CrimsonEclipse

You giving away your bikes again?

tds101 

I just found a new home for the Dahon today, so it's no longer available. A tree fell on my house, so I'm giving it to one of the contractors. People act like I'm trying to scam someone... Oh well.

CrimsonEclipse

Wasn't trying to be a jerk.
Apologies if it came out wrong.

Duragrouch

I hear ya.

Absolutely, zero surprise on response from Dahon. I wish Thor was still in business, he might have sold a pin kit, or if not, knows the dimensions. If I ever take that tour, I'll first pull the pin, see if there is a hardened and ground dowel pin at my local industrial screw supply that matches, they have an astonishing amount of hardware, just to have on hand with me in case the pin breaks, sure wouldn't occupy much space or weight. Come to think of it, I'll try to pull the pin from my old cracked Dahon frame that I saved to use as a truing jig, rather than risk my daily rider. Back when I worked in industry, every place I worked at had a full machine shop, and I was cockpit-qualified from working my way through school as a toolmaker, I could make anything I need. Last year of college, had bought my first new bike ever, a road racer, wanted to true the wheels, old spoke wrench I had didn't fit new bike, Sunday, bike shop closed, I just fired up the lathe and mill, half hour later...

tds101 

Oh, no, I wasn't directing that at you. I'm sorry if I wasn't a clear. Others thought it was a scam, not you. I apologize for the confusion. I did find a new home for it though. My house was damaged by a tree during the storm on Tuesday night/Wednesday morning. I gave it to one of the workers. And I made sure his bosses knew I actually gave it to him. It was one hell of a horrible night.

Duragrouch

(above) Very sorry to hear that. Someone I know had that happen a few years back, was lucky, big tree knocked against side of garage, damaged the roof overhang but the wall held. Still over $20k to repair, insurance covered. They were able to get a crane out there the next day, lift and cut the tree up, tarp and tape the roof until it could be repaired. Be careful: Some time later, the water main to the house broke under the driveway where one of the crane pads was, connection couldn't be conclusively proven, so the owner had to eat that repair cost. Man it was gusty as heck about the same time on the west coast as well, I was worried about the same person.

Good on ya for giving the bike. If any difficulties with them replacing the derailleur, have them reference one of my posts above (if it's a Dahon compact derailleur, I don't know if they even sell those any more, but a conventional style is an upgrade).

tds101 

Thank you. I appreciate the kind words. As for the bike, I'll let him know about the advice. The original Neos derailers was horrid.

Duragrouch

(above) Yeah the Dahon "compact" derailleurs, were not that compact, they mounted just a skosh higher than a conventional one, they just had a short cage (typical road race length). The flaw, in my opinion, is that they mounted far enough forward that the jockey pulley was far enough away from the sprocket that any lateral compliance in the chain caused poor shifting, either delayed shifting, and/or overshoot onto the next cog or into the spokes. A pulley directly under the sprocket and close to it, works better. The following is from the Sheldon Brown website, talking about a wide range derailleur on a closer-geared cluster (not ideal), so greater vertical distance gap instead of horizontal like the Dahon compact, but I think the same logic applies:

"A wide-range rear dérailleur will work with medium-range or even close-range gearing, but it will not shift nearly as well as the appropriate type. The main reason for this is that the jockey pulley (the upper one) is too far away from the freewheel sprockets. This means that the chain angle created by shifting your dérailleur is less pronounced. It is this angle that makes the chain move from one sprocket to another.

If the jockey pulley is too far from the freewheel sprocket, you have to shift your dérailleur farther to create an angle sharp enough to make the chain climb out of its comfortable bed. When it finally does, the chain probably will overshoot and shift two gears when you only meant to shift one. This is because the dérailleur cage has moved farther than the normal 5.5- to 6-millimeter distance from one sprocket plane to the next. Once the chain is derailed, it is just as easy for it to jump two gears as one."

Jonesandrew

Pin removal is not an easy task in this case because the pin is inserted into a blind hole. Purely by chance, I’ve just been removing the main hinge pin from a little used 2006 Dahon Speed Pro so even though bentstrider may already have chosen a different solution and my method might not work on a bike with a severely worn centre hole like his, I thought I’d share my experiences with a view to helping others who may also want to save a frame from the scrap bin. Even though my bike has been very little used, it still had too much movement in the hinge for my liking. I could see and feel the flex in the main frame when putting pressure on the pedals.



I had already removed the old pin and replaced it with a temporary one before taking this shot.

I was keen to try and pull the pin out from the bottom because the paintwork is still in excellent condition and I wanted to preserve the finish as much as possible. I attempted to drill and tap an M6 hole into the bottom of the pin but was unable to drill deep enough despite using a brand new tungsten carbide tipped drill. I guess I may have hit a super hard section of the pin or the cutting edges of the drill had blunted too quickly.

So plan B was to drill down from the top to expose the top of the pin and then make a press tool to drive it out from top to bottom.

I started by using a mini drill (e.g. Dremel) fitted with a tungsten carbide rotary burr with a flat end to create a flat area on the top of the hinge plate above the centre of the pin. After that I had to eyeball the centre position of the pin on the flatted area (tricky!) and centre punch the location for the drill point. Knowing my punch mark was likely off centre of the pin below I started with a 5mm carbide tipped drill in an attempt to avoid cutting into the parent material around the 8mm diameter pin.

I drilled down about 8mm, which with hindsight was unnecessarily deep, 4 or 5mm would have been enough. (Difficult to be sure, but I think the top of the hinge pin was about 10mm above the upper joint in the hinge). At this point I could clearly see this hole was not concentric with the pin and switched back to using a 6mm diameter rotary burr in the mini drill to simultaneously enlarge and re-centre the hole. I was still eyeballing the centre position at this point, and hoping I wouldn’t cut into parent material. The final hole was inevitably larger than 6mm diameter and later I found I had cut into the parent material on one side – see pic of removed pin at the end of this post.

This is the ‘quick and dirty’ press tool I made. I used mild steel square bar and a short piece of angle section and a M8 high tensile bolt with the end ground down to 6mm diameter.


One leg is notched to accommodate the protruding hood at the top of the front hinge plate.



The “feet” locate in the centre holes of the hinge plates.






When using the tool the pressure from the screw on the pin caused the legs to bend, but shortly after that the pin yielded to the pressure and I was able to progressively jack the pin out by dropping ball bearings down the hole each time I ran out of travel on the screw thread of the press bolt.

The obvious improvement to my press would be to make the notched leg thicker behind the notched area to resist bending especially if the pin shows signs of being corroded. I was too in too much of a hurry (or too lazy) to make that amendment on this occasion.

I’ve identified an oversize (8.1mm diameter) Volkswagen door hinge pin to replace the original pin with. The image shows a spiral lubrication groove cut into the surface of the pin. Seems like a good idea. I’m waiting for delivery of an 8.1mm dia reamer to finish the job.


As you can see from the old pin below, I failed to prevent the 6mm burr from cutting into the parent metal on one side. I’m optimistic that the splines on the head of the new pin will still bite into the now oversize hole in the top of the hinge.




Below is the aborted tapped hole in the bottom of the old pin. Note that despite my best efforts the tapping drill wandered off centre too.



The cost for the rotary burrs, the reamer and the new pin will be 65 GBP but it’s definitely worth the spend in this case as the bike is in such good condition.
I plan try the DIY Deltech idea suggested above to give the new pin some support and prolong its useful life. I've was very disappointed how quickly play developed in the hinge so I'm hoping to get a lot more miles out of it this time.
Hope someone finds this helpful.

tds101 

See if replacing the pin and acquiring a deltec cable are options. Dahon makes it quite difficult nowadays to obtain replacement or upgrade parts. Here's the official link to the deltec cable on their website, but I didn't find a way to order it.
https://eu.dahon.com/gears/deltech/

wesgreen

Good luck!
I have the same frame in aluminum (Vitesse), and it's almost like new, has no play, after 11 years of almost daily riding through NYC pot holes. (Not folded daily; knock on wood!)

Duragrouch

I emailed Dahon USA on Jan 5, after seeing the Deltech article (internationally) but it not listed on their USA site. Their reply:

"Hello, and thanks for contacting Dahon Bicycles. USA availability on the Deltech is currently Summer 2024. Best Regards, Dahon"

I personally think the add-on Deltech may be superior to the OEM one, as the OEM welded tabs the cable attaches to, are small and I think may fatigue (crack) over time. The add-on envelops the bottom bracket tube and head tube, which to me, looks structually superior, assuming no collapse of either tube due to clamp loads, no fretting wear, etc.

Duragrouch

Jonesandrew,

Damned impressive tenacity and improvisation on your repair!

If I had to design this all from scratch, I would design it with a hard and replaceable pin, and it riding on replaceable hard bronze or stainless steel bushings. But this sort of thing is rarely designed for "maintainability", a big mantra in design for the military. I don't like the idea of an expensive folder for only occasional use and with a limited lifespan. The newish Dahon Launch appears to take pressure off the hinge pin and onto the locking jaws, the pin (I think) existing only to hold the two parts together when folded. I'll be curious to see the durability of the locking jaws, which are aluminum, same as the frame. Curiously, the Launch seems to be selling poorly compared to the Mariner, in fact recently, the Launch was discounted just below Mariner pricing; I don't know why, the Launch has discs, and perhaps a better folding joint. The Mariner comes with a rack and fenders that the Launch does not, and it's a more well-known name, points made to me by a local Dahon dealer. I can add a rack and fenders, I can't add disc brakes.

The whole steel vs aluminum debate is still open with me. All Dahon models in the upper range are now aluminum (and I hope the hinge has bushings, because even high-strength aluminum, does not approach the hardness of steel; my guess is no bushings, does anyone know?). I don't think there is much difference at all in ride, not on this style frame. Quality (chrome-moly) steel used to be king for ride quality (frame can have more flex, whereas on aluminum, too much flex drastically reduces fatigue life), but also expeditions overseas, as the frame could be welded competently nearly anywhere, however I don't know how much aluminum welding has expanded in the third world (my guess is, probably a lot), and any differences in weld repair durability between the two materials (heat affected zone in the welded parts, as well as strength of the weld filler material).