How to hand crank start a Yanmar 2GM20

Re: You have just described.....

Actually it's turning the alternator to no load when it's running that knackers it. Starting with the exciter circuit disconnected (by a switch, by not switching the batteries on) won't harm it. I admit, though, that you need to be sure what you're doing.
 
Often, when I'd contrived to flatten my batteries to the point where they wouldn't turn the engine over normally, I would decompress my 3GM30F and it would spin and start when the first lever was dropped.
The workshop manual shows how you can fit two bolts into the flywheel and then use a bar or winch handle to hand crank with decompression levers engaged but I never needed to try it, fortunately.
I often wondered if it would be possible to start the engine by sailing with the prop engaged and the decompression levers engaged, dropping them when the engine was spinning nicely. Never tried that either, but several people have told me they have done it.
 
Re: How come....

Virtually brand new - first season when the boat had only one battery - soon remedied! however, I was fitter then!

Steve Cronin
 
Re: Please....

spin an alternator when it's connected to nothing and you get

no load=no excitation=no charge=no knackered diodes (even though there is no load)

however spin an alternator when it's connected to a load and you get

load+excitation=charge in circuit=knackered diodes if load is removed when alternator is turning
 
I agree with early bird - it's a subtle combination of impossible and dangerous. I think the starting handle is supplied for only two reasons - to enable you to find TDC for the winter lay up and to tease you into trying to start the engine.

An even more exciting option is to think of it as motor bike and set the handle at the right angle to jump on it. This does not of course start the engine but a broken ankle makes a change from a dislocated thumb.
 
Re: Please....

What actually kills the diodes is a voltage spike induced by sudden rapid change in current. It is exactly the effect that causes the spark in an ignition coil.

When the battery is connected you get a current, when it is not connected there is no current. Neither of these states are damaging, it is the rapid change between the two that causes the problem. It's just like jumping out of a plane really - falling through the air is not dangerous. Lying on the ground is not dangerous. The rapid change between the two states is usually fatal.
 
[ QUOTE ]
Often, when I'd contrived to flatten my batteries to the point where they wouldn't turn the engine over normally, I would decompress my 3GM30F and it would spin and start when the first lever was dropped.
The workshop manual shows how you can fit two bolts into the flywheel and then use a bar or winch handle to hand crank with decompression levers engaged but I never needed to try it, fortunately.
I often wondered if it would be possible to start the engine by sailing with the prop engaged and the decompression levers engaged, dropping them when the engine was spinning nicely. Never tried that either, but several people have told me they have done it.

[/ QUOTE ]


I managed to start a Yanmar 3GMF with a flattish battery by engaging forward gear and surfing down a wave at the same time pressing the starter button, it was just enough to "bump start" it into life
 
French marine sell a pulley to go on the front of the engine. Then you can lift the valve er... lifter and spin the pulley with a bit of cord, like an outboard. It only takes a little bit of movement to start an engine with good compression.
 
Re: Please....

Since, there is always a load in most modern yacht circuits due to the rev counter, fuel guage, temperature guage etc. being powered from the "ignition" switch, just disconnecting the battery and making sure that all the domestic circuits are dis-connected won't protect the alternator. You would need to physically disconnect the outputs from the alternator as well as the battery to completely isolate it. This would hardly be much help in the flat battery scenario unless you intended to carry on motoring back to base and shorepower before attempting to resume charging.

When we managed to hand start our 20 I didn't disconnect the alternator nor the battery. I do not deny though that it took a supreme effort but having done it some years earlier on a 25hp Volvo in a Centaur in Cherbourg marina, I had some idea of what I (we) were in for. I (with the help of a young and fit harbour attendant at Ryde IoW) had the further incentive of getting out of a tidal berth before it was too late. However, that Yanmar normally always started after only half a revolution of the crankshaft so I knew that I just had to get it over one compression to succeed. The Volvo was also quite new but it took several attempts by myself and our neighbour, four hands on the handle to persuade it into life.

Steve Cronin
 
Re: Please....

You're right there is always some sort of load, but if you put a switch in the excitation wire from the so-called 'ignition switch' you can isolate the alternator from it. That way when starting a small Yanmar with a big alternator like mine you can discount the alternator. I can start my 1gm10 by hand and would expect to able to do so easily up abt 15 hp... above that, good luck with it!
 
Would it be worth undoing the alternator fixing bolt and swinging it inwards to slacken the belt? During the time I've owned it my engine has been out of the boat in pieces longer than it's been in it, so my memory of the layout is hazy - would attempting to tighten it up again with the engine running be suicidal in the finger department?

If it could be done it'd be a good way to get some load off the engine; same with the water pump in theory.

Pete
 
eebygum said:
Does anybody know how you hand crank start a Yanmar 2 GM20 ?

I know you need to switch the water cock off (until started) but what else ? I seem to remember you raise the compression levers but now sure what you do next.

The reason for the question is ..... we were heading off to Ireland at the weekend from Anglesey and decided to turn around half way and head for Holyhead in the rising SW F6-7. About 8 miles from Holyhead we noticed a voltage drop on the instruments and decided to start the engine .... no joy the starter battery was also drained (loose alternator belt and poor connections proved to be the problem).... I spent a very unpleasent 20 minutes down below leafing through the engine service manual trying to find the cranking instructions but could find nothing ! Fortunately the wind vane was wizzing around in 24-28 knots and after an hour had put enough charge back into the batteries to get started.

I promised myself when I got back that I would find out how to start the engine by hand cranking !

Thanks in advance.

Cheers
Andrew
Click to expand...


Andrew,

Honestly, you do not want to handcrank - your back will telll you about it for weeks afterwards. Like you I had a slipping fanbelt - your first target should be to tighten the fanbelt so that your alternator charges adequately. Also upsize your battery bank if this problem re-occurs. It should not happen - great you were able to sail out of the situation, but the long term solution is not in handcranking.
 
Just realised what an ancient thread I've dragged up - I had some tabs open with current threads for general reading and replying, and some tabs with other pages for general research (including a few old posts to this forum and others). Guess I got the two sets mixed up.

Pete
 
Oh am I am enjoying all this. My Centaur still has the original Volvo but I have never ever managed to hand start it, even when it was almost new.

Any way, the story I want to tell is from way back when I was a lowly apprentice. We visited a light ship that was re fitting in Newcastle. The generator ran for ever once the ship was on station. It had an air starter however, it was provided with a hand starter too. A rope was wound round the flywheel which several fit folk pulled and, well, the rest is academic.

On the occasion of our visit the hand starting was being “tested”. Of course it all went wrong or I would not have a story to tell. Just as tdc approached whoever was on the de compressor miss timed their activity and the engine started backwards. I have never seen so many people evacuate a generator room as fast. Luckily someone turned the fuel off while someone else set the fire system off, flooding the room, and engine air intake, with halon gas. Or was it CO2?

Once the excitement has settled we were told that the over speed regulation did not work backwards, the engine would have “exploded”, well, damaged its self.

73s de
johnth
 
steve_cronin said:
... a classic "How to destroy your Alternator" scenario.

Any idea as to why your boat has a little plaque stating "Do NOT run engine with batteries dis-connected"?

Running it until operating temperature is reached should do fine.

Steve Cronin
Click to expand...

Because he forgot to mention that the ignition switch was in the OFF position, Ive seen him do it.
 
Killing alternators

I'm not sure that the (electrical) drag of an alternator makes much difference until the engine is running.
I've spun up few alternators to test them with an electric drill, I would think the engine would be running and developing power by the time the alternator imposes much load, ASSUMING the engine is working well.
I do know that some alternators (maybe not all) can develop damaging voltage levels under no load conditions, with no load and no excitation current, given say half revs. There is enough residual magnetism in the rotor to do this. Maybe not all alts, but definitely some.

So I would never start without a battery loading the alternator.
However, leaving the 'ignition' switch off until the engine is running, will at least delay the load coming onto the engine. Provided of course there is no electric fuel cut off etc.
In which case, take the charging light bulb out until the engine is running.

Personally, I've never succeeded to hand start either 1GM or 3GMF that I had, but being able to operate the decompressors to start has saved me embarassment a few times.
 
I started a 1GM10 by hand once. I tried lots of times from cold, but never could keep it turning after the decompression lever went down. So one day I tried it warm, just out of curiosity. It bounced back as usual when the compression came on.

The cabin doesn't half fill with smoke quickly when the engine's running backwards.
 
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