Café Commando build thread

The stem is easy to press out of an alloy bottom clamp, some heat and a small press. Even a threaded rod up through the centre and a washer on top, then a short tube bigger than the pressed in bit and a washer and nut, Heat the alloy and tighten the nuts and the rod will come out easy.
 
That shaft is easy to remove, you press it thru the bottom a little to expose a circlip, then you press it back twards the shaft and it;s out. I learned this the hard way after lots of heat and I pressed the clip thri the lower tree. Needledd to say I dammaged the hole. I had to shorten the shaft and adjust for bearing size, so I bored the hole and made an adapter/plug to weld in. After turning it on the lathe I pressed it back in, all is good now.

Café Commando build thread



The way you cut it, just put a sleeve on the inside of the shaft, drill some holes in the shaft, and use a few rosette welds on each side of the cut.
 
The bottom yoke is a forged part and it is welded to the stem. Impossible to remove without damage. I just clamped the two pieces in an angle iron and welded ell the exposed joint, then I welded the rest, stayed straight and true. I will try to find a picture of the yokes I was talking about only held with a threaded rod and post it here, I will also ask about what I did in the chassis design list and see what they say about it.

By pressing it out of the bottom part, there is no garantee it will be true and square when pressed back together, the way I did it, at least it is as square and true as it was.

Jean
 
I'm with you on this one, Jeandr. There is very little tension load on the stem, and a welded steel one is plenty strong enough. The only significant load on the stem is shear load at the bearings and yokes. There was a lot of discussion of using just upper and lower stub stems on the chassis list a while back, and Tony Foale, among others, pointed out how little need there is for much material in the middle part of the stem.

Ken
 
I'm with Jean as well. I've heard of stems being made quite successfully from aluminium. Even if it broke, what's going to happen? The clamps holding the fork legs won't let anything go anywhere.
 
I like the idea of the 21" rims, not from a looks perspective, which, as far as I'm concerned, is ALWAYS secondary to performance, and I think you will be surprised at how sharp the steering will be. What width rims did you fit? I'm looking forward to this one as well.
 
Fullauto said:
I'm with Jean as well. I've heard of stems being made quite successfully from aluminium. Even if it broke, what's going to happen? The clamps holding the fork legs won't let anything go anywhere.

Indeed. Many race bike stems are aluminum. I've used TZ250 forks for several race bikes, and they come from Yamaha with aluminum stems.

Ken
 
Fullauto said:
I like the idea of the 21" rims, not from a looks perspective, which, as far as I'm concerned, is ALWAYS secondary to performance, and I think you will be surprised at how sharp the steering will be. What width rims did you fit? I'm looking forward to this one as well.

The rims are WM3 and the tires (tyres) will be Avon 90-90 AM26 Roadriders. I was told by Avon to fit the front as it is meant to be (follow rotation arrow) and the back reversed with respect to the front.

Jean
 
lcrken said:
Fullauto said:
I'm with Jean as well. I've heard of stems being made quite successfully from aluminium. Even if it broke, what's going to happen? The clamps holding the fork legs won't let anything go anywhere.

Indeed. Many race bike stems are aluminum. I've used TZ250 forks for several race bikes, and they come from Yamaha with aluminum stems.

Ken

While searching for backup to what I did I found one post from a drag racer who had made his own triple trees all from aluminum, both upper and lower tables and the stem. While a dragster runs on glass smooth tracks, most of them have severily raked front ends to get lots of trail and high speed stability so they have more stress on the bearings, the neck and even the fork tubes yet a complete aluminum triple tree was OK and the racer totally confident in his design.

When I look at how bicycles are made, I am more worried about the front end coming apart than what I did, how often do you hear of a stem breaking on a bicycle? My onw bicycle has a fork made out of carbon fiber, a plastic part :!: totally safe and sound with more stress on the bottom than my weld will ever see.

"What me worry" Alfred E. Newman

Jean
 
My machinist simply chucks the japanese bottom yoke/stem assmblies into his lathe from the threaded end, turns down the appropriate bearing surface sections, then fabricates a new threaded section where required and chops off the excess stem length.

Voila.
 
x
Disregard!
I had a couple of threads open at once and messed up my posts.
 
If you are fitting forks from another bike, its sometimes possible to press out the original steering stem, and fit this into the new yokes, which can either be bored or sleeved to suit. This method allows use of the original bearings, seals and adjuster nuts etc, and of course the stem is the right length to fit the headstock perfectly.
 
I couldn't find the picture of the triple trees held with a threaded rod, but here is a drawing of the forks from a Greeves. Look at the size of the bolts tying the top yoke to the fork legsand the long thin bolt tying the top and bottom yokes together.

Café Commando build thread


Jean
 
Fullauto said:
I'm with Jean as well. I've heard of stems being made quite successfully from aluminium. Even if it broke, what's going to happen? The clamps holding the fork legs won't let anything go anywhere.

Yes, I have over reacted to a poor engineering job, I just found it stunning that someone would cut and weld when it could so easily be done properly, as grandpaul suggested,I would have no problem with a properly designed alloy stem, although would prefer steel stem shrunk into alloy yoke.

Whers it going to go if it breaks , nowhere, but take a look at your 850 and tell me where the stems going if it breaks
Would also be illegal to put on the road here, welded steering components...
 
Hi Jean
I brought a set of Ceriani forks that had a Maxton set of yokes in magnesium. I keep them as a pattern as they were not looked after.
The spindle is a 5/16inch rod!
They were on a TZ & had been used on the Isle of Man.
Chris
 
No offense intended, but some of you guys clearly didn't read what Jean said.

First of all, forget about simply pressing the shaft out. Jean explained that the bottom yoke is steel, not aluminum, and the shaft is welded to it at the bottom. Yes, you could bore the weld out and then press the shaft out, but he also explained that his lathe doesn't have enough swing to chuck the shaft up and turn it with the yoke attached.

Same comment about all the suggestions on shortening and cutting new threads. Can't do it if it won't fit in the lathe.

I don't think it's right to call it "poor engineering". It appears to be a sensible way for Jean to do it without taking it to someone else for machine work. And it seems clear there is really no safety issue with the technique.

I really don't see what all the concern is over welding on "steering parts". Traditional British clip-ons were welded together, and I don't recall any concern over it. Plenty of people have fabricated fork yokes from welded sheet steel, again with no concerns. Some wheels (Performance Machine) are welded together. It used to be common to cut Honda Hawk wheels apart and weld them back together with more width. I've seen older steel fork sliders fabricated with welding. There's nothing wrong with a proper welding job.

Doesn't seem fair to insult Jean over his solution, just because you wouldn't do it that way.

Ken
 
[quote="lcrken
I don't think it's right to call it "poor engineering".

Ken[/quote]

I will call it what I like and to me it is a piss poor solution, no more will be said
 
Jeandr said:
I will update with new pictures as I make progress.

Jean

Jean,
So far I love the project and will be following it closely. I am thoroughly impressed by the talent on this forum! i am also enjoying the debate on the engineering of your stem. I won't comment on that but, In looking through your opening photos for the second time I suddenly had to laugh.

Are you the cyclist?
Gary
 
T95 said:
Jeandr said:
I will update with new pictures as I make progress.

Jean

Jean,
So far I love the project and will be following it closely. I am thoroughly impressed by the talent on this forum! i am also enjoying the debate on the engineering of your stem. I won't comment on that but, In looking through your opening photos for the second time I suddenly had to laugh.

Are you the cyclist?
Gary

My daughter has a blog and she was very pleased when she had her first "haters" I am sure Hobot loves it too. Keep watching and look at my other crazy ideas when I put up new pictures. You know the best way to end an argument is to agree with everything.

Jean
 
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