7 won't start

[Septum.Insania]

I have a Caterham 7 with Vauxhall 1600 8 ohc which won't turn over, but turns over freely with the spark plugs removed.

The battery is fully charged and also tried a jump start battery with no effect.

Any ideas?

[HustleRussell]

try again with an extra jump cable connecting a metallic part of the engine block or gearbox to the negative battery terminal, this eliminates bad earth.

[BertBert]

When you say won't turn over, I assume you mean that the starter isn't man enough rather than the engine is locked solidb with the plugs in?
Then after Jame's test, I'd strongly suspect the starter motor.
Bert

[Septum.Insania]

Thanks to both for suggestions, not had a chance today to try but will be at it am Monday.

[HustleRussell]

The fact the starter motor will turn the engine over with the plugs out tells us the switch works, the solenoid is throwing out and making contact, the pinion gear is meshed with the ring gear and the motor itself is turning. The fact it won’t do it with the added resistance of engine compression tells us that the motor probably can’t draw enough current- either because oxidised wiring or bad connections are causing a load of extra resistance, or the motor itself is no longer working efficiently.

[Septum.Insania]

Big thanks to all, although not being able to remove the starter motor, could not get the right angle to undo the top fixing bolt, I undid all the earth connectors fixed to the engine and one or two more that I could see, cleaned them all back to shiny metal and refitted the lot, result my seven is back on the road.
Thank you all for your advice
Septum Insania

[BertBert]

Great result, spot on James!