Issues with alignment, derails

Xenno · Feb 8, 2015

Hello motorbicycling.com community. I'm happy to have found you and look forward to cooperating with you, as I plan to build many motorized bikes in the future.

I begun taking interest in this project several weeks back, and started to learn the process through youtube videos, and any viable information I could find on the internet. I learned the steps quickly, and ordered a 2-stroke motor kit + bicycle.

When the parts arrived, and I proceeded to the build, which turned out good I thought considering it was my first. Everything was LOOKING good, but after testing it, noticed something must be terribly wrong somewhere.

I couldn't keep the motor-side chain from derailing for the life of me. I made sure the back wheel sprocket was nice and flat, that the engine was centered, and the stock "derailer" seemed to be correctly placed with wheel spinning, but the chain would randomly flip over on one side of the sprocket or the other.

I yesterday I was tweaking it, and for about an hour everything seemed fine, the bike was running smooth, and then all of a sudden chained derailed while speeding up and was completely destroyed ( got all caught up and bent out in the back wheel sprocket.

I have the materials to build another motor bike, but before I start I'd be really thankful for your help to get this bike working perfectly, I don't want to get hurt. Please share with me your secrets and wisdom of motor-bike building.

Let me know if I can provide pictures or additional information to help the diagnosis.

Thank You.

Honestly,

-Xen

2door · Feb 8, 2015

First of all let me welcome you to the forum. We're glad you've joined us and I'm sure we can get you running. I'm an old south Florida transplant. Coral Gables was my home for many moons.

By "derailer" I'm assuming you mean the chain tensioner. That's funny because maybe it should be called a derailer. It often does a good job of it.

The kit tensioner bracket and wheel can be a real source of trouble if not installed with care. You must consider how much force is applied to the tensioner when the engine is pulling the bike. It is considerable and if the bracket that attaches to the frame can move, it will. It must be installed in such a way as to prevent it from rotating on the chain stay.
There are many pages of discussion on the tensioner and ways to install it and even to run without it. Use our search feature and type in 'chain tensioner' and you'll have pages to read on the subject.

The brackets, almost without exception must be bent or twisted to get the tensioner wheel to align with the chain path. As it comes in the kit the wheel will usually pull the chain off to one side causing the chain to derail. Clamp the bracket in a vice and use a tool like a big crescent wrench to twist the bracket. This might take some trial and error but it must be done.

Sprocket alignment and chain tension are also critical. The drive and driven (engine and rear wheel sprockets) MUST be in alignment. Lay a straightedge against them and the straightedge must touch 4 places to assure the sprockets are in line.

I'll post this diagram to help explain.

Good luck.

Tom

Xenno · Feb 8, 2015

^

Hello, and Thank You kindly for your response.

Cursed tensioner.. I'm having to get a new chain right now.

How important is the chain length ? I've been getting them cut as short as it fits, is this correct? I did notice a lot of pressure on the motor-side chain but couldn't imagine it any longer. Are there any alternative chain tensioners with better success that I could purchase from an online store?

Your support and knowledge is very meaningful and important to me. I plan to build many more these as a hobby / business, and their functionality is very important. I tried to absorb as much information as possible before starting, but its the small details that can get you. I hope I'm doing most of this correctly and only need to fix the tensioner.

2door · Feb 8, 2015

Depending on the bike frame you might be able to run without the dreaded tensioner. Frame design is important here. If you have horizontal rear drop-outs that is a plus in your favor. Also chain stay design plays into it.
If you can install the chain and have frame clearance with the chain and a way to move the rear wheel to adjust chain tension, you don't need the tensioner.

Chain slack should be 1/2" to 3/4". A chain that is too tight or too loose will cause problems.

Have you read any of the information provided on the tensioner? Here is a link to many pages of discussion > http://www.google.com/cse?cx=partne...15#gsc.tab=0&gsc.q=chain tensioner&gsc.page=1

One option that I and many experienced builders are not impressed with is a spring loaded tensioner. They allow chain slack when you least want it. I try to guide people away from using them. They are a band aide used to bridge the hurdle of proper chain and sprocket alignment and installation.

Providing us with some photos of your bike and installation will help us make more recommendations.

Tom

fatdaddy · Feb 9, 2015

2door never gives bad info, So first, do it just like he said, then I'll tell ya how to check and fine tune it. The rear sprocket is the hardest part of the build, and almost impossible to get perfect, unless you use a sprocket hub adapter. Barring that, What ya gotta do is make sure the chain is running centered on the rear sprocket. So. roll the bike forward a couple feet and STOP... DONT roll it back AT ALL. Look at where the chain is rolling on to the sprocket, bottom side. You'll be able to see if the chain is going to one side or the other. You'll probably see a little space between the chain and sprocket. If that space is all to one side its not running centered.The sprocket has to hit the chain in the very center. If your pretty sure you have everything else as close as possible, then you can use the tensioner to make VERY SMALL adjustments to the chain centering. If everything else is still way off this will probably NOT work. If the chain wants to go to the inside of the sprocket then pull out the tensioner just a little. if the chain wants to come off the outside then push in the tensioner JUST A LITTLE. It usually dont take much. Roll yer bike forward and PUSH IN or PULL OUT the tensioner untill the chain is hitting EXACTLY centered on the sprocket. THEN, TIGHTEN UP THAT TENSIONER so it dont move. Most chain problems stem from a loose tensioner.. Leave a little slack in the chain. 3/4" or 1" of play should be enough. if you didn't install the sprocket perfect, then yer gonna get a little back-forth play and that will make the chain go... tight-loose,tight-loose. So a little slack in the chain helps with that. I hope I explained things in a way thats easy enough to understand. EVERYONE will tell ya, the rear sprocket is a PITA. Sorry i didn't get to ya before ya fubar'd a chain.
fatdaddy. usflg

maniac57 · Feb 9, 2015

About all I can add is that once you get everything lined up, make sure it rolls the same backwards.
More noise or any binding when rolling backwards shows mis-alignment somewhere and it still needs work.
But BE VERY CAREFUL when rolling it backwards as the masterlink clip can sometimes pop off if it hits the tensioner roller just right....
I prefer to do without the tensioner if possible, but if forced to use one, I tack weld it to the frame once it's correctly aligned.
Once everything is quiet and rolling free in BOTH directions, it's good to go.

fatdaddy · Feb 9, 2015

YUP, backwards is almost as important as forward. If its chunkin and clunkin backwards then ya still got somthin wrong. But ya dont really ride it backwards, do ya. LOL. laff

If it chunks anyway ya roll it, fix it AGAIN. But usually If it rolls well forward, It'll do the same backwards, MOST of the time. If it chunks going backwards then yer alighnment is STILL TOO FAR off.
fatdaddy. usflg

Xenno · Feb 21, 2015

Hello, im back. My apologies for the delay, was hit by a wave of stuff.

Here is a couple pictures of the bike im currently working on.

Everything looks and feels good about it, except that tensioner..

While searching, found these on ebay;

http://www.ebay.com/itm/49-66-80cc-...ensioner-Spring-Loaded-Michigan-/181196082385

http://www.ebay.com/itm/80cc-motorized-bicycle-Spring-Loaded-Idler-chain-Tensioner-/221659274921

http://www.ebay.com/itm/Spring-actu...-chain-tensioner-80cc-66cc-50cc-/331479867845

http://www.ebay.com/itm/49cc-60cc-6...ng-loaded-chain-tensioner-idler-/281445081064

Could any of these or something like it help or solve my difficulties ?

How long or short should I be cutting the chain ? ( Cut this one as short as would fit.. )

Thanks so much for your help !

2door · Feb 21, 2015

Try to avoid using a spring loaded tensioner. Most experienced builders will agree. They are a band-aid and not needed if your sprocket alignment and chain tension are correct. They also allow slack when you least want it.

Chain tension (slack) should be 1/2" to 3/4". With the clutch engaged roll the bike forward very slowly until you feel the piston going into compression. At that point the top chain run will go slack. Measure for that 1/2 to 3/4" somewhere near the center of the chain run between the two sprockets. Actually from your photo, your tension looks good.

Good luck

Oh, and I think I recognise that picture behind your bike. If I'm right that's an island in Thailand. I've been there

Tom

2door · Feb 21, 2015

Just looked at your photos again and noticed you have the small spring on the clutch cable. The one between the arm and the cable guide. We always suggest to get rid of it. It serves no purpose but to make the clutch harder to pull.

You'll also probably get warnings about the fenders. Do a little reading here, use the search, and you'll find lots of information on how to reinforce them to help reduce the potential of injury from a fender coming loose while riding.

Tom

Xenno · Feb 22, 2015

Can the back wheel sprocket be placed backwards? @~@

2door · Feb 22, 2015

Xenno said:
Can the back wheel sprocket be placed backwards? @~@

No.
But yours is a dished sprocket with the teeth off-set from center. It can be installed with the teeth toward the inside or the outside. But it can't be installed "backwards".

Tom

fatdaddy · Feb 22, 2015

Your sprocket is on right. The problem is probably the tensioner. Try looking at the chain as it rolls onto the bottom of the rear sprocket. roll yer bike a few feet forward, then STOP. DONT let it roll back. look very closely at the chain. Is it hitting the exact center of the sprocket or is it off to one side more than the other. sometimes a very small adjustment on the tensioner makes all the difference. if the chain is going to the inside pull out the tensioner a little to help guide it on the sprocket. if its going to the outside, push in the tensioner a little. small adjustments on it can help out that chain problem a lot. NOW for the disclaimer. If yer chain alighnment aint real close to start with, this probably wont work. if everything else is as close as you can get it it'll prolly work great. Push the thing in out out, whichevere is needed, roll it and check again. do this sevarel times untill yer happy its hitting center on the sprocket.
I've explained this process a few times now so I'm gonna copy and save this to paste for the next time someone has this issue.
fatdaddy. usflg

2door · Feb 22, 2015

Refer back to the first page of this thread, my post #2. I provided a diagram that should explain what we mean by chain/sprocket alignment.

I'm going to redo that diagram and include the tensioner and show how it must be centered on the chain. Your bracket probably needs to be bent/twisted to allow the tensioner wheel to align with the chain if it is pulling the chain off to either side as Fatdaddy explained very nicely.

Have you tried laying a straightedge against the drive (front) and driven (rear) sprockets? That will tell you if you have the sprockets aligned. If they do then consider that the tensioner wheel must also be aligned/centered on the chain so it only applies tension and doesn't pull the chain either in or out.

I've seen some suggest that the tensioner wheel can help "guide" the chain onto the rear sprocket. I have to disagree with this. I'd much rather see the sprockets aligned than trying to guide the chain. If the alignment is correct you don't need to guide it. It will track itself and not derail.
But here again, this is an issue of 'what works for you'. I'm just saying what is good engineering practice when it comes to roller chain applications.

Tom

fatdaddy · Feb 22, 2015

2door said:
Refer back to the first page of this thread, my post #2. I provided a diagram that should explain what we mean by chain/sprocket alignment.

I'm going to redo that diagram and include the tensioner and show how it must be centered on the chain. Your bracket probably needs to be bent/twisted to allow the tensioner wheel to align with the chain if it is pulling the chain off to either side as Fatdaddy explained very nicely.

Have you tried laying a straightedge against the drive (front) and driven (rear) sprockets? That will tell you if you have the sprockets aligned. If they do then consider that the tensioner wheel must also be aligned/centered on the chain so it only applies tension and doesn't pull the chain either in or out.

I've seen some suggest that the tensioner wheel can help "guide" the chain onto the rear sprocket. I have to disagree with this. I'd much rather see the sprockets aligned than trying to guide the chain. If the alignment is correct you don't need to guide it. It will track itself and not derail.
But here again, this is an issue of 'what works for you'. I'm just saying what is good engineering practice when it comes to roller chain applications.

Tom

And if those things went on perfectly straight every time I'd agree with ya tom, I'm not talking about using it to guide the chain so much as push it in or out till the chain hits center on the rear sprocket. Then you'll know for sure the tensioner wheel is rolling straight in line with the chain and sprockets. if the tensioner wheel aint centered perfectly between the sprockets it WLL throw a chain. Best way, if ya can, is to throw that F'n tensioner in the trash and run a straight chain. I'm thinking about spending a couple day's in the shop and try to come up with something, (anything,) BETTER than that POS tensioner. And yer right about spring loaded tensioners, They just dont work.
I think I explained it wrong when I said the roller can guide the chain. Only that if its not centered right it WILL guide the chain OFF the rear sprocket. Making sure the chain hits center of the sprocket with the tensioner is the best way I've found of centering the tensioner wheel. I cant be the first to find a way of exactly centering the tensioner wheel.LOL And I think getting the roller perfectly in line is just a ("good engineering practice when it comes to roller chain applications,") ( Just messin with ya bro.) But I hope I explained it better this time.
fatdaddy. usflg

2door · Feb 22, 2015

Fatdaddy,
You know we're always on the same page.

I base my opinions on years of dealing with roller chain powered systems and the results of misalignment between the drive and driven sprockets. I can't begin to tell you how many 'band-aids' I've seen folks try to get around improper sprocket alignment or chain tensioning.

Everything from chain guides, spring loaded tensioners, even modified sprocket teeth in an effort to keep the chain from derailing or otherwise causing drive system problems.

For the last 15 years of my working life I was directly involved with production line work in a plant that made products that were assembled on a chain driven conveyor system. One production line in particular had no less that fifty devices all driven by electric motors and roller chains of various sizes running at various speeds. The line mechanics were constantly having to adjust things to keep the chains from derailing or causing problems. I was consulted countless times when a chain drive system started giving trouble and almost without exception the problem was traced to a sprocket that had slipped on a shaft, a shaft that had shifted from parallel to the drive or faulty chains that would not properly conform to the sprocket. (binding links).

I've seen the same things on motorized bicycles many times. A builder who doesn't understand the importance of aligning the drive and driven sprockets and expects the chain to run at an angle between the two or a chain that is either too loose ot too tight.

This is why I preach "Tension & Alignment" in nearly every thread that comes up regarding chain/sprocket problems. Folks with little to no experience working with this seemingly simple drive system often do not grasp the importance of alignment. They base their installations on pedal bicycles and their experience with the chain on them.

When you motorize a bike you are dealing with a lot more force and stress on the chain drive as well as acceleration and deceleration forces and to keep things working, it must be properly installed (aligned and tensioned).

If everyone who embarks on a project to bolt an engine to a bicycle had years of mechanical experience behind them we wouldn't see the problems we do. Unfortunately this isn't the case. Many new builders, evident by the posts we read, do not even own basic tools and don't know how to use them if they had them. Asking them to suddenly grasp the concept of how a roller chain system is supposed to work is asking a lot.

To many of us it is common sense but it isn't to everyone. I'm sure there are members here who can do things I have no idea how to do, and do them well. They have the natural ability to do them...I don't. But I was blessed, or cursed, depending on how you look at it, with a mechanical appitude. This hobby would be so much easier for many if they had been too. But that just isn't the case.

That's why you and I are here. To take them by the hand and lead them along to a successful bike build.
Let's keep trying, brother.

Tom

fatdaddy · Feb 23, 2015

("That's why you and I are here. To take them by the hand and lead them along to a successful bike build.
Let's keep trying, brother.

")

Till the wheels fall off bro. Never give up, never say die.
fatdaddy. usflg

bdawson85 · Mar 11, 2015

Had the same issue with mine. Chain was off at the master, and looking the links I needed to remove another link and set it up better. Also, mine is a mountain bike(pain in the ass) ! Lol, it was more difficult to get chain and wheel aligned due to the gears and the breaks constantly throwing it off center or interfering. I had to loosen the bolt and manually turn the pedal and just watch to see where the chain moved naturally with out derailing. Once I felt confident that's where I'd tighten the bolt down at. The standard stock tensioner isn't the greatest but it made a difference too. I had to do the same, trying to find the right place and amount of tension.

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