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MG Midget and Sprite Technical - Alternator, battery or starter motor

I've just got my 1275 back on the road after a long break, new engine clutch hydraulics.

It runs quite well (needs final tune up) but I'm having some trouble with the starting. Battery has been charged several times and tested at the local auto shop who said they couldn't find a fault.

When I come to the car after a couple of days standing I have a good charge in the battery 12.6V and the car starts first time. At 1500 revs I have a voltage of 14.8V at the battery so I guess it is charging. However after a short run of 20 mins I return home park on the drive leave it for a few minutes come to start it again but the battery struggles to turn the starter motor over until it wont turn over at all. I still have a good charge at the battery 12.6V. Leave it for a further 20mins whilst I have a cup of tea and she starts up again.

Sorry if the answer is in the archive somewhere but I couldn't find it.

So whats going wrong. I have a continuity setting on my digital meter which buzz's happily whilst I check all the earth points. Not sure this is a suitable check though? But if it was a earthing problem wouldn't it be consistent problem?

Is it the alternator... but it seems to charge OK

Is it the stater motor... failing when its hot.

Is the battery dead...

Where do I start looking

Thanks in advance
tm wainwright

since it comes and goes, I would suspect the starter, or the ground points (a partial ground will test fine at low voltage but fail at starting current).

You might try loosening, jiggling and then re-tightening the ground strap and the starter mounting, and while you are at it, do the same to the +12V feed to the starter, from the battery to the solenoid, to the starter.

Never know, might just be a bad connection, and doing this ought to help.

And if that doesn't do it, then it is probably the starter.

By the way, your engine wasn't just rebuilt, was it? New piston rings will be rather tight, until they are run in.


Norm
Norm Kerr

Yep, engine was just rebuilt (currently 12 miles on the clock but at initial start up it spins quite happily.

I guess I need to revisit the earthing straps to ensure these are up to the job.

regards
tm wainwright

Hmmm obviously the battery seems to be OK and also the charging seems fine so what is the problem?

I too have experienced the effect suggested by Norm, (mainly when racing) at times with a fresh engine everything is a bit tight and when the engine gets hot the starter can struggle to turn it over. Whether a new starter would cure it who knows? however I would be tempted to let things bed in a bit and also without doubt check the engine earth and battery connections.
Bob Turbo Midget England

I'll go to work on the earth straps.

Its a little difficult to get any miles on the car as I fear not being able to restart if I stop for any reason. I think a quick blast up the A127 to see if this can loosen anything up.

Many thanks
tm wainwright

in the old b&W days we used to just park on a slope if we had starting problems or get mates to push start the car out of the pub car park

once the engine is warm they bump start very easily
Nigel Atkins

This thread was discussed on 19/07/2010

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