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-   -   Old manitou three steer tube short (https://www.bikeforums.net/bicycle-mechanics/773931-old-manitou-three-steer-tube-short.html)

skieslord 10-08-11 01:08 PM

Old manitou three steer tube short
 
Hello Folks,
I just got an old suspension manitou three that I resusited, I bought some sprigs to replace the non-selling elastomers.
My problem is that the steer tube (threadless) is too short, I just need about 3/4 of an inch to reach the top of the steam, in other words, the steam only grabs half of the tube.
My thinking is that I could make an inner thread on the tube, then grab another pipe with the same diameter, internal and outside and make a kind of 3/4 bushing with a male thread so I can screw it in, I can make a thred at least 2 inches long so it gets support.
I am not sure if I explain myself well enough. I would like to know if this is a good idea or it's better to replace the whole tube for the correct size..???
I did a little drawing to help a little bit, I am not to good at drawing as you can see.

http://postimage.org/image/pbc16tl0/
http://postimage.org/image/pbdoq62s/

Or if you guys have a better recommendation.

skieslord 10-08-11 01:09 PM

1 Attachment(s)
http://bikeforums.net/attachment.php...hmentid=222021
Here is the image. The dotter area shows where the threads will be

dsbrantjr 10-08-11 03:29 PM

skieslord: The problem I see is that the walls of the steerer tube are quite thin and cutting threads into it might weaken it to the point where it might fail at the base of the threads, leaving you with the handlebars no longer attached to the fork. Funny in the cartoons, not so much on a fast downhill run.

HillRider 10-08-11 03:31 PM

Get a fork with the correct length steerer. There is no way to lengthen a steerer that is both safe and cost effective.

dabac 10-09-11 03:14 AM

Depending on your fabrication skills, riding style, and risk tolerance(!), there are a couple of options on how to extend a steerer tube. But for an old fork, none of them are rational choices.
But if you like the machining, and are OK with the risks and waste of time - go for it.
I'd advice against the internal threading though, unless you have some serious tool access. Anything but a fine thread would remove a scary amount of metal from that tube.
If I wanted to do it I'd probably make an extension piece that'd look like a quill stem with a stepped diameter. I'd use a thicker-than-average screw for the wedge, and run a thread inside that for a normal top cap.
Or if it's a steel steerer, I'd make an extender with an internal press-fit guide and then braze it in place.
Some really old forks had a pinch wrap arrangement holding the legs and the steerer to the crown. If that is the case you may be able to replace the whole steerer. Don't expect smooth sailing though. Steerer tubes are usually a bit wider at the bottom than along the rest of the length. Getting a good pinch and getting the crown race to seat properly may be a challenge.

skieslord 10-09-11 09:16 PM

I think all of you are right, it will weak the tube and I may get into some serious problems. I don't really want to get rid of this fork it is really good. I think i can follow DEBAC's advise of replacing the steer tube. I can also get a machine shop guy machine a whole new steer tube, I see the diameter on the bottom is wider, it means the tube has a taper and it is installed by pressure. I am not sure it this involves risks as well.
thanks for all replies

fietsbob 10-09-11 10:25 PM

a kludge : tube stem raiser, for 1" or 9/8" fork, it will gain you height.
To maintain the threadless headset adjustability , a expansion nut,
typical for carbon forks will go in and be removable,

as the tube quill stem raiser has a bolt to tighten it inside your fork..
Can be serviceable .. for normal riding, I cannot recommend it for hard riding off road.

BoozyMcliverRot 10-09-11 10:28 PM

If I remeber right,Manitou sold steerer/crowns for that fork.try ebay,I think 3/4EFC were all the same crowns.You could buy a bunk fork just for the crown. These might work....

http://www.ebay.com/sch/i.html?_nkw=....c0.m270.l1313

skieslord 10-10-11 01:48 PM

I got a private message from a memeber that has an exceptiona idea how to extend the tube, I will try this and I will post some pictures in later time. I was unable to answer on that private message because I do not have enough posts. thanks cobba

skieslord 10-18-11 12:21 PM

3 Attachment(s)
Well,
here is how I fixed the steer tube.

I got a bar or metal and made the extension for about 1" with the external diameter, and shaved the bar with the internal diameter. That way i introduced each side inside the tube and I did two set screws to secure the bar. See pictures attached.

http://bikeforums.net/attachment.php...hmentid=223513http://bikeforums.net/attachment.php...hmentid=223514http://bikeforums.net/attachment.php...hmentid=223515

skieslord 10-19-11 10:06 AM

Cobba-
Thanks for you tips.
There are two inch inside each side.
The metal piece was machined few mils wider so it get some pressure to fit.
Yes, we tapped threads and made set scrubs with red loctite.
The screws, according to me, are only holding the bar from moving, there is some pressure put when inserting the metal bar ends, it is very strong.
There is loctite, the screws are around 3/4 long chances of screw to come out are minor.

I suggested the machinist to put some MarineTex on the interior of tube but he said it was not neccesary.

hey thanks again for the info.. I hope I can keep my theeth in place.

fietsbob 10-19-11 11:33 AM

Machine shops are handy things to have.

skieslord 10-19-11 03:08 PM

And gets better when have friends working there.


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