudos for being able figure it out and fix the problem!

Now that you know she's running, see if you can hand crank her. ;) I'll give you a hint, start the engine with the battery first, run her for 20mins, then shut her down. That's the right time to practice hand cranking. After you've done that a few times, you can graduate to doing it with a heater warmed engine, and WD-40. ;) After that, you'll be able to start her anytime.

MedSailor
 

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Still interested in hand starting? Some say "practice makes perfect" but I say practice makes muscles! :D
 

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Glad that you got the electrical problem corrected. The YSM12 can be hand cranked "fairly easily". My previous boat had a YSM12. I used an extendable boat hook to hold the decompression lever open by wedging the boat hook between the lever and the galley (just make sure that if the boat hook were to slip, it cannot get into the running gear). Then with both hands on the crank, crank like crazy. When you get it turning as fast as you can, pull the crank and boat hook away. The decompression lever closes and with any luck at all, the engine will fire up. If it doesn't start the first time, repeat the process, until it does (if it's cold, it seems harder than in warm weather). Good to be able to do it in case your electrical system drops you again at an inconvenient location.
 

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Discussion Starter #12
I tried to hand crank, but can't even turn it with compression chambers closed. The electric starter powers right through them closed to get it going. I can spin it pretty good open but I think my problem lies with my hand crank. I am using an old car hand crank that I cut to fit the bracket on the Yanmar. It is not a real snug fit and slides off. Not to mention it almost rubs the alternator pulley on every other rotation. I bought a Yanmar handcrank off eBay for $29 but low and behold the inner diameter is about .5" too small to slide over my mount. I do like the WD-40 trick though!
 

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I tried to hand crank, but can't even turn it with compression chambers closed. The electric starter powers right through them closed to get it going. I can spin it pretty good open but I think my problem lies with my hand crank. I am using an old car hand crank that I cut to fit the bracket on the Yanmar. It is not a real snug fit and slides off. Not to mention it almost rubs the alternator pulley on every other rotation. I bought a Yanmar handcrank off eBay for $29 but low and behold the inner diameter is about .5" too small to slide over my mount. I do like the WD-40 trick though!
Nobody, not even the incredible hulk can spin the engine with the compression levers closed!

The procedure is to have them open, then spinspinspinspinspin until you have a good head of rotational steam and then you quickly slam the levers closed. Only the momentum of the quickly spinning flywheel that you have gotten going with open levers will allow it to have the compression force you need once you slam them closed.

If I ever get access to another hand crank engine I'm going to make a YouTube video for the world.

EDIT: There already ARE YouTube videos on the subject! Note in this video his left hand is on the decompression lever. He gets it going and then releases the lever. On you Yanmar you'll have to get it going at least twice as fast as this, and like in the video it might take several tries, but each try will put lots of heat into the cylinder wall which is one of the main barriers to starting.

Again, try hand cranking after you've run the engine for 20min and shut her down. With the levers open, a good very fast spin going and suddenly closed decompression levers she should start right up!


MedSailor
 
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