New cranks loosen every 5 minutes?

I bought a virtually new Qu Ax trials uni on ebay, it only has a couple of rides on it however, I tightened the cranks and put pedals on, after about a two minute test ride the left crank arm came loose, I retightend and the same happened. The cranks are on the right side, I had my local bike man tighten and add locktight, it came loose in about 5 minutes.
I can’t see any obvious defects, any suggestions?

The cranks might be wrecked.

Is it an ISIS model? Maybe try removing the spacer between the cranks and the bearing, it might be preventing the crank from going far enough on.

I was reading information off a piece of paper that came with my unicycle recently and it said that the left crank is a counter clockwise thread. Would that do anything for you…

ISIS it is, no washer to remove.

If it has aluminium cranks it is normal for it to need tightening many times before it will get properly tight. My Qu-ax cranks had to be tightened about 20 times maybe before being so tight they couldn’t go on any further. Every time I rode at first I carried my crank tool and tightened it before and after riding. There should come a time when it will not keep coming loose- I guess.

I had the exact same problem with my Qu-Ax. Bought mine brand new at the end of last year. After the 2nd ride the left crank started to come loose. It got bad enough that it started coming loose every 2 to 5 minutes of riding. Bought myself some Loctite, and let it set for at least 24 hrs (which is important).

I had to replace the left crank after I bent it quite seriously on a small drop, and could easily get the crank bolt loosened. Put my new crank on with some Loctite straight away, and so far have not had to tighten the crank again. Definitely let the Loctite set for at least 24hrs before trying to ride again.

Another thing I did to make sure the crank bolt was on tight is I used a rather large spanner to give me some extra leverage on the allen key to apply more torque. Managed to give the bolt an extra turn or so tighter.

That refers to the pedal thread, not the thread on the crank bolt.

oh ok. Sorry about that

How does everyone tighten their hex crank arm bolts? It seems that after I tighten and loosen the bolts a lot the bolts get a little rounded out and it makes me paranoid that I will eventually strip the bolt, so I end up replacing them. What is the best and safest method to tighten them so the bolts dont get ruined at all?

a high quality 6 point socket is your best bet. Make sure that it’s held on the bolt very well when you’re putting a lot of force on it. Using a good long bar will decrease the foce you have to apply so give you more control. Don’t ever strike or jerk the bar.

That is probably my problem, I usually just use a standard L shaped hex key and have to apply a lot of force to get it to be as tight as I need it. I should invest in a nice tool with more torque so I don’t have to keep replacing bolts!

oh sorry by hex you mean an allen key, I thought you meant a six point bolt head. I’ve not had so much trouble with those as they’re a better design, but still a good quality tool that you can easily apply enough force with is the key to long lasting bolts.