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MG MGA - Starter Motor Occasionally Does Not Mesh

I have an annoying random situation of the starter failing to mesh. By random, I mean about once a week. Stacks of juice in my battery. When the motor does mesh it spins away quite happily at full speed.

This problem has been there for a year or 2 now. I originally assumed it was the motor bendix on the way out, so a year ago I fitted a brand new one, but with the same results.

I have wiped the spindle to ensure it is not causing the bendix to stick, all to no avail.

Suggestions please.

On the same note, could there be merit in fitting a pre-engaged High Torque Starter Motor (HTSM)? For instance, is there enough room down there to fit one of the new style HTSMs advertised for the MGB? I have the 1800 engine with the high position starter.

Cheers

Steve
Steve Gyles

Steve, does it engage on the susequent attempts? If you have to turn the engine manually to get it to work, I'd say it was a badly worn ring gear. If it engages on a subsequent attempt, I'd say it's the stater switch not making a good enough contact to give the motor the impetus it needs to fling the bendix in. Try pulling the 'S' knob harder maybe?
Lindsay Sampford

Lindsay

It engages after 2 or three attempts; then probably one other failure during the day; then fine for say a week; then a couple of failures - so it goes on. Makes no difference whether it's first start of the day or the twentieth. The ring gear was satisfactory last time I had the engine out 2 years ago.

Most of these things end up being electric contacts somewhere in the system, so I am going to clean up (once again) all the obvious ones. I have changed the starter switch 3 times in the last year. None have made any difference to this problem. Getting quite a collection of them now - 5 at the last count.

Probably find it's a bad/intermittent battery earth or connection at the back of the car. I run 2 x 12 volt batteries in parallel, both with isolators (only ever use one at a time), so plenty of connections to look at!

Steve
Steve Gyles

Steve, have you serviced the starter? two things I can think of. The first is the bendix mechanism could be bound up by rust or old grease. It should not be lubed with grease but a graphite lube. 2nd could be internal Lucas bits flying around inside the starter. Brushes, brush wires and their bolts come to mind. also you could have an open winding in the rotor. causing a weak energizing force on startup depending on where it came to rest upon last start.

Since you already have replaced the starter switch, Oh wait! Check the wire connection at the starter. this is normally not tightened fully and could work slightly loose. Back to the switch, since you have replaced the starter switch it is an unlikely, but not eliminated suspect.
Chuck Schaefer

Chuck

18 months ago I replaced the bendix. However, a year ago I bought a brand new starter.

Of course, the starter is behaving perfectly today so any fiddling around and cleaning I do this weekend will not become immediately apparent.

I take the point about the cable tightness at the starter. First on the list to clean and tighten. I will only tackle one connection at a time so that I can zero in on the precise problem as time elapses.

Went out to start work and got diverted by the wife into planting trees. Oh, where does the time go when you are retired!

Steve
Steve Gyles

Steve,this sounds very familiar and reminds me of a lesson I learnt with BMC stuff years ago regarding the Lucas starters from similar symptoms.It is that although the outer nut which holds the cable onto the starter feels tight it is imperative that the nut behind the cable ie holding the very long bolt through the starter body is tight up against the starter body Then place the cable/lead and then tighten the outer nut.Bettya it works.Good luck.
M Blencowe

I bet it's that beastly starter switch again. Mine is not all that convincing. Sometimes the motor just engages but wont turn the engine. Try it a second time and it turns over just fine. I seem to remember that some folks have changed to solenoid switches, that probably is the answer if you want a reliable turn-over every time.
Lindsay Sampford

Steve, I bet it is the normal wear and tear of the starter motor gear and/or the ring gear.

I fitted a High Torque Starter Motor 2 years ago and it, very occasionally, skates off the ring gear.

One way to be sure this is the problem is to select 3rd. or top gear, rock the car back and foward, then try the starter again. With mine it is a sure cure every time. It then selects a section of the ring which is in better condition and starts with no fuss.

Happy Motoring, Barry.
Barry Gannon

Hi Steve, I was just talking to one of our club members and he had trouble with a new starter motor in his midget - something to do with the size/angle of the teeth.He said that it had wrecked his flywheel ring gear and he had to have a new one fitted - he is still trying to sort out compensation from the vendors. Hope that this is not the case with yours - cheers Cam
Cam Cunningham

I have been thinking about it overnight. Bearing in mind I have suffered similar symptoms with 3 different bendixes, 2 separate starter motors (one brand new) and 4 starter switches (3 original, 1 new), all of which involve refastening the starter cable (both ends from time to time), I feel the problem can only be: 1. the ring gear, or 2. battery connections further back towards the battery.

As I said at the beginning, this is random, occurring about every 20 starts or so.

Steve
Steve Gyles

Sounds like the ring gear Steve.

The problem is that the starter tends to only engage in two locations on the ring gear
and the teeth in those locations wear far more than the rest of the teeth.

However I'm surprised you didn't notice it when you removed the engine for repainting.

Regards...John
J Bray

Bad ring gear will always make a really horrible noise as the teeth bounce off each other. If it does NOT make such a noise, it is not the ring gear.
The drive works on inertia of the pinion causing it to screw along the threaded sleeve as the motor accelerates very quickly. If the motor accelerates too slowly, because of friction or low voltage, the drive will not function. If the drive pinion or screw itself has friction, it will not function.
It may sometimes make the noise if the drive is sticky or the motor accelerates too slowly. The pinion is meant to engage the gear before the motor gets to speed; if engagement is delayed but still happens, then the teeth bounce off each other. This leads to, but is not in itself, a bad ring gear.
Ring gears normally take many years to fail, I've seen about two that were that bad. Gear teeth can be worn 3/4 across the gear and still work fine. You can easily look at the ring gear teeth if you remove the starter. As mentioned, teeth wear in two positions only. Some cars will actually break teeth off, but BMC ones always seem to just mash them over after extreme wear.

Electrical faults that are a matter of degree can easily be checked with a voltmeter. You need to make up some leads for the meter that can be securely fastened in place, especially if you want to drive around with it to check intermittent conditions. Connect the meter across whatever section of the circuit you are interested in. Here that would be Battery hot to starter post, at least to begin. Polarity is not important; you are checking the magnitude of voltage drop. Any drop over about 0.5V when starting is too much - it will cause slow acceleration of the starter drive. If you find such, then you can relocate the leads to check subsections of the circuit - like across the stupid switch. Watching the voltage as you start it can be instructive; you may find the V going 5V dropping to 1V, which indicates the switch is making bad initial contact, which would explain your problem.

FRM
FR Millmore

Spent an interesting few hours cleaning every battery power lead connection. In my case, because I keep a spare battery in the second cradle, I have numerous connections - about 13 in all. This includes 2 isolators, 2 earths, 4 battery terminals, starter switch and the starter. I cleaned all in turn, working from the back to front, checking the starting after cleaning each connection. It made no difference at all on the first 12 connections. The starter span very fast, engaged the engine and started the engine first pull each time. The final connection at the starter at first felt tight, but I noticed both nuts turned slightly. Tried the starter and it failed to mesh! Got it going after about 4 pulls. Went for a drive, did several switch-offs. Failed to start each time for about 4 pulls. Got back home, undid the starter connection. Found I could put another 3/4 turn on the first nut on the terminal post. Took it off, cleaned it all up. Tightened that first nut up really tight, followed by cable and nut, also really tight. Vroom, vroom. started first time every time for the next 20 start-up tests. Time will tell of course, but it seems that M Blencowe may have got it right. Many thanks.

Steve
Steve Gyles

Start up from cold today excellent. Engine fired absolutely immediately, rather than the couple of seconds it normally takes, just because of that 3/4 turn on the starter motor post locking nut. It was not as if it was loose, just able to tighten it that little bit more. Surprised it made so much difference. Can anyone explain?

Steve
Steve Gyles

Result Steve and well done M Blencowe for the prediction - something to remember for the future. Amazing that a slightly loose nut could cause such a drop in PD at the starter terminals.
Cam Cunningham

Cam

Yes, I'm delighted it seems to have done the trick. But I do not understand why. I have my spare starter apart on the bench and that post is quite rigid and hard wired.

Baffled but delighted.

Steve


Steve Gyles

This thread was discussed between 19/11/2011 and 21/11/2011

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