Engine won't turn over.

Jaku_Knapu · Jul 20, 2015

I've recently purchased a 66cc motor from the internet and installed it on my bicycle. It ran great for about 15 minutes before refusing to turn. It seems to be the front drive sprocket (the smaller one) that just will not budge no matter what I do. Considering sending the engine back for a replacement.

I have the proper oil/fuel mixture (16:1 for break-in).
The clutch does not effect the engine (engaged/disengaged)
I have taken the spark plug out and proven that the piston is NOT seized by moving the piston.

I have no idea what may be causing this. I have made a video and attached the link which clearly shows exactly what my problem is in much better detail than my writing.

VIDEO: https://youtu.be/ofXRVVzhaPY

Any help is GREATLY appreciated.

Chaz · Jul 20, 2015

hello,, good video, that will help diagnose. Have you taken the drive sprocket cover off? It sounds a lot like the chain stretched and got bound up on the drive sprocket/engine case. Check that out if you haven't already and let us know.

Slogger · Jul 20, 2015

I see the clutch shaft won't turn. The sprocket cover needs to come off to see if anything has fouled the sprocket in there. The chain might have come part way off the sprocket and is now jamming up the works. Not having a tensioner can lead to problems if it isn't tight enough though at a glance yours doesn't look too loose.
This would still be my first guess.
Hope you get it going.
Regards!

EDIT: Whoops, I didn't see Chaz's post.

Chaz · Jul 20, 2015

Hey Slogger, great minds... ha ha
And he got a second opinion. I see he's offline now, probably (hopefully) taking that cover off. Fifteen minutes is enough time for a new chain to stretch.

Slogger · Jul 20, 2015

Chaz said:
Hey Slogger, great minds... ha ha
And he got a second opinion. I see he's offline now, probably (hopefully) taking that cover off. Fifteen minutes is enough time for a new chain to stretch.

I didn't think of the stretching. I figured his back sprocket being dished out plus a loose chain.. and.. Bup!
Arrrgh!

That's a nice looking new bike by the way, Jaku. Nice looking engine, pretty clean bike.

Chaz · Jul 20, 2015

I didn't even notice the wheel sprocket. Good eye. A bit of both issues I imagine.

Jaku_Knapu · Jul 20, 2015

Great theory!! Although at the time I did have the chain tensioner on, it probably came a bit loose and jammed in there? I certainly hope this is the case. Unfortunately i CANNOT for the life of me get the drive sprocket cover off. They are cheap Chinese flathead screws and they are stuck. I can't remove them without stripping them, even though I plan to replace all the hardware (providing I can get it running). I even tried blowtorching the screws to crack them loose but no luck. Even the smack of a hammer failed!

Jaku_Knapu · Jul 20, 2015

Unfortunately I cannot remove the drive sprocket. There are cheap Chinese flathead screws that I cannot remove without stripping. They're stuck. Any suggestions? I hit it with a hammer and blasted it with a blowtorch.

Chaz · Jul 20, 2015

Bummer. Well, you can use an impact driver with a bit that fits the screw really well. If you don't have one they are pretty cheap at a place like harbor freight. If you have to resort to drilling off the screw heads then that is your last resort or not, I guess a few screws are cheaper than the impact driver. Once you've drilled off the heads there will still be some of the screw shaft exposed when you pull off the cover. Then you use vise grips. Give them a shot of wd40 and let it soak in overnight.

and you should be able to get an impact driver for twenty bucks or so.

good luck and be patient

Jaku_Knapu · Jul 20, 2015

YESSSSS!!! You were correct. I blasted the joints with WD-40, let it sit for about 30 minutes, got a huge screwdriver with rubber grips, pushed as hard as I could and ripped the sucker off.

NO torqued/stripped bolts, so I can safely replace these with Phillips-head bits. And best of all, the chain was just jammed. I can't wait to test the bike out tomorrow morning!

Thank you for the help everyone. I just found this forum and I can see how helpful it is already. This is my first week with my bike and I can tell it will become a new passion/hobby of mine now.

Chaz · Jul 20, 2015

Excellent news! You can remove a link or two of chain, whatever the situation demands. You might have to use the chain tensioner but just make sure it's on there good and solid so it doesn't pull into your spokes.

A job well done! Yeah, you came to the right place. Always somebody here to help out.

cheers

Slogger · Jul 20, 2015

Jaku_Knapu said:
YESSSSS!!! You were correct. I blasted the joints with WD-40, let it sit for about 30 minutes, got a huge screwdriver with rubber grips, pushed as hard as I could and ripped the sucker off.

NO torqued/stripped bolts, so I can safely replace these with Phillips-head bits. And best of all, the chain was just jammed. I can't wait to test the bike out tomorrow morning!

Thank you for the help everyone. I just found this forum and I can see how helpful it is already. This is my first week with my bike and I can tell it will become a new passion/hobby of mine now.

That's great. Things seem all serious and bad sometimes at first glance on these engines, but then you find out what it was and it's no big deal most of the time.
Invest in a set of allen head screws, they pay off every time you have to pull a cover.
They sell them in sets on Ebay and even SBP, I think.
Now you might want to look into why it jammed in there, and correct whatever it was.

crassius · Jul 20, 2015

watched the vid - was shocked at the brutality in it

both chains are too loose to be dependable

next time, sit down & read stuff here about what to look for and what to do about it before reaching for the hammer - I'd say you're lucky not to have damaged it past the point of repair - most be close to 1000 threads here about jammed chains

2door · Jul 20, 2015

I know what your next problem is going to be so I'm attaching a link to tell you how to adjust the clutch corretly after you put it back together. It isn't as simple as just tightening the nuts and putting the cover back on.

Read this > http://motorbicycling.com/showthread.php?t=22726

And tighten the chain and check your sprocket/chain alignment. 1/2" to 3/4" of slack in the chain. Measure by leaving the clutch engaged, gently roll the bike forward until the piston comes into the compression stroke. Stop rolling the bike and check the slack on the upper chain run. At the center of the run is where you'll want to see that 1/2 to 3/4 inch of slack.

Tom

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Engine won't turn over.

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