On Friday, September 21, 2018 at 5:34:11 PM UTC-4, Joerg wrote:
Snipped
He is a machinist and tool & die maker by trade, has a fully equipped
garage with lathe, mill and so on. He is building stuff for his various
vehicles all the time and made a couple of parts for my MTB so I could
build a sturdy rack.

120mm is a pain though, 10mm is a lot of widening. Looks like this one
can be shortened by grinding off the outer cog:

https://www.ebay.com/itm/Shimano-TZ3...4/322007138705
Snipped

Is he going to grind down the body too?

He should read Sheldon Brown: https://www.sheldonbrown.com/speeds.html and https://www.sheldonbrown.com/freewheels.html

"The freewheel threading on these older hubs is generally interchangeable except for some very old French units. If you go from a 5-speed freewheel to a 6- or 7-speed freewheel, you will usually need to add some spacers to the right end of the axle between the cone and the locknut. Once you have done this, you'll also need to re-dish the wheel to bring the rim back to the centerline. You may need to re-space the frame if you have added spacers to the axle. See my Frame Spacing Article for details on this."

"How Many Speeds?

The first multiple-speed freewheels had 3 sprockets, using the traditional 1/8" chain.

In the 1950s, narrower 3/32" sprockets and chains were introduced, permitting the move to 4-sprocket freewheels within the then-standard 114 mm (4 1/2") frame spacing
5 Speeds
In the late 1950s, spacing was widened to 120 mm to permit the use of 5-speed freewheels. This required adding spacers to the right-hand end of the axle to keep the chain from rubbing on the frame. The added spacers required additional dish to the spokes, causing wheels to become somewhat weaker.
6 Speeds
In the 1970s, there was a move toward 6-speed freewheels. These were of two types:

"Standard" spaced 6 speeds had sprocket-to-sprocket spacing the same as the existing 5 speeds, around 5.5 mm

Standard spaced 6-speeds required increasing the frame spacing to 126 mm, aggravating the problems introduced with the move to 5-speed, but still providing satisfactory service in most cases.

'"Ultra Six ®"' spaced 6 speeds used a closer spacing, around 5 mm. This permitted an Ultra Six ® freewheel to directly replace a standard 5-speed unit on a 120 mm hub. The key to making this work was the use of a narrower chain. The interior width of the chain was the same as always, but the new narrower chains used shorter rivets, so the ends of the rivets didn't protrude past the outer chain plates, as the rivets in traditional chains did.

7 Speeds
In the 1980s, these two approaches were combined to create 7-speed freewheels, with 5 mm ("Ultra") spacing that would fit the same 126 mm hubs as "standard" 6-speeds."

So, to cold set a steel frame you only need to move each dropout 3mm. That's not hard to do and Sheldon tells you how to do it easily.

https://www.sheldonbrown.com/frame-spacing.html

"Do You Need To Permanently Spread Your Frame?

Ideally, the frame spacing should exactly match the hub spacing. This makes for easiest wheel replacement. In practice, however, there's a fair amount of latitude in fit. In fact, when the first 130 mm 8-speed hubs were introduced, they had locknuts with beveled sides, so that you could "spring" apart the rear triangle of a frame made for the then-standard 126 mm spacing.

A conventional cup-and-cone hub tolerates some bearing misalignment, and in general, you can safely go up one size in spacing this way, just springing the frame apart. I can't give you an absolute guarantee that this won't cause damage, but the odds are very much in your favor.

Having to spring the frame every time you replace the wheel is inconvenient, especially if it has a quick-release axle .An internal-gear hub or sealed-bearing hub is very likely to be damaged if the dropouts are not parallel. In this case, cold setting is the better way to go.

If you're going up more than one size, say from 120 to 130, or from 126 to 135, you should definitely cold set the frame.

Spreading the Frame

There are a number of ways to do spread a frame. Probably the easiest way is to use a lever. A piece of 2 x 3 or 2 x 4 lumber, roughly 5-6 feet long works well for this:

1.Remove the wheels, fenders and any seat-tube mounted bottle cage.
2.Lay the bicycle on its side with the handlebars turned to face upward
3.If you are unsure about the strength of attachment or tubing at the chainstay or seatstay bridge, you might clamp them together with supports made by drilling a block of soft pine wood and then sawing it in half along the middle of the drill hole. This precaution is usually unnecessary, but it might be a good idea if you are making a major change in spacing.
4.Insert the lumber through the rear triangle, so that it goes underneath the upper rear forkend, and above the seat tube. The lumber should extend out past the rear end of the frame.
5.Place the far end of the lumber onto a chair, crate or other raised structure, so that only the head-tube/fork area of the bike is in contact with the floor.
6.Press down gently on the lumber where it crosses on top of the seat tube.
7.Measure the spacing to see if it has changed.
8.If the spacing hasn't changed, try again, pressing a little bit harder. Repeat until you get a result, applying a bit more force each time, until the spacing has increased by about half the total amount you are seeking.
9.Turn the bike over, and repeat for the other side.

In the illustrations below, the stays will be bent to the left (up in the photos) by pressing down on the end of the 2 x 4.

The other end of the 2 x 4 is on top of a stool. The longer the 2 x 4, the less force is needed.

The bike does not actually need to be stripped down this far, most parts can remain in place."

If you're not ham fisted cold setting a steel frame is NOT hard.

Cheers