Wits end!! Advice with planet x frame/headset

thehamo

Ive done 2 previously rebuilds and its gone fairly run of the mill but this frame has thrown me completely!

Having an issue with the stem/headset. As normal tightened stem cap, and then pin bolts in the stem. However, stem/headset kept turning when fork stayed stationary. Then the stem cap becomes lose.

This is what im dealing with https://www.bikeinn.com/bike/fsa-plug-pro-carbon-fork-1-1-8-inches/136071988/p?utm_source=google_products&utm_medium=merchant&id_producte=3132450&country=ie&gclsrc=aw.ds&&gclid=CjwKCAjw_qb3BRAVEiwAvwq6VpCABTirLl2J3RcIshUEfgFN-FMecm7gQv7eYZiUs5cAGkeWZP5dfRoCWjsQAvD_BwE

Ive reached my amateur limits at this rate. Any idea ls what might be the issue?

Plastik

My guess. Compression bung isn't expanding and tightening against the inner of the steerer fully/properly. When you're tightening the top cap afterwards you're probably pulling the bung upwards instead of compressing the stem downwards.

thehamo

Plastik wrote: »

My guess. Compression bung isn't expanding and tightening against the inner of the steerer fully/properly. When you're tightening the top cap afterwards you're probably pulling the bung upwards instead of compressing the stem downwards.

So suggestion would be a new compression bung?

Plastik

Well first I'd be checking that you're doing everything right with the one you have. With the top cap removed the bung needs to be tight inside the steerer. You tighten the bung into the steerer and the top cap into the bung to create compression on the headset.

thehamo

Ok. Heres what i just did.

1. Checked compression bung and is working in the steerer.

2.Threw on the spacer, stem and tightened on the stem cap.

3. Tightened pin nuts on the stem. All fine. Forks move with bars.

Now.

As soon as the forks are held in place and bars turned (with very little force) the stem just seems to move on the steer tube, and in turn seems to unscrew the stem cap 🙄??

Could it be the stem is too big for the steerer? That said pretty sure the steerer is 1 1/8

nilhg

Are the compression bung and the stem aligning on/in the steerer?

Are you sure there's nothing in the slit on the stem that's stopping it tightening properly on the steerer?

Carbon or Aluminium steerer?

triggermortis

So the stem isn’t gripping the steerer tube?
Do you have another stem you could try? It could be the wrong size. I couldn’t open your link you put in an earlier post

thehamo

nilhg wrote: »

Are the compression bung and the stem aligning on/in the steerer?

Are you sure there's nothing in the slit on the stem that's stopping it tightening properly on the steerer?

Carbon or Aluminium steerer?

Yeah had a good scan of it this morning. Its s carbon stearer, planet x pro carbon fork

thehamo

triggermortis wrote: »

So the stem isn’t gripping the steerer tube?
Do you have another stem you could try? It could be the wrong size. I couldn’t open your link you put in an earlier post

Yeah stem isnt griping to the steerer tube it looks like. Its a standared stearer tune size and stem so i dont know why😕 Ive another i can take off a bike and try that.

route66

Maybe consider using carbon friction paste (E.G. This) - as used for seat posts?

I have used it for a seat post - according to the blurb:

The Fenwicks carbon assembly paste is used to provide grip when fitting carbon or alloy components such as seat posts, handlebars or stems. The application of the paste stops slippage between mating surfaces, meaning you will need to apply less torque to bolts to gain the same level of security.

Plastik

Is the bung far enough down in the steerer so that the top cap when tightened is compressing the stem or any spacer on top? Try sticking another small 2.5/5mm spacer above the stem and tighten the top cap down on that.

thehamo

Right, seems to be sorted. Took a stem off an old hybrid that i had and it had a rubber shim on thr inside which seems to have worked nicely. Seems as tho the stem was the issue

Paul Kiernan

I'd be a little concerned as to what's causing the problem. You shouldn't need a rubber shim! A standard 1 1/8" stem should fit. Those carbon steerers are very fragile. Ideally you should use carbon paste and a torque wrench.

The traditional purpose of the bung is to "temporarily" compress the headset until you tighten the stem onto the steerer. Then it can be removed and thrown away!

However with a carbon steerer it acts as a reinforcement for the steerer i.e. the steerer is pinched between the stem and the bung as you tighten the stem. Without the bung the steerer would/could crack!

Mefistofelino

Sounds like a 1 1/8" stem on a 1" fork steerer.

What frame is it and how old?

Icyseanfitz

probably not great advice but i had a similar issue with my mtb, clamped the top cap down tight, and then really over tightened the stem bolts which stopped the headset loosing

thehamo

Mefistofelino wrote: »

Sounds like a 1 1/8" stem on a 1" fork steerer.

What frame is it and how old?

Planet x pro carbon circa '14