Polly1
Well-Known Member
My Volvo Penta MD22L also Perkins M50 has three relays by the engine. The start key has 5 positions starting from anticlockwise, being Engine stop, Off, Instruments, Glowplugs, Starter motor engage.
To stop the engine the stop solenoid is earthed via one of the relays and positive is supplied at the same time. Hence a past attempt to stop the engine via adding live to the solenoid had no effect (it is not normally earthed). The engine will run with the key in the off position. In order for the alternator to energise and generate current the instrument light connection needs to be made.
Since owning the boat I have had a variety of electrical faults often due to bad connections. I replaced the loom connector at the engine end with direct connections (I soldered the wires together). The lack of an engine earth puzzled me for a while.
I have had the engine fail to start at sea a few times but live onto the starter solenoid has always worked and it was always down to corroded or sulphated contacts. This time I swapped two of the above relays looking for poor connections and found I could start the engine but not stop it and vice versa. One of the relays had burnt out (originally the glowplug relay), the other two energise the solenoid contact and the glowplugs. I replaced the 50A relays (4 pounds each) and saw the glowplug light on the instrument panel for the first time (it had been burnt out since I owned the boat). However the light wouldn’t go off when the engine started and the relay was getting hot again. This lead me to look for a timer or a system whereby the alternator voltage would cause the relay to switch off, but the solution was the start switch had a worn position that I had overlooked, position 3 in my list. Now I need to take care to avoid running the engine with the switch in position 4
I don’t think this is the last I will hear from my electrical system!
I also have read on a variety of forums that this engine is free wheeling or words to the effect that if the cam belt breaks the valves will not hit the pistons. After replacing the head I found this not to be the case, if you rotate the camshaft separately from the crank the valves will contact the pistons.
I hope that this will be useful to someone, the engine seems to be quite common on older boats.
To stop the engine the stop solenoid is earthed via one of the relays and positive is supplied at the same time. Hence a past attempt to stop the engine via adding live to the solenoid had no effect (it is not normally earthed). The engine will run with the key in the off position. In order for the alternator to energise and generate current the instrument light connection needs to be made.
Since owning the boat I have had a variety of electrical faults often due to bad connections. I replaced the loom connector at the engine end with direct connections (I soldered the wires together). The lack of an engine earth puzzled me for a while.
I have had the engine fail to start at sea a few times but live onto the starter solenoid has always worked and it was always down to corroded or sulphated contacts. This time I swapped two of the above relays looking for poor connections and found I could start the engine but not stop it and vice versa. One of the relays had burnt out (originally the glowplug relay), the other two energise the solenoid contact and the glowplugs. I replaced the 50A relays (4 pounds each) and saw the glowplug light on the instrument panel for the first time (it had been burnt out since I owned the boat). However the light wouldn’t go off when the engine started and the relay was getting hot again. This lead me to look for a timer or a system whereby the alternator voltage would cause the relay to switch off, but the solution was the start switch had a worn position that I had overlooked, position 3 in my list. Now I need to take care to avoid running the engine with the switch in position 4
I don’t think this is the last I will hear from my electrical system!
I also have read on a variety of forums that this engine is free wheeling or words to the effect that if the cam belt breaks the valves will not hit the pistons. After replacing the head I found this not to be the case, if you rotate the camshaft separately from the crank the valves will contact the pistons.
I hope that this will be useful to someone, the engine seems to be quite common on older boats.
