Replaced chainring and now the crank bolt keeps becoming loose

[Ant in the NL]

I replaced the original 32t chainring with a 36t at my LBS here in the NL, and yesterday after about 40kms a strange creaking sound emerged...I checked the chainring bolts and tightened them where I could, but the bolt in the crank needed almost a full turn to tighten up. Problem solved until this am, after about 15kms the creaking/clicking noise appeared again and the bolt had loosened up...any ideas as to why this would be happening?

Edited May 30 by Ant in the NL

[Martin PJ]

What crankset is this? The torque indicated is very low, it's not this bolt that is holding the crank on. If the crank is being held on by this type of bolt the torque is 40 plus N.m.

[BaGearA]

Undo the botls on the side , do up the one in the centre (pre load ) 

 

THEN torque the ones on the side 

[Ant in the NL]

1 hour ago, Martin PJ said:

What crankset is this? The torque indicated is very low, it's not this bolt that is holding the crank on. If the crank is being held on by this type of bolt the torque is 40 plus N.m.

@BaGearA fyi 

Edited May 30 by Ant in the NL

[Martin PJ]

Thanks as BAgearA said, the pinch bolts hold the crank on, the centre bolt is to ensure everything is flush before you tighten pinch bolts. This is the Shimano design, take a look at some videos with Shimano crank problems. There may be some damage now to the crank splines, I have never had good luck fixing the problem once the Shimano crank falls off a few times.

Edited May 30 by Martin PJ

[Ant in the NL]

1 minute ago, Martin PJ said:

Thanks as BAgearA said, the pinch bolts hold the crank on, the centre bolt is to ensure everything is flush before you tighten pinch bolts. This is the Shimano design, take a look at some videos with Shimano crank problems. There may be some damage now to the crank splines, I have never had good luck fixing the problem once the Shimano crank falls off a few times.

Ok, so loosen up the allan key bolt, then loosen the 4 bolts holding the chainring to the crank. Tighten up the allan key bolt to bring the chainring flush, then torque the 4 bolts on the chainring, once done, torque the allan key bolt as indicated? 

One would have thought the rotation of the crank would assist in keeping the centre bolt tight? 

[Martin PJ]

The pinch bolts is only two bolts, they are not touching the chain ring at all. Once the pinch bolts are tightened the allan bolt has served it's purpose. 1.5nm of torque is very low. On the Shimano design you tighten a plastic piece (like your allan bolt) by hand, not supposed to be tight, it doesn't come out. The pinch bolts being tight does contribute to holding the allan bolt tight.