Stem slipping on steerer...

[The expat cyclist]

Now this is new for me. Never had this before, probably because I never used a torque wrench before:

 

I have a KCNC stem fitted onto an alu steerer tube of my mtb. Now the torque rating on the stem is 5Nm for the clamp bolts...but at 5Nm, every small stone I go over, twists the stem on the steerer tube.

I had the torque wrench checked and it is fine.

 

So, I tightened the clamp bolts to 8Nm and although it happnes less, it still does happen.

 

So, what to do?

1. Carbon paste?

2. New stem?

3. Some very obvious thing I did not think about about.

[Tony datoy]

I'd go with a new stem, the one you have is probably slightly oversize.

Manufacturing tolerances on mass production is sometimes an issue.

T

[openmind]

Carbon paste is magic stuff, try that first (and ease your bolts back to the right torque spec). If it still slips, something is wrong. Try another stem to check, your LBS should have one to lend you for a few days.

[Mongoose!]

Make both contact surfaces rough with sand paper and use then carbon paste.

[WrightJnr]

Stem not "coming together when clamping" ?? Is there a decent sized gap by the pinch bolts?

[V12man]

Lube the bolts before torquing - a dab of grease on the threads - bicycle torque settings are usually lubed rather than dry - and there is a significant difference in the end torque achieved

 

 

How did you test that torque wrench? Needs a special test rig few places have.

[Goodbadugly]

Now this is new for me. Never had this before, probably because I never used a torque wrench before:

 

I have a KCNC stem fitted onto an alu steerer tube of my mtb. Now the torque rating on the stem is 5Nm for the clamp bolts...but at 5Nm, every small stone I go over, twists the stem on the steerer tube.

I had the torque wrench checked and it is fine.

 

So, I tightened the clamp bolts to 8Nm and although it happnes less, it still does happen.

 

So, what to do?

1. Carbon paste?

2. New stem?

3. Some very obvious thing I did not think about about.

Your problem

[BenReaper]

I would suggest a new stem, your problem coud be caused by the bolts that might have stretched or the stem itself having deformed.

 

KCNC products are made to be very light and that might compromise their strength. I would get a new stem for peace of mind and see what happens from there.

 

As they say, rather safe than sorry.

 

Sent from my S40 using Tapatalk

[The expat cyclist]

Lube the bolts before torquing - a dab of grease on the threads - bicycle torque settings are usually lubed rather than dry - and there is a significant difference in the end torque achieved

How did you test that torque wrench? Needs a special test rig few places have.

I compared it to one we have at work that was recently sent in for calibration. At 5Nm there was no difference between the torque wrenches.

[Martin PJ]

Try making a small shim from a coke can. Worked for me with this problem.

[Groenkloof1]

Try making a small shim from a coke can. Worked for me with this problem.

Have been using KCNC on my Tallboy for years now- no issues

 

Carbon paste is definitely the answer! You will be surprised what difference it makes

[The expat cyclist]

Thanks for the advise gents. I shall try the carbon paste and V12's suggestion. If that fails, it will be a new stem.

[igg]

In case you missed the earlier suggestion, put anti-seize on the bolts.

Had this issue recently. Turns out the bolts were binding on the threads and 5nm was definitely not 5nm. Discovered this when I came off a jump and my bars were not facing the same direction as my wheel .