is unequal gaps ok for stem clamp bolts ??

buder

Hi

Just checking my stem and I noticed the gap of thelower of the stem clamp bolts is slightly less tan the top one.

Does this matter should the gaps be the same between top and bottom ?. I used a torque wrench and both bolts are torqued to the same value so why is the gap different ?

Any help much apreciated

desweller

I take it you're referring to the gap between the faceplate and the stem?

You should try to make them equal. You'll get uneven gaps if you tighten one screw to full torque before the other.

sungod

simplest way is to start by just lightly tightening to get even spacing, then do a quarter turn on each one alternately until tight enough

btw you don't *have* to use maximum torque, just enough to clamp securely, which is often a fair bit less

P_Tucker

buder wrote:

Does this matter should the gaps be the same between top and bottom ?. I used a torque wrench and both bolts are torqued to the same value so why is the gap different ?

I'm really struggling for an analogy that would explain why the tightness of the bolts and the gap are independent of each other; suffice to say that to eradicate this unsightly problem, loosen the one thats next to the smaller gap, and tighten the one next to the bigger gap (don't worry about torque for now) - once you have the gaps equal, undo both bolts by say one 360 turn, then do them up alternately a with your torque wrench one quarter turn at a time until you hit your desired torque.

Hopefully whilst you are doing this the penny will drop.

Yossie

Loosen them all off completely, grease up the bolts.

Do up finger tight with no allen key.

Start at the top left with the allen key, when you feel some resistance go to the bottom right, do the same on a diagonal working - ie top left, bottom right, top right, bottom left.

Toqrue into place in the same manner: by doing them up diagonally it will spread the load across the faceplate, stop the face plate from splitting, make the gap equal and hold everything flush and straight.

Do the same for the bolts holding the stem to the fork steerer - ie don't do the top one up all the way before you've done the bottom one up some.

Re torque: its generally safe to go 1 Nm below the max stated (it is a maximum, not a stated exact, so if it says 6Nm its fine to go for 5, and so on).

HTH

Y

buder

Sorry all I referring to the clamp bolts to steerer interface. Ive tried everything alternating the turning etc and using the torque wrench for the last bit but the bottom gap is slightly less. To achieve exactly equal gaps I would have to have uneven tension ?.

Is it safe that the bottom gap is less it's not creating a pinch area or something ?

just added a pic here:

Bolts are at 4Nm so no where near the 8Nm Max PX states :shock: :shock:

Thanks
[img][/img]
photo (8) by 7e2ca155e724efbf4147f41dda72eb2c, on Flickr

sungod

bolts don't have to be the same torque, but it's possible there's an asymmetry in the stem, if the top is a smidge thicker then the gap will be wider for the same clamping force

what you show, i wouldn't worry about, just make sure the stem is clamping enough to prevent it moving on the steerer tube and leave it at that

plowmar

+1 sungod, my thoughts exactly.

buder

Thank you everyone for the replies really re-assuring.

As it happens I sanded down the stem to smooth the edges off prior to fitting, and the bottom edge is thinner on one side so that makes sense !.

cheers again

neeb

What sort of bung do you have in the steerer? Is it one of those ones that sits right at the top of the steerer with a little lip on it? If so, the lower bolt might be below the part of the steerer where the bung extends down to, so the top bolt is "braced" by the bung inside the steerer and the bottom one isn't. Solution would be to cut the stem so that you don't need the spacer on top and the bung can extend further down.

With other types of bungs that go deep down inside the steerer, you often get the opposite problem - the top of the steerer is less supported internally and so is more "compressible".

It's not ideal either way as it can concentrate the clamping forces on particular areas of the steerer.

buder

neeb wrote:

What sort of bung do you have in the steerer? Is it one of those ones that sits right at the top of the steerer with a little lip on it? If so, the lower bolt might be below the part of the steerer where the bung extends down to, so the top bolt is "braced" by the bung inside the steerer and the bottom one isn't. Solution would be to cut the stem so that you don't need the spacer on top and the bung can extend further down.

With other types of bungs that go deep down inside the steerer, you often get the opposite problem - the top of the steerer is less supported internally and so is more "compressible".

It's not ideal either way as it can concentrate the clamping forces on particular areas of the steerer.

I was exact with my measurements of the steerer top 5mm spacer is to allow proper pre-load. Bung is the lip type but an long expander plug which measures 4.8cm when measuring from the top of the steerer to below the bottom clamp area of the stem the bung extends a further 0.8cm so the entire stem clamping area is supported by the bung.

Did you mean cut the steerer as opposed to the stem ?, as per above thats not an issue.

. I was concerned about causing a pinch point but the torque on the clamp bolts are currently at 4Nm I see no point for that minimal difference in gaps having the bottom one less than the top etc both bolts are supported by the bung I made sure of that when it was built.

Thanks

neeb

Bung is the lip type but an long expander plug which measures 4.8cm when measuring from the top of the steerer to below the bottom clamp area of the stem the bung extends a further 0.8cm so the entire stem clamping area is supported by the bung.

If that's the case then as you say that won't be the issue. Have you allowed for the bung becoming a little shorter when it is tightened though?

I'm just very sensitive to this issue as I did stupidly manage to crack a steerer once using one of those lipped bungs. I had more than 5mm of spacers above the stem though, and I tightened the bolts above the recommended torque.

Did you mean cut the steerer as opposed to the stem ?

Yes, sorry. You don't want to cut the stem..

Personally I think that with those lipped bungs you are better to cut the steerer to 2-3mm below the top of the stem (allowing for the extra 1mm or so added by the bung lip) and not have any spacers on top. Still, 5mm should be OK. If the bung goes way down inside the steerer I think it's best to have a 5mm spacer above the stem, as then the clamping force isn't being applied to the unsupported edge of the top of the steerer. Just my possibly unsupported prejudices though..

buder

neeb wrote:

Bung is the lip type but an long expander plug which measures 4.8cm when measuring from the top of the steerer to below the bottom clamp area of the stem the bung extends a further 0.8cm so the entire stem clamping area is supported by the bung.

If that's the case then as you say that won't be the issue. Have you allowed for the bung becoming a little shorter when it is tightened though?

I'm just very sensitive to this issue as I did stupidly manage to crack a steerer once using one of those lipped bungs. I had more than 5mm of spacers above the stem though, and I tightened the bolts above the recommended torque.

Did you mean cut the steerer as opposed to the stem ?

Yes, sorry. You don't want to cut the stem..

Personally I think that with those lipped bungs you are better to cut the steerer to 2-3mm below the top of the stem (allowing for the extra 1mm or so added by the bung lip) and not have any spacers on top. Still, 5mm should be OK. If the bung goes way down inside the steerer I think it's best to have a 5mm spacer above the stem, as then the clamping force isn't being applied to the unsupported edge of the top of the steerer. Just my possibly unsupported prejudices though..

I appreciate your posts as I was very worried about making sure my set-up was 'safe' so to speak so tried to pay particular attention to these details.

To be honest its the Planet X long expander plug which I have. Ive had out to look at I cant see how it becomes any smaller when tightened !?, are you referring to the length of it or its position in the steerer ? I made sure its tight and not slipping.

I dont get the top spacer issue however. I understand what your saying about the 2-3mm steerer cut below top of stem, thats how its been done but even with this the top cap was bottoming out, I needed a 5mm spacer to get the pre-load right. The 5mm spacer at the top is sitting ontop of the stem its just for pre-load. The steerer is exactly as you say around 2mm below top of stem. I didnt want to go shorter as it would have meant I was at risk with the top clamp bolt being unsupported.

If I wanted to I could remove the spacer after adjustment its not doing anything at this point !?.

Ill measure it all again later but the stack height of the stem is 4cm and the bung is 4.8cm. The steerer is cut just under top of stem around 2mm so assuming for this example its level with the top of the stem im extending below by 0.8cm is this right ? and is this enough ?

neeb

I don't know the particular bung that you are using - although actually, taking a look at a picture from a google search it is different from my Deddacciai one. It is longer and obviously won't shorten when tightened. So if it is definitely extending below the bottom stem bolt then it is completely fine, spacers or no.

I dont get the top spacer issue however. I understand what your saying about the 2-3mm steerer cut below top of stem, thats how its been done but even with this the top cap was bottoming out, I needed a 5mm spacer to get the pre-load right. The 5mm spacer at the top is sitting ontop of the stem its just for pre-load. The steerer is exactly as you say around 2mm below top of stem. I didnt want to go shorter as it would have meant I was at risk with the top clamp bolt being unsupported.

If I wanted to I could remove the spacer after adjustment its not doing anything at this point !?.

If the top of the steerer is sufficiently below the top of the stem when everything is tightened you shouldn't need a spacer above to get the preload. Sometimes 2mm isn't enough though and it needs to be 3mm... The top cap probably has a bulge on the bottom that is touching the top if the steerer and preventing you getting the preload, i.e. the steerer is probably still a mm or so too long. But cutting off another 1 or 1.5mm would be a fiddly task that might end in disaster, so is perhaps best avoided unless you feel confident..

I would probably leave it as it is and not worry about it. I wouldn't remove the spacer after adjustment - if your headset ever became loose out on the road you wouldn't be able to tighten it.

P.S. if this is a new bike and the headset does become loose after the first couple of rides, it's probably just the headset bedding in (crown race being pushed down another fraction of a mm etc..). Don't make the mistake of thinking that you need to over-torque the stem bolts...

P.P.S. If you do crack the steerer, you will probably hear it...

buder

neeb wrote:

I don't know the particular bung that you are using - although actually, taking a look at a picture from a google search it is different from my Deddacciai one. It is longer and obviously won't shorten when tightened. So if it is definitely extending below the bottom stem bolt then it is completely fine, spacers or no.

I dont get the top spacer issue however. I understand what your saying about the 2-3mm steerer cut below top of stem, thats how its been done but even with this the top cap was bottoming out, I needed a 5mm spacer to get the pre-load right. The 5mm spacer at the top is sitting ontop of the stem its just for pre-load. The steerer is exactly as you say around 2mm below top of stem. I didnt want to go shorter as it would have meant I was at risk with the top clamp bolt being unsupported.

If I wanted to I could remove the spacer after adjustment its not doing anything at this point !?.

If the top of the steerer is sufficiently below the top of the stem when everything is tightened you shouldn't need a spacer above to get the preload. Sometimes 2mm isn't enough though and it needs to be 3mm... The top cap probably has a bulge on the bottom that is touching the top if the steerer and preventing you getting the preload, i.e. the steerer is probably still a mm or so too long. But cutting off another 1 or 1.5mm would be a fiddly task that might end in disaster, so is perhaps best avoided unless you feel confident..

I would probably leave it as it is and not worry about it. I wouldn't remove the spacer after adjustment - if your headset ever became loose out on the road you wouldn't be able to tighten it.

P.S. if this is a new bike and the headset does become loose after the first couple of rides, it's probably just the headset bedding in (crown race being pushed down another fraction of a mm etc..). Don't make the mistake of thinking that you need to over-torque the stem bolts...

P.P.S. If you do crack the steerer, you will probably hear it...

Thanks allot for all that Neeb much appreciate the information

Im sensitive to it aswell as its a 4 week old bike and ive sent the forks back once due to a 'stress riser' on the steerer inline with the bottom edge of stem going all the way around !. I was adamant it wasn't me, I torqued to 4Nm which is below the max by some way and that part was supported by the bung also I measured it all when removed.

Yes your spot on about the topcap it does recess a bit, hence the spacer on top to help out with the adjustment.

Im happy aslong as its all supported which im sure it is I have measured it a few times now but it does worry me. Ill leave it and check it every 200 miles I think.