"Persuading" a 120mm OLN Pompino frame to be a 130/5mm

[CAMRAMan]

I've read threads about changing the size of rear triangles using a block of wood & a hammer, but I was hoping to get some specific advice.

I've been looking for a frame to suit my next project. In the course of my search, I found a bike that would perfectly suit a mate. It's a Pompino frame with a Nexus 3-speed hub gear fitted. It has a 120mm OLN dimension, but I believe my mate would be better off with a SRAM Spectro hub that I can get for about £100. That has a 135mm OLN dimension.

So, my questions are:

a) Exactly how do you widen the frame percussively?
b) What likelihood of success is there? I don't want to advise a mate to do summat that's going to knacker his bike

TIA

[Karla]

You don't need to do it percussively.  Get a bit of threaded rod, put a couple of big nuts and washers in the middle, insert into dropouts and crank the nuts outwards.  I've slimmed a 4130 mtb rear end down to take a Sturmey AW in this way, so there's a fair amount of give in these things.

[CAMRAMan]

Thanks. I assume that you need to crank the nuts on a trial and error basis (slightly) in excess of 135mm so that it springily returns to approx. 135? Or do you simply open it up enough so that the hub fits in and then untighten the nuts? I assume the former, as it'd be a bugger to get the wheel out to fix a puncture.

[Karla]

Yes, you need to push it further than it's meant to go, so that it returns to the correct width.  I did it in several stages, going so far slacking off and seeing where it had got to.  It's a slightly nerve-wracking process. 

Once you've done, you'll probably need to straighten the dropouts with a Stillson wrench or similar, a they'll be splayed outwards like the rest of the rear triangle.  On a Pomp with track ends, this will be a crucial step and could be the trickiest part to get right.

[CAMRAMan]

On a Pomp with track ends, this will be a crucial step and could be the trickiest part to get right.

Thanks again. That's the bit that worries me!

[border-rider]

Heh

I wish I'd read this a few months ago; I had a 135 Pompino frame that I took down to 120

We could have just swapped....

[CAMRAMan]

Same colour as yours too!

[Tewdric]

I have used this technique successfully a couple of times:

Bicycle Frame/Hub Spacing

[oncemore]

I know it is done, but 120 to 135 (and indeed beyond in the first instance) has always sounded a lot to me - especially the force on the chain stay bridge area.

I assume that the frame end of the chain stays and upper end of the seat stays are somehow reinforced during the procedure so that the bending is beyond the bridges?

[rafletcher]

I know it is done, but 120 to 135 (and indeed beyond in the first instance) has always sounded a lot to me - especially the force on the chain stay bridge area.

I assume that the frame end of the chain stays and upper end of the seat stays are somehow reinforced during the procedure so that the bending is beyond the bridges?

Nope, you just push the rear end apart. provided there's no corrosion it'll bend ok.

[David Martin]

Don't under estimate how much you will have to spread the frame. When I did my Ribble 653 frame (120 to 130) I was pushing it out beyond 200mm with the nuts/threaded rod before it set back to 130..

For the city bike I just laid it on the floor, put one size 9 on the inside of the lower rear fork, took the other in my hand and lifted firmly but gently. That did the trick quickly but is less controllable than the alternative methods

[Somnolent]

On a Pomp with track ends, this will be a crucial step and could be the trickiest part to get right.

Thanks again. That's the bit that worries me!

If you are doing the width change with threaded rod rather than the timber method.... after "spreading" use a piece of threaded rod on each drop-out.... so they almost but not quite meet in the middle. Penny washers each side and nuts up really tight.  Then you can use the rod that's "outside" to lever away until you get the "inside bits" pointing directly towards each other.    Then the drop outs will be parallel.    Not easy to describe, but quite simple in practice.

[oncemore]

Having thought about it.... I rather agree with this view:

"Troy Courtney writes:

> In my posting I clearly stated that stays should always be done one
> at a time with the bottom bracket locked down and support placed at
> the bridge junctures to prevent the bridges from being separated
> from the stays.

> If I used the methods other than what I stated and what you espouse,
> then I should just sell all my tools and quit repairing frames and
> quit building customs frames...because I surely would not be
> qualified to be doing either." (My italics)

Makes sense to my amateur engineering brain!

[Wobbly John]

I have used this technique successfully a couple of times:

Bicycle Frame/Hub Spacing

Here's a photo of me using the method on a set of forks for one of our weird bikes:



BTW, I once got a nasty hand injury when the threaded rod slipped out of one drop-out using the screwing method.

[marcusjb]

There's something about that photo that makes me want to duck for cover!

[robgul]

+1 for the threaded rod (although I have tried to "Sheldon piece of lumber" method too")

Have a look at   Beewee - Home of Rob's Miscellanea   and the Briefings section - there's a bit there about threaded rods etc

BTW - nobody has mentioned yet that these techniques should only be used on STEEL FRAMES ....

Rob

[The Mechanic]

You also have to make sure that you set the two chain stays the same amount otherwise your frame will be out of alignment.  Sheldon's method allows for this as you do each side independantly.  However, the threaded bolt method could move one only or bother unequally.

[Tewdric]

I took some piccies last time I did it:

New frame!

[CAMRAMan]

Well, it pays to look, doesn't it?! Sturmey Archer's 8-speed hub comes in a 120mm OLN. Now, it's not my cup of tea, what with direct drive being gear 1 and all that, but the bloke who's paying for the bike is happy with that.

I have another frame at the back of the garage that needs similar teatment, so I shall dig it out when needed and work out the pros and cons of the threaded rod & plank methods before going to town on it, figuratively before literally, so to speak.

Thanks for all the tips.

[Somnolent]

You also have to make sure that you set the two chain stays the same amount otherwise your frame will be out of alignment.  Sheldon's method allows for this as you do each side independantly.  However, the threaded bolt method could move one only or bother unequally.

You are right, in theory, but I've never found it an issue in practice.   However I do always use a piece of string running from one drop-out, round the head tube, back to the other drop-out and stretched tight.  You can soon spot any asymmetry, by the distance from string to seat tube being different on each side.