Engine not starting - advice urgently needed

[awol]

I finally got round to applying power to my old 2GMF starter to see what happened. The answer suprised me. The opposing views were a) shorting the 2 studs without the solenoid activation terminal makes the starter work; and b) shorting the studs only causes the motor to spin and cannot engage the starter cog. What actually happens is that on shorting the studs the motor spins and the inertia of the cog causes it to be thrown forward spinning. Without the solenoid activating the cog returns while the motor spins. As I know the stud shorting caused my donk to start I postulate that inertia causes the cog to engage, the load on the teeth while the starter motor is energised is enough to keep it engaged until power is removed and the cog disengages. Now for cold fusion ............

 

[ducked]

I finally got round to applying power to my old 2GMF starter to see what happened. The answer suprised me. The opposing views were a) shorting the 2 studs without the solenoid activation terminal makes the starter work; and b) shorting the studs only causes the motor to spin and cannot engage the starter cog. What actually happens is that on shorting the studs the motor spins and the inertia of the cog causes it to be thrown forward spinning. Without the solenoid activating the cog returns while the motor spins. As I know the stud shorting caused my donk to start I postulate that inertia causes the cog to engage, the load on the teeth while the starter motor is energised is enough to keep it engaged until power is removed and the cog disengages. Now for cold fusion ............

IIRC "Inertial starter" is actually a/the recognised term, so if you worked that out from first principles and observation, good on yer.

 

[awol]

IIRC "Inertial starter" is actually a/the recognised term, so if you worked that out from first principles and observation, good on yer.

This one is designated "pre-engaged". I think you are referring to the rather older design with a "Bendix" and no engagement solenoid.

 

[billskip]

Without the solenoid activating the cog returns while the motor spins.

So if I am understanding you correctly, if the 'cog' hits the ring gear without gear meshing the engine wont start?
Edit
Ps.
Also most boat engines are at an angle, is the inertia enough to throw the 'cog' up at an angle (presuming the starter is mounted in this orientation)

 

[billskip]

This one is designated "pre-engaged". I think you are referring to the rather older design with a "Bendix" and no engagement solenoid.

Also with the "pre engaged " I always thought that the "fork" was attached to the 'cog' and physically moved the 'cog' along the shaft to engage/ disengage.
Is what you are saying the 'cog' moves without the fork? If so what disengages the 'cog' from being stuck in the ring gear?

 

[awol]

Also with the "pre engaged " I always thought that the "fork" was attached to the 'cog' and physically moved the 'cog' along the shaft to engage/ disengage.
Is what you are saying the 'cog' moves without the fork? If so what disengages the 'cog' from being stuck in the ring gear?

I have an explanation in my mind as to why shorting the studs works on this model Hitachi starter. The cog can be slid by hand agaist a light spring load on a stationary shaft and rotates slightly when it does. It is free to rotate in the same direction as the motor drives and locks in the other. Disengagement, I presume, both in normal action and with shorted studs is because of the spring after the shaft is no longer energised.
If anyone wants to bung me £100 for the motor so they can do their own study they are welcome!

 

[ducked]

This one is designated "pre-engaged". I think you are referring to the rather older design with a "Bendix" and no engagement solenoid.

I'm usually referring to older designs, since they tend to be the ones I have, or at least have heard of.

 

[vyv_cox]

Also with the "pre engaged " I always thought that the "fork" was attached to the 'cog' and physically moved the 'cog' along the shaft to engage/ disengage.

That is correct. I just checked with a spare starter motor, a Citroen one but my recollection is that Bosch are exactly the same. The starter cog moves axially, no spiral involved, and it takes a good force to move it. I was only using my penknife and did not wish to risk snapping any of the tool blades. I was unable to move it against the solenoid and lever more than a few millimetres.

 

[billskip]

I have an explanation in my mind as to why shorting the studs works on this model Hitachi starter. The cog can be slid by hand agaist a light spring load on a stationary shaft and rotates slightly when it does. It is free to rotate in the same direction as the motor drives and locks in the other. Disengagement, I presume, both in normal action and with shorted studs is because of the spring after the shaft is no longer energised.
If anyone wants to bung me £100 for the motor so they can do their own study they are welcome!

This to me indicates its an inertia design with a pre engage solenoid mechanism built on. Best of both worlds
This is not your normal bog standard pre engaged starter.

 

[Mistroma]

This to me indicates its an inertia design with a pre engage solenoid mechanism built on. Best of both worlds
This is not your normal bog standard pre engaged starter.

Seems logical. With no spiral inertia would simply cause the cog to remain stationary and not spin initially if free to rotate. I thought the usual design would have the cog splined to always spin with the motor. A slight spiral would make sense as it would aid disengagement when the engine turns faster than the cog.

 

[billskip]

Seems logical. With no spiral inertia would simply cause the cog to remain stationary and not spin initially if free to rotate. I thought the usual design would have the cog splined to always spin with the motor. A slight spiral would make sense as it would aid disengagement when the engine turns faster than the cog.

Yes, it all.points to it being an inertia type, the pinion he moves with his finger, this I don't believe (as vyv says in post #88) woud be easy.
I'm guessing, I don't think there is a mechanical "fork" connection between the solenoid and the pinion.
Still guessing, it is an inertia type with the solenoid switch mounted on the motor.

 

[Boater Sam]

Consider the influence of the hold in coil in the solenoid which is connected and engaged when the motor connection is energised by shorting the solenoid contacts.