Battery MKIV

[RobMoore606]

Looks like my battery may be shot, however since there are no markings on it I am unsure what to get as a replacer.
Does anyone know what amphour I require and what cranking amps i I need?

[Clive]

original is the 038 or the heavier duty 015.
Easier to find are 063/065, as used on loads of cars today. Terminals then at the rear, but still on the correct side. May need longer j bolts for the battery clamp (if fitted!)

[thescrapman]

Vauxhall Vectra fits fine in teh tray.

There are a number of threads on it in teh archives.

Cheers

[aar0sc]

I've just nabbed the one out of dad's Toyota Aygo - fits perfectly!

[RobMoore606]

Cheers, I take it then that I am not needing a specific Ah or cold cranking power and so long as the dimension are ok then pretty much anything will do.

Need to test my starting circuit first for leakage, sometimes its as though there is no power in the battery at all and it really struggles to turn it over then all of a sudden away she cranks.
I do know the battery is holding its charge and reads 12.8v and with engine running im getting the same although once the revs are up a little I get the expected 14v so it may be that the battery is still shot as far as its cranking capacity goes.

[thescrapman]

Double check your engine earth straps, it might be a faulty one, high resistance initially then it breaks down the resistance and it spins over normally.

Cheers

Colin

[RobMoore606]

Well I tested the battery 12.9v constant dropping to 10.7 cranking so I now know the battery is good.
Earth straps removed, cleaned and put back.
The fault is intermittant, this morning it was a trial to get her started yet at the end of the day she started first turn of the key to come home and tonight on pulling her out the garage and testing the battery she was vigorously cranking away with ease then when it was time to put her back in the garage again a struggle to start.
I am now thinking perhaps a faulty solenoid, or maybe even the ignition barrel since I know that has issues with original key in so much as it didn't always self return.

Tomorrow its time to examine a little further.

[junkuser]

Try putting a heavy cable, such as a jumper lead, from battery -ve to engine block or gearbox temporarily and see if it makes a difference with the starting.  Assuming car is -ve to frame.

[bodders1]

3472 wrote:

or maybe even the ignition barrel since I know that has issues with original key in so much as it didn't always self return

I think that the ignition barrel is the one place you can safely assume the problem does not reside.
The ignition switch provides a +12v feed to energise the solenoid.  If it wasn't working, then the solenoid will not energise, and the high-current circuit to the starter motor will not be completed - resulting in no cranking at all.

Your first test should be (as others have already suggested) when the fault condition is present, run a jump lead directly from the battery +ve terminal to the starter motor.  Does it still crank slowly?  If the answer is yes, then you can rule out the whole battery-->solenoid-->starter part of the circuit and concentrate on the earth return side of things, or the starter motor itself.
Conversely, if the jump lead cures the slow cranking, then you can be confident that the fault is between the battery and starter.

A couple of intermittent slow-cranking faults that I've had over the years that you might want to consider:
1) an oil leak on a Renault (I know, sorry!) that smothered the starter motor in gunk.  Sometimes the gunk got into the starter itslelf and caused slow cranking due to the brushes getting gummed up.  This would miraculously cure itself with a good heavy thump on the starter motor using the handle of my trolley jack.

2) over-advanced ignition - I've mentioned this one before on this forum - at cranking speeds if the ignition is too advanced, the fuel/air mix can ignite before the piston has passed TDC, thus trying to force the engine to turn backwards and fighting against the starter motor. This results in seriously slow cranking and difficulty starting.  Could it be that the advance-retard mechanism in your distributer is sticking in the advanced state?  This happened to me on a mini:  the dizzy would sometimes stick in the advanced position and make the car difficult to start, with the slow cranking symptoms you describe.

With intermittant faults, you should always test several times - it is too easy to get a positive result and assume that you have rectified the fault only for it to re-assert itself later

[junkuser]

Just thought it was safer to start with the frame side and often it is the "earth" strap and connections that cause the problem.
If things not improved then jump the +ve side, as suggested by Bodders but be aware you may well get big sparks, especially if you make the contact slowly.