Sprockets Rear wheel sprocket

[JIFFY]

my apologies if this is the incorrect section to post... but it looks like where it should go.

Just bought my first kit. It came in the mail on Monday. I put my kit on the bike. Now I have a big smile on my face. but.... I have one little problem and I've been working on it for a couple days now. I'd like to turn to you guys to see if you have an answer for this.

My drive chain goes slack and taut, slack and taut. i was pretty sure this was because the sprocket wasn't centered on the hub... but took it off for a string test, and whaddy know, it was perfect. (when you take a piece of string, and measure all the teeth from the center) Since then, I've been trying to adjust the sprocket while it's on the bike but haven't had any luck whatsoever. The wheel appears to be spinning true, and the sprocket is spinning without any up and down wobble... it's centered just fine on the hub. yet.. the chain will not remain tight. No matter what I do, it goes slack, taut, slack taut...
Any thoughts on this? Anyone ever run into this? common problem?

once again, sorry if this is posted in the wrong spot

 

[Barry]

Hey IFFY,

You know I had trouble with the chain itself once. I've done a few builds with a 5G and 4G gearboxes and I can't remenber which kit had the bad chain but, one of them didn't mesh well with the sprocket on the gearbox end. If, like you say, all is well with centering your rear sprocket, you might look at the chain.

Barry

 

[Greg58]

One thing you can try, remove the sprocket cover and spark plug so you can roll the bike around while watching what's happening. Sound like the chain is riding up on one of the sprockets.

 

[loquin]

I moved the thread here, as the general bicycle forum isn't the right spot for a drive-train issue. (That forum is for issues relating to the underlying bike itself, not for added items to support an engine drive.)

That being said, you haven't said what kind of drive you have - Happy Time style frame mount or rack mount. Since you talk about centering the rear sprocket, I assume it's a frame mount.

What kind of bike is the kit installed on? If it has a rear suspension, every time the rear wheel goes over a bump, the drive line between drive and driven sprocket is going to be a little shorter (causing slack in the chain.) The reverse is true when you go over a hole or dip in the pavement...

 

[JIFFY]

lol, thanks for the replies. I've been so frustrated with this thing that I let it sit for a couple weeks so i didn't destroy it!! This is my first build, and I think it's a rack mount...
turns out it was just the sprocket off center. I thought it was good, but nope... it's really gotta be centered within a half a millimeter otherwise the chain will sag. Thanks for all your help guys. and NEVER buy a 40cc engine from live fast motors!! lol

 

[Stoltzee]

Mines doing the same thing, and I can feel it a little when I'm riding. Now I know. Maybe I'll check the gap between the hub and the sprocket with a feeler gauge. Just thought of that. Don't know if it will work.