Can a starter motor get weak

[Mostin3]

Hi guys, as previous posts suggest I?ve been trying to fix the starter system on my bike for ages but think I?ve got a few faults leading me up the garden path. I replaced the bendix the other day with a new gasgas item and it?s now engaging every time but as soon as it engages, the motor stops spinning and the motor gets very hot. This would suggest a bad battery, but the battery is a new lithium ion and is giving me a reading of 14.4v. I have also hooked it straight up to my car battery with jump leads and getting exactly the same symptom, ruling out any of the bikes cabling.

It total, I have replaced, the bendix, the two shafts, both helicoidal gears, all New bearings and battery. The only thing left to replace is the motor.

 

[Zman]

it is possible that the motor has internally shorted windings that will make it consume lots of current and not spin. It can also have a Mechanical problem that would lock the rotor but I would think you would have noticed that when replacing the Bendix.

 

[Neil E.]

You are right to suspect the motor. If water got into it you could have a short circuit or corrosion. Bad bearings in the motor would draw more current.

 

[Mostin3]

I will buy a new motor anyway as it?s the only thing left to replace, however...

I gave my motor to a friend who is a motor specialist and rewinds motors for a living. He stripped it down and found two issues. The resin was starting to degrade on the windings and the positive brush was tracking to earth. He re-dipped the windings and sprayed the inside of the casing with anti-tracking spray and reassembled and apparently the motor now tests fine. I got it back off him this evening and was really hopeful that it would fire right up, but on fitting to the Bike, it?s exactly the same, which is worrying.

I think I?ve ruled out it being any thing mechanical as when I remove the spark plug, the motor will turn the motor over all day so it?s almost like the bike has too much compression for the motor to turn it, leading me to believe the motor has somehow got weak. I have read on various KTM forums that you can buy a 410w starter as opposed to the 350w model fitted to the 14-15 gasgas models, so I think I?ll get one of those and see how I go.

 

[Neil E.]

There is something else to look at. The starter relay is signaled by your handlebar switch and closes to send power to the starter motor. If the relay contact is badly worn from arcing, it may not be passing enough current to turn the motor under load (compression). It could be good enough without the spark plug installed.

The ground path is also important. The battery, frame, and starting motor must have good grounds. Make sure every point of contact is clean (no paint or rust).

Take an old nut and tighten it on the starter motor stud. Connect jumper cables to a car battery. Connect the negative cable to the stater motor body. Strike the positive cable to the stud nut and see if the bike cranks (sparkplug installed). The old nut is a sacrifice piece, it will be damaged by arcing.

If the engine cranks fine you have a bad ground or a bad starter relay.

 

[Mostin3]

Hi Neil,

I tried that both before and after sending the motor Away with my friend who repairs them.

I connected the motor up to my car battery with big jumper leads, negative to motor case and then touched live voltage onto motor stud and the motor just gets hot.

 

[Neil E.]

All you can do now is try a replacement motor.

 

[Neil E.]

One last thing: Cam the bendix fully open, the force must be against the clip. Measure across the assembly to get the overall length. Measure the internal depth of the housing from face to face where the bendix fits. You may need some measuring tools and spacers to get it done (you might need to measure individual distances and add them up).

The point here is to confirm that there is enough space available that the bendix does NOT wedge inside the cases. This means it can cam all the way open and still have some end play. There may be some shims used to reduce wear on the aluminum cases, add them to the measurements.

If the bendix wedges, the drag will cause it to draw higher current. If everything measures OK, then you're back to replacing the starter motor.

 

[Mostin3]

Hi Neil, that's a really good point, I'd overlooked that.

I've done just that tonight and have about 0.5mm of free play with the bendix fully extended against the spring clip near the top of the shaf so it's not that that's causing the issue.

I will report back once I've got my new starter on to let you know how it went. I hope the starter cures it as I'm looking forward to having a fully functioning starter.