Starter motor not engaging

[David Collingbourne]

Hi Club T

I tried to start my Herald 13/60 today and the starter motor would not engage.

It whirs/spins, but doesn't turn over the engine.

The car bump-started easily, but the issue is still there with the starter motor.

Is it a replacement? Refurbishment? 

Is it easy to do, i.e. me, with very little mechanical experience?

Any help/guidance most welcome.

With kind regards

[Clive]

it is probably teh pinnion jammed by gunk. Remove the starter, and check teh pinnion slides really easily. It doesn't take much to make it stick.

A good clean in the solvent of your choice, I like brake cleaner, but white spirit, petrol, almost anything will do it. Work teh pinnion back and forward. Let it dry, ideally blowing with an airline. Then lubricate with grapite powder, if you don't have any a pencil rubbed on abrasive paper or a nailfile will make it. under no circumstances use oil or grease. 

[David Collingbourne]

2 minutes ago, Clive said:

it is probably teh pinnion jammed by gunk. Remove the starter, and check teh pinnion slides really easily. It doesn't take much to make it stick.

A good clean in the solvent of your choice, I like brake cleaner, but white spirit, petrol, almost anything will do it. Work teh pinnion back and forward. Let it dry, ideally blowing with an airline. Then lubricate with grapite powder, if you don't have any a pencil rubbed on abrasive paper or a nailfile will make it. under no circumstances use oil or grease. 

Splendid, thank you Clive, I'll give it a try.... very kind !

[Nick Jones]

What Clive says.

Graphite powder, sold as lock lubricant, is the business on these…..

[standardthread]

If it sticks again before you sort it place a long screwdriver on the end of the protruding square shaft on the starter and give the screwdriver a wack with a hammer.

Alternatively put a !/2" OE spanner on the end of the shaft and turn the shaft, either method should free the bendix

[RobPearce]

1 hour ago, standardthread said:

either method should free the bendix

Not really. Those methods are for unsticking a Bendix that's jammed in mesh, and won't have any significant effect on one that's stuck at its rest position.

[standardthread]

51 minutes ago, RobPearce said:

Not really. Those methods are for unsticking a Bendix that's jammed in mesh, and won't have any significant effect on one that's stuck at its rest position.

It's work for me in the past to free a spinning shaft.

[glang]

I think theres a chance it'll unstick the bendix but of course it will probably do it again especially if the starter is left unused for long periods of time.....

[JohnD]

David,

The above diagnosis, of a Bendix drive stuck on its spiral spline, is worth investigating!  Graphite powder is available for as little as £4, so don't bother grinding down a pencil!    Especially on sand paper which will allow abrasive particles to mix with the graphite!

But also consider an electrical fault.   The starter draws a very high current, 300Amps or so, which is why it has that massive starter cable.     But there are several connections in that cable, and any cable fault or dirty connection will reduce the current that reaches the starter.     It's that massive surge of current and the sudden jerk of the spinning axle that throws the pinion at the flywheel to engage with the ring gear.     If the current is too low, it won't make it!

Inspect the cable all along its run.    Any kinks that could have broken the wires in the cable, or wear that could lead to short circuits?   Replace the cable.     Are all the connections, at the battery, the starter solenoid and at the starter itself, all clean, bright metal-to-metal, and tight?    If not correct that.   

You can't measure that high a current with ordinary workshop instruments, but your multimeter can measure the resistance across the connection, which should be nearly zero.     Even a simple battery-powered test light may help - if its not just as bright across the connection as it is directly, then the connection has excess resistance!

Good luck!

John

PS See this video: (1) Bendix-Drive on a Triumph TR4A starter (Lucas M418G early, not 2M100-Type), mode of operation - Bing video

[RobPearce]

2 hours ago, JohnD said:

your multimeter can measure the resistance

Probably not usefully. If you're putting 300A through the cable then a typical multimeter's resolution of 1ohm is way too coarse - you need to confirm that it's well below 40milliohms. Same goes for the bulb test - all it can tell you is that it's hopelessly scrap, which we already know it isn't because the motor does spin.

A more useful electrical test is a bulb across the starter motor, while trying to crank. If all is good, that bulb should come on brightly almost as soon as you start cranking. If it only glows dimly, or takes half a second to come on, then the cable is dropping too much voltage.

[drofgum]

Hi,

If you really want to use a multimeter to test the connections from the battery to the starter use the volts scales and measure the voltage drop in the whole run from battery positive to starter battery connection.  It is likely you will need one of the lower voltage scales to read this drop, but start with the normal scale to check 12 V. That is kinder to the instrument.

Cheers,

Paul

Edited August 11, 2022 by drofgum
clarification

[JohnD]

Rob, Paul,   By his own admission, David has "very little mechanical experience"!

I was hoping to encourage him to try for himself, within that experience and likely equipment.   But thank you for your suggestions, with reveal my own lack of electrical knowledge!

But Rob, I don't understand the basis for using a test bulb, or multimeter, across the starter.  I presume that means one lead on the starter terminal, the other to earth?    So the bulb is 'seeing' the same potential as the starter, while drawing little current?

Paul,  Same reason and to help David, who wants to learn!   You mean test the volts between battery and starter solenoid, at any time?     Then solenoid to starter while cranking? The further this is from battery volts, the worse is the connection?

John

[glang]

I think the original diagnosis will be the correct one as the main surge of current doesnt occur until the bendix has engaged. Much less current is needed to spin the starter and throw out the bendix so any resistance in the circuit shouldnt have any effect until the hard work starts... 

[RobPearce]

35 minutes ago, JohnD said:

But Rob, I don't understand the basis for using a test bulb, or multimeter, across the starter.  I presume that means one lead on the starter terminal, the other to earth?    So the bulb is 'seeing' the same potential as the starter, while drawing little current?

Yes. The thinking is this:

- your standard multimeter is good for "a few volts" or "a few amps" or "a few ohms"

- What we're dealing with is "huge loads of amps" and "almost no ohms at all"

- So all that we can deal with is the volts.

- By looking at the volts across the motor (without loading anything up enough to matter) we can observe the effects

- If the resistance of the cables is the problem, the voltage will not be what we expect, and we should be able to see that.

This is the same logic as lies behind Paul's suggestion.

 

36 minutes ago, glang said:

Much less current is needed to spin the starter and throw out the bendix so any resistance in the circuit shouldnt have any effect until the hard work starts

While I agree that the problem is probably not electrical, John's idea isn't as daft as you suggest here. The motor will draw the same stall current when first energised as when in mesh - it doesn't "know" why it's stationary, only that it is. So if there's resistance in the cables, it will get less voltage (and hence current) than it should, and it will accelerate slower. That reduced acceleration will reduce how positively the Bendix moves, and may be enough to stop it short of engaging.

[glang]

Hey no suggestion its a daft idea😁 In fact on a larger motor with more load I wouldnt be at all surprised if that was the problem....

[JohnD]

5 hours ago, glang said:

I think the original diagnosis will be the correct one as the main surge of current doesnt occur until the bendix has engaged. Much less current is needed to spin the starter and throw out the bendix so any resistance in the circuit shouldnt have any effect until the hard work starts... 

Er, No, glang!

You are thinking of a "Pre-engaged starter", in which a solenoid throws the pinion at the flywheel.     As it does so, it closes a switch that connects the main starter motor to the battery, so that only a little current flows, until the starter and flywheel are engaged.

While those may be found that will fit a Spitfire, the OE was a starter with a Bendix, or inertia drive.    That draws maximum current at once and the inertia of the heavy drive pinion moves it along the spiral splines and into mesh with the flywheel gear.   This video from Moss explains the difference: 

 

 

[glang]

No, I was thinking of the bendix type as the motor starts initially with very little mechanical load because the bendix gear isnt in contact with the flywheel gear ring. As Rob says theres a starting current draw but this goes up even more when the gears mesh and theres a dramatic increase in load on the motor.

Im suggesting that a slightly high resistance connection somewhere is unlikely to stop the bendix from engaging (here it does whir/spin fine) but then when the current ramps up could cause sufficient drop in supply voltage to give problems with starting the engine.

As I say I think the diagnosis of sticky bendix is far more plausible👍

[glang]

Ive just thought of a good example. When Ive tried to start my Vitesse (bendix type starter) and the battery is rather discharged so the supply volts are low the starter engages ok but I get slow turning of the engine. Cant say in those circumstances Ive ever had the starter spinning but failing to engage although I suppose its possible if the volts dropped low enough...

[drofgum]

19 hours ago, glang said:

I think the original diagnosis will be the correct one as the main surge of current doesnt occur until the bendix has engaged. Much less current is needed to spin the starter and throw out the bendix so any resistance in the circuit shouldnt have any effect until the hard work starts... 

Hi,

I agree the sticky Bendix is most likely the cause of the problem. Thorough cleaning and colloidal graphite is the fix.

My multimeter test would find high resistance connections in the high current starter circuit without requiring a special meter. The initial test should be made from the battery positive terminal to the starter power connection post. That way all of the connections will be tested. If a large voltage drop is found in that test the trouble can be isolated by moving either meter lead to the next spot in the line: battery post-battery clamp-cable-solenoid battery connection post-solenoid starter connection post-starter cable-starter connection post.

Kind regards,

Paul

[glang]

Yes and that test wont be affected by the normal drop in the battery's output voltage during starting unlike measuring at the starter motor terminal to earth👍

[David Collingbourne]

A public note of thanks to all for your help and insights on here.

So, turns out the starter motor is an inertia one, similar to the one in the link in John D's post above.

I managed to get the motor out (a tad fiddly, needed to jack the car and move the petrol supply) and it ta-da, was sticky as Clive suspected - maybe an oil residue?

Got it clean (not quite as clean as the one in John D's post above), but close - WD and then petrol.

Maybe it's possible to take the spring mechanism apart to clean the parts separately? Pretty strong springs though and not sure how they'd go back!

The car fired up first time, without issue.

So again, thanks all, it was indeed a learning process and I think my late-pa (who completely re-furbished the car) would have been proud that I avoided a garage.

The electrical thread is helpful too and all noted, so thanks for that also.

[glang]

Great and think the moral of the story is to use it more often! But thats something which applies to myself and probably many others🙁

[Dave Clasper]

On 20/08/2022 at 12:43, David Collingbourne said:

So again, thanks all, it was indeed a learning process and I think my late-pa (who completely re-furbished the car) would have been proud that I avoided a garage.

 

Well done. Especially as often garages these days, from my thankfully, very low experience, seem crap, and have caused more problems.

I'm sure there must be some good ones? 

[JohnD]

David, well done and thanks for the feedback.  Sometimes we never hear what the problem is, and even gurus can't work without information.

If you can bear taking the starter out again,then lubricate the Bendix with graphite powder.   Don't grind down a pencil!   Buy some online, or even at a local hardware store. Non-sticky, so won't attract dirt and very effective!

John

[standardthread]

An alternative to graphite is PTFE spray, Screwfix used to sell it for lubricating circular saw blades and other woodworking cutters.