How to....Spread a frame rear!

[brett4christ]

I was given an old Ross Europa I frame the other day....no real pland for it, until I had an idea of building a klunker/kruiser morph for a future
Virginia Creeper Trail ride this summer....mostly downhill, all paved or bridges.

The rub is the frame clears the 26x2.125 cruiser tires everywhere but right behind the bottom bracket.

What's the best way to spread the bottom legs about 1/2 to 3/4 inch?

 

[expjawa]

If you want to widen the chain stays right behind the bottom bracket, I think you're out of luck. At least with regards to a simple solution. Spreading them at the wheel end is easy. But at the attachment point, the only option you have to detach and reattach them as far as I can see. You could try spreading them with a scissors jack or something like that, but you'd have to bend them back in again as well. And it might well be disasterous, or damage the attachment welds.

Basically, depending on the actual shape of the stays, you'd likely have to cut/weld a splice in that spreads them out. On Columbia middleweights, for example, the left and right chain stays are formed out of one tube that is bent into a "U" and attached with a stamped yoke, for lack of a better term. In that case, you could remove the "U", cut it in half, and weld in a piece to widen it. But that wouldn't work if the stays are attached directly to the bottom bracket.

I suppose it might be possible to use a tubing bender to form a sharp double bend that offsets the tube, but it would require doing the same thing simutaneously to the seat stays, and would shorten the wheelbase.

 

[brett4christ]

Thanks for the info, Rick!

I don't have pics yet, but....

The "seatstay" portion of the rear is plenty wide enough for the setup I want. The "chainstay" tubes are completely straight and each are welded directly to the bottom bracket. Each tube is "dimpled" about 2 inches for clearance for the original tire, which is in the same location as the tire I'm trying to fit. Between the bottom bracket and the dimples, there is crossbrace welded to each tube that the rear fender mounts to. I'm not going to run a fender, though, so I can remove/relocate this piece.

I was thinking about heating the tubes with a torch, just in the dimpled area, and then spreading the tubes with a piece of pipe or wood, reforming the straight tubes into and offset shape. I do have to pay attention to the chainwheel clearance at this spot. If I spread it too much, I may have to go with a smaller diameter chainwheel.

My other option is cutting the chainstay tubes around the crossbrace, welding a longer crossbrace onto the tubes connected to the bottom bracket, then spread and reweld the tubes connected to the rear dropouts.

Which approach do think would give the best results? Any other ideas out there?

 

[gcrank1]

Use 24" wheel back there?

 

[brett4christ]

Yes, 24" will fit, but I have some really cool 26x2.125 Electra tires (on alloy rims/black stainless spokes/3-speed Nexus hub) I want to use, and the 24's look kinda out-of-place on the "diamond" shaped frame. The 26's may not work, but I'm going to try!

 

[gcrank1]

Its gonna take some work! You are in the danger zone there...........But, you are gonna try anyway, so........
Make a jig with the original frame set up (if its is straight). If nothing else, I think a plank with some blocks to hold the dropouts and bottom bracket would do it (I love construction screws!!!), then do your plan. If the tubes give out cut them off from the BB and back where they have enough width and make a new U shaped piece to go in there, using the pin and weld method to join the tubing ends. The jig will make life easier in the long run.

 

[expjawa]

I said you'd have to bend the seat stays as well because they are attached to the chain stays at the dropouts. If you can rebend it, the process would require that you bend the chain stay outward, then bend it back inwards again, creating an offset. But when you do that, since the seat stays are attached, they would have to formed out and back in again as if the whole triangle was a flap.

I think that astetically, a rebent chain stay would look better than a widened brace that the stays get rewelded to. It would look cleaner. But heating up the tubing to bend it will change it, on a structural level. Most likely, the tubing is mild steel and isn't heat treated. But applying heat can anneal something that has been heat treated, or temper something that wasn't. Either way, it possibly alters the material properties. Of course, welding would probably do that too...

 

[brett4christ]

Thanks, G/Rick!

Good info and food for thought. I'll assess the situation and post my approach. Who knows, I might actually get it to work!

 

[Uncle Stretch]

They stuck a hub without a rim in the dropouts and then put a car coil spring compressor backwards on the chainstays and spread it that way. Looked like it worked really good.

so i bolted a hub to the rear and put a coil spring compressor in reverse and spread the frame :mrgreen:

now PLENTY of room :mrgreen:

 

[expjawa]

That's kinda what I was thinking before, but I hadn't made the leap of installing a hub to restrain the rear of the stays. That would be one approach; cold-forming is definately preferrable. As long as you don't deform the stays where you're applying pressure, it should come out fairly even. I'd still watch for stressing the welds at the bottom bracket.

 

[ndaway]

^^^ that's from my coke bike build..I don't know where you are at but around here there are auto parts stores called Autozone and you leave a deposit they loan you the coil spring compressor for free you get you deposit back when you return it...the only thing is the one I had has one hook that slides free and bottoms out on one end of the compressor..well in reverse there is nothing for it to bottom out on so I had to buy two nuts and double nut behind it...it will make sense once you see it..Im not sure how far we moved it but it was quite a bit :mrgreen:

 

[gcrank1]

Did you find that moving a little at a time, then letting it 'rest' a bit before proceeding, was the way to go, or just crank it and keep it moving?

 

[ndaway]

My son helped so he cranked nice and slow and I watched the welds and held some calipers to watch how far we were moving really went nice and smooth