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Had a failed starter motor that left me stranded a couple weeks ago. Rebuilt the starter with a new core and body. Cost about $100 in parts. Now the bike cranks SUPER FAST! Faster than it's EVER cranked on the stock motor or built motor + lithium battery. I suspect what happened is that long ago, the magnets in the motor started coming loose and that caused slow cranking. Since there are multiple magnets, the bike still started without issue but was a little slow.

It's 100% certain now that the starter motor was bad from even before the motor build, and the extra stress from the high compression motor tore up the loose magnets in a matter of weeks.

If your bike is slow to crank (<200rpm per service manual or <3 cranks a second), then I strongly recommend you inspect the starter motor magnets particularly if it's an older bike. After some research, I found a case of this happening to someone's ZX10R's as well. Starter motor will not fail overnight, but rather it's a gradual onset of slow cranking and eventually difficult and no starts. Once the loose magnets break into little pieces that jam the motor and short out the battery, you will be stranded and unable to even push start the bike because 2009+ has a slipper clutch!

My starter was bad for ALMOST 5 YEARS and I even tried to remedy the issue with a lithium battery, which did not address the underlying issue. You can inspect the starter by removing the two long bolts that hold the motor in one piece. All magnets should be evenly spaced with no fractures.

Here is the failed starter. Several magnets are loose and cracked.
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Good advice. I had one motor with permanent magnets loose their magnetism, did know that was possible, but the motor got weaker than quit working at all. Had to just replace it.
 

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This is interesting. I have no idea how similar starters are year to year or gen to gen.

My old '06 cranked pretty slow (to me). Slow enough that I ended up creating a thread here (or on fireblades.org...it was a long time ago) asking if it was an issue. Bike always started just fine, just cranked slow.

What is interesting is I now have a 2018, purchased new, and it has cranked just as slow as my old bike since day 1. I just assumed this was by design.
 

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Had a failed starter motor that left me stranded a couple weeks ago. Rebuilt the starter with a new core and body. Cost about $100 in parts. Now the bike cranks SUPER FAST! Faster than it's EVER cranked on the stock motor or built motor + lithium battery. I suspect what happened is that long ago, the magnets in the motor started coming loose and that caused slow cranking. Since there are multiple magnets, the bike still started without issue but was a little slow.

It's 100% certain now that the starter motor was bad from even before the motor build, and the extra stress from the high compression motor tore up the loose magnets in a matter of weeks.

If your bike is slow to crank (<200rpm per service manual or <3 cranks a second), then I strongly recommend you inspect the starter motor magnets particularly if it's an older bike. After some research, I found a case of this happening to someone's ZX10R's as well. Starter motor will not fail overnight, but rather it's a gradual onset of slow cranking and eventually difficult and no starts. Once the loose magnets break into little pieces that jam the motor and short out the battery, you will be stranded and unable to even push start the bike because 2009+ has a slipper clutch!

My starter was bad for ALMOST 5 YEARS and I even tried to remedy the issue with a lithium battery, which did not address the underlying issue. You can inspect the starter by removing the two long bolts that hold the motor in one piece. All magnets should be evenly spaced with no fractures.

Here is the failed starter. Several magnets are loose and cracked.
View attachment 264200
I get a quite a few no cranks in here. The most recent a little 110 Chinese quad. If you put an Amp Metter anywhere in the starter circuit including the kill switch you be surprised how much a bad starter can affect the rest of the system. It cooks the wires inside over time causing burned or bad connectors you name it. Serious culprit.
Great Post Blade!
 
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