The thing keeps getting loose and falling off.

A bit of background
Bike going fine until loud squeaking heard (once every revolution of the pedals). Not chain squeak; chain is well-lubed. Anyhooo, more and more loud squeaking, until one day... the left pedal starts to feel wonky when pedalling; every time you turn the pedals one full revolution you can feel the pedal movement in your left foot (the bad pedal/crank) caused by loose bolt.

Anyhoooo, bolt tightened. Got loose some weeks later. Bolt replaced and tightened again (really well) but this time getting loose far earlier (like every 10KM).

long story short
the thing keeps falling off within trips, necessitating on-the-road tightening on trip. Highly unsavoury. See pic. Help?

https://i271.photobucket.com/albums/j...r/DSC_0069.jpg

bykr,

If you have a lbs (local bike shop) you might stop in and ask them to tighten it a bit. Another option is to get them to do a tune up and they should catch things like that, and if it's a good shop they should point out any other problems they see. Sometimes it takes a few visits to find a good lbs.

If you plan to ride a lot you might consider doing your own maintenance so you may end up buying the proper tool if you don't currently have the correct one.

Don't be discouraged.

Hi guys
The thing was tightened with the proper (long arm) tool from a friend.

The thing was/is definitely tightened more than well. Just to clear that up. The first time it was tightened it lasted for a relatively long time (2 months or so of nearly everyday riding), but now it seems all has gone south because no amount of tightening can keep it put for long.

Bob, not sure what you mean by square taper but I'll have a closer look at the crank arm. As you can probably guess I'm mechanically inept

LastPlace,
I ride probably 100KM per week, on average, I think. This bike was given to me because my other bikes had a tendency to get stolen (Giant Boulder). Nobody likes this rustbucket, including thieves, but I have grown to like it simply because I don't have to buy a new bike so often

Thanks for the advice so far. I'll take a closer look at things, though I suspect it might be cheaper to buy a rustbucket version 2 (if it comes to that) than to spend too much on this thing, at this point.

If there is a simple cheap fix, that'd be great.

Maybe bad threads?

Anyways, square taper is the style/design of the bottom bracket. The bottom bracket would be the assembly your cranks are attached to that allows you to spin the darn thing (has something inside to reduce friction) and "square taper" just means the exact area that attaches to the crank is squared off ; taper means that it gets slimmer. For comparison the tips of pencils are tapered and rounded off.

Sounds possible that the soft aluminum left hand crank arm has moved a bit around the square bottom bracket spindle and now just does not fit flush with it. Once this occurs, you can tighten the bolt till kingdom come and it will still keep coming loose. If you are a big person and this is a low to medium quality crank, this could be happening. Basically, the square fit of the left hand crank arm becomes more rounded around the square of the spindle.

+1 on this. I had a left crank arm that was doing this. I replaced it. Problem solved.