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Autobanmod
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9,908 Posts
Discussion Starter · #1 ·
Engine cranks but won't start unless I keep it turning for almost a full minute. Then it does start reluctantly, no idle and I need to give some throttle to keep it running. After one minute at 2000 RPM both the exhaust headers were bright read. The AFR was around 12,5 when this happened.

I noticed that the rear spark plug is firing once when I stop pushing the starter button. No spark during cranking and only one when it stops cranking. On the other hand after a minute of cranking it seems to kick in as described above.

Same problem with new sparkplug and ignition coil.
No error codes at all.
Battery voltage is fine, earth connections are ok.

I don't get it :banghead:

Maybe alternator moved on crankshaft (but it's keyed!) and timing is completely off, maybe ECM broken.

:(
 

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The Hawk
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3,920 Posts
What did you do to the bike right before this started acting up? Kind of sounds electrical to me but not sure. I would unhook both battery cables and touch them together then reinstall and try it. If you had the injectors off make sure the injector wires are attached to the correct injector. Since no error code I would assume that all sensors hooked up OK? You may have to run it a little longer to get any error code to set, get it out of warm up mode.
 

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Autobanmod
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9,908 Posts
Discussion Starter · #5 ·
yes! yes! yes!

I found the failure :dance:

Unbelievable!!!

The little key for positioning the rotor assembly on the crankshaft is shorn off. One half is inside the rotor, the other half is stuck in the conical shaft end.
Both rotor and shaft are still looking fine, no serious scratches.
The screw of the rotor was still fast, very very strange thing to happen.
The rotor moved some 45 degrees or so and this caused the ignition and injection timing to be completely off.
That's been one of the most difficult failures to find I ever experienced. It's so simple and yet so unlikely to happen that you start looking into all other kinds of directions...
Ok, where's my shoulder clapping machine? :D
Looking forward to ride again finally :moped:
I'm happy :)
 

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Autobanmod
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9,908 Posts
Discussion Starter · #8 ·
I thought about it a bit more and the only thing that came to my mind is that the tight fit of rotor/shaft got loose when the engine got warm and fast again when it cooled down. In other words I must have made a mistake during assembly. Will make a blueprint to see if the surfaces of rotor and shaft are matching propperly.
 

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Autobanmod
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9,908 Posts
Discussion Starter · #10 ·
And it just happened to me again, looks exactly the same :(
Strange, the rotorbolt was torqued to spec and the rotor was sitting tight on the crankshaft konus, yet it slipped and shore off the woodruff key.
The konus surfaces were clean and dry during assembly.
This time I will heat up the rotor to 200 °C before I put it back on.

So if your exhaust headers start glowing and engine runs like crap, then don't waste your time and check this.
 

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Registered
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1,178 Posts
I would never have guessed that the key could shear. Unless the motor seized up - the sudden stop of the crank could probably cause that.

Weird. Think I'll check my bolt.
 

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Autobanmod
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9,908 Posts
Discussion Starter · #12 ·
For the sake of good order I have to point out that the crankshaft is not the original one.
So the konus could be slighly different, I'm going to lap it and make a "blueprint".
 

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Autobanmod
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9,908 Posts
Discussion Starter · #14 ·
maybe the rotor bolt is bottoming in the threads and so not locking the rotor to the taper.
Good point, but this is not the case here.
Lapping the surfaces revealed an uneven contact pattern, so most probably this was the reason.

Something to remember:
old rotor + new crank => attention!
 

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Registered
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126 Posts
Just thinking out loud here. That happens all the time on purpose on lawnmower engines when the blade hits something solid. The keys are aluminum to shear easily and not break something expensive. Your motor doesn't have a blade to hit something, but what if engine knock or timing causes a kickback? 8000 RPM has a lot of inertia, and a sudden jolt could do it.
 
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