Chain won't line up to the Drive Sprocket

Discussion in 'Frame Mounted Engines' started by Ryno, May 15, 2011.

  1. Ryno

    Ryno Member

    I have everything put together on my first build here. I'm running a 48cc Grubee Skyhawk.

    Initially, the chain wouldn't line up on the rear wheel sprocket. The chain would fall off when it was rolling. I got that "straightened out". The rear wheel sprocket is now as close to the spokes as it can be while still clearing the chain.

    Now, when my bike is rolling for a little bit the chain falls off of the front drive sprocket in the engine. It falls off to the left of the sprocket.

    It seems that my engine may be on a strange angle, and the chain is not lining up with the sprocket correctly. However, it's mounted on the bike right where it should be.

    I was thinking that the bike frame itself may be bent somewhat, so that the rear wheel doesn't line up correctly.

    What do you think the problem is, and how can I fix it?

  2. DuctTapedGoat

    DuctTapedGoat Member

    Okay, multiple questions here.

    * How are you mounting the sprocket to the rear wheel?

    * How much slack is on the chain?

    * Are you using a chain tensioner/idler pulley?

    * If so, how is it installed?
  3. Al.Fisherman

    Al.Fisherman Active Member

    And of course a picture wouldn't hurt either.
  4. Ryno

    Ryno Member

    First it was mounted just as suggested, with the rubber parts on the inside and outside. But that didn't work because the chain would pop off of the back sprocket, even when it was straight. The person helping me had his set up a certain way, so I copied it. This is how it is:

    the dish side is IN, and there is no rubber part on the outside of the wheel. There is enough room for the chain to clear the spokes.

    The chain does not have a lot of slack, but it's not pulled tight either. It seems to be a reasonable amount, but there might be too much.

    I'm using a chain tightener just the way it's supposed to be used.

    I can post a picture later
  5. Al.Fisherman

    Al.Fisherman Active Member

    I had a chain that was popping off the wheel sprocket and caught between the sprocket and spokes. The gear teeth were the furthest away from the spokes that would allow. What was causing it was that the chain was hitting the frame just enough to derail from the sprocket...a added washer just inside the frame where the axle fits solved the problem.
    Last edited: May 16, 2011
  6. Ryno

    Ryno Member

    Are you suggesting that this could solve my problem?

    I suppose an added washer for the axel could move the wheel over just enough to line the chain up correctly with the drive sprocket.
  7. Ryno

    Ryno Member

    "Rubber rag joint installed up against the spokes on both sides, 3 washer plates on the inside of the wheel up against the rubber, and sprocket against rag joint on the outside."

    I know that this is how it is supposed to go, but the chain would not line up with the back sprocket when it was set up like this.

    The person helping me has his set up like mine and his works just fine.

    As for 'beveling each tooth", no I haven't.
  8. Al.Fisherman

    Al.Fisherman Active Member

    I had to do that to mine and it works fine...can't tell when riding it other then the chain stays put. Is the engine mounted CORRECTLY???
  9. Al.Fisherman

    Al.Fisherman Active Member

  10. DuctTapedGoat

    DuctTapedGoat Member

    Looking at the bike from the rear, is the sprocket to the left or the right of the motor's drive sprocket?

    And when you say the dished side is in, is the chromed side out, or in?

    Just for extra clarification between now and when we get pictures.
  11. Ryno

    Ryno Member

    Looking at the bike from the rear, the two sprockets actually line up pretty dang well. This is why we attached the rear sprocket in such a way- so that they would line up perfectly.

    The problem is,(I think) the front drive sprocket is crooked. Not that it isn't lined up with the back sprocket.

    As for the chrome side, I'm not sure which side is chrome or not. The convex side is pointed away from the wheel. This is how we got the chain to line up on this particular frame.
  12. DuctTapedGoat

    DuctTapedGoat Member

    When you got your kit, did it come with 415/410 chain, or standard bicycle chain?

    If it's standard bicycle chain put everything on pause and go buy some 410/415/bmx stunt chain from a bike shop, or get some #41 from a tractor supply store. That will take care of a lot of it right there. The standard bike chain doesn't give you any room for error, while the larger stuff gives you more play in the alignment.

    Now that being said - the only way you're going to be able to use your sprocket on the inside (backwards from how it should be, they are dished to keep the chain away from the spokes) is with small standard bicycle chain. When you do get 410 etc you'll need to flip it around so the concave side is facing out.

    I know what you're thinking - "But my alignment will be off". But don't worry, it won't be. The tensioner has a second role to that of keeping the chain tight - and that is aligning your chain as it comes out of the engine and onto the drive sprocket. You could have some variation in the TOP of the chain, but that will only affect you if you're reversing, which you can counter with a second chain tensioner on the seatstay tube. The most important is that the bottom of your chain is aligned with the tensioner in such a way that it feeds it nicely onto the rear sprocket. You can bend and tweak that tensioner as well to get a straighter guide as well.

    That is one of the HUGEST things I hate about Grubee engines, and that's that every one I've seen comes with dinky little pedal chain stock.

    Anyways, to summarise - regardless of if that's how your friend did his, you need to put the concave side of the sprocket to the left/outside of the wheel. That should fix your skipping issues. And when you get a chance, get some #41, 410, 415, BMX Stunt Chain to replace the standard bicycle chain you have on the motor side currently.
  13. Ryno

    Ryno Member

    Alright! That's some good advice, thanks.

    Also, I made a video for diagnosis purposes.

    I am hoping that a chain like that will solve my problem. It seems like the small chain is so precise , and having a tiny bit of wiggle room will be just what I need.

    Check out the video though, tell me if you still think that will help.
  14. Ryno

    Ryno Member

    Oh, and I forgot to mention: The chain no longer falls off of the front sprocket, but it skips on it (bumps up and down). You can see it in the video.
  15. DuctTapedGoat

    DuctTapedGoat Member

    I do see that - I feel incredibly confident in saying that reversing the rear sprocket and getting some 410/415/#41 chain will help. It looks as though the chain is trying to fall off the right side of the drive sprocket in the motor, but is popping back on.

    I could only see the sagging of it when it was stationary, but how much play is in your chain? It looked fairly loose. Granted, it needs some play especially with the chain skipping issues, but it seems you might be able to tighten that up slightly.

    If you don't have access to some newer chain for a time, you can try just reversing the sprocket and using your standard bike chain for now - that might give you better alignment if I'm right in that it's skipping to the right of the motor's drive sprocket. It surely wouldn't hurt - as either way that sprocket would have to get reversed (to fix alignment with your current chain or getting larger chain).
  16. Ryno

    Ryno Member

    I realize that there was a lot of slack when I made the video but that was temporary.

    I'm going to pick up some new chain today, assuming that my town's bike shop has some. I guess I'll try reversing the sprocket with my standard chain first, and if that doesn't work I'll switch chains.

    Thanks for the help, if this works I'll be a happy man!
  17. Ryno

    Ryno Member

    So I went out and got the bigger BMX chain. However, just by looking at it, there doesn't seem to be a noticable difference between this chain and the one that I already have. I'm concerned that I already had the bigger chain...

    Would I be able to tell by eyeballing it?
  18. DuctTapedGoat

    DuctTapedGoat Member

    The difference is going to be between the plates - the stock stuff is 1/8". You're wanting to get chain that's 3/16", 1/4", or 5/16" between the plates to give you the right amount of left to right play.

    A lot of people swear by #41, which is stronger than #415, but #41 has a smaller distance between the plates.
    Last edited: May 18, 2011
  19. Ryno

    Ryno Member

    A guy on Youtube noticed that my motor was mounted on a diagonal, so I moved it over. Now, I can ride the bike but it's still skipping I think because it still makes that horrible noise that you see in the video. That IS from the chain skipping, right?
  20. DuctTapedGoat

    DuctTapedGoat Member

    When the chain skips you can hear it and sometimes feel it popping. You've got a grinding metal to metal sound, which could be the chain rubbing sideways on the sprocket or contacting the frame, maybe even rolling on a tensioner that's seized.