1GM10 owners take note

I accidentally connected my starter battery in reverse polarity. This led to the expense of a replacement alternator and a replacement starter battery. Afterwards the engine really struggled to start. Now resolved, here is what I learned along the way.

1) Connecting a starter battery with reverse polarity will trigger damage needing an alternator repair, ~£70, and replacement battery. There is no reverse polarity protection on the 1GM10.

2) Just Alternator and Starter Motors jasmtech.com (Botley, Hampshire) repaired mine in a few days.

3) Yanmar supply two types of alternator. The original costs a ridiculous >£600. Strangely, Yanmar also supplies a copy alternator for ~£100, they call it a 'pattern' alternator. My local Yanmar shop fitted a pattern alternator at my request. I should not have taken this step and it is disappointing that they did not know better. If you have a 1GM10, get the original repaired and avoid using a pattern alternator. Read on to learn why.

4) Before the reverse polarity mistake, the engine always started instantly from cold at idle throttle. After the incident, it just did not want to start at all, coughing and struggling at low revs, with no difference when the throttle was increased. During this time black grunge was emitted through the exhaust. After several tries, the engine would, after 30-60 seconds, pick up. After that it was completely normal all day and restarted easily when warm.

5) I searched online for 1GM10 starting problems but nothing seemed to match my symptoms. I then searched for 1GM10 alternator problems and eureka - there were my symptoms. There was even good advice on the PSSA forum that I had missed until 'alternator' was in my search.

6) 1GM10 and pattern alternator are incompatible. Uniquely on the 1GM10, Yanmar fit an alternator with a larger pulley, which therefore spins more slowly at engine startup and presents less of a load than the smaller pulley on the pattern alternator. The original alternator is rated at 35A. The pattern alternator rating is not shown. Maybe it was higher.

7) Starting engine with the pattern alternator fitted but with the belt removed quickly showed that the engine started easily and that the pattern alternator really was the problem.

8) I also learned is that it is not a good idea to slacken the alternator bolts, lean it out of the way and remove the belt and then attempt to start the engine. Unfortunately the 'bat' terminal, seemingly protected with a rubber cover, will short out on the engine and a pop and puff of smoke tells you the pattern alternator electrics are now damaged.

9) Replacing an alternator is easy. Ensure battery power is off. Slacken the three alternator bolts. Withdraw fully the top left bolt that goes through the bracket. Remove the bottom bolt holding the adjusting bolt bracket. At the back of the plug are one plastic plug, one nut fitting and one bolt fitting. The alternator is easily removed for repair and replaced when fixed.

10) While you are in the area, the engine anode is accessible so you might as well check that - another easy job. Just have a replacement gasket handy when refitting. You can see the procedure on YouTube. Annoyingly I found the old gasket had another fragment of gasket attached, not by me, which had lead to a leak and rusting. There was not enough water to gather in the engine tray but there was enough water to cause extensive rusting. It seems to me that service is best done by yourself unless you can fully trust your marine engineers.

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A joint Oops award, you and Sue!

There is a lot of this Oops business in the seals it seems.

Philip

Ken,

you are an absolute genius! Flamingo has been suffering exactly the symptoms that you describe since fitting a new starter and (pattern) 35 Amp alternator three years ago (although I did connect them the right way round). I have always attributed the problem to the starter motor or the engine and tried all sorts to fix the problem. This weekend I have removed the drive belt and hey-ho the motor starts in an instant; happy days.

My first avenue to explore is whether my very helpful electrical factors can supply a bigger pulley, I'll report back on how I get on.

If anyone has the dimensions for the correct pulley I would be most grateful.

Thanks again.

Phill

It should be given that whenever you replace an item with something new, you compare the two items to ensure that look similar, however we are all guilty of just blindly replacing an item, especially if it has come from a supposedly reputable source. A few years back, when I wanted more battery power to run my electric coolbox, I refereed to Nigel Calders excellent Boatowners Mechanical and Electrical Manual and discovered I needed to increase my Alternator to provide between 25%~33% of the rated capacity, otherwise the batteries would never get fully charged. Since I had 240 Ahrs of batteries fitted, this meant at least a 60 Amp alternator. I scouted around and found a 65 Amp one from a local scrap yard that suited my requirements and had a similar sized pulley and was also off a diesel vehicle so would be rated to run at a similar rpm to my engine, important points to bear in mind. I fitted it to my 1GM10 which I had in my boat at the time and it worked fine. I never had a problem starting and that was with only a 55Ahr starting battery, however, I do have a Merlin Smart regulator, along with a Merlin Smartbank Lite. The Smart regulator (four stage) inhibits the regulator load until the engine is running and then ramps up the charge thereby significantly reducing the starting loads. Unfortunately the amount of power the 65Amp took out of the 1GM10 meant that I could no longer get hull speed from the boat so I ended up changing the engine for a secondhand 2GM20, but thats another story, although, I still use the 55 Amp start battery and the 65Amp alternator is fitted to it and it still starts without any problem. Another snippet from Nigel Calders manual, if you try to increase your alternator to over 70Amps, you will need to either go to a twin pulley system or a multiple 'V' belt system since the loads are such, a single pulley belt will slip. This is not easy to achieve on a Yanmar 1GM10 or 2GM20 since they do not make a double pulley or multiple 'v' pulley for these engines, and whilst one could possibly drill and bolt another pulley on the front of the existing one, you would still have difficulties in trying to obtain two exactly matched V belts since they all vary slightly in length even if it is only by a mm or so and would end up with one belt slightly slacker than the other, which would aggravate the wear on one or the other. Matched belts are available but not in all sizes and they are significantly more expensive.

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