Dangerous chain jaming ..

Discussion in 'Frame Mounted Engines' started by Bobbyoutback, Nov 16, 2009.

  1. Bobbyoutback

    Bobbyoutback Member

    Hi All,
    I've searched for chain jamming & lock-ups with little success .
    Has anyone solved this HP motor engineering flaw when the chain gets bound up trying to clear the small drive sprocket causing the back wheel to lock up .

    Sick of locking up my back wheel , my chain is tight enough , think it must be poor original design that allows this :confused:

    Cheers Bobby .

  2. bluegoatwoods

    bluegoatwoods Well-Known Member

    You're talking about jamming up at the front end, aren't you? Under the clutch lever?

    If I've got that right, then I have to suspect that yours has some kind of flaw since what you're describing isn't common. At least I don't think so. I think I'd have heard of it and it hasn't happened to me.

    Is that cover fastened down tightly?
  3. Bobbyoutback

    Bobbyoutback Member

    Yep thats it , I've got three bikes & its happened to all of them , but only once to the one with a centrifugal clutch .

    I think I know what happens :idea: the chain slows downs on top as the bottom tightens up causing the jam kink on the clutch housing .

    Bobby .
  4. Mountainman

    Mountainman Active Member

    yes it has been discussed around here in a few places

    would say -- since you have stated chain is tight enough

    something mis matching at speed -- teeth to chain

    better quality chain may help ?? ((slight)) file to gear teeth -- taking off sharp edges if any ??

    good thick grease on chain -- try for a while ??

    Last edited: Nov 16, 2009
  5. Bobbyoutback

    Bobbyoutback Member

    Thanks I've done that & ridden around the place with the motor off to double check smooth chain meshing , bikes are going great then for many miles then "WHACK " a lock up that can kill me :sweatdrop:

    Cheers Bobby.
  6. 210061741

    210061741 Guest

    Iv'e noticed with mine that the chain stretches quickly and loosens up.
    Also if you walk the bike a couple of sprocket teeth at a time does your chain go tight loose tight loose?

    Once the chain gets a little too loose it'll jump off.
    Usually happens to me at low speed.
    If you watch the chain when your riding.
    When you first start the thing up and it is 4 strokin alot.
    The bottom of the chain bounces around alot.

    I'm not sure what the best soloution to this is yet.
  7. Bobbyoutback

    Bobbyoutback Member

    Yes Sir , that always happens , also did you notice when you lift up your back wheel and increase revs the chain bounces Big Time .

    Gotta think the Chinese just make stuff but don't ever think of fully testing anything ?
    Maybe I just got a bad bunch of motors put together by assemblers who didn't get fed or didn't give a hook at the time ?

    Gees " what does quality control mean in China ? Answer output output :ack2:
  8. 210061741

    210061741 Guest

    What i have found is the 10T sprocket is a little small for the chain.
    It causes alot of excess pin pressure.

    The other thing that isn't realized is even moving the motor .030 of an inch will make the chain loose by allmost a link.

    Dosen't seem to make sense....

    I know this cause i use shims behind the rear motor mount to adjust my chain tension.
    I have found through experience that eve .030 of an inch makes a big diff.

    I'm thinking that i want to design a Motor Mount that makes adjusting the chain tension the turn of a bolt.

    Of course you would have to loosen the 4 bolts first but that can be done alot easier than getting thoose shims in place.
  9. Bobbyoutback

    Bobbyoutback Member

    Appreciate your input , I'll check that out , so you think the supplied 10T is part of the flaw in there design ( whoops copy ) also your point regarding motor placement as the problem , that I agree is critical .

    I noticed the torque will always pull a motor to the left even though all bolts are tight , gee that could be it !! :evilgrin:

    Regards Bobby.
  10. AussieSteve

    AussieSteve Active Member

    Hi Bobby. Mine wasn't as bad as yours, but every now and then there was a pretty decent clunk from the vicinity of the countershaft sprocket. There are marks where the chain has hit the front edge of the inside of the countershaft cover. I found that the cause was a stiff joining link, staying more or less straight as it passed over the 10-tooth sprocket. It only happened when my chain got a bit loose. I think that a spring tensioner is a necessity on these things. In my opinion, to make things reliable and trustworthy, we need a decent roller on the bottom as a main tensioner, then an additional spring tensioner on the bottom to take out slack as the chain tightens/loosens as it rotates and a simple non-roller UHMW (ultra-high molecular weight) plastic guide on the top to stop the chain jumping around too much during starting/throttle off/downhill with clutch in.
    ... Steve
  11. 210061741

    210061741 Guest

    If you put a longer bolt through the clutch cover and housing.
    The one right by the seat tube and attach a small metal bracket to the bolt to brace the motor against the seat tube it will not tip too the left.
    But the chain will still stretch and come loose.
    BTW there isn't anything we can do about the 10T
  12. Slackbiker

    Slackbiker Member

    One of the reasons i went with friction drive (despite the inefficiency) was because of "paranoia" about chain jamming, it happens often enough on regular bikes. I think if i was to upgrade i would go with a belt drive.
  13. Bobbyoutback

    Bobbyoutback Member

    Hi Steve ,
    I've built a good spring tensioner out of 2 ball bearing nylon glass door rollers , works OK .
    Think I've fixed the jamming problem by taking off the clutch cover and bolting a half rubber brake shoe in the top left corner where it always kinks up & locks the back wheel .
    Had to drill a hole through the inside casing for the thin bolt to hold it in place , now it can't lock up !
    Also its now got a rubber stopper bolted to the seat tube to stop the chain flicking up .

    Have Fun
  14. Bobbyoutback

    Bobbyoutback Member

    Good idea thanks , as for the 10T , beats me sorry .:thinking:
  15. meatwad

    meatwad Member

    Is HP the same as a Happy Time? If so mine had the same problem. The chain that came with mine I think is a 415.

    It looks to me that the chain is having a problem getting over the very tall teeth of a very small front sprocket and sometimes climbing it. I have read in the past that some have filed on the front sprocket but I couldn't remember where on the teeth to do it. I was going to do that but my kit didn't come with a puller.

    Then I just figured fug it and rode the thing as a bicycle for a few miles with the clutch lever pulled in. That seemed to help things match up a bit.

    After that I got the thing running and it seems that when the chain is being pulled tight by the motor there hasn't been this problem however it can still be seen when riden as a bicycle.

    (granted Ive only got about a mile on the motor and there is still time for a chain related catapult)

    I don't know if any of that can help you but I did notice that lubeing up the chain real good helped a bit. Also that the chain is rubbing against the clutch cover a bit and against the engine quite a bit. Hopefully it wont self-destruct.
  16. AussieSteve

    AussieSteve Active Member

    I think that Bobbyoutback is on the right track. A guide inside the countershaft cover that only allows room for the chain to stay on the sprocket sounds good. I'd still use that white, high density plastic (UHMW) that's used on dirt bike chain tensioners etc., though, for longer life.
    meatwad, I found that mine definitely was worse when backing off the throttle, rolling down a hill etc. That's when the top of the chain is loose, allowing it to pull off the sprocket. If your chain is also hitting the engine case or mounting bracket, then the chain is probably a bit too loose.
    If you turn the back wheel until the chain is at it's tightest, then adjust the tensioner until you have about 1/2", (13-15mm), of slack, you'll reduce your problems.
    I've tried centring my back sprocket so that the chain tension remains even, but I'll need to file out the sprocket's centre hole to do it properly. I still get a little bit of variation. That's why a spring tensioner would be good on the bottom to remove slack while under power, with a guide on the top to keep the chain in line when the throttle is backed off or during starting.
    ... Steve
  17. AussieSteve

    AussieSteve Active Member

    You know, in my opinion this is the weakest link with these kits. Over the next week or two I'll get the new tensioner setup organised and see how it goes.
    I have plenty of faith in the engine, it's running reliably and at a nice temperature etc, with over 200 km, (120 miles), on the clock, but I'm cautious about going too far from home with the standard chain setup. It's an accident waiting to happen. (I'd give my right arm for a shaft drive strong enough for these engines.)
  18. Bobbyoutback

    Bobbyoutback Member

    Hi there Meatwad its a HT not a HP my typo whoops "
    I have never had to file the sprocket teeth down on my bikes , nor any rubbing on the housings , sorry can't help there.
  19. Bobbyoutback

    Bobbyoutback Member

    Yep Steve thats the worry , notice that when the motor is not pulling the chain under power the top of the chain slops about ( even when tension is right ) causing the lock ups .
    This can happen anytime unless they are modified ..
  20. meatwad

    meatwad Member

    meatwad, I found that mine definitely was worse when backing off the throttle, rolling down a hill etc. That's when the top of the chain is loose, allowing it to pull off the sprocket. If your chain is also hitting the engine case or mounting bracket, then the chain is probably a bit too loose.
    If you turn the back wheel until the chain is at it's tightest, then adjust the tensioner until you have about 1/2", (13-15mm), of slack, you'll reduce your problems.

    Yeah I think I'll try to take more slack out of it and see if that helps. Also like the guide near the front sprocket idea. Thanks.