Technical Starter motor test

[Ralf S.]

My sister's Renoort Megane isn't cranking over. Apart from it's not a Fiat, or a 500... I think the problem is a generic "starter motor" one that the combined wisdom of the FF Oracle can help me with.

I've had a look into it.... There is power at the starter motor, and the little exciter circuit also goes "live", while I turn the key to the "MAR" position... so it looks like the car is trying to do it's thing. I suspect it's the starter solenoid itself that is dead.

I've removed the starter (fun!) and hooked it up directly to my spare battery.

Positive on the battery is connected to the positive post on the starter.
Negative on the battery is connected to the body/frame of the starter (the starter normally earths through the engine block)

There is no current in this "circuit" .. which I guess is normal when the starter is inactive.

If I then also connect the Positive on the battery to the exciter tab on the starter, nothing happens.
I would expect the solenoid to activate and the starter to spin, so unless I don't know how it works, I presume that this is conclusive that something in the starter is knackered.

I don't have a "good" starter to compare the old one with, unfortunately... so before I order a new part, it would be handy to know if I'm right or I missed something..

Ta.


Ralf S.

 

[John202020]

Sounds bust, manually turn the starter cog(to turn the motor) a bit then try again, if it works then its still bust but with a dead sector.

 

[portland_bill]

Starter seems dead.
You've made the right connections. Main battery power to the large terminal, earth to the body of the starter.
When battery voltage is applied to the small terminal, the solenoid should move, pushing the pinion out, to engage with the flywheel. When the solenoid gets to full travel, it makes a big contact inside, that then puts the full battery voltage, from the fat wire, through the motor.
Solenoid could be dead.
Pinion could be tight on its shaft, but I would still expect the solenoid to try to move it. Freeing it off is probably little use, as the solenoid may well be fried from trying.
It is difficult to get replacement solenoids, and they're a pain to fit. Get a complete new starter. Or a replacement car.

 

[Ralf S.]

Starter seems dead.
You've made the right connections. Main battery power to the large terminal, earth to the body of the starter.
When battery voltage is applied to the small terminal, the solenoid should move, pushing the pinion out, to engage with the flywheel. When the solenoid gets to full travel, it makes a big contact inside, that then puts the full battery voltage, from the fat wire, through the motor.
Solenoid could be dead.
Pinion could be tight on its shaft, but I would still expect the solenoid to try to move it. Freeing it off is probably little use, as the solenoid may well be fried from trying.
It is difficult to get replacement solenoids, and they're a pain to fit. Get a complete new starter. Or a replacement car.

Thanks Bill.. that's what I was hoping.

There was a bit of "green" corrosion on the female connector to the starter motor tab.. but my hopes that it was just a dirty connection were soon dashed..

The Renault FR7 engine has the exhaust manifold at the back with the inlet at the front. It's neat, since the exhaust doesn't have to pass under the sump .. it disappears straight out under the bulkhead, so the engine is lower and can also be mounted lower. I can see the "pro's" of the arrangement.

The starter is in the usual place (so between the engine block and the exhaust manifold) protected by a cover. This makes it a proper PITA to remove... but keeps it nice and isolated from dirt, dust and moisture. I just wonder if it gets just a bit hotter than it would in a more conventional layout.. but anyway, it's lasted 20+ years (the starter is made by Bosch) so can't complain too much.


Ralf S.

 

[Gina500]

While you experiment on the bench, make sure the starter is well fastened. Otherwise the momentum will make it jump (most likely off the bench…)
I agree on the diagnoses above. And starters are not that expensive normally, so unless some greasing of the solenoid mechanics helps, it is better to get a replacement.