When won’t my engine start battery start my engine?

[PhillM]

This year my start battery was dead flat. Tried to recover it but it still wouldn’t crank the engine. Yesterday I bought a new one. It was weak but didn’t start the engine. Had it on charge all night and th ctek charger showed it as fully charged. But it won’t need crank the engine.

 

[Toodle-oo!]

Check cables to the starter motor - if they're loose at all it won't start...
Presumably you can turn the engine over by hand? Via belt or flywheel - make sure it's not seized...

 

[anoccasionalyachtsman]

And the earth/negative connections.

 

[Stemar]

Can you turn the engine with a big spanner on the flywheel? If so, the engine isn't seized, which is a good start.
Does the starter make any effort to turn the engine? If so, but it's too feeble to spin it, I'd start by cleaning all the connections between battery and engine, + and -.
Is there a clonk from the starter solenoid when you try to start? - again, clean connections. If that doesn't fix it, get an auto-electrician to check the starter.
If not, will it turn over if you touch a wire direct from the battery to the small terminal on the solenoid? If so, the issue is in the "ignition" or starter button circuit.

That covers most bases.

 

[cherod]

jump leads onto your house battery

 

[cherod]

This year my start battery was dead flat. Tried to recover it but it still wouldn’t crank the engine. Yesterday I bought a new one. It was weak but didn’t start the engine. Had it on charge all night and th ctek charger showed it as fully charged. But it won’t need crank the engine.

did you try a volt meter

 

[mjcoon]

Have you got decompressor levers?

 

[PhillM]

Fixed it! So the engine start battery was dead. I know that because it had the ctek charger directly connected and it wouldn’t charge. Voltmeter showing 11v.

Put the new one in. It failed to crank the engine but change the 1:2:all from 1 to 2 and the engine fired perfectly.

Head scratching.....

Turns out the 1:2:all switch is wired the wrong way round ... engine start on 2 and domestic on 1. So ... I’d flattened the domestic thinking it was the start battery. Have charged it back up and will either change the switch around or just make sure to use the right battery for the right job.

Thanks all. Another mystery solved!

 

[Aardee]

Oh God no, the last thing we need is another 1-2-Both switch discussion...

 

[cherod]

after rebuilding my water pump ( bearing , seals , impellor etc ) , why would my pump not pump ???!!! ,,,, until i primed it ,, is that normal ??

 

[PhillM]

To make things worse, I also tried time charge the leisure battery separately. It failed to get past 12.3v. I’m assuming ing that’s dead too. Both are 7 years old so I guess that’s not too bad. But it has cost me a few days of messing about locally when I wanted to be off west.

On a more positive note, my sail bag was coming unstitched. The sailmakers in Shepherds Wharf sorted that out in an hour and for not much more than a cheap bottle of whisky.

 

[RichardS]

after rebuilding my water pump ( bearing , seals , impellor etc ) , why would my pump not pump ???!!! ,,,, until i primed it ,, is that normal ??

It's deffo nothing to do with the battery.

Richard