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MG MGA - Starter question

1958 MGA 1500 roadster. The starter appears relatively new and came with the car when I got it a year ago.

The problem is the starter engages the flywheel, turns the engine over, but as soon as the engine starts to catch, the starter disengages and spins freely.

Would be a good thing.... but most often the engine hasn't started, just slightly kicked over. The cycle can be repeated as often as necesary.

I'm wondering if this by design... a clutch mechanism of somesort? If not any suggestions?
Brian Denis

It is like a clutch, it keeps the engine from over revving the starter and spinning it apart, but yours is slipping too much. I have never had a problem like you describe on a MGA though.
What is the condition of your ring gear?
Any one out there? if you clean and lube the starter drive and does it help?
R J Brown

Brian,
I would check the spring on the starter shaft. The spring provides a pre-load of the pinion to the ring gear. Sometimes a coil in the spring will break (often metal fatigue on old starters, but possibly just poor material) causing the symptom you mention.
Regards,
GTF
G T Foster

As others said clean and lube the drive. No grease-oil only. Grease dries out and creates too much drag on the Bendix mechanism.
John DeWolf

I had the same problem about two years ago, and fixed it by replacing the spark plugs. The car had not been run for about 6 months, and when I tried to start it, the starter would do exactly as you describe. The starter would turn it just fine, but as soon as the engine tried to fire, the starter bendix would disengage, and the engine would stop. I did clean the starter bendix, and all the springs appeared intact, and the teeth that I could see on the ring gear appeared fine. I checked the timing, and it was spot on. I checked the float bowls, and they were full, and even emptied the bowls and filled with fresh gas. Always the same, as soon as the engine tried to catch, the starter disengaged. Finally, even though the plugs looked good, I replaced them anyway, and it fired right up. There may be something weak in my starter, but it has been two years since then, and it has started fine every time.

Jeff Schultz

I have those same symptoms occasionally. If the engine is in good tune, it's usually started by the time it kicks out, but maybe I haven't pulled the choke quite right or something. I wouldn't worry too much about it, as long as it still does start the car. My favorite mechanic (who's not perfect, but knows his stuff) advised me to clean the bendix, not lube it one bit. He was right, I had cleaned and oiled the tracks of that high pitched screw. And when I cleaned the oil off, it worked a lot better.
Tom

Thanks for the information and suggestions. I've been slowly refurbishing the car since July. I've started it only 6+/- times since so several of your ideas fit the situation.

I'll have to wait until spring to put them to use however since I packed up the car for the winter yesterday.... it's already snowed twice here.

To check the condition of the ring gear, is the only way to look through the hole for the starter?

RJ, GT, John, Jeff & Tom, thanks again for taking the time to help out.
Brian Denis

Hi Brian. You could pull the engine or transmission instead! lol. Yes the only non mega invasive way to check the ring gear teeth is to remove the starter motor and peer in through the orfice. Once the starter is out, you can have an assistant slowly turn the engine with the hand crank. That way you can check all the ring gear teeth for damage. If you dont have a hand crank, you might be able to use a long screwdriver to "pry" on the ring gear teeth to move the flywheel. If you intend to check the ring gear teeth, be sure to put a dab of paint on the flywheel where you start, so you know when you have covered a complete revolution. It is quite common to get ring gear teeth wear in only one or two sections on the ring gear's circumference. This is apparently because engine compression causes the engine to stop in the same position or positions, when it is shut down. Therefore the starter engages in these spots on a consistent basis and causes wear. Apparently it is sometimes possible to remove the ring gear in one piece, and reposition it on the flywheel, so that the non worn areas of the ring gear come in contact with the starter. However, I am not sure how one would go about doing this. I suspect the ring gear would need to be very hot to expand it enough to be driven off the flywheel. Hope this helps. Glenn
Glenn

Firstly there is no preload spring just one large spring to absorb impact and a very light one inside the barrel to return it. Tom has given the correct information in that the drive must be completely dry so that means washing out the pinion barrel together with the spiral bush etc and putting it all back together completely dry.

I cant remember whether the A has an inboard or outboard drive but in any event remember that the engine will naturally stop at two positions 18 degrees apart check the few teeth at that point tenn rotate the crank half a revolution and check again. You can see the tooth form at the mid points and they have a 45 degree chamfer in front or behind depending whether inboard or outboard. This chamfer provides easy engagement of the pinion. If there is any damage this can be rectified using a fine triangular file but if the teeth are severely worn then its new ring time. The pinion can also be dressed up but may be freely available and best replaced.
Iain MacKintosh

Glen to install a ring gear you get it red hot with a torch. Once hot enough it drops on with a little tap from a hammer. To remove the ring gear I have always used an air hammer or a 32 oz or larger hammer and large dull chisel. To remove with a chisel you walk around the circle loosening a little at a time as you go around.
R J Brown

Heating a ring gear to red hot will destroy the temper hardness which will lead to rapid wear. Installation calls for heating to blue or light straw color, which is just below the tempering temperature.

If you overheat the ring gear, turning it red, it should be then be heated to a minimum dull red all around and quenched with oil for the proper cooling rate for re-tempering. That does make a major mess, but it's the only way to get the hardness back.
Barney Gaylord

I'm with Jeff. It is most likely an engine tune problem rather than a starter problem. Take away the spark and crank it. It should crank smoothly for ever. The pinion is meant to kick out on starting. The problem is the motor won't catch.
Art

I have changed several by putting them in an oven at 450 degrees for 30 minutes or so. A large brass drift and heavy duty hammer will install it then. Be careful that you press it down evenly .
Sandy
Sandy Sanders

The starter ring sits in a groove in the flywheel so so to remove it cut with a bandsaw until the blade just touches the flywheel surface. Then with a cold chisel insert between two teeth and split with a sharp blow.

Barney is of course spot on regards refitting. Temperature is vital and this can be achieved using a large freestanding gas ring. Then pick the ring up with two pairs of tongs and drop it over the flywheel. No drifting or hammering, it will drop straight on and shrink tightly within a minute or so.
Iain MacKintosh

This thread was discussed between 28/11/2005 and 30/11/2005

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