Electric Start Blues

marshg246 · Apr 19, 2023

Carl H said:
I had a Boyer MK3 in for years , but now I have a Boyer MK4 to freshen up the old box. The OEM starters can work well, If you maintain them. I replaced the brushes once when the starter failed to work.

Interesting. I thought Boyer's required more than "a little below 10 volts" to work.

Uncle Frank · Apr 21, 2023

concours said:
Now perform the same test with voltmeter at the battery. Then at the relay. (Both sides)
Report back the three data points.

Ok here we are. I charged the battery - it's a 500CCA car battery and borrowed a friends Fluke mulitmeter.
Battery voltage 13.3
When cranking:
Battery 9.4
Battery side of solenoid 4.1
Starter side of solenoid 4.0
Starter 3.5

marshg246 · Apr 21, 2023

Uncle Frank said:
Ok here we are. I charged the battery - it's a 500CCA car battery and borrowed a friends Fluke mulitmeter.
Battery voltage 13.3
When cranking:
Battery 9.4
Battery side of solenoid 4.1
Starter side of solenoid 4.0
Starter 3.5

You're losing 5.3 volts in the wire between the battery and solenoid! 0.1 volts in the solenoid. And 0.5 volts in the cable from the solenoid to that starter! Truely amazing! All should read the same when cranking! It's 2 cables and a switch - nothing should be lost in them. Change the cable from the battery to solenoid first - that alone should make it start but keep working until all the three match the battery voltage when cranking.

L.A.B. · Apr 21, 2023

Uncle Frank said:
Battery side of solenoid 4.1
Starter side of solenoid 4.0
Starter 3.5

Measuring from each point to 'ground' and the same ground each time? If so, where?
Or directly to battery positive each time?

dobba99 · Apr 21, 2023

Uncle Frank said:
Ok here we are. I charged the battery - it's a 500CCA car battery and borrowed a friends Fluke mulitmeter.
Battery voltage 13.3
When cranking:
Battery 9.4
Battery side of solenoid 4.1
Starter side of solenoid 4.0
Starter 3.5

Are the cable connections clean and tight? I ask because this is a classic cause of poor starting. Just because you can not wiggle the cable doesn't mean its got a good connection. Clean the terminals of the battery and cables and solenoid, scrape away all the corrosion so every thing is bright and shiny.
I recently fitted one of my modified two pole prestolite starters to a Mk3 that still had its original weedy cables and solenoid, pressing the button revealed a battery that although powered the ignition (the owner was kick starting the bike) wouldn't power the starter, changing the battery for a used but good one and the engine fired up on the button first press, weedy cables and all!

Uncle Frank · Apr 21, 2023

L.A.B. said:
Measuring from each point to 'ground' and the same ground each time? If so, where?
Or directly to battery positive each time?

The cylinder head.

Uncle Frank · Apr 21, 2023

dobba99 said:
Are the cable connections clean and tight? I ask because this is a classic cause of poor starting. Just because you can not wiggle the cable doesn't mean its got a good connection. Clean the terminals of the battery and cables and solenoid, scrape away all the corrosion so every thing is bright and shiny.
I recently fitted one of my modified two pole prestolite starters to a Mk3 that still had its original weedy cables and solenoid, pressing the button revealed a battery that although powered the ignition (the owner was kick starting the bike) wouldn't power the starter, changing the battery for a used but good one and the engine fired up on the button first press, weedy cables and all!

All connections are clean and tight.

L.A.B. · Apr 21, 2023

Uncle Frank said:
The cylinder head.

Ok, then I suggest you repeat the test but grounding to the starter body also the positive starter cable connection at the crankcase and see if the readings are the same.

B+Bogus · Apr 21, 2023

My T160 starting performance improved quite markedly after I soldered all the original crimped power cable terminals.

Uncle Frank · Apr 21, 2023

L.A.B. said:
Ok, then I suggest you repeat the test but grounding to the starter body also the positive starter cable connection at the crankcase and see if the readings are the same.

I have the positive starter cable returning from the cylinder head.

L.A.B. · Apr 21, 2023

Uncle Frank said:
I have the positive starter cable returning from the cylinder head.

It would normally be attached to the crankcase. Ideally, it should be as close to the starter motor as possible. Edit: I believe even the position of the crankcase ground has been known to cause problems if there's poor electrical contact between the primary case and the crankcase.

Also, although the harness has a battery ground (red wire) ring terminal and the Mk3 wiring diagram shows a secondary ground wire connected to the battery positive, the harness ground wire should not be connected to the battery positive terminal whenever an electric starter is used. This was a serious factory error that could potentially burn out the harness ground wire (if not the complete bike) if the main cable becomes loose, detached or has a high resistance!

Only the heavy gauge cable should be connected to the battery positive terminal so all the electrical circuits use that as the battery 'return/ground' via the head steady ground connection to the engine.

concours · Apr 21, 2023

Now test starter only. Jumper cable hooked to the power lead on the starter. The other jumper cable for the earth. Attach these to a known strong car battery.
Completely isolated from the bikes wiring.
To be clear, not using ANY of the bikes wiring or devices.
This test will confirm the starter is capable of rolling the engine over as expected.

kommando · Apr 21, 2023

I have just repaired some jump leads that stopped conducting by putting the crimped ends in an ultrasonic bath, then once dried and tested as working I soldered the crimps to the cable. The copper cable had gone green inside the crimp so no conductivity, the ultrasonic bath removed the green from the copper cable and the solder will stop the green from reappearing.

Uncle Frank · Apr 21, 2023

L.A.B. said:
It would normally be attached to the crankcase. Ideally, it should be as close to the starter motor as possible. Edit: I believe even the position of the crankcase ground has been known to cause problems if there's poor electrical contact between the primary case and the crankcase.

Also, although the harness has a battery ground (red wire) ring terminal and the Mk3 wiring diagram shows a secondary ground wire connected to the battery positive, the harness ground wire should not be connected to the battery positive terminal whenever an electric starter is used. This was a serious factory error that could potentially burn out the harness ground wire (if not the complete bike) if the main cable becomes loose, detached or has a high resistance!

Only the heavy gauge cable should be connected to the battery positive terminal so all the electrical circuits use that as the battery 'return/ground' via the head steady ground connection to the engine.

I think I ran it from the head out of convenience only. You have me thinking now could it be something this simple. I will be investigating tomorrow. I have rewired the bike and have the earth bus to the head and returning to the battery from there by the starter cable.

Uncle Frank · Apr 21, 2023

concours said:
Now test starter only. Jumper cable hooked to the power lead on the starter. The other jumper cable for the earth. Attach these to a known strong car battery.
Completely isolated from the bikes wiring.
To be clear, not using ANY of the bikes wiring or devices.
This test will confirm the starter is capable of rolling the engine over as expected.

Will do.

Uncle Frank · Apr 22, 2023

L.A.B. said:
Ok, then I suggest you repeat the test but grounding to the starter body also the positive starter cable connection at the crankcase and see if the readings are the same.

Still the same - 3.5 volts.

Uncle Frank · Apr 22, 2023

concours said:
Now test starter only. Jumper cable hooked to the power lead on the starter. The other jumper cable for the earth. Attach these to a known strong car battery.
Completely isolated from the bikes wiring.
To be clear, not using ANY of the bikes wiring or devices.
This test will confirm the starter is capable of rolling the engine over as expected.

Still the same it won't turn the engine over.

Uncle Frank · Apr 22, 2023

Well I've tried connecting the battery straight to the starter motor and it still won't turn the engine over. Took the primary cover off to remove the starter and saw that the shouldered nut on the anti backfire device has broken - guess I'll have to see to that before I proceed any further.

L.A.B. · Apr 22, 2023

Uncle Frank said:
Took the primary cover off to remove the starter

That should only require removing three screws. No need to remove the primary cover.

L.A.B. · Apr 22, 2023

Uncle Frank said:
and saw that the shouldered nut on the anti backfire device has broken - guess I'll have to see to that before I proceed any further.

The anti-backfire device slip-torque will need to be reset.

Old Britts, Overload backfire device assembly and adjustment

Electric Start Blues

marshg246

Uncle Frank

marshg246

L.A.B.

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dobba99

Uncle Frank

Uncle Frank

L.A.B.

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B+Bogus

Uncle Frank

L.A.B.

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concours

kommando

Uncle Frank

Uncle Frank

Uncle Frank

Uncle Frank

Uncle Frank

L.A.B.

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L.A.B.

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