Chain pop off issue, please help solve mystery.

dmfelicia

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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):geek::

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. :unsure: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:

Cheers
David

I have created an album showing the photos of the problem.
 
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
 
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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.
 
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 bend...it 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.
 
Thanks for your suggestions Steve. They are much appreciated. They give me some new avenues to explore.

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
 
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