Need Help With Motorized Bike Engine / Crankshaft Wont Turn

mbilleaud

New Member
Aug 15, 2018
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Hi All,

Let me try to explain my problem in as much useful detail as possible here. I'm not the most savvy mechanic, although this bike being quite fun and a pain in the ass has taught me a fair deal so far.

I've been riding a seeutek motorized bike mounted on a Schwinn for approximately 100 miles. So it's a relatively new bike.

I was riding my bike along when the rear tire suddenly locked up and left me unable to pedal.

I got the bike home and started trouble shooting / taking things apart. Here's where I stand.

With the chain connected to the front and rear sprocket, I can pedal with some effort, and the rear tire is no longer locked up (I took off the back tire and tightened things up / re-aligned things); however the piston does not move up and down (and obviously the crankshaft is not turning either). This is the same case for whether the clutch is engaged or not (or so I think; more on this in the next paragraph). What might be the reason for this? When the front (engine) sprocket turns, shouldn't it turn the crankshaft as well? Is this what is defined as having "no compression" or is this in some other problem category?

Without the engine chain on, I can pedal the bike freely, no problem.

I have removed the clutch casing and have tinkered with the clutch cable tension. This doesn't seem to be the problem, though I guess I'm not sure Even with the clutch seemingly engaged, the crankshaft will not turn (and the piston will not move up and down. No compression.) The bike behaves the same way whether the clutch lever is in or out, which leaves me a bit confused but leads me to think it is a clutch issue. And again, I'm only assuming I did this correctly. I tried both tightening and loosening the wingnut but didn't see any obvious problems. Does the crankshaft only turn with the clutch engaged? Is there someway to make absolutely sure the clutch is or isn't engaging?

I have removed the head of the motor and examined the head gasket. It doesn't seem to be faulty (although it is poor quality).

With the spark plug out, and my thumb over the hole, I am sensing no compression. This seems like a no brainer. If the piston does not move up and down, you won't get compression in the engine. I just don't see how this problem could be related to the spark plug. Correct me if I'm mistaken though.

So to sum it up, my crankshaft will only turn / piston will only move if i put a ratchet to it. Any help would be greatly appreciated. I can also post pics if it would help.

Other tidbits :
- removed front sprocket cover, chain isn't snagged
- disconnected kill switch
- removed clutch plate and replaced, having tightened and loosened wingnut
- examined magneto, though haven't tested it
- am clueless about how the CDI would interact with the crankshaft
- had to clean the carb and flush out a gas/oil mixture with too much oil about a week ago
- tried to see if i got a spark from the plug - test inconclusive


Thanks a bunch,
Matt
 
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mbilleaud

New Member
Aug 15, 2018
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One more question while I continue to work on this. When the crankshaft turns (and the piston moves up and down) under normal operation, is the smaller gear under the clutch plate (as opposed to the larger one that surrounds the clutch pads) automatically supposed to spin? Because right now, only the screw in the middle is spinning.

I'm hoping this image clarifies what I'm looking at when I say only the screw inside the smaller gear is turning when I turn the crankshaft from the magneto side.

https://goo.gl/images/FLgh2n
 

mbilleaud

New Member
Aug 15, 2018
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OK so check out the vid. I think I figured out the problem but I could use some confirmation and the recommended fix. Tank ya. Also, bonus featuring me getting crushed by falling bike at end.
 

mbilleaud

New Member
Aug 15, 2018
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need some keyway or make your own!
Does anyone know what the dimensions for the key are / where I can order one?

Also, I'm guessing I need a tool to take off the large gear and re-mount it. Or do you think it's perma-damaged?

Cheers,
Matt
 

crassius

Well-Known Member
Sep 30, 2012
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first, look around your work area (drag a magnet if you have one) to see if woodruff key just fell out - sometimes factory guy gets it wrong and key slips out backside while he puts on small gear

key is half-moon shaped and in a pinch can be made by cutting some steel washers in half and jamming them in the slot

best to find a real one and use that though (note: all 4 keys are same size, so you can take another with you to h/w store)
 

mbilleaud

New Member
Aug 15, 2018
5
0
1
35
first, look around your work area (drag a magnet if you have one) to see if woodruff key just fell out - sometimes factory guy gets it wrong and key slips out backside while he puts on small gear

key is half-moon shaped and in a pinch can be made by cutting some steel washers in half and jamming them in the slot

best to find a real one and use that though (note: all 4 keys are same size, so you can take another with you to h/w store)

No go on finding it. The auto shop near my house has replacements that I'll be picking up tomorrow.

What about the large gear? How likely is it that the shaft between the engine sprocket and the gear is done for? Should I simply take it off and try to put it back on?

Many Thanks,
Matt