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Intermittent slow cranking speed

Car is a 1978 Triumph Spitfire 1500. Pretty standard except for electronic ignition and 12V coil. The battery is in good condition.

When cranking the engine on the starter, most of the time it will work fine. Occasionally, it will crank very slowly (as if the battery was flat) then pick up to normal speed again. Sometimes this doesn't happen at all, other times it'll crank slowly for ages eventually reverting to normal operation (which can then start the engine). There seems to be no telling when it'll behave like this.

I thought at first the alternator was playing up and trying to charge the battery when the car was being cranked. I've since changed the alternator with no improvement. I have checked thoroughly the wires from solenoid to starter, and from ign. switch to starter and all seem well. I think this is a coincidence, but it started doing this shortly after I bypassed the ballast resistor to install the 12V coil. Any ideas?

I appreciate that this isn't much to go on, but I wondered if this was a 'classic symptom of starter motor/solenoid/ignition switch failure' etc?

Many thanks, David

Reply to
David Balfour
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this is a classic set of symptoms for a bad connection or two in either the battery leads or earth connections. (especially engine to chassis) Other slim possibility is a battery with a cracked connection internally.

mrcheerful

Reply to
mrcheerful

I had this problem once on a P4 Rover. An oil weep from the rocker cover had spilt oil on the starter motor, which had got inside its works. The wearing of the brushes releases carbon particles which were collected by the oil film and produced a partial short across the commutator, which was eventually (but temporarily!) flung off/wiped clear as the starter was used, when it ran normally.

I would take the starter motor off and give it an internal clean (Meths on the commutator will remove oil traces without harming it). If it looks good and doesn't need an internal clean, then you are probably looking for a bad or missing earth connection. Try starting it while looking under the bonnet in the dark. If the choke cable glows dull orange, you have a bad earth.

Jim

Reply to
Jim Warren

Thanks for all that, I'll have a go at cleaning it up - I did have quite a major leak from the rocker cover just before this all started so I expect it is shorting as you say.

Out of curiosity, why would the choke cable glow?

David

Reply to
David Balfour

"David Balfour" realised it was Sat, 23 Jul

2005 13:39:19 +0100 and decided it was time to write:

If the earth cable between the body and the engine is not properly attached, the choke cable will function as an earth connection and heat up. Better to feel it heat up before allowing it to glow, though...

Reply to
Yippee

Feel it if you like, but rememember it can get very hot indeed. BTDT,GTTS.

Ron Robinson

Reply to
R.N. Robinson

David

The classic spitfire oil leak from the back of the cylinder head tends to run down the bellhousing to where the engine earth strap connects. It would be worth disconnecting and cleaning this up.

Doug.

Reply to
DougP

Final comment: try a different battery.Borrow one?

I had a similar problem with a "classic" battery on my TR5. Turned out that one of the cells was intermittant, both in supplying the juice, and in getting charged up. Replaced it with a new one, and it starts brilliantly. Slow cranking will generally mean lousy voltage at the points, and less spark (if at all).

HTH

J.

Reply to
JH

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