1969 750 Starter Issue

S

Simon Yates

Senior member
At the end of August last year Robson and Francis Rewinds repaired the starter from my Laverda 750.  This involved machining down the commutator and replacing some of the wiring. 
Initially the starting was 100% reliable but recently, about 10% of the time pressing the start button does not turn the engine.  I release the button immediately and then put the bike in gear and move the bike backwards which turns the starter.  The bike then starts immediately.
I do not want to remove the starter at the moment but wondered if anyone has experienced a similar issue?
Robson and Francis have suggested I return the starter to them but, before I do, has anyone else experienced a similar issue or could anyone comment as to what could be the cause of this issue.
 
Putting the bike in gear should have no influence on your starter motor unless your starter freewheel is dragging which is only a step away from autodestruction of the starter.
Is the relay clicking when starting aborts?

Paul
 
At least on many vehicle starters this is caused by if the fault is inside the starter itself (external relay):
-Faulty rotor windings, open circuits. or
-Carbon brushes do not move easily enough. (Faulty brush holders, wrong brushes, faulty brushes etc.)

I would first try is there voltage on starter with volt meter when the fault is on. This checks the relay and wires.

And yes the starter should rotate when pushing bike rearwards with gear (engine rotating backwards).

-Rusty brush holders on those 750 N.D. starters. There is also no water hole (can be drilled, keeps more dry).
 
Sticking brushes could be an issue as it seems to occur periodically not all the time.
I will check but am confident there is current on the odd occasion when the starter does not respond.
These were new brushes used during the re-assembly and may now have worn in to full brush width being in contact with the commutator.
 
Simon Yates said:
These were new brushes used during the re-assembly and may now have worn in to full brush width being in contact with the commutator.
Click to expand...
They should be full brush width right from the word go!
Otherwise there may be a wee bit too much arcing going on!
 
Assuming the solenoid is pulling in with a solid, audible click and you have good battery and wiring to starter & earth...then I'd take up F&R's suggestion. When I had a similar experience of occasional failure to start (before the starter was rebuilt), the issue was down to a developing short circuit in the field winding.

Personally I'd replace the solenoid first. Chasing an intermittent problem isn't fun. Maybe get in the habit of turning on your headlight before operating the starter to see how much it dims (yes, I know - but it's pulling less than a twentieth of what the starter does and may provide a clue)
 
Rob said:
Maybe get in the habit of turning on your headlight before operating the starter to see how much it dims
Click to expand...

But you can't see the headlight while sitting on the bike.

Maybe that's not an issue in Britain's grey and dingy weather because you could see the beam on whatever it's illuminating. But here in Australia where the sun shines, we'd need to start the bike in front of as mirror to see the headlight dim.  ;)
 
How many amps does the starter draw when operating, but I expect it is more than 10A? 
Every time I start the bike I want to put the multi-meter (which is 10A capable) between the starter and earth to check the consistancy of the 12V current.    I can then watch the display waiting for the occasion when it does not operate.
Thankfully it is winter so now is the time to sort the last remaining time-consuming issues out.
 
Around 170A on a triple - never troubled to measure the 750. So unless you have a suitable meter, checking volts is the only option. It'll dip to around 10.5, depending on how quick reading your meter is; state of battery and thickness of oil!
 
As the 750 starter is greater power than the triple must be more than 170A :o :o :o
Volts it is then.
You can bet your bottom dollar ???that it will be a while before it misbehaves now that I am monitoring it.
 
Simon Yates said:
Every time I start the bike I want to put the multi-meter (which is 10A capable) between the starter and earth to check the consistancy of the 12V current. 
Click to expand...

Putting a multimeter in the starter motor circuit on the 10A scale will let the magic smoke out of the meter in a fraction of a second.  Even if you had an ammeter that'll handle 200A it won't tell you a whole lot, unless it's drawing massive current and not cranking the engine - then either your engine is seized or your starter motor is short-circuited.

A voltmeter will give an indication of battery health while cranking the engine (but only if you're cranking long enough for the meter to settle on a steady reading). If the voltage dips to much less than 10V then your battery is cactus. I have a digital voltmeter installed on the dash of my Jota. It starts pretty quickly when I jab the button so the meter rarely has time to dip below 11V.

 
Started today immediately showing approx. 10V.  As I said I shall continue to fit the multi-meter until this non-response issue occurs.
 
To help make sense of what your voltmeter does when the starter fails to crank, listen for the click of the starter relay when you hit the starter button.

If there's no click and very little voltage depression, then your starter relay isn't energising. Most likely cause is dirty contacts in the starter button, but could be a poor connection somewhere in the relay wiring, including a poor earth (ground) connection.

If the relay clicks and there's still no cranking, then the fault is somewhere on the high current side of the relay - the starter motor itself, the battery, and the big heavy wires that connect it all together. Possibly a poor connection somewhere (eg. at a battery terminal or earth connection), or problem with power getting from the brushes to the rotor windings.

If turning the starter by putting the bike in gear and rolling it backwards cures the problem, then the commutator may have a dead segment or two. In that case, take the starter motor back to the bloke who re-wound it and whinge about their rubbish re-wind.
 
Dellortoman said:
[...]

If turning the starter by putting the bike in gear and rolling it backwards cures the problem, then the commutator may have a dead segment or two. In that case, take the starter motor back to the bloke who re-wound it and whinge about their rubbish re-wind.
Click to expand...

Yep, might be just a bad solder on one of them aka open circuit, or short circuit in one of the windings, as Rob suggested. Before messing around for ages, I would follow R&F's advice to send the rotor back in. They have a kind of magic wand, which enables them to find the defective winding in less than one minute. Nearly all motors in tools and household appliances are actually DC motors running on AC, not too bad a chance that even the old-fashioned electrickery workshop just around the corner has such a magic wand at hands.

Probably better to do it now, rather than waiting for the riding season coming back into full swing... ::)
 
As a seperate issue, I just noticed that the resistance of the original HT leads differ markedly.  One is zero and the other is 1090 ohms.
I presume the new leads I Have got with zero resistance are what I need?
 
Is that with or without plug caps? They deteriorate with age. Copper leads with suppressed caps is my preferred solution.
 
It was measured with plug caps - I brought some Champion caps.
One of the old leads had a join inside the old Lodge plug cap!
 
Resistor caps are usually 5K Ohms. If you're getting 1K, then you probably have non-resistor caps and leads, with a dirty connection between them.  Zero resistance on another lead would tend to confirm that unless you have a mixture of lead and cap types.

With non-resistor leads and caps, you might find it works better with resistor type plugs, such as NGK BR8ES (or whatever plugs the 750s use - I only know B8ES for the triples). Just look for an "R" in the designation.

Potential problem: Motorcycle plugs are hard enough to find, especially in hic country towns. The resistor version of your preferred plug is likely to be even harder to find. So you could make life easier for yourself by using resistor caps and buy "normal" plugs.

The resistor reduces RF interference (radio frequency noise) that could upset any electronics on your bike, such as the ignition system. It also makes the spark duration a lot longer, which is good for starting and smooth idling.
 
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