Cycling UK Forum

Hi, novice cyclist here so apologies if this is a stupid question.

I got a stem riser for my daughters frog bike. But when I install, the long screw doesn't centre and I can't secure it properly. See couple of photos..

https://thumbsnap.com/3NweFU7b

https://thumbsnap.com/denyeNf2

Happy to take it to a bike mechanic if that's advisable but I thought I will ask here in case I am missing something basic and also can learn something maybe..

Thanks

Welcome.

I recommend starting with the two great maintenance sites:

Sheldon Brown "Headset adjustment"
https://sheldonbrown.com/headsets.html#threaded

Park Tools "Handlebar, Stem and Seatpost"
https://www.parktool.com/blog/repair-help?query=&area%5B%5D=54

Then come back to this thread and ask if it doesn't make sense.

Jonathan

PS: The only stupidity would be not asking.

Is the riser a very loose fit when initially placed over the steerer? Stem risers are typically designed for inch and an eighth steerers whereas the one on a child’s bike may well be just an inch. If the riser didn’t come with the necessary shim then the bike shop should be able to supply one easily.

TheBomber wrote:Is the riser a very loose fit when initially placed over the steerer? Stem risers are typically designed for inch and an eighth steerers whereas the one on a child’s bike may well be just an inch. If the riser didn’t come with the necessary shim then the bike shop should be able to supply one easily.

No the fit is fine. Frog bike stem is 1 1/8 size.

Jdsk wrote:Welcome.

I recommend starting with the two great maintenance sites:

Sheldon Brown "Headset adjustment"
https://sheldonbrown.com/headsets.html#threaded

Park Tools "Handlebar, Stem and Seatpost"
https://www.parktool.com/blog/repair-help?query=&area%5B%5D=54

Then come back to this thread and ask if it doesn't make sense.

Jonathan

PS: The only stupidity would be not asking.

Thanks I will have a look. I did Google for a problem where the bolt doesn't centre but couldn't see anything relevant...

What is it bolting in to? A slug or a star nut? The bolt is presumably being moved off centre by the "nut". Either it isn't fixed in place or it it is but an angle.

I think you need to find another headset spacer and fit it under the cap... from the photos from the top it looks like your stereer tube is proud of your headset stack...
...any chance of a photo from the side just to confirm my thoughts?

Can you share a link or an image of the design of the stem riser from the side? There are types that work/install in different ways. The most suitable type has a lower portion that fits over and around the top of the existing fork steerer, and clamps with 2 bolts onto the steerer like an ahead stem. Like this one:
If this is the type that you are using then the long bolt is supposed to be used in the same way that the original cap bolt was; to reach down and screw into the existing fork star nut and add a little light compression to pre-load the headset bearings before securing the riser properly with the 2 other bolts. Often the star nut in a fork will be installed a little wonky which causes the top cap bolt to lean a bit, but the lean is magnified into a huge displacement with a bolt this long to the point where a problem such as yours results. You can remedy this by removing the riser, re fitting a shorter M6 bolt in the star nut and carefully tapping it to vertical and central with a hammer. You need to make sure that doing this you don't knock the star nut much further down into the fork. You may bent the bolt in doing this so count the bolt you use as a sacrificial one. Once you've got the star nut properly straight in the steerer you can re fit the riser and longer bolt.

Please also note that with this type of riser the steerer of the fork needs to end inside the riser at about the mid point of the upper of the 2 clamp bolts or a bit above (if shorter than this it's potentially unsafe), but not butt up against the stepped reduced diameter inside the riser, which will result in a loose headset. Using spacers under the riser can adjust where the steerer ends inside it.

If you have a different design of stem riser to this you may have an unsuitable type for the job at hand, and it could be unsafe. Please post a photo of the one you have.

gregoryoftours wrote:. . . . . If you have a different design of stem riser to this you may have an unsuitable type for the job at hand, and it could be unsafe. Please post a photo of the one you have.

Thank you for a detailed reply. Stem riser I have is exactly like the one in your picture. I will try to find a spare M6 bolt and see if I can straighten the star nut.

To me it looks like your star fangled nut is misaligned in the steerer tube. With a short bolt (your old stem) this doesn't matter too much since it only puts the securing bolt a few mm off centre. Over a long bolt the off centre displacement is much more ..hence it's way out.

Solution - I see Gregory of Tours has suggested the same

Google "star fangled nut" so you know what you are dealing with.

Then take all the extender gubbins off..eyeball the star fangled nut and gently tap the high side with screwdriver/mallet until straight...