threadless headset and stem question

kieranb

hi, I just fitted new bearings to a threadless headset and have put the fork back on and realised that the top of the fork and the top of the stem are level with each other so no gap of a few mm as recommended (see this thread http://www.bikeradar.com/forums/viewtopic.php?=12596408&highlight=threadless+headset

So I will need to get a narrow spacer for the fork but can anyone tell me why leaving a gap of a few mm is so important??

Thanks

maddog 2

so when you preload the bearings the stem can slide down a bit.

If the stem was perfectly level with the top of the steerer then when you tightened the top cap bolt it'd push down on the steerer and not the the stem and so the stem wouldn't move and the headset bearings would remain unpreloaded.

a 5mm spacer wil do it

onbike 1939

I'm not sure why fitting new bearings should increase the height of the steering tube as if everything went back together correctly it should be the same. Make sure that you haven't put the new bearings in upside down before you do anything else.
However, if this is OK then you will need a spacer of 3mm. To pre-load the bearings the top cap must sit on the stem (or spacer) 3mm above the steering tube. When the screw in the top cap is then threaded through the star-fangled nut set in the steering tube, it draws the bearings together, in that it is resting on the headtube and pulling up the steering tube by means of the star-fangled nut. When you actually do this make sure that the stem clamping bolts are not tight otherwise the steering tube cannot move. The stem clamping bolts are tightened when the correct pre-load is achieved.

On second thoughts, have you just fitted a new Headset or just new bearings? The above advice refers to the latter.
See Parktool.com for a good explanation.

kieranb

thanks, the headset is an integrated headset and when looking at the bearings there was no up or down to the bearing house?. The frame was 2nd hand and came with the forks fitted, I guess the fork wasn't correctly fitted the first time and may not have been tightened enough so that the stem was higher than the fork? I have fitted it all together now and seems to turn ok.

gundersen

there is always a up and down side with bearings.

if they are steel balls in a retainer then the open part of the retainer should be on the smallest ring and the closed part of the retainer should fit inside the biggest ring.