Chain pop off issue, please help solve mystery.

Discussion in 'Frame Mounted Engines' started by dmfelicia, Feb 15, 2010.

  1. dmfelicia

    dmfelicia New Member

    So I am almost done with my first build, there is just one problem. The chain will not stay on, it continues to pop off. At first this seems like a simple problem but as I dug and trouble shot I saw this wasn't the run of the mill chain pop off issue.

    Here is what happens. If I start to roll the bike with the clutch disengaged I hear a weird grinding type noise (periodic to some extent) then a pop (master link) then the chain is off. This happens at moderate speeds and after a couple feet.

    Here is what I have checked. I have made sure that the master link clip opening is oriented opposite to the way the chain moves. Problem persists.

    I have adjusted the chain tension (loosened it). Problem persists.

    I have lubricated the chain (silicon lube). Problem persists.

    The engine cog and wheel sprocket look to be pretty close in alignment although this is just my visual judgment. How do you measure this?

    I took it into my workshop and slowly rolled it back and forth until the problem arose. Here are my observations (clues for the mystery):detective::

    1)When problem arose I went slow enough that the chain did not pop off. I discovered it seizes up just before failure. (see picture)
    2) The chain starts off slack and upon failure is pulled very tight. So much so that with moderate finger pressure their is no visible play (see picture)
    3) The spocket doesn't appear to be off alignment in the lateral direction but it definitely is off alignment prior to failure in the forward/back direction so that the chain does not fall properly on the small engine cog. (see picture)
    4) There is evidence of grinding but no signs of grinding marks on the chain.
    5) One of the links close to the master link has trouble flexing in one direction. Not sure which direction the chain was oriented upon workshop failure.

    If anyone has any insights into this mystery I would be much obliged. :idea:My theories are that a) that tight link somehow throws the chain off alignment in the front/back direction or b) the chain is in fact off alignment in the lateral direction.

    If b) I have no idea how to measure this alignment or correct it.:confused:


    I have created an album showing the photos of the problem.

  2. srdavo

    srdavo Active Member

  3. AussieSteve

    AussieSteve Active Member

    I've always had a similar problem. (Don't have the full cure yet, sorry, but hopefully I can contribute my bit.)
    I'd hoped that it was related to the rear sprocket/tensioner and would disappear when I fitted the shift kit but it goes deeper than that.
    You didn't say, but I'll assume that you have a 415 chain, as I do.
    Mine still does it. I noticed some time ago that the chain was stiff in one spot and as a result was occasionally hitting the inside of the countershaft cover, at the forward side. I filed it away and freed up the chain, which eased the problem, but it persisted.
    Every now and then there's a crunch but then everything continues working as usual without dropping the chain.
    Since it's still been happening with the shift kit, I've been watching more closely trying to figure it out.

    First, I found that one of my master links had too much side-to-side movement and a grind mark where it had tried to derail. Luckily, I always keep my chain tight. I replaced it with a better one and partly alleviated the problem, but it's still there.

    Next, I carefully examined the 10T drive sprocket as the chain went over it - just below the teeth is a wider section of the sprocket, too close to the teeth. As a result, the chain doesn't seat properly on the sprocket and the side plates ride on the collar below the teeth on the sprocket. That's part of the problem, I think - those sprockets aren't quite suited to a 415H chain. I think that using a chain-breaker/joiner to assemble the chain without a master link would help, but ideally I think that some work on the sprocket or a lower profile chain would be the answer. The sides of the master link were even taller, so I ground them down to match the clip and things improved a little more.

    Also, the sprocket was poorly made and the teeth seem to be different thicknesses or misaligned. After 400km, some teeth have very heavy wear on the side but others have none.

    After I finish getting my gearing right, this is the next thing I plan to tackle.
    My chain still goes tight every couple of turns for no apparent reason, but it's not much of an issue with the shift kit, compared to the stock tensioner/sprocket/rag-joint setup.

    Just saw your pic of the inside of the countershaft cover. Identical damage to mine.

    Your pics make it look like the pitch is wrong. Does your chain ride up while centred or only when held to the side?

    I want to add that my assumptions might be totally wrong. When I looked at your pics I noticed that your chain doesn't quite ride on the inner collar to potentially cause the problem. I was thinking a different chain, possibly a 410. I've heard that they fit and maybe better than the 415H. If anyone can shed any more light.....

    ... Steve
    Last edited: Feb 16, 2010
  4. Go buy a 410 chain, a bmx chain for single speeds will work,make sure u get one long enough.
  5. professor

    professor Active Member

    To detirimine chain alignment, place a straight edge on the side of the largest sprocket (chain off) and place the other end of it on, or as near to the same edge of the far sprocket. (This is assuming the wheel is straight within the bike frame.)
    Is the straight edge lining up with the smaller sprocket? Is it within a quarter inch or so? If it is not- you must shim the rear wheel,or move the engine sprocket or engine into alignment.
    I do not know how much missalignment the chain will tolerate- I am saying a quarter inch because to me it is acceptable.
    When I was fitting the drive chain for the scooter motor, I found snagging spots in the large sprocket to the #25 chain. I removed the chain and held it in my hands and placed it on the sprocket for a few inches and tried unchaining it- just like it would be operating. All he way around, and found there was a spot where the chain was actually caught in the sprocket as I unwrapped it carefully.
    The sprocket v/s chain was too tight at that spot, even using a different section of chain- the spot was still there. I marked it and ground down each edge (they are beveled ) until the chain went on and off perfectly. I assume the sprocket was thicker there.
    Speaking of the bevel- that slight bevel on the sides of the sprocket is there to accomidate alignment that is not perfect. I notice regular bike sprocket are just stamped out and lack the bevel but HD stuf has it.
  6. motorpsycho

    motorpsycho Active Member

    take the chain off the bike.use your hands and move every link back & forth and feel for stiffness. sometimes the links are put together too tight. wen a tight link gets to the sprocket, it will not want to make the will want to keep going straight, and it will pop the chain off. this is what happened with mine.
    I had to pry the tight link open a bit with a screwdriver and work the tight link back & forth by hand several times while lubing it with grease.
    thes chains are not the best, and they are not put together with great precision.
    This was how i fixed my problem, but you may not have the same problem with your chain.
    is your chain popping apart at the master link? or is it just coming off the sprocket?
    if the chain is popping apart at the master link, make sure that you have the master link clip on the inside, towards the wheel where it can not rub on anything. My friend had an issue like this, and he found that the master link was rubbing on the frame(because the clip was on the outside facing away from the wheel) and the clip would come off from rubbing on the frame.
  7. dmfelicia

    dmfelicia New Member

    Thanks for your suggestions Steve. They are much appreciated. They give me some new avenues to explore.
  8. dmfelicia

    dmfelicia New Member

    Thanks for the info on aligning Professor. Also thanks for the other tips regarding sprocket thickness.
  9. dmfelicia

    dmfelicia New Member

    Thanks motorpshycho. I will ensure the link is on the inside. I had identified a tight link. I will work on that.
  10. AussieSteve

    AussieSteve Active Member

    The answer might well be the 410 chain. I'll get some ASAP, to find out.
    It's more of a drama with your full-length chain, but still gives me the *&%$ with my short one on the shift kit. It should run smoothly[/].

    If I get time later, I might try to find a source of decent 410 chain and order some. Best way to find out.

    I'll keep you informed, if I find a miraculous cure.
    Otherwise, optimise everything else and keep the chain too tight to come off.
    If you haven't already, put a twist in your tensioner bracket so that the chain perfectly aligns with the rear sprocket.

    I haven't had a master-link clip come off yet, but this sounds like one more argument to use a chain-breaker/joiner and omit the master-link.
    (I wonder, mechanically, how the clip is popping off?)

    Just thinking - on my bike, the other end of the chain, on the 17T sprocket on the shift-kit jackshaft, runs smoothly and never grabs. Also, the alignment between the countershaft sprocket and the jackshaft sprocket is near perfect, within about 1-2mm, yet the problem persists. This is an issue only with the supplied countershaft sprocket, it looks like.

    ... Steve
    Last edited: Feb 16, 2010
  11. meatwad

    meatwad Member

    I have the same chain on my kit and its trying to eat the inside case of my engine just like yours. My conclusion is that the chinese dont care. Boxes of sprocket boxes and piles of chains, whatever... this ain't no burger king.. You're going to get what youre gonna get and youre gonna like it :)

    After fixing and having to tweak every single part of my kit (no exaggeration) and seeing the damage the chain was doing to my engine case I just said to myself La La La I don't care don't care! Hopefully it won't cut through the case and send the piston up into my man jewels.

    This is all with having perfect alignment.

    I think the chain was called a heavy duty version and it could be that other chain plates or pins aren't as wide and might not rub . Kind of think that they still would.

    When the engine is pulling the chain, the problem of the chain riding up the teeth of the front sprocket doesn't seem too happen, it's only when it is riden as a bicycle does the bunching occur. I think its a matter of slack distance between the rollers of the chain and how they mesh with the teeth of the front sprocket. Personally I'm just going to ride it and see if it doesn't wear into shape.

    As for the masterlink I don't know. Could be popping off the c clip when it hits the cover . Mine doesn't do that. I'd buy another.
  12. dmfelicia

    dmfelicia New Member

    Yes I plan on optimizing everything in order to narrow things down. I know now why the clip pops off.
    1) The chain does not properly go around the smaller sprocket, it doesn't seat properly (I don't know why yet)
    2) This causes the chain to be pulled very tight
    3) The weakest link i.e. the master link is pulled outward at each end (see pictures)
    4) This outward pulling of each master link pin in opposite directions allows actually causes the pin to pop off.

    One solution short of a new chain could be a chain tensioner with a spring set up. I saw a post on this with pics and it looks very doable. I generally would not like to introduce more moving parts into the drive train but this will provide an appropriate amount of tension while allowing slack when the chain runs into troubles traversing over the smaller cog. Of course this is more or less a bandaid fix since the true fix (for me) would be figuring out why the chain does not traverse the small cog and addressing that issue.
  13. dmfelicia

    dmfelicia New Member

    LOL meatwad that response cracks me up. I feel the same way. I wonder if there are any american companies that make a kit which incorporates pride for craftsmanship. I am sure it would cost more but I am willing to pay for quality especially when my life is on the line.

    I do think you are on to something with the source of the problem however, a mismatch between the chain and the front sprocket. This sub-optimal fitting seems like it could be a source of issues.

    One question for everyone which may shed light on this mystery. How easy is it to turn the small cog when the clutch is disengaged. Mine is still somewhat tough to turn. I am thinking that if there is a lot of resistance this could cause problems when the bike is in pedal mode rather than engine mode. Reasoning is this. In engine mode the small cog is pulling the chain so it is unlikely that a misalignment of chain and cog will happen. When in bike mode the chain is pushing the small cog and this seems to me to be a much less optimal situation if that cog is resisting a lot I imagine chain bunching and so forth.

    Any thoughts.
  14. meatwad

    meatwad Member

    << In engine mode the small cog is pulling the chain so it is unlikely that a misalignment of chain and cog will happen. When in bike mode the chain is pushing the small cog and this seems to me to be a much less optimal situation if that cog is resisting a lot I imagine chain bunching and so forth.>>

    Pretty much yeah.

    In bike mode the chain is just being layed onto the sprocket and therefore it wants to crawl. I's still getting pulled but from the bottom and not the top.

    Engine running the slack is where the chain it is coming off the sprocket. Not a problem.

    Bike mode the slack is where the chain is going onto the sprocket. problem.

    Personally i was going to file the teeth down a bit and take some of the square edges off but my kit didn't come with a puller.
  15. Stan4d

    Stan4d New Member

    I have nothing to add, but wanted to say that this disscussion is helping me. I would hear a slight poping sound ocassionally, and this disscussion has caused me to look into it. Guess what? Same problem though not as severe as dmfelica'a. If I find a diff fix I will let you the mean time I gotta try what is listed. THANKS!
  16. Turtle Tedd

    Turtle Tedd Member

    Cabinfever says go buy a 410 bmx chain...THAT WILL DO IT........ 415 chains look like they fit but they will stack ..wind the chain all the way around the sprocket as far as you can to check fit...the smaller the sprocket the worse this is...The KMC KOOL chain (bmx) is one of the best..according to many on this forum..I got one after having similar probs....415 fits only some and is overkill anyway I think
    Last edited: Feb 18, 2010
  17. My Grubee kit came with a 415 chain and it had several tight spots. I went to Walmart and purchased two packs of Bell chain. That smoothed out my bike considerably. I would suggest trying that first. My chain popped off occasionally also.
  18. Stan4d

    Stan4d New Member

    OK...after looking at how the chain rode along the sprockets, I noticed that my rear sprocket was off center. The poping noise occured at different points in the chain. So That eliminated tight links and the master link. My sprocket was also not true. After centering the sprocket and truing it to the best of my ability the popping noise dissapeared. It may not work for your problem but it solved to go make up to my wife for spending too muck time with the motored lady.
  19. Hajuu

    Hajuu Member

    Which kits are you guys using? My chain fits very nicely and apart from a small issue with getting master link clips to go on, I haven't had any issues so far.

    Sounds dumb but I assume that the clip *is* going on with a nice kind of *snap* as it comes to rest in the front and rear grooves of the master link pins? Cause I lost a master link by having a clip look exactly like it was on, but it wasn't quite on propperly, which will cause it to come off very easilly, especially when going around the small sprocket obviously as thats when the angles are most intense.
  20. dmfelicia

    dmfelicia New Member

    This has been great. I think collectively we have identified most possible solutions to this problem. I think this problem could be caused by different sources but regardless of the source I think we have identified a fix. Here is a summary of the fixes:
    1) Check for tight spots in your chain.
    2) Consider replacing the 415 chain with a 410 chain. The thicker 415 chain could cause multiple problems.
    3) Check the alignment of your sprockets
    4) Check the thickness and beveling of the sprockets, test to see if the chain can ride on and off of the teeth smoothly without sticking. Consider grinding problem spots (on the sprockets)
    5) Make sure your chain is well lubricated.
    6) Ensure that your sprockets (both of them) are true.
    I think I may get the 410 chain to see how it goes. But last night I was investigating and eliminated all tight spots on my chain and also found that the chain went on and off the sprockets well. The alignment between the cogs looks fine as well. But what I did find is very similar to what Stan has found, that is I think my sprockets may be untrue. I suspect this because the chain periodically becomes slack and tight as I spin the wheel. It always gets tight at the same portion of the rear sprocket (for about a third of the sprocket the tension is increased). Before I must have been setting the tension at a "slack" portion of the sprocket and when it went through its high tension point it was over the top tight causing all sorts of problems.

    Stan I imagine you trued the rear sprocket by tightening the bolts at the points where it bowed out. How did you determine the true of the smaller sprocket and how did you fix it?