Technical Chain set/idler advice (a home project)

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Edward Reckitt
Hi all,

Many thanks to anyone who takes the time to read this and offer help.

I need some technical help regarding chain sets, #420 chains, sprockets, and idlers/tensioners. This question is about a home project, not a go kart, but the general principles are the same, just much simpler. I do not want abuse this forum, so I am sorry if you consider this post to be inappropriate/not for this forum - I don't know who else to ask.

I will state what I am looking for first, and then below you can read more about my project.

What I'm looking for:
I'm looking for a chain tensioner with a sprocket (not a roller) for a US/ANSI #420 chain, and I'm having difficulty finding one. Note that it doesn't have to be a tensioner - it's more the sprocket that I'm interested in, but it would help if it came with a bolt and bracket rather than me having to source the bracket and bolt/axle separately.

My goal is to place an idler sprocket (aka jockey wheel) on the bottom/return side of the chain to help feed the chain onto the sprocket that is being driven, thus helping to keep the chain on the driven sprocket. I can get this idler sprocket from azusa, but this sprocket is 16 teeth which is a bit big - a 9 tooth would be sufficient, with ideally a smaller bore size. I can't find anything like this, and the items that could potentially work are either ISO/British Standard sprockets, or sprockets for a #428 or #520 chain, which is not what I am using (I'm using #420).

In many ways, I have made life difficult for myself by using an American produced axle, sprocket and chain, but I didn't have a choice really.

Here is an example of the kind of thing that would work for me, but this is for a #428 chain.

Here is another example but it is of British Standard...

About my project:
I am working on DIY project where I am converting my hand pulled cart to be powered by an electric motor. I call the cart my "beer wagon" and use it to transport my camping equipment when I go to festivals. I sourced an aluminium axle, a sprocket, hub, and chain to run off the motor. The motor is a wheelchair motor and can supposedly move 20 stone (weight). Top speed is about 4mph.

Although the chain set ran well when the cart was upside down, I found that the chain would ride the sprocket (the sprocket on the axle, not the crank), and would eventually come off. I tried a lot of different chain tensions but the problem still occurred.

I did a lot of work trying to ensure the axle and sprocket was straight, but there is still a small 'anomaly' where the sprocket doesn't run entirely true. It's not that the whole sprocket isn't straight - it is straight, but when I slowly turn the axle, there is one part of the sprocket that moves "off centre", by about 3 mm. I have tried to mitigate this by putting spring washers between the hub and the sprocket, and tensioning the 4 different bolts separately, this didn't make much difference though. I can't believe the axle, hub, or sprocket is not straight, but out of them, I would put my bet on the hub not being true.

I decided to mitigate the problem as much as I could and started to build a frame around the chain set so I could install rollers and chain guards, but this has proved more troublesome and awkward than I anticipated.

I've been advised that a jockey wheel might be enough (also known as an idler, or a tensioner sprocket). My main goal is to feed the bottom/return part of the chain onto the sprocket by the way of an idler. A tensioner sprocket unit would do the same job - and if it tensions as well, then fine. I think a sprocket (rather than a roller) would be much better, but my problem is sourcing the right equipment for me to put this on.

I have a web page which discusses my endeavour, if you want to read more, or see videos, you can use the links below.

Straight to the problem
If you want to jump straight to the problem you can use this link to get to that section: ( Home )

The project
Use this link to get to the beginning of the site and read all about the wagon and my journey, including rational, requirements, planning, implementation, as well as the problem I have and how I've tried to fix it ( Home )



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Essex - UK
James 'Adam' Pell
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J. A. Pell & Son Motorsport
Hey Ed, welcome! I can't really help you with your issue in regards to a tensioner etc, but I just wanted to post and say sounds like a cool project! 😁👍

Instead of a tensioner have you thought of a protector style plate system to help keep the chain on? It would be two plastic plates either side of the sprocket, this would stop the chain coming off.



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