Starter Motor solenoid chattering

[mach2andy]

When I go to start my car, the starter solenoid just chatters with no SM rotation. I've had a good look at all relevant wiring connections but it's very unlikely to be wiring related as the wiring is all brand new. The engine earth strap is in good order and the resistance between batt earth and the engine is .5 ohm. The SM is the standard Lucas unit. If anyone else has had this issue, can you tell me what you found.

Many thanks in advance

Andy

[mgcjag]

Hi Andy....you should have a starter relay.......is that chattering and causing the solonoid to chatter.....Steve

[christopher storey]

This is usually a symptom of low battery voltage under load.First of all, fully charge the battery , then if you have a voltmeter, measure the unloaded voltage , which should be about 12.6 to 13 volts minimum, and then, with the voltmeter still connected, get someone to operate the starter . The voltage should drop only to something in the region of 11 volts, and if it drops below about 10.5 volts then the battery may well be goosed.

[mach2andy]

Hi Steve
As soon as I'd posted, I thought that I should have clarified that it was the main solenoid on the starter that was chattering, not the starter relay which is fitted. Thinking about it though, I hadn't even considered the possibility that the starter relay may be the culprit. I guess I can connect the brown directly with the WR on the starter relay with the ignition on which should eliminate the starter relay?
I'm hoping that it is the battery rather than the SM which I had professionally tested and overhauled before refitting it to the car. I'm assuming that once the solenoid closes and the SM starts to draw current, with a weak battery, the voltage at the solenoid coil is dropping to a level that is insufficient to keep the solenoid closed, and it opens. The voltage then rises and the solenoid closes again so on and so forth. Christopher's suggestion of leaving a voltmeter connected should prove that. I've had my doubts about the battery for a while, as when connected to the trickle charger, the green fully charged indicator never comes on.

[Gfhug]

Andy, as a way of checking if it is your battery can you jump start from another car? If it starts nicely then the solenoid and relay should be ok. Battery shouldn’t cost over £100 iirc from comments/suggestions by David Jones (Heuer).

Good luck

Geoff