Graham376
Well-Known Member
Yes it does, I've done it several times in the past. In the OP's case, it wouldn't of course due to the negative fault later found.
Engine not starting - advice urgently needed
- Thread starter webcraft
- Start date
Yes it does, I've done it several times in the past. In the OP's case, it wouldn't of course due to the negative fault later found.
PaulRainbow
Well-Known Member
With what engine ?
PaulRainbow
Well-Known Member
Disagree all you want and feel free to waste your time in your garage with your antique 2GM starter. The OP has a modern, pre-engaged starter and it categorically WILL NOT start by shorting the two M8 terminals on the starter solenoid.
Graham376
Well-Known Member
Several, I served apprenticeship in motor trade. My old Capri had a sticking starter and if hammer tap didn't free it, short across the terminals did.
P.S. Just remembered, did it on our last boat engine Thornycroft T80 (Mitsubishi K4D).
Boater Sam
Well-Known Member
The solenoid may pull in if the battery is well charged by just shorting the solenoid contacts because the solenoid has 2 windings, the pull in which the has spade connector, and the hold in which is connected to the starter motor connection on the solenoid. If you are lucky and the battery is really good the hold in winding may be strong enough alone to pull in the pinion and hence the solenoid contacts too.
PaulRainbow
Well-Known Member
I have also started several old engines, fitted with inertia starters, but the OP has a pre-engaged starter, shorting the battery and motor terminals on the solenoid only spins the motor, it is physically impossible to start the engine this way.
Thresher
Well-Known Member
I had exactly tha same happen to me a few years ago and now keep a hefty pair of jump leads on the boat to be used for fault finding. The fault turned out to be with the cable that ran from the starter battery to the engine block. The fault in the bad cable was not visible to the naked eye.
VicS
Well-Known Member
A couple of diagrams ( choose the monochrome one or the pretty coloured one according to your personal preference) which will explain how shorting the two main terminals might just engage the starter.
I am surprised in does though.
Mistroma
Well-Known Member
Happy days with pre-solenoid starters. They either didn't work because of no lubricant or too much, usually grease. A tap usually did it, especially if unlubricated. Sometimes you'd get an electrical fault (brushes, connection, etc.) and a tap would still get it to work.
I think at least some of the Thorneycrofts had inertial starters.
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billskip
Well-Known Member
This ^^^^^^
awol
Well-Known Member
May I suggest you actually try doing it, but do try and avoid welding the shorting devive to the studs - it makes undoing the nuts more difficult. And despite your implication, my 2GM had a pre-engaged starter, that's probably why it had a solenoid attached with terminals to short.
webcraft
Well-Known Member
And of course if the issue is a poor earth then shorting across the solenoid will do nothing . . .
awol
Well-Known Member
Stay out of this, Webby, your starting problem is sorted! A statement has been made, and doubled down on, that generations of Yanmar owners know from personal experience is erroneous.
PaulRainbow
Well-Known Member
I'd also be surprised if it does work, but it seems it sometimes does, at least with a 2GM starter.
That said, given the option of shorting the spade to the battery cable, which is sure to work (if anything will), or shorting the M8 terminals, which might occasionally work, i'm not sure why anyone would do the latter.
billskip
Well-Known Member
Shorting the M8 terminals (if it works) will result in the "dog" trying to align with the ring gear at high speed which could cause damage such as a broken tooth or excessive wear, the pre engage is an early mechanical make and a late electrical make (as you know anyways) causing least mechanical wear.
vyv_cox
Well-Known Member
If I can butt in here, Paul is correct but his statement could do with some explanation. This photo shows a pre-engaged type starter motor, a Lucas is shown but Bosch, Hitachi and many others are similar. There are two 8 mm threaded terminals, and a spade terminal at the top although this position varies. The upper terminal is connected to the positive terminal of the battery, the lower one is permanently connected to the windings of the motor. Applying a voltage to the spade terminal, or bridging this to the upper screwed terminal with a screwdriver, wire or other metal, throws the iron core of the solenoid to the left, bridging the two threaded terminals and supplying current to the motor. At the same time the iron core acts through a lever, throwing the rotor to the right, where the gear engages with the starter ring on the flywheel.
As Paul says, connecting power to the lower threaded terminal will rotate the rotor but it is not engaged with the flywheel, so the engine will not start. As we know well, bridging the spade and upper terminal, which is exactly what pressing the button or turning the key does, will start the engine.
PS: The bridging is quite crude, just a piece of copper flat bar. In some older units this can be opened up and cleaned but many modern units are sealed. Similarly, on some modern units the lower terminal is sealed inside a plastic cover.
PPS: the connection between the lower terminal and the windings is braided copper. In a wet engine bay this can corrode away. I once spent some hours berthed in Portpatrick harbour trying to effect a solder repair to one like this.
As Paul says, connecting power to the lower threaded terminal will rotate the rotor but it is not engaged with the flywheel, so the engine will not start. As we know well, bridging the spade and upper terminal, which is exactly what pressing the button or turning the key does, will start the engine.
PS: The bridging is quite crude, just a piece of copper flat bar. In some older units this can be opened up and cleaned but many modern units are sealed. Similarly, on some modern units the lower terminal is sealed inside a plastic cover.
PPS: the connection between the lower terminal and the windings is braided copper. In a wet engine bay this can corrode away. I once spent some hours berthed in Portpatrick harbour trying to effect a solder repair to one like this.
awol
Well-Known Member
Oh, what fun! Just dug out the old Hitachi starter motor from my old, but not fondly remembered, 2GM - it looks remarkably similar to Vic's picture. Using my home multi-meter there appears to be a solid connection between the stud connected to the motor and the small activating tab on the solenoid - reads 1.0 ohm on the meter which is the same as joining the probes. Of course, both are connected to the motor body via their windings but I get slightly greater resistance from both individually to the body. Could this explain why shorting the studs activates the solenoid?
Sea Change
Well-Known Member
And does shorting the studs cause any damage?
billskip
Well-Known Member
I think it can...arcing can damage the thread, high speed engagement of the pinion and ring gear can damage both or either, can cause excessive stress on bearings and casting, and risk of bending the shaft.
The pre engage puts the pinion (dog) teeth into the ring gear teath before the starter motor rotates or has any energy.
The inertia type throws the pinion (dog) into the ring gear prior the the starter motor being under full.load...
Shorting the terminals on a pre engage type puts the starter motor in full speed with a lot of energy at the same time trying to ram a pinion into the ring gear...
Yes it works but it's not designed and built fot that abuse, even less so with today's plastic gear box in some starter motors.
vyv_cox
Well-Known Member
There is no mechanism to 'ram a pinion into the ring gear'. The pinion is firmly attached to the motor rotor. The whole rotor needs to move, energised by the solenoid, before engagement can occur. Totally different from a Bendix gear, which was used successfully for almost 50 years
