Retrobike Forum Index

It is currently Sun Dec 04, 2016 5:39 am

* Login   * Register * Search  * FAQ



Post new topic Reply to topic  [ 12 posts ]  Go to page Previous  1, 2
Author Message
 Post subject: Re: Clockwork
PostPosted: Sat Jun 30, 2012 4:16 pm 
Old School Grand Master
User avatar

Joined: Wed Aug 08, 2007 12:15 am
Posts: 7563
Location: North Yorkshire
jmsjabb wrote:
Wold Ranger wrote:
That looks tidy. Looks like a 93.
Make sure you use a proper internal barrel bolt for the seat post, external QR's or bolt ups, twist the lugs inwards and permenantly twist the lugs.
Looking forward to seeing this built up 8) 8)

Could you explain this to someone who knows little about this, and had just bought a QR for my seat post so I can make easy adjustments while I get used to the bike. ( Either on this thread or PM if you don't want to pollute this )
See pic for what I have bought.


It's a question of pure engineering and Physics really and quite a long story! Pull up a chair :wink:

Road bikes always used to have lugs attached to their seat tubes with a slot to the rear, to "nip" up the tubes on the pin (pretty obviously) but they did this with a barrel bolt, which was like this: http://www.ribblecycles.co.uk/products/ ... _large.jpg

The bolt had two halfs of the same diameter with an internal male/female thread and Allen sockets at either end to tighten.
As these were a tight fit within the round slots on the frame, when you nipped them up the lugs could not twist inwards at an angle and both bend and put a pressure point on the seat pin, I.E. they "nipped up" parallel to the bolt.
When MTB's came along, they copied this design, fine no problems, as most of the road bike frame makers got into MTB's and just made Beefier road frames to start with (OK with this so far?)
Then some bright "mud plugger" spark, realised, it would be an advantage to be able to drop the seat on steep downhills and technical terrain, then raise it again for flat and up hill work.
So they adapted QR skewers for seat bolts (like the ones you just bought really)
This is when all the problems started, as they utilise a thinner bolt and can put a lot of pressure on the lugs, they started to bend the the lugs inward and in many cases, cracking the frame, scoring or grooving the seat post and removing all the paint from around the lugs. I've seen hundreds of frames ruined like this!
So the answer then was a seperate seat clamp, that is divorced from the frame and applies the "nip" evenly all around the seatpost, through the frame Just like all modern bikes!
You will see on a lugged seat bolted frame, a lip inside the lug where the barrel bolt fits and also a square cut out in one side or possibly little taperd grips, to stop one side of the barrel bolt turning.
If you want to use the qr seat bolt, fine, but it will eventually wreck and mark your seat post, then the frame, not to mention very quickly crack all the paint from around the lugs.
I have just removed a pair of these lugs, by machining them off an Orange frame, as the previous muppet had used a qr and one lug was twisted about 15 degrees inwards and the seat tube was no longer round at the top (it is perfect now, after a couple of days in my workshop)

Sorry to witter on, but that is the reason why you must not use a QR seat clamp bolt, on one with captive lugs, if you want to do this, have some one who knows what the are doing, machine the lugs off and fit a seperate clamp to the frame, then it will work just fine for you!
:oops: 8) :D :D :D


Top
 Profile  
 
 Post subject:
PostPosted: Sat Jun 30, 2012 4:31 pm 
Dirt Disciple

Joined: Fri May 25, 2012 8:28 pm
Posts: 20
Anthony wrote:
pumpduse wrote:
I have the same frame, I stripped all the components from it and got it shot blasted and powder coated. Cost £55.
https://docs.google.com/file/d/0B-SkrC_mNl0lUmF1d0M3NWJqQzg/edit

No, not quite the same! Yours is a 94, made of Orange Series 7 tubing.


Thanks, I see the difference now.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 posts ]  Go to page Previous  1, 2

All times are UTC [ DST ]


Who is online

Users browsing this forum: Google Adsense [Bot] and 12 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  

About Us

Follow Retrobike

Other cool stuff

All content © 2005-2015 Retrobike unless otherwise stated.
Cookies Policy.
bikedeals - the best bike deals in one place
FatCOGS - Fat Chance Owner's Group

Powered by phpBB® Forum Software © phpBB Group