Lotus Elan

Starter motor fault check list

PostPost by: jimj » Tue Apr 10, 2018 12:44 pm

So, the battery is fully charged and attempting to start the car results in a click and dimming of lights. Jammed bendix, I thought, but I can rotate the starter motor easily with a spanner on the end. The car bump starts easily and drives as normal which would surely free off a jammed bendix anyway.
I`ve tried running a jump lead from the starter motor terminal straight to the positive on the battery which does nothing. Similarly, shorting out the 2 big terminals on the solenoid just causes a spark but nothing from the starter motor.
I`ve cleaned up the earthing point on the chassis where the negative cable is attached, but everything electrical works fine anyway.
Am I right in thinking that the starter motor must be faulty or have I missed something?
Jim
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PostPost by: Elanman99 » Tue Apr 10, 2018 1:23 pm

The dimming of lights indicates that the starter motor is drawing a large current so its probably OK. I think you need to check through all the (high current) connections as its most likely one of those that is the problem.

A connection can test as perfectly OK when little current is flowing, but be almost open circuit at 200A or whatever.

Every metal to metal junction in the starter motor wiring is suspect until you prove otherwise. Even the humble battery negative (ground) connection has several metal to metal interfaces between the battery post and the chassis. First one is the underside of the bolt head to the chassis, next is the bobbin to chassis, then the cable ring tag to the top of the bobbin, also wire core to the ring tag. There is some duplication of connection here as the bolt as well as the bobbin might conduct.

On way to seek out the bad connection is to measure the voltage drop across each individual joint whilst current is flowing (the higher the better, so headlamps ON might be OK). You need a sensitive meter (to read very low voltages) and sharp pointed meter probes to touch the two bits of metal that should be in electrical contact with each other. If there is no voltage difference then the two bits are in 100% contact (or there is no current flowing).

It may be that by visually checking the engine grounding strap (at both ends) as well as all the battery ground wiring you uncover the fault without needing any electrical tests.

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PostPost by: MarkDa » Tue Apr 10, 2018 1:27 pm

I've been waiting to post this link because of the modern fad for Hi Torque motors I thought it might be worth going back to basics which this instruction manual from Lucas way back when does.
The point often overlooked is that electric motors produce their maximum torque at start up and once they've overcome initial resistance soon put energy into the flywheel to continue rotation past compression.
You should only need 90/100 rpm to start an engine.
There's a really good section on circuit fault finding.
It's one of a series covering all automotive electrics.

lucascourse2.pdf
Lucas Starter Motor Course
(1.86 MiB) Downloaded 86 times


I rather think that if the motor is pulling a large current but not rotating then it is faulty.
Last edited by MarkDa on Tue Apr 10, 2018 2:12 pm, edited 1 time in total.
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PostPost by: richardcox_lotus » Tue Apr 10, 2018 1:49 pm

Fuse ?
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PostPost by: alan.barker » Tue Apr 10, 2018 1:52 pm

Jim,
if i were you i would remove the Neg Earth cable from Battery to Chassis.
Then remove the Earth Screw Bobbin to Chassis and give it all a good wire brushing.
Fit new Screw with shakeproof washer under screw head and tighten.
Fit Battery earth + shakeproof washer + nyloc nut.
Check and clean earth from Chassis to Engine.
If there is wear in the Starter Motor bush you can get a new one from "AES" + Bendix.
Alan
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PostPost by: SENC » Tue Apr 10, 2018 2:43 pm

MarkDa wrote:I've been waiting to post this link because of the modern fad for Hi Torque motors I thought it might be worth going back to basics which this instruction manual from Lucas way back when does.
The point often overlooked is that electric motors produce their maximum torque at start up and once they've overcome initial resistance soon put energy into the flywheel to continue rotation past compression.
You should only need 90/100 rpm to start an engine.
There's a really good section on circuit fault finding.
It's one of a series covering all automotive electrics.

lucascourse2.pdf


I rather think that if the motor is pulling a large current but not rotating then it is faulty.

Thanks for sharing!
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PostPost by: elansprint » Tue Apr 10, 2018 4:05 pm

When I rebuilt the sprint engine had exactly the same problem on first start up the positive lead was shorthing to earth when tightened up fully put a lock nut on the thread and locked the lug against this problem solved
Ian
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PostPost by: Craven » Tue Apr 10, 2018 4:15 pm

Run a jump lead from the negative battery post direct the starter motor fixing bolt.
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PostPost by: Mick6186 » Tue Apr 10, 2018 4:17 pm

Have you tried taking the solenoid out of the circuit by putting a dead short across the big terminals to see if the starter then spins. I normally use a hefty screwdriver,
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PostPost by: Elanman99 » Tue Apr 10, 2018 4:22 pm

Craven wrote:Run a jump lead from the negative battery post direct the starter motor fixing bolt.

...... and gaffa tape it along the bodywork from a notch cut in the boot lid to another notch in the bonnet, that way you can continue to use the car until you fix the bad connection. :wink:

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PostPost by: john.p.clegg » Tue Apr 10, 2018 4:44 pm

Don't cut your bodywork , charge the battery.

John :wink:
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PostPost by: David1953 » Tue Apr 10, 2018 7:32 pm

MarkDa wrote:I've been waiting to post this link because of the modern fad for Hi Torque motors I thought it might be worth going back to basics which this instruction manual from Lucas way back when does.


Mark thanks for posting, do you have any more like that, Dynamo?

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PostPost by: MarkDa » Tue Apr 10, 2018 8:27 pm

Jim's original post covered hot wiring battery to starter, jumping solenoid terminals and cleaning up earth connection.
So the only thing left is to eliminate all wiring and jump starter direct off a battery as suggested by Craven.

From what we've heard my money is on a duff starter.
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PostPost by: MarkDa » Wed Apr 11, 2018 7:21 am

I've started a new thread with 9 courses either pasted or linked.
I've not been through them all but I'm sure they'll be worth a read and might even be useful!

lotus-talk-f50/lucas-training-course-t41661.html

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PostPost by: john.p.clegg » Wed Apr 11, 2018 7:26 am

"The dimming of lights indicates that the starter motor is drawing a large current " , or more accurately that the battery voltage is dropping on load , which could point to a duff battery...

John :wink:
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