Front end flex - why!!!

[Matt_wood55]

Dear All

I am just putting the final bits and bobs on a rebuild.

The stem and bars have just gone on, and there is a degree of flex (more than expected) when pressure is applied to the bars.

I am a bit clueless when it comes to headset sizes, stem diameters etc. Any idea what could cause the flex? Frame and forks show now signs of cracking and pulling on them I get only minimal flex. I can see a bit of play between the stem and the headset, could it be a mismatch in sizes?

What size headset and diameter stem should I have - 1989 Raleigh 653 (see link below for pics in Readers Bikes).

Thanks
Matt

http://www.retrobike.co.uk/forum/viewtopic.php?t=167946

 

[monty dog]

Quill stems are a lot more flexible torsionally than modern stems - if you want something stiffer look for something like an ITM Pro constructed from steel tube rather than an aluminium alloy forging.

 

[Matt_wood55]

Hi

Thanks for the reply. I have a few bikes with quill stems, and have never had flexing anywhere near this degree. It is not normal. Just wondering what the possible causes are?

Cheers
Matt

 

[ekallus]

When you say play between the stem and headset, what exactly do you mean?

Have you tightened the headset enough? If not, it will allow a small amount of movement that could appear to be 'flex'. It can be surprising how much tightening is required. (Without causing any binding, obviously!)

Ernst

 

[Matt_wood55]

Hi

Headset is tightened correctly - no play in it when front brake applied.

When I hold the bars, they flex to a higher than normal degree. Can it be due to a stem - headset size mismatch??

Cheers

 

[fiks]

Hi

Thanks for the reply. I have a few bikes with quill stems, and have never had flexing anywhere near this degree. It is not normal. Just wondering what the possible causes are?

Cheers
Matt

Maybe the stem is 22mm but your frame needs a 22.2mm (inside diameter of the steerer tube). What stem is it?

If it hasn't got the size marked on it, you could compare it with your other stems using some calipers.

 

[monty dog]

If you stand over the bike and flex the bars, you should be able to tell whether it's movement at the steerer or the torsional twisting/ flexing of the stem or bars. What bars and stem are they? If the bars have a sleeved centre portion unlike the upset/bulged section of a modern bar, they won't be as stiff.

 

[Lazarus]

Hi Matt Seems pretty much that you want someone to confirm what you already suspect, that the stem is a good few thou slack in the tube /headset. I guess you're just wondering "why" its slack after all your other rebuilds.

Maybe its been polished / cleaned up ?

Highly unlikely that it's your headset that is a mismatch, most likely the stem, but, and it is a but, new stuff / old stuff pairings can raise all sorts of issues. I've got a French Turbo Mecacycle that really likes to test my patience. Its latest trick is to refuse all of the stems I want to fit as replacements for the 3ttt currently on it. I guess this is your proof of stem/headset/steerer tube conundrum.

French headset on French threaded forks that will only take a "French ?" stem ? The difference IS only about 0.2mm but enough to prevent other stems going in. Sounds like you have my stem on your Italian/English bike. Hope this helps buddy, yours Laz.

PS: Lovely looking build by the way, especially the rear block LOL. My kind of ratio, nothing wrong with hill climbs on a 53-19 ... good for your soul Got bikes with bigger blocks on and more teeth, but never use them. Brought up on sprint ratios.