chain rides up sprocket

[alexV]

Hi,
I'm looking for advice, I want to understand the problem, and also fix it.

In the video you see that under high load, the chain rides up the small sprocket, and violently snaps down the vibrations are frightening. happens only when starting from a standstill.

this is my arachnid build from the forum, original honda gx270, chinese clone of tav2 30 series.

the tav2 comes with [edit] 10T #41/420 [edit], so i bought a matching chain, we call it size 420 here in Europe. The large sprocket is a different size: 428. same pitch but the roller is marginally larger.

if the large sprocket is the cause, i need to understand why, before I buy another one. Thanks!

https://www.youtube.com/watch?v=3uSgxNv2svk

 

[anickode]

420 chain cannot run on a 40 sprocket. The chains are not the same. The pitch and roller diameter are the same, however:

#40 chain has a 5/16" roller width
#420 chain has a 1/4" roller width

Your 420 chain is "riding up" because it's not wide enough to fit smoothly over the sprocket. A #40 sprocket is about 1/4" thick, leaving zero clearence for a 420 chain, whereas a 5/16" wide #40 chain would leave ~1/32" clearence on each side.

Your 428 sprocket is also too wide.

Some #40 cahin should solve your problem, though it will run sloppy on the 428 sprocket because the roller diameter isn't big enough.

428 chail would likely skip on your #40 sprocket because the rollers won't seat fully.

 

[bob58o]

I just measured my TAV2 sprocket to be 0.238" - Closer to 41/420 than 40.

http://www.gizmology.net/sprockets.htm

41/420 should have a sprocket thickness of 0.227".
So that should work with #41 chain (0.250" between plates) and #420 (0.250" between plates).

#40 and #428 chain have 5/16" between plates (0.3125") and use a sprocket with thickness 0.284".

41 uses 0.306" roller diameter
40 and 420 use 0.3125" roller diameter.
428 uses 0.335" roller diameter.

The 428 sprocket is too thick for the 420 chain.

428 chain will be a bit wide for the front sprocket and will have a roller diameter a bit big. So Instead of changing front sprocket and chain, I'd Keep front sprocket, Keep chain, replace 428 sprocket with 41/420 sprocket.

Or try 428 chain.

 

[alexV]

@anickode, thanks for pointing this out, i made a small edit to my original message. i checked the supplier information and i have the "10T #41/420 reverse gearbox"

so the small sprocket and chain are a perfect match, and brand new. bob58o, you are right about the measurements.

about width: on the workbench i put the 420 chain on the large 428 sprocket . even though the sprocket is thicker, there was still a small clearance side-to-side, in the chain. i rule out the width as suspect, based on my engineer's opinion.

about 428 roller diameter: i tested a larger 428 chain as well, which has larger rollers. this chain does not physically fit the 420 sprocket. even though the sprocket is only 10T, the large chain rollers do not drop down in the sprocket all around.

about 420 roller diameter: i tested the 420 chain on the large 428 sprocket, 48T. the chain fits all around, but there is a noticeable play lengthwise of the chain, due to small chain rollers fitted in a sprocket with large diameter teeth. i can feel this by hand.

@bob58o, i plan to replace the large sprocket. i still don;t understand why the issue occurs on the small sprocket (which matches the chain perfectly...)

 

[anickode]

Tension under load is another thing to consider. If your gearbox mount is flexing down, it would slack the chain, allowing it to skip. It could be the camera wiggling, but in the slow-mo it looks like the gearbox is wobbling all over the place. A result of the skipping, or the cause? Who knows. But it's worth investigating.

 

[Denny]

Is the chain rusted or froze up or is it free at all links?


Denny

 

[alexV]

i like the new idea: tension under load, gearbox flexing down...

actually it does not even have to flex down, remember the noticeable play lengthwise of the chain, on the large sprocket? where does that play end up under tension? maybe it influences the small sprocket..

ok, i will get a new 420 sprocket, and slightly larger, 50T.

Denny, all components are brand new, the issue occurred the first time i mounted them on.
the wobbling is the direct result of chain snapping back down violently. also the video is from a hand held iphone, while moving.

i will post a conclusion in about 1 month, after i order and install everything.

 

[T-man]

Also AlexV look closly again at your alignment...
https://www.youtube.com/watch?v=YRc-Mxf9jPg

 

[alexV]

Thanks guys, I identified the top suspects for this behavior: too much chain slack. This is not visible in the video, because the slack is on the other side, hidden from view.
Add to this a tiny small sprocket, just 10 teeth, and your chain will do that.

I tested with even more chain slack, and the chain rides up all the time. I'm sure i saw somewhere on the internet there is a max slack calculation, taking into account center distance between sprockets, and the small sprocket diameter.

The thing is well aligned, the steel frame is not flexing, at most vibrating. a chain tensioner is not an option, since I have a reverse gearbox, which can pull both sides.

Lastly, the wrong-type large sprocket was not a direct cause. I replaced it though with a 420 sprocket matching the chain type, because it shows heavy signs of premature wear: teeth visibly bent backwards towards the tip.

conclusion: too much chain slack causes the behavior you see in the video. non-matching sprockets may work, but can wear out in hours or days.

 

[Molloy]

Could you you use a spring loaded tensioner? May help a little...

https://www.mcmaster.com/#roller-chain/=1a5rtu1