Chain alignment - need 1/2"

Discussion in 'Frame Mounted Engines' started by creeble, Jul 12, 2008.

  1. creeble

    creeble New Member

    Hi, I'm helping my son build a 70cc Happytime, and the chain alignment is about a 1/2" off. I'm trying to figure out the best way to correct it.

    I could maybe get an 1/8" with a thinner spoke gasket (without the chain hitting the spokes), and could maybe shift the axle another 1/8", but I've read here that a 1/4" is still too much misalignment.

    That pretty much leaves shifting the motor around. This seems quite difficult, given the positioning of the mounts; I'm not quite sure how I'd approach this but suspect others must have had to remake mounts somehow. It's a shame since the motor fits perfectly in the frame now, but "perfectly" doesn't include the chain alignment!

    Any pointers on the forum would be most helpful; I've done some searches but "chain alignment" is such a common problem that I haven't found anything yet.


  2. srdavo

    srdavo Active Member

  3. HI,

    Interesting that the chain would be so far out of alignment.....I suppose after trying thinner rubber mounts , re-spacing the rear wheel, possibly re-dishing the you could probably take a round or half round file to the engine mounts (not as hard as it seems since they are made of relatively soft aluminum) 1/8 here and a bit here eventually all adds up to a (hopefully) a near perfect chain line....Do you by any chance have any pics?

    One thing tho...if you put the sprocket too close to the spokes your chain (provided of course your chain doesn't hit the spokes as you mentioned) may start rubbing on tire itself (affects wider tires more than narrow tires)....

    Good luck!

  4. Show us a pic from the back of the sprocket if you can so we can see what's going on here.
    How close is your rear sprocket to your spokes? When you look down your tire how close does your sprocket get?
    1/2 inch off is a WHOLE LOT.
    Your frame may be designed wrong if it's a weird one off frame or home built. But hard to tell without pictures!
  5. creeble

    creeble New Member

    Thanks for responding, folks. I'll try and get some pictures up today.

    It's a flat sprocket, not dished. I got 1/2" by measuring the distance from frame center to motor sprocket, then measuring the width of the rear wheel's axle, subtracting offset to sprocket, etc. I'm sure I'm within 1/16" or so with that measurement. And yes, the chain comes off in one revolution.

    I think if the sprocket were 1/2" closer to the spokes, the chain would probably rub; bummer. I'm beginning to wonder whether this is just the wrong bike, but then again there must be a way to get this aligned?

    Okay, I'll post some pictures later!
  6. HoughMade

    HoughMade Guest

    Those pics are the key to being able to figure this out. Trust me when I say that there are very few problems with these kits that have not been figured out by someone on this forum!
  7. creeble

    creeble New Member

    Okay, here are some pics -- a little tough to show; the chain's off but you should be able to see down the line of sight from the rear sprocket to the front sprocket and see the 1/2" difference.

    There's also a "top down" (really bottom up, the bike's upside down) view of the rear sprocket. There's currently pretty good space between the top of the sprocket and the spokes. Simply tightening the sprocket bolts would reduce it some, but the big washer isn't a 1/2" thick.

    Bigger, dished sprocket? Have a look guys; I can post more pictures. Really appreciate the help!

    Attached Files:

  8. creeble

    creeble New Member

    Dang, not sure how you guys cleverly embed the pictures in the post....
  9. Ozi

    Ozi Member

    Its hard to tell by the pictures, but that hub looks pretty wide. the spokes are way out there.
    Maybe measure it and compare it with another mtb hub ????might be a one off style ???

    just athought

    Last edited: Jul 16, 2008
  10. Hmmmm interesting.....An offset sprocket will NOT help in your case since it seems that you want to move the sprocket CLOSER to the spokes.....(offset sprockets are only helpful if you want to push the sprocket teeth outward (away from the spokes).

    Hard to tell from the pics but is the rear wheel centered between the rear wheel stays?...It is possible somebody may have repacked the bearings at some time possibly put things together improperly? (if so you can readjust the cones).

    Has anybody trued the rear wheel?...It is possible the rear wheel is dished incorrectly (I only mention this because spoke clearance with a stock 44T (most likely size) is generally not an issue....Another area to check for alignment is the relationship of the front chain rings to the rear freewheel....On a triple front chain ring the center chain ring should be in line with the center of the freewheel cluster...If you have 2 chain rings up front, the
    center between the 2 chain rings should be in line with the center of the freewheel.

    Barring the bike being in an accident and bending the frame, checking the 2 items above and making any corrections as needed should take care of your problem (proper dish and proper spacing). The bike looks like fairly standard bicycle so it should work out Ok.

    Hope this helps you.


    PS - Are the sprocket teeth (both front and rear) beveled and chamfered correctly? (as you may have read here on this forum Chinese kits often require a little "tinkering" sometimes) ....THAT can cause the chain to come off more than possibly anything else (The 415 chains that come standard with the kits are wide enough to make up for a fair amount of misalignment)...most or at least some instructions recommend filing the sprocket teeth a little....Actually in thinking about it...THIS is the most likely cause for the chain coming off....If you have a bench grinder handy (or a simple file will work too) you can bevel the teeth fairly easily BUT you will have to take the sprocket back off....I know AAARG...especially after spending soooo much time getting the sprocket wobble free BUT I really thing that could be the solution to your woes.

    Good Luck!
  11. creeble

    creeble New Member

    The wheel may indeed be offset improperly -- the bike was modified to be a single-speed (no derailleur) and they may have shifted the cones. I'll look into that... haven't taken apart an axle since I was a teenager, but maybe I can figure it out again...

    Yes, it's a chinese kit w/415 chain. So you're saying that those sprockets lack enough chamfering? I have a bench grinder. What do you think is the maximum misalignment possible?

    It's a pretty standard bike; don't really know the brand. The rear wheel axle width (width between the two axle mounts) is 5-1/4".

    So -- possibly shifting the wheel on the axle, and grinding the teeth to give them a bit more bevel. Will take a look at those.

  12. My rear sprockets on both my bikes are closer to the spokes. It seems you have enough clearance to do this: Try taking the inside the frame nut off from the pedal side then replace it with a thinner one. Then on the engine side add that much more inside the frame. That should move your sprocket over a bit. Then also try getting those sprocket bolts a bit tighter. That rubber spoke hugger looks like you can compress it a bit more.
  13. datz510

    datz510 Member

    You might also look into some #41 chain. its a good 1/8" wider than the #415, so will put up with a little bit of misalignment. My bike has around 1/4"+- misalignment between the drive sprocket and the wheel sprockeet. I just adjusted the tensioner to help guide the chain back onto the wheel sprocket straight and its been fine so far.
  14. HI,

    I am not 100% sure how far you can go with misalignment but my guess is pretty far (NOT that you would want to intentionally.....better alignment is ...well.... Better..).The reason I am suggesting that alignment doesn't have to be perfect is shown by the very nature of the multi speed bike using multiple chain rings up front and the freewheel out back....The is WAY more than 1/2 inch deflection when one uses the many of the possible gearing combinations ) but the chain does not fall off there right?.... But again, it is best to be close in alignment....especially on a motorized bike at speed....You really do not want the chain to fall off if at all possible...

    Yes, beveling the sprocket teeth (and sometimes the front sprocket too) can work wonders for the chain to feed properly....Also, you may want to take the time to see if all the links on the chain itself are free to move and that you don't have and "stiff" links....sometimes that can cause problems too...

    After trying some of the ideas above, you should have the problem solved.....if not we'll try harder! ;-)

    Good luck!

  15. creeble

    creeble New Member

    And I guess it still fits in that tight chamber at the front sprocket? This is a happy time motor, and I know it's pretty tight in there.

    And thanks for those tips, Andy -- weekend's here and it's time to start messing with it! I'll first try moving the wheel on the axle, then grinding the sprocket. You guys are great! I'll come back Monday with my progress.

  16. HoughMade

    HoughMade Guest

    The #41 is actually stronger than 415, but the side plates are thinner. This leaves more room between the plates even though they are the same external width.