Seven speed cassette single speed conversion

How do I best convert my seven speed Shimano freewheel to a single speed
setup? All the conversion kits I have seen are for 8/9 speed freewheels.
Is there that much difference in the length of freewheels? I know I could
use lots of 3mm spacers but how many would I need? All (sensible)
suggestions gratefully received.

Ta

Whole load of questions here I'm afriaid but they will help get to the right
answer:

Do you want single speed no-freewheel or single speed freewheel?

What chainset do you have on at the moment?

Do you have a particular crank + chainring + bottom bracket combination in
mind?

Have you got horizontal (or semi-horizontal) dropouts at the rear?

What is your over-locknut dimension (distance between inner faces of rear
dropouts)?

What is the distance between the middle sprocket and the inner face of the
right-hand dropout?

Ian

"Me" wrote:

How do I best convert my seven speed Shimano freewheel to
a single speed setup? All the conversion kits I have seen are
for 8/9 speed freewheels.

Is there that much difference in the length of freewheels?

A few millimetres - enough to make a difference.

I know I could use lots of 3mm spacers but how many would
I need? All (sensible) suggestions gratefully received.

Before commercial conversion kits became available, the usual way to space
out a single sprocket on a freehub body was to dismantle a few worn out
cassettes and use the spacers so obtained. You need around 30mm of spacers
in total, depending on the freehub body, so 2 to 3 cassettes worth,
depending on the cassettes you use (many cassettes have several sprockets
with integral spacers).

This method allows far more chainline adjustment than the commercial kits
that provide just two large spacers and a sprocket.

If you don't have any worn out cassettes, a local bike shop might agree to
reserve any they replace for you. I've heard of people using PVC plumbing
pipe to make spacers, but haven't tried this myself.

HTH

James Thomson