Drive chain issue (all help appreciated!)

[willdoucette]

Working on my first two stroke motorized bicycle build, and the engine is secured onto the bike, and the drive chain in on with a tensioner, but when I move the bike forward, the chain slowly builds up pressure and edges towards the side of the sprocket. How can I make the chain stay secure and so it stays straight? (Here is an images attached, I circled where the chain is moving off)
Thank you in advance!

 

[The_Aleman]

You have your idler wheel on the tension side of the chain, which is generally a bad idea. It's stressed under load, which will accelerate wear on any idler wheel you put on it. There is a lot of chain travel on the return side, which is where an idler or tensioner helps the most. You might need to put another idler wheel on the return side.

Your choices are quite limited, having the engine mounted on an open frame. For the best results, mount the engine on a traditional closed-frame bicycle, it'll save you some headaches.

 

[gary55]

Agree with Aleman. This bike is a bad candidate for motorizing for seat stay to chain clearance issues, but if you have solved this with the upper idler you just need to do the same thing with a lower idler bushinged to sprocket alignment.

 

[Lukesky36]

Put your chain tentioner on the bottom chain

 

[CrazyDan]

Put your chain tentioner on the bottom chain

If he did I bet it scrapes the seat stay. As aleman and gary said, this bike was a bad candidate for a simple kit build. The only way to do this build right would be a jackshaft around where the top tube meets the seat tube, to give it a straighter chain line. Only issue with that is now you have more moving parts and 2 chains to worry about.

 

[Old Busted Hotness]

Chain is also too loose. The whole point of a tensioner is to take up enough slack that the chain won't come off.

 

[JerboaJohn]

seems a tricky build!

 

[FurryOnTheInside]

How can I make the chain stay secure and so it stays straight?

Easiest way: Put it on a different bike.

 

[willdoucette]

Thanks for all the ideas everyone. I understand now that this bike was not the best candidate for the engine; however it is the only bike I have. I have access to a welder so what if I cut off the top tube of the bicycle and welded on a completely horizontal top tube on the bicycle, then my engine would be lower down like other bicycles, would this work??? ( here is a diagram below, the red is the tube I would take out, the blue is the new top tube, and the green is where I would put the engine)
Thanks again

 

[CrazyDan]

That should work.