Faulty Solenoid

[electrokid]

Ooh, fight!

I'll clarify - I can't see how if the earthing strap is the problem, why it would be intermittent. If it turns over well 9 times out of 10, that (to me) proves the fundamental fixed part of the circuit is OK. Hopefully you can understand my logic even if you disagree...

Leeks at thirty paces then should be safe enough

If the earthing strap is high resistance then the starter motor is earthed through the engine / through anything that connects with very low resistance to the bodyshell and hence back to the -ve of the battery via the -ve bodyshell connection. On the BX that's likely to be transmission components - CV joints / driveshafts / front suspension components so it depends where these components end up as to whether you get a good enough connection or not - remember we are possibly trying to get 60 - 200 amps through there so bearing surfaces 'just touching' isn't always going to do the job.

On the Granada the situation is much worse because the engine is almost completely isolated from the bodyshell because the transmission includes a giubo joint...

http://en.wikipedia.org/wiki/Giubo

which can, and I speak from experience, really screw up your day when looking for starting problems and the engine earth strap is flakey.

I'm not sure either way whether you can hear the starter solenoid operating from the driver's seat,

Oh yes - it's quite loud - and if you can hear it obviously something 'downstream' is missing - either the solenoid isn't providing volts to the starter or the starter is O/C.

Probably the reason I suggested it is that I'm having the same problem at the moment!

My suggestion is the same as for Tim - first check that the earth to engine is solid - it needs to drop next to no volts at big amps so it needs not to be frayed and it's nuts should be tight as b**gery.

Then whip the starter motor off - there's usually a flap that can be removed to eyeball the brushes - the amount of wear on the brushgear will give a good indication of the amount of wear potentially left in the other starter components - ie: solenoid and solenoid contacts. If the brushes look ok then the problem is likely to be elsewhere - but I'll bet they are about done-in and it's time for a new starter motor. Or you might be able to get to the flap without removing the motor - depends on which one is fitted.

Diesel starters spin SLOWER but with more torque, i assume due to windings,

I thought it was an epicyclic gearbox with around a 3:1 ratio ?

The old fat starters are archaic technology,

Indeed they are - modern ones have no field coil relying on ceramic permanent magnets instead. The downside is - if you have a problem with this type of starter then giving it a good bash, which is a fairly normal procedure, can easily break chunks of the magnets which will turn it into scrap straightaway.

try bashing the starter body whilst someone turns the key to the starter position,

is fine on the original starter motor.

[mat_fenwick]

CV joints / driveshafts / front suspension components so it depends where these components end up as to whether you get a good enough connection or not

OK - point (grudgingly ) taken!

In my case though, the earthing lead is only a couple of months old, made from 35mm sq cable I had left over from a winch installation, new terminals too. The starter motor was a brand new Bosch unit that's only been on 40k miles, so unlikely to be at fault although I accept that newness is no guarantee. Battery is also only 2 months old, and I cleaned up all the terminals in the multiway connector above the gearbox recently too after problems with the reversing lights.

When I remember I'll rig up a voltmeter across the ignition switch, to see if next time the problem occurs there is a larger than normal voltage drop.

[electrokid]

Hmmm - you do seem to have covered all the bases there - I'm assuming the cable you used is copper - if it had been steel then the resistivity is 8.5 times that of copper so 35mm steel = 4mm copper. Or if it was stainless that's 41 times more resistive than copper 35mm stainless = less than 1mm copper.

The only other thing I've had cause intermittent starter motor is grubbiness in the solenoid making it sticky and sometimes not travelling far enough to hit the contacts - that was a pre-engage jobby though so more for the solenoid to do. Where such muck is the problem it will be less inclined to start when the engine (and therefore the solenoid itself) is warm because it's higher up the curie curve - higher temp - less magnetic field for the same applied volts.

[citronut]

try bashing the starter body whilst someone turns the key to the starter position,

is fine on the original starter motor.

have i missed somthing here

not the first time


regards malcolm

[mat_fenwick]

The only other thing I've had cause intermittent starter motor is grubbiness in the solenoid...it will be less inclined to start when the engine (and therefore the solenoid itself) is warm

Ah, you might be onto something there! I can't recall the problem happening with the engine cold, or straight after a run (where the moving air would keep the engine bay temperature down). IIRC it's been after a run and then left for half an hour or so, so heat soak could be a factor. I did once spill oil onto the starter area during a change, which would attract dust if it got into the solenoid.

That said, there is no noise from under the bonnet whatsoever so no evidence that the solenoid is moving at all. The wiring is copper!

[electrokid]

have i missed somthing here

Having someone give the starter motor a bash while you turn the key is a normal way to get a dodgy motor to run.

However, some modern starter motors have ceramic (ferrite) permanent magnets instead of the field coils - if you bash those then it's very easy to break one or more of the ceramic magnets and for the pieces to fall into the motor and stick between the rotor and the motor body thus jamming the whole shebang permanently.

But then you were going to change the starter motor anyway - right ?

which would attract dust if it got into the solenoid.

That's pretty much what I found in the solenoid that gave me that problem (it was on my 2 litre Granada) - just a small amount of black dust held in place by a thin film of oil. And it was worse after a run then left standing for a short while. Quite a few times I went back into the shop I'd just visited to but a bottle of water from the chiller to pour over the solenoid - and once when it happened outside Wickes and there was no chilled water - I bought a new hammer to bash the thing to try and unstick it.

If you strip the solenoid out to give it a clean, and if it's constructed the same way as mine was, you could find that one of the connections to the solenoid coil goes through the starter motor body and is soldered to a connection inside. If you remove the solenoid housing you may find it still attached to the starter motor body by this skinny wire which is easily broken.

IIRC there was no noise from under the bonnet (when it failed) - which is logical - it's going to be harder to start the solenoid moving because that's the time when the magnetic poles are furthest apart, and if it doesn't begin to move it aint gonna 'click'.

That's your weekend sorted then

[citronut]

have i missed somthing here

However, some modern starter motors have ceramic (ferrite) permanent magnets instead of the field coils - if you bash those then it's very easy to break one or more of the ceramic magnets and for the pieces to fall into the motor and stick between the rotor and the motor body thus jamming the whole shebang permanently.

i aint seen that type on a BX yet Brian,
and it doesent require to heavy a bash to jar the brush's anyhow if there going to that is,

this thread seems to be getting far to complex for what is more than likely a simple/slandered starter fault

Tim is going to get all


regards malcolm

[Tim Leech]

Im lost with all this technical babble, I will just buy a new starter I think!

[electrokid]

Check the earth straps first Tim - the terminals will be bolted to bodywork / engine - no point in forking out for a new starter if it's just a loose bolt or two.

If the earths are ok then remove the starter motor and inspect the brushes - if they are worn out (quite likely) then it's time to replace the starter motor.

i aint seen that type on a BX yet Brian,

They won't be original equipment - only if it's been replaced Malcolm. Mine is a replacement and has the ceramic magnets.

[Tim Leech]

Will do Brian thanks.