Stem bolt torque

MAMB

Whilst out riding this weekend my handlebars slipped round in the stem clamp. I hadn't adjusted them before so I guess the bolts had just worked loose. Both the handlebar and steerer clamps were marked 8Nm so I assume this was the recommended/maximum torque setting for the clamp bolts. Does this torque figure seem a a bit high to anyone ? It's just that when I started to tighten the bolts I chickened out at about 6Nm as the bolts seemed really tight and I was getting concerned about stripping threads etc. (BTW both steerer and handlebar are alloy, not CF).

Thanks.

Slow Downcp

8 will be okay - thing to remember is to tighten each bolt a little at a time so that the load is evenly spread. Try a bit of assembly compound on the bar to help it grip.

chriskempton

5nM is quite enough on carbon or alloy IME. 8 is, as you say, a mighty tight feeling tightening on bars and stems.

bigmat

On a similar note, I have just had a second carbon seatpost "crack" on me. I used a Ritchey torque key to fit it which limits torque to 5Nm I think. Its the second post in a row that has failed - basically there's a crack in the lacquer above where the post enters the frame. This didn't happen straight away but was apparent when I checked it after a ride. The first time it happened I was sent a new one free of charge, but I'm now thinking I should just get my money back unless its my fault and I am overtightening it?

chriskempton

Mat, what seatpost is that? I love my Torqkey, but if I were you i'd trying checking it against another torque wrench if you can - maybe it's overtightening?

bigmat

Its a zero racing one, bought it off ebay. Looks nice, 195g and only £35.

http://cgi.ebay.co.uk/Zeroracing-Full-C ... m153.l1262

I'm now thinking it may be a little under-engineered for the job. I've had no problems with previous carbon posts, handlebars etc. WIll check out the torque key though - my brother has one the same so will check I don't have a dodgy one.

Is a crack in the lacquer a serious cause for concern? If it was just cosmetic that is one thing, but if there's a risk of a crackin the post itself then I'm not too keen on riding it anywhere in a hurry!

chriskempton

I think most carbon seat posts suffer cracks on the laquer when clamped. As long as it's just superficial it's no cause for concern. You can afford to a be a little less fastidious with seatposts than with carbon bars....

MAMB

Not being a mechanical engineer, am I right in thinking that the torque figures specified on parts generally refer to 'dry' (i.e. non-lubricated) assembly ? I'm guessing that if I use anti-seize or assembly grease (which I tend to on pedal threads and some other components) the torque figures should be reduced - or am I barking up the wrong tree ?

onbike 1939

MAMB wrote:

Not being a mechanical engineer, am I right in thinking that the torque figures specified on parts generally refer to 'dry' (i.e. non-lubricated) assembly ? I'm guessing that if I use anti-seize or assembly grease (which I tend to on pedal threads and some other components) the torque figures should be reduced - or am I barking up the wrong tree ?

I've always assumed that these figures applied to lubed fittings.

MAMB

After posting my last comment, I did a bit of research on the web and also asked one of the mechanical engineers at work. Seems like the whole 'wet' versus 'dry' torque question is a minefield - depends on what the lubricant is, the fastener material, whether they are plated or anodized ....

I'm told that the major fastener manufacturers usually quote several torque figures depending on whether they're used dry or with different lubricants. Seems like the only sure way to tell is to measure thread stretch (haven't got a clue how this is done).

FWIW, I lubricated the screws, set the torque wrench to about 25% less than the figure stated and then checked whether it felt tight enough.

mm1

Have made the mistake of following Deda torque instructions (8NM) and wrecked a carbon steerer. 5NM seems fine.

keef66

If it's marking the seat post significantly, it would be worth checking the inside of the seat tube and the clamp for any burrs or sharp edges, and rub down anything you find.

pinkbikini

mm1 wrote:

Have made the mistake of following Deda torque instructions (8NM) and wrecked a carbon steerer. 5NM seems fine.

Never, ever follow the stem/component instructions for torque if you own a carbon frame. If you bust your frame or steerer the component manufacturer will do precisely nothing. Always follow the frame torque guidelines. Lubricate with assembly paste and undertorque seems to work for me - if they say 5Nm then I'll try 4Nm - haven't had anything slip yet (and I weight 85kg).

on-yer-bike

MatHammond wrote:

On a similar note, I have just had a second carbon seatpost "crack" on me. I used a Ritchey torque key to fit it which limits torque to 5Nm I think. Its the second post in a row that has failed - basically there's a crack in the lacquer above where the post enters the frame. This didn't happen straight away but was apparent when I checked it after a ride. The first time it happened I was sent a new one free of charge, but I'm now thinking I should just get my money back unless its my fault and I am overtightening it?

My Ritchey Pro carbon post cracked at the back where it was clamped. I only used 4 nm max. It may only be a superficial crack though.