Yanmar B12 mini digger starter issue.

[Baldbloke]

Any advice much appreciated here. Little digger’s been a faithful and reliable starter over the last 12 years but after an attempt at a hot start yesterday wouldn’t even try to engage the solenoid dog let alone operate starter.

The starter is at the back of the block so very tricky access.

Gave the side of the motor a couple of taps for no result.

The wiring is strange as the low amp feed that you normally see going to the solenoid appears to enter the actual starter motor. I took a voltage reading off that feed wire where it enters the starter motor with ignition on and while on start position. 2.65V and zero while in crank position. Seems low but I’m an ignoramous on electrics. No power to the big thick lead that cranks/powers the actual motor. The wiring has multiple connections and some of it I cannot access.

Since the motor was operating without fault until that moment am I right in thinking it’s perhaps the ignition switch that’s wanked out, or, could it be an issue with the feed wire that I suspect eventually leads to the solenoid in a convoluted way?

[doobin]

Yeah, no power going to the start wire. Start with the switch and work back from there, assuming battery voltage normal. 
 

althoygh that big thick wire should be connected directly to battery so should read the same as the battery voltage. Check battery voltage. Check battery terminals. Check earth terminals.

Edited April 17, 2021 by doobin

[dig-dug-dan]

1 hour ago, doobin said:

Yeah, no power going to the start wire. Start with the switch and work back from there, assuming battery voltage normal. 
 

althoygh that big thick wire should be connected directly to battery so should read the same as the battery voltage. Check battery voltage. Check battery terminals. Check earth terminals.

Had a similar issue with the kubota. Working loom had got corroded giving a bad earth. Try earthing out the starter and check neg on battery terminal

[Baldbloke]

Yeah, no power going to the start wire. Start with the switch and work back from there, assuming battery voltage normal. 

 

althoygh that big thick wire should be connected directly to battery so should read the same as the battery voltage. Check battery voltage. Check battery terminals. Check earth terminals.

 

[emoji1303]Thanks for the reply.

Battery voltage @12.7V

Earth straps ( there’s one connecting the frame to the engine block immediately beside the starter motor) and connections at battery all checked and good.

I’m assuming that the bigger positive feed to the starter will remain dead until the correct 12V signal from the fine wire that feeds the solenoid is activated, and then they work in conjunction?

 

I can’t find a new 5 pole ignition original switch, but I can find plenty of 6 pole ones. I think I’ll order a new one anyway and once I’ve figured out how to wire it in leave one pole unused.

Edit: I’ve just found a 5 pole one[emoji1303]

[Baldbloke]

Had a similar issue with the kubota. Working loom had got corroded giving a bad earth. Try earthing out the starter and check neg on battery terminal

I’m sure your on the right track, as any time I’ve had vehicles with mechanical starter issues the problem gets worse over time rather than suddenly going from good to zero.
The 2 earth straps I’ve seen are in good order and their connections sound and un-corroded due to the general oiliness🤣

[doobin]

17 minutes ago, Baldbloke said:

 

Thanks for the reply.
Battery voltage @12.7V
Earth straps ( there’s one connecting the frame to the engine block immediately beside the starter motor) and connections at battery all checked and good.
I’m assuming that the bigger positive feed to the starter will remain dead until the correct 12V signal from the fine wire that feeds the solenoid is activated, and then they work in conjunction?

I can’t find a new 5 pole ignition original switch, but I can find plenty of 6 pole ones. I think I’ll order a new one anyway and once I’ve figured out how to wire it in leave one pole unused.

 

No, the thick positive wire is connected directly to the battery and therefore live all the time.  The solenoid connects it to the starter when you turn the key to start. The starter earths back through the chassis so the chassis to earth terminal strap needs to be good also. 
 

if you are sure you have no voltage on the thick wire then that’s your problem. Check the battery terminals again, take apart the ring terminals that are bolted on to the battery terminal itself and polish them back to copper. 

Edited April 17, 2021 by doobin

[woody paul]

As Doobin has said. But earth leads may look good but unbolt them and clean up metal to get good contact. if battery terminal has screws holding in cable check them as well.

[topchippyles]

I had a problem back last year on my B15 yanmar and i put a long jump lead from the battery to the starter and she turned over. Faulty wiring on the live terminal 

[Baldbloke]

Thanks for all the useful replies[emoji1303]. Think the switch may be my problem as battery terminals double checked as was connection to starter. Off working on the Out of Hours job today, but will return to it tomorrow and report back on (hopefully) successful conclusion.

[dig-dug-dan]

11 hours ago, Baldbloke said:

I’m sure your on the right track, as any time I’ve had vehicles with mechanical starter issues the problem gets worse over time rather than suddenly going from good to zero.
The 2 earth straps I’ve seen are in good order and their connections sound and un-corroded due to the general oiliness🤣

The problem could be in the loom from the ignition switch. Mine was discovered under the footplate!