Decompression lever on Yanmar 1GM10

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david100952

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I cant find any other references to this problem so am posting a new thread. My 1GM starts immediately and faultlessly in all but freezing conditions but every once in a while the first press of the starter button results in a click from the starter motor but the engine does not turn over. I have replaced the alternator and installed a battery with higher "cold cranking power" but there is still the odd occasion when this occurs. I note there is what appears to be a compression release lever on the top of the motor and wonder if the problem is just that the piston has just come to rest at a high compression point in the cycle and would benefit from dumping the compression rather than just "clicking away" as I have done thus far. This motor was fitted in 1991 and the boat was then sold to a Caterpillar Diesel mechanic so it has the best of care for the last 20 years - it has never let me down.
 
Sounds more like you have an earthing problem. Check all wiring between switch and earth strap to engine if this has not already been done.

Regards

Donald
 
Nope - it's the infamous Yanmar electrical loom problem :)

The exact mechanism by which it causes these symptoms (ie, why the click and then a successful start) was still under debate the last time it came up, but the practical way to fix it is to go over all the wiring on the engine and make sure all the connections are clean and tight. In particular, there is a small fuseholder tucked away which most people aren't even aware of; this is the usual culprit. Clean it up, including sanding any corrosion off the contacts, and the engine should become much more reliable.

Pete
 
Very sensitive to poor and dirty connections, including the often forgotten fuse in the wiring loom. The starter switch itself can also be unpredictable. What you are experiencing is quite common and usually fixed by cleaning all the connections. Don't think it is anything to do with the decompressor as all this does is lift a valve open when you operate it. Useful in cold weather to turn the engine over for a short time with the valve open, then shut it. Makes starting a bit easier.
 
Another suspect is a worn flywheel ring gear. Single cylinder engines always stop in roughly the same position, so the starter motor gear is always trying to engage with the same few ring gear teeth which get worn. If the gear doesn't engage the motor is never energised, though it may shift the ring gear just enough that the next attempt works. Or the next. Or the next.

Beefing up the electrical supply to my engine has reduced the problem from every cold start to one in five, but it's still there.
 
Could be several things.
1) battery volts. Is the battery properly charged? Measure it!
2) Starter motor faults. Does the motor draw a large current? It could have an armature fault, either open or short on one pole. so it may not generate the necessary torque when stalled at a particular angle.
3) Wiring. When the motor clicks and stalls, does it drag the battery volts down by pulling a big current, or is there a big drop across the wiring?
4) Start solenoid contacts. When the motor is switched on, the solenoid pulls in, making that 'click' but does it actually switch current to the armature?. If not, it could be the contacts, or something is jamming preventing the solenoid from engaging the starter gear and moving far enough to fire the contacts.

You could try touching something across from the +ve supply lead to the solenoid +ve coil terminal and see if it cranks harder.
You can also try shorting solenoid contacts with a stout old screwdriver or similar (it will get a little burned!), this bypasses the contacts.

Check the motor is getting good volts first.
 
You can use the screwdriver trick to confirm the diagnoses too. touch the small 'd' tag on the starter solenoid to the battery plus terminal adjacent.

BTW, Pete and all; my push button sometimes needs a couple of presses, no clicks though, just a tired button.

So on Saturday coming back into Hartlepool when I got NO response I was reaching for the screwdriver, thinking what I needed to get off the berth to get to the starter when SWMBO suggested it would work better with the ignition turned on...
 
I had a 1 GM10 for 12 years and went through this problem very intermittently.
I replaced the engine fuse and holder with a really good quality flat style, bolt in fuse and holder. It made no difference, the engine would crank quickly enough after a few presses of the button. (I am not convinced that the starter even clicked) I now have a different boat with a 2GM20f the engine is 13 years newer but still has the same fault ! (I have also replaced the fuse holder and fuse on this engine)
Last Sat the engine started after being dormant for 3 weeks, at the first press of the button but on Sun I had to press the button around 3 times to get a response. Unfortunately when it does not crank I usually don't have time to look into it, both of these engines are in very dry boats and look almost like new?????
 
Thanks for all the replies so far. Just for the benefit of any future readers of this thread, I completely replaced the fuse panel and added a VSR (BEP cluster), battery leads and cabin wiring over the last few years so I am confident there is no drain in that sector but the wiring loom is original ( although the push start button is new). The starter was rebuilt professionally also. When battery is charged ashore it relieves the problem for a few weeks so it is likely that the charge level IS DROPPING however the alternator is new so the wiring harness/connections look like the most likely culprit. I will make this my new focus. Thanks again
David
 
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