Stumped! Calling all you trouble-shooters! GN250 won't start

[maspito]

Hi experts!

I come to you as I am utterly stumped and not sure which way to move with troubleshooting of my sick Suzuki GN250.

I was riding her the other day, pulled out of a junction and as I changed up gear, something went clunk and the bike died. After pushing her for 2 miles home, I started trying to figure out what has gone wrong...

1) Changed gear and think I heard a sort of clunk noise then died. Refused to restart.
2) Start switch doesn't activate the starter motor. When pressed, a single click can be heard from the starter relay, but then all power seems to fade - green "neutral" light goes out and no further click on subsequent attempts. After a while, power seems to return.
3) Battery checked and is good.
4) Main fuse checked and is good.
5) Jumping the starter motor, directly from the battery, spins the starter motor and turns engine, but nothing more. Engine doesn't fire up.
6) Engine can be turned manually using a ratchet and socket on the crank, so doesn't appear seized.

Any advice on what I should check next would be greatly received!

[jaffa90]

""""" Battery checked and is good.""""""
What`s the battery voltage as in 12.6v ?
A safety switch / kill switch could be faulty prevented starting / sparking.

[maspito]

Hi jaffa90,
Yes it's a 12v "maintenance free" type battery.
I will check the kill switch and circuit this evening! Thanks for the input!

[maspito]

Is there any way of checking if the CDI unit is faulty?

[Teflon-Mike]

Not tackling these i order:-

[Teflon-Mike]

[chris-red]

I'd test the starter solenoid first.
____________________
Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
WANTED:- Fujinon (Fuji) M42 (Screw on) lenses, let me know if you have anything.

[Chris45]

[maspito]

... but would a faulty starter motor cause the bike to breakdown whilst riding?

[Chris45]

[maspito]

Ok! A HUUUGE thanks to you all for posting your comments. So much to read and learn from you all there. I will take the next couple of days to work through everything you've told me, and will let you know how successful I am (we are)!
Again, massive thanks to you all!

[Teflon-Mike]

Does the GN have a battery topped, live-rail ignition though? If so; then genny should be putting all its output through the reg/rect onto the live rail, that will supply the ignition circuit, and once engine running, supplying sparks to keep engine running.

A flat battery should only take excess amps not being drawn by the ignition or equipment to 'charge', so once running engine should stay running on the amps banged out by the genny as long as its spinning... give or take...

Instances it wont, are likely if the motor was running at lower revs where the genny wasn't banging out too many amps, and other equipment like lamps were competing for them. In that situation head-lamp would tend to dim, long before sparks dropped out, and the ignition would more often start to intermittently 'drop out' rather than just 'die' suddenly, unless you co-incidentally turned on some other high-draw equipment, like pressing the brake pedal, turning on stop-lamp.

Battery, could rob amps, and sufficient to make the motor conk, if faulty, and plates warped and potentially shorting, and actually drawing current, but like a head-lamp, wouldn't expect it to suddenly make engine die; if that bad, I wouldn't expect it to start the engine to begin with; after that, I'd expect sparks to drop out intermittently, as it robbed amps from ignition, and make motor conk, most likely when revs drop.

Given how a tired solenoid and starter CAN kill a battery like that, I wouldn't dismiss the suggestion they may be to blame.... But, fact that bike don't start, isn't the same problem as why it stopped running.. that's what needs to be bottomed out.

Starter-motor, and solenoid help start bike, they don't stop it running, so cant 'directly' be the answer to that one. Battery 'may'... among host of possible electrical faults from a bullet connector shaking loose, to a wire fretting and shorting to the frame, through CDi giving up the ghost, or the reg-rect going toast-wise, or loosing a winding the genny. All of which may need to be bottomed out.... after primary course, 'just' checking for sparks, at the plug, on the kicker or a know good, preferably well over-rated car battery, after popping the rocker cover and checking for obvious, like snapped cam-chain, wide tappets or a lost lock-nut! (and performing basic service adjustments, just to eliminate dumb questions later!) And doing basic compression test, even if only rule-of thumb over the hole!

Nothing is really 'off the menu', but starter systems start engines.. they don't stop them! So not really at the top of the list for proddings and pokings, yet. But that's what needed here, I think; logical prodding and poking, looking at stuff that can stop engine running, once started, not what isn't starting it, and working down the list, methodically, no straw clutching.

'Trouble' with electrics is that they are too easy to tackle, to avoid looking at oily-bits, and then have you chasing your own shadow, rather than actually getting anywhere helpful... like repeatedly replacing battery, when root cause is a knackered starter motor!
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[bypass2]

Does a gn250 have a flywheel if so maybe the woodruff key as broken/ Just a guess. does it have a kickstart if so try starting it with the kickstart

[MahatmaAndhi]

I'm not adding much here, but on my GN125, if I try and bump start it by running alongside and dumping the throttle, I get nothing.
However, if you're sitting on the bike and pushing then it works almost every time, even though I'm going a few MPH slower.
____________________
2008 Aprilia Sportcity 250

[maspito]

I think that's because you need the traction from the rear wheel to drive the engine over, so when you sit on the bike, your added weight massively improves that traction.

[maspito]

UPDATE:

Today I remove and dismantled the Start Motor. She looked clean as a whistle inside. Wiring and connectors were undamaged. I saw evidence that the brushes are making good contact. There were hardly any carbon dust (so I suspect the previous owner had replaced this part not too long ago). Most importantly, there was absolutely NO sign or arcing or other electrical failure.

Therefore, I will rule out the Starter Motor as being faulty.

Once reinstalled, I tried to jump the Starter again. This time, the ignition was turned on, the Spark Plug removed and grounded to the Engine... but sadly there was NO spark

The battery had no issue to keep turning the engine over and over like this, so I am also ruling a bad battery our of the equation.

I've ordered a new Spark Plug to cut that from the equation (I know, probably should have been my very first action!)

The good news was that while she was turning over with the Spark Plug removed, I was able to feel air pumping out of the Spark Plug hole, so there is compression (exactly how much will obviously need further investigation)

I've also checked the entire Wiring Loom and find no signs of failure.

So once I receive the new Spark Plug, I will resume testing! Any further comments would be greatly appreciated!

[maspito]

UPDATE:

Just tested the Ignition Coil:

4.2 Ω across the terminals (primary coil)
24.45 kΩ from Ignition Coil Terminal to Spark Plug connection (secondary coil).

4.2 Ω for the primary seems good.
24.45 kΩ for the secondary seems a bit on the high side... But I have no idea if that would be enough to cause an issue...?

[maspito]

UPDATE: NO LONGER STUMPED!!!

So, after checking every single electrical component for correct resistance / continuity, I was non the wiser. All the electrical components checked out work (FYI 24 kOhms was a good measurement).

At this point, I'm really starting to hate this machine!

So I start playing around aimlessly, and notice that the sound of the engine turning over had changed - I could now hear the starter spinning freely but the crank and engine was no longer trying to turn over. So I remove the LH engine case and see that the Rotor Generator wasn't spinning with the Start Motor. I guess something is up with the starter clutch not engaging, so I pull the Rotor Gen off to find a rather classic problem: a sheared Rotor Gen Clutch bolt. I've attached pics below.

Now we have explanations for all the effects I experienced:

1) The clunk noise: This was the noise of the bolt shearing.
2) Immediate loss of power: Sheared bolt head jamming the Rotor Generator and Starter Driven Gear, slowing down the Rotor Generator (maybe even driving the Starter Motor), reducing electrical generation / power.
3) Not activating the starter motor and draining power: Sheared bolt head jamming the Starter Driven Gear, causing the Starter Motor to be unable to turn, yet sapping battery power.
4) I think the Sheared bolt head eventually worked loose when I was manually turning the engine on the Crank, which allowed subsequent efforts on the Starter Motor to turn the engine, but as the Starter Clutch was not engaging, no power was being generated to kick the engine into life.

So this (I think) explains EVERYTHING!

There were no signs of Locktite on these bolts, which I believe they should have. Luckily, I have a complete spare engine! So I'll rob the parts to replace all the damaged ones and will put her back together later this week.

[maspito]

Thanks to you all for your inputs earlier.
I hope the findings I've posted add something to your knowledge arsenal!

[pepperami]

This thread does not end until you come back and tell us that it's running again.
Pictures/video or we come round your house late at night wearing hockey masks
____________________
I am the sum total of my own existence, what went before makes me who I am now!

[maspito]

Haha Peperami!
You are right; I've jumped the gun slightly.... I could very well come back crying to you guys later this week with egg on my face...

[maspito]

In case it wasn't clear, the picture of the two bolts with thread damage are the two bolts that were left holding the Starter Clutch to the Rotor Gen. They were completely loose; I was able to simply remove these with my fingers.

[maspito]

Ok.. shoot me... Egg on my face....

Thumbs up to Bypass2.... Respect.

Started to rebuild this evening but just noticed the issue with the Woodruff Key...

If you take a look at Pictures 1.jpg and 5.jpg, you will see the Woodruff Key on the crank Shaft has sheared and been worn down smooth with the Crank Shaft.

The remaining part of the Woodruff Key is pretty solid in there! Not sure how I'm gonna get it out! I'm not keep on pulling the Crank Case apart and replacing the Crank, so I think it's gonna be some careful hammer and chisel action...

Any tips welcome!

[maspito]

So no Woodruff Key (aka Rotor Generator Key) means no spinning from the Rotor Gen, and hence catastrophic loss of power, which makes MUCH more sense than just the bolt shearing.

[maspito]

Hey guys... Still having issues!!!

I rebuilt the flywheel generator, installed a new woodruff/flywheel key, put everything back together, started her up and...

STILL!! The starter motor just spins. The flywheel generator stays stationary and doesn't seem to pick up on the starter gear.

Now, to be clear, I rebuilt the Sprag/Start Clutch correctly, torqued the 3 bolts that attach it to the Magneto, lined the Magneto/Starter Clutch Assembly up on the Woodruff key and torqued the main nut holding it all in place.

The Starter Motor and Idle Gear are spinning clockwise, which I believe is correct.

So all I can think of is that the springs/rollers of the Sprag/Starter Clutch aren't doing what they should be doing. Any thoughts?