Clutch stuck? Rear tire won't spin forward

GoldenMotor.com

mpl535

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Jul 14, 2012
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Hi, my names Mike. I am new to the forum and am in the process of building my first bike. I have been reading threads on here for a while now to assist me in my build and have found you guys to be unusually (in a good way of course) helpful in troubleshooting problems. I have a 66cc HT engine kit off ebay.

My problem is I finally got the bike completely put together but found that when I try to pedal or spin the rear wheel the clutch (maybe wrong word? The sprocket on the engine turning the chain) gets stuck after a few feet or so, locking up the back tire. I know the clutch is working because I cant move the wheel at all until I disengage, and then is seems fine. I made sure the chain is aligned, and cut to the right size so I don't think its because the chain is falling off. And I also found that when I spin the tire in reverse it seems to spin perfectly without any problems.

Any ideas?

Thanks for the help in advance
 

2door

Moderator
Staff member
Sep 15, 2008
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Sounds like your alignment is off. The drive and driven sprockets MUST be in a straight line. If they are offset to each other the chain can/will bind or derail.

Tension is also important. You want 1/2 to 3/4" of slack in the chain. More or less can can cause problems.

Are you using the kit supplied chain tensioner? If so it too must align with the chain path. If it doesn't it can pull the chain off to the side. Most kit tensioner brackets must be bent/twisted to get the tensioner wheel to align with the chain.

If you'll use the search feature, keyword 'chain', you'll have plenty to read on the subject of chain/sprocket alignment and tension.

Good luck. Let us know what you find.

Tom
 

mpl535

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Jul 14, 2012
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Hey thanks for the quick response. I'll definitely try changing the length/amount of slack in the chain and the spring tensioner angle because I'm pretty sure the alignment is on point. I'll let you know how it works out.
 

mpl535

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Jul 14, 2012
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So it turns out my alignment was fine, I just had to make the chain really tight with the tensioner to stop the problem. But now I have run into another problem.

With the clutch disengaged I was able to ride around my block fine, without the chain falling off. But once I try to start the bike (engage the clutch at speed), the rear wheel locks up completely, forcing the chain to yank off the rear sprocket and get stuck between the sprocket and the spokes of the tire.

Should I be able to spin the rear wheel with the clutch engaged? I tried to spin the gear by pulling the chain by hand but it is extremely difficult and only got it to move a few links. Any Ideas?
 

Greg58

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May 1, 2011
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It sounds like your engine has very good compression, some members have had to run two head gaskets to get their engine to turn over consistently. Try adding a few drops of oil in the spark plug hole and push the bike around a little with the clutch out letting the piston cycle up and down before installing the spark plug. Maybe a little lubrication will help it turn over.
 

mpl535

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Jul 14, 2012
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Hmmm so do you think that adding a second head gasket would reduce the effort needed to pedal/the air pressure and fix my problem?

And I did some searching around other threads and this person ( http://motorbicycling.com/showthread.php?t=29831&page=2 ) seemed to have a similar issue and fixed it by adjusting the flower nut on the clutch. Is this something I should consider doing?
 

Greg58

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May 1, 2011
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If you can pull in the clutch lever and release the clutch and let it out and slide the tire everything in the clutch area is doing its job.
 

mpl535

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Jul 14, 2012
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If you can pull in the clutch lever and release the clutch and let it out and slide the tire everything in the clutch area is doing its job.
Ok, well then I don't think the clutch is the problem. It lets go and catches, but doesn't allow the rear tire to spin for more than a couple inches once it's engaged. I tried starting it again today after I put some oil down the spark plug port and the back wheel locked up after a few feet again.


Any other ideas? I dont know if this is a stupid question but could the spark plug be interfering with the piston or something?
 

Greg58

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May 1, 2011
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If you are running a stock plug you should be ok, if the piston was hitting the plug it would close up the gap. You may want to try the two head gaskets.
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
If the plug was hitting the piston it would hit on every crankshaft revolution. Not just 'sometimes'.

Remove the spark plug, with the clutch engaged, roll the bike forward. You should feel some resistance but everything should turn. If not check that the chain isn't binding on the engine drive sprocket. You indicated that you had to tighten the chain. How tight is tight? 1/2 to 3/4" slack is what we've recommended.

You said that the rear wheel locks when you "pedal up to speed". How fast is that? Anything below about 10 mph and you might experience what you're seeing. Some engines have more compression than others and they will lock up the rear wheel if you're not moving fast enough. 10mph is about right and then release the clutch lever. Let us know what you find.

Tom
 

mpl535

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Jul 14, 2012
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If the plug was hitting the piston it would hit on every crankshaft revolution. Not just 'sometimes'.

Remove the spark plug, with the clutch engaged, roll the bike forward. You should feel some resistance but everything should turn. If not check that the chain isn't binding on the engine drive sprocket. You indicated that you had to tighten the chain. How tight is tight? 1/2 to 3/4" slack is what we've recommended.

You said that the rear wheel locks when you "pedal up to speed". How fast is that? Anything below about 10 mph and you might experience what you're seeing. Some engines have more compression than others and they will lock up the rear wheel if you're not moving fast enough. 10mph is about right and then release the clutch lever. Let us know what you find.

Tom
Hey sorry, works been kinda crazy and I havent gotten a chance to work on my bike.

I tried moving my bike without the spark plug in and yes everything turns and you can hear the engine kinda "choking". I have tightened the chain to about 1/4"-1/2" of slack.

I'm not using a speedometer but I am probably going right around 10 mph down a slight hill when I engage the clutch.

On the suggestion of someone on the forum I adjusted the clutch plate (2 pedals on the flower nut) and now when I engage the clutch the rear wheel doesnt lock up anymore but regardless of my speed I can not get the engine to turnover.

Would installing a second head gasket really make that much of a difference ?

And would purchasing a pull start fix my problems?

Any suggestions/ideas are greatly appreciated
 

Greg58

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May 1, 2011
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Greg here, if your kit came with a spare head gasket as mine did I would give it a try. As for the clutch what's happening now is its slipping, I would tighten the clutch then install the head gasket. Once you run it awhile you may be able to run just one gasket.
 

mpl535

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Jul 14, 2012
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Greg here, if your kit came with a spare head gasket as mine did I would give it a try. As for the clutch what's happening now is its slipping, I would tighten the clutch then install the head gasket. Once you run it awhile you may be able to run just one gasket.
I don't think mine came with a spare gasket but maybe I'll just order a spare set from online.

And how would I know if the clutch is slipping? With the clutch engaged (from a stand still) I can't spin the rear tire more than a few inches
 

GearNut

Active Member
Aug 19, 2009
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With the clutch hand lever released, you should not be able to roll the bike more than an inch or two forwards or backwards.
When you squeeze in the clutch hand lever the bike should be able to roll as far as you want it to, but expect some resistance due to the extra drag of the engine drive chain and the internal parts rotating inside the transmission.
 

Greg58

Well-Known Member
May 1, 2011
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Like GN said you shouldn't go more than a few inches before the engine turns over or the rear tire slides, you want positive hookup of the clutch pads or they will wear quickly.
 

mpl535

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Jul 14, 2012
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Ok well, I don't think my clutch is slipping then. When its engaged the back wheel locks up after a couple inches but rolls freely disengaged. And I don't think my kit came with any spare gaskets so maybe i'll just order a set online.

When engage the clutch when I try to start my bike, the bike feels like I hit the brakes. The back wheel is still turning but you can feel the resistance of the engine. I have tried riding faster down a hill and pedaling while engaging the clutch but I still havent been able to get the engine to try to start.

I also don't know if this matters, but I also have not put the exhaust on the bike yet because I was kinda waiting to see if I could get the engine started before I had to bend it. That wouldn't cause any problems starting up would it?

Will buying a pull starter fix my problem? I'm not sure if I want to continue investing money in a project I'm starting to lose faith in (It always seems I need to buy one more thing to get it running)... but if it means that I get the bike working it will 100% be worth it. I just realllllyy hope theres a light at the end of the tunnel.

Do people commonly have bike builds that never work out? I have been working on the build for a couple weeks now and feel that everything has been assembled correctly and the basic mechanics seem to be working; But now im worried that maybe some component of the kit is broken/defective and I'm never gonna be able to figure out which piece. Im probably wrong, I hope Im wrong; because if I'm at fault then it should be an easy fix.

:-||
 

tooljunkie

Member
Apr 4, 2012
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Manitoba,Canada
i would check the manual,making sure the magnet is installed correctly,it could be installed backwards,putting timing out.
in the manual there will be a page about this.
its a matter of bringing the piston up to the top and making sure the magnet is pointing at the right position.

http://www.motorizedbicycle.ca/pages/SkyHawk.pdf
this is a link to an install manual,you will need to browse through to find the magneto placement.

dont lose hope,the gods on this here site will figure it out.
any chance you could post a pic of your setup?