How to undo cogs on a shimano freewheel ?

[bduc61]

I have hot an old Shimano HG20 freewheel

I want to undo the cogs but

it seems to me that contrary to the maillard or sachs freeewheels, it is not the first cog that is actually holding first the freewheel but an independant threaded lockring with tiny indentations - see pic

Am I right ?
to me it is not attached to the first cog - I have tried to undo the first cog but nothing happens ( true I haven't been very energetic yet)
maybe not ? as Sheldon and other internet pages don't show any specific tool for that small ring ?

second question is , what is the internal profile of the cogs ? are they similar to Maillard , or proprietary ? and not at all similar to later HG cassette cogs ?

Thanks for your info

 

[bagpuss]

Depending on the age of your block you may find that the first cog has a thread on it . To undo this you will need two chain wip tools . One to hold the block and one two undo the first cog . Once removed the rest will follow . This is a lot easier with this block on a wheel . I have never tried to split one by its self .

More info here on SB's web site.
http://sheldonbrown.com/k7.html#uniglide-old

 

[torqueless]

it seems to me that contrary to the maillard or sachs freeewheels, it is not the first cog that is actually holding first the freewheel but an independant threaded lockring with tiny indentations - see pic

Am I right ?

Yes, you are right, If yours is similar to the one I've got- a Singapore-made HG. It looks to be so. You can get the lockring off (anti-clockwise) with a hammer/carefully aimed screwdriver. Under that, two banks of splines, one for the three bigger cogs, and one for the three smaller. Here's a photo... not a great one. hope it helps..

 

[bduc61]

it seems to me that contrary to the maillard or sachs freeewheels, it is not the first cog that is actually holding first the freewheel but an independant threaded lockring with tiny indentations - see pic

Am I right ?

Yes, you are right, If yours is similar to the one I've got- a Singapore-made HG. It looks to be so. You can get the lockring off (anti-clockwise) with a hammer/carefully aimed screwdriver. Under that, two banks of splines, one for the three bigger cogs, and one for the three smaller. Here's a photo... not a great one. hope it helps..

it does
it confirms my analysis
don't think its particularly well designed !
now I know that later cogs certainly won't be compatible and that I would probably be wiser to go for a 8 speeds sachs freewheel as I need one rather than a shimano one :idea:

 

[bagpuss]

Remember to check rear drop out width if changing to 8 speed ie 130mm required . Consider Suntour if staying 6/7 speed .

 

[47p2]

A lockring spanner should remove that

Something like this

 

[bduc61]

Remember to check rear drop out width if changing to 8 speed ie 130mm required . Consider Suntour if staying 6/7 speed .

I am not changing
I have got two sets of wheels with freewheels in 130mm width


probably the last sales before 8 speeds cassettes completely took over, or cyclist upgrading from 7 to 8 just changing the axis and redishing

and its amusing because one set is on nice mavic 501 hubs which give the opportunity to easily lengthen the width because the part that inserts into the fork is actually screwed on the axis !