Front chainset running uneven

[bach-biking]

Hi guys.
Im a new member although I have been visiting this site for sometime now and have had many of my questions regarding buying a bike answered thru existing threads.

I have bought myself a Diamondback XR3 as a cheap starter bike and plan to upgrade to a mid range road bike in the future.

Im hoping i can get some advice regarding the front chainset. Ive noticed that it isnt running true and straight as it rotates. Id say there is about 6mm variation. It is far enough out of alignment to cause the chain to come off when Im on either the largest or smallest cog.

Im wondering if this is adjustable perhaps with spacers between the cogs or is it likely the whole crank is out?
The crank itself is firm and shows no signs of wobble.

Any help would be appreciated.

[cny-man]

Their called chainwheels or chainrings in the front, and if they move in unison either the BB spindle is bent (unlikely), the crank is not seating square on the spindle, or an arm of the spider is bent. Get a crank puller, remove the right arm, rotate 90 degrees and reinstall to find the best position on the spindle. If still off you will need to bend an arm of the spider to align the chainwheels. DO NOT sue spacers.

[bach-biking]

(12-27-2014, 11:08 PM)cny-man Wrote:  Their called chainwheels or chainrings in the front, and if they move in unison either the BB spindle is bent (unlikely), the crank is not seating square on the spindle, or an arm of the spider is bent. Get a crank puller, remove the right arm, rotate 90 degrees and reinstall to find the best position on the spindle. If still off you will need to bend an arm of the spider to align the chainwheels. DO NOT sue spacers.

Thanks mate.
Ive had another look and i think the crank and chainrings are not sitting perpendicular to the spindle. Ill try removing it and ensuring its seated properly. If this doesnt resolve the issue i will try rotating it 90 as youve suggested.
Really appreciate your help.
Cheers.

[cny-man]

Rotating 90 degrees is what you should try to check not seating properly. There's no way to change the way it seats without doing so, as long as it's properly tightened. Once the crank is removed you can generally tell if the spindle is bent by rotating it. Typically if the spider is bent the variation will be over a rather short area and only in one direction, whereas if not seated square the change will be continuous, and both in and out (it should be logically apparent why that would be so).

[bach-biking]

(12-28-2014, 10:26 AM)cny-man Wrote:  Rotating 90 degrees is what you should try to check not seating properly. There's no way to change the way it seats without doing so, as long as it's properly tightened. Once the crank is removed you can generally tell if the spindle is bent by rotating it. Typically if the spider is bent the variation will be over a rather short area and only in one direction, whereas if not seated square the change will be continuous, and both in and out (it should be logically apparent why that would be so).

Thanks again.