Sun Race freewheels, eg 6s vs shimano MF-HG22

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Brucey
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by Brucey »

once the spacers are ground thinner (including the built in spacer on sprocket #6) there is enough of the smaller spline on the shimano UG body protruding beyond sprocket #5 for sprocket #6 to engage with, and the SunRace lockring even uses the same threading as the UG top sprocket (*), which means it turned out that it was almost trivially easy to convert the standard 6s UG freewheel to a compact-spaced HG type freewheel.

(*) actually the SunRace lockring fits the threads on the shimano UG body; however the shimano threaded UG sprocket is often an unacceptably tight fit on the SunRace body threads.

Shimano body, SunRace sprockets, HG-esque shifting, compact 6s spacing, 14-28T ratios
Shimano body, SunRace sprockets, HG-esque shifting, compact 6s spacing, 14-28T ratios


Sun  Race standard 6s (left), compact spaced 6s (right)
Sun Race standard 6s (left), compact spaced 6s (right)


The resulting compact spaced 6s freewheel is about 3mm narrower than the standard 6s spaced one, which means it will allow a less dished wheel and/or fitment to older, narrower-spaced hubs/frames. 3mm doesn't sound like much but it makes a fair difference to the tension balance in the wheel (typically moving the RH hub flange 3mm rightwards improves the tension balance in the rear wheel by 12-14%; a compact 6s build at 124mm OLN can give a tension balance of about 76% in the rear wheel, which is quite reasonable).

The compact 6s freewheel will work with 7/8s 3/32" chains and can be spaced to work with 7s or 8s based indexing. In point of fact the SunRace sprockets are thin enough to work with 9s chain, but I have not tried this, (or 9s spacing) yet; they also have manipulated tooth shapes which may mean the narrower (11/128" vs 3/32") chain will not be so well tolerated, or will run noisily perhaps.

Anyway this gives you more choices when running vintage frames/hubs; no manufacturer currently offers a compact-spaced 6s freewheel, and vintage ones simply don't exist with slick-shifting HG type sprockets. It also means that if you want to use decent modern indexed shifters (you can buy 6s ones, but they are not exactly primo quality), you can do so.

A further benefit may be in 'capacity stretching' for vintage RDs. Old campag RDs (Nuovo Record etc) would normally accept a 26T or maybe 27T sprocket. The mech cage is swinging upwards more and more, the further to the left it moves; this means it doesn't swing as high to reach the #1 sprocket on a compact 6s freewheel as it does a standard spaced 6s freewheel. In addition the HG type sprockets use shorter teeth than UG or other non-indexed freewheels. Between these effects I think it is quite likely that the RD capacity can be stretched by 1T or so, which may make using a 14-28T freewheel practical with some older mechs where it mightn't be otherwise.

A final comment is that I used a cheap Shimano UG freewheel body here. I have little doubt that some of the same tricks will work on posher shimano UG freewheels including 600EX and Dura-Ace 7400 models (although some of these may use different threading etc for the top sprockets). Anyway as long as SunRace and others continue to make freewheels which use this pattern of sprockets, there will be a good supply of spare sprockets to rebuild/improve such freewheels with.
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Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by Brucey »

I also built the compact 6s sprockets on the

SunRace 6s body

compact 6s sprockets on sunrace 6s body
compact 6s sprockets on sunrace 6s body


and Sunrace 5s body

compact 6s sprockets on sunrace 5s body
compact 6s sprockets on sunrace 5s body


both worked but on the 6s body the lockring had to be inverted (it would bottom out otherwise) and this makes the whole freewheel wider than it needs to be. On the 5s body the stepped spacer needs a specific modification without which the first three sprockets are not held securely and furthermore the #6 sprocket may not have any splines to engage with. So neither is perfect but either can be made to work.

cheers
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Brucey
Posts: 44999
Joined: 4 Jan 2012, 6:25pm

Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by Brucey »

Shimano MF-TZ37 is one of those (usually unloved) 'Megarange' models. However unlike other (mostly later) megarange freewheels it appears to use shimano HG-type freewheel splines for the sprockets. Today I dismantled a MF-TZ37 14-34T 7s model (with sprockets 14-16-18-20-22-24-34T) , mostly in the expectation that I could use the 34T sprocket in another freewheel.

Sure enough the threaded top sprocket uses a 40mm x 24tpi (shimano calls '40 BC') thread and the splined sprocket appear to use the HG spline which is like the UG spline but with a single timing spline;

HG spline is like the UG spline but with a single squared 'timing' spline (centre of image). UG sprockets fit HG splines, but HG sprockets won't fit UG splines without modification.
HG spline is like the UG spline but with a single squared 'timing' spline (centre of image). UG sprockets fit HG splines, but HG sprockets won't fit UG splines without modification.


However the larger spline in MF-TZ37 is modified differently to the usual HG sprockets;

The larger HG-type spline in MF-TZ37 is modified beyond the usual HG type; there is effectively  a second timing spline, offset from the usual position (centre of image)
The larger HG-type spline in MF-TZ37 is modified beyond the usual HG type; there is effectively a second timing spline, offset from the usual position (centre of image)


there is one offset spline which means that (without modification) this freewheel body will not accept UG or other HG sprockets and the three largest sprockets from MF-TZ37 will not fit any other freewheel body. Fortunately it is easy enough to modify the sprockets so that they will fit other UG/HG-esque freewheel bodies. The smaller splines on MF-TZ37 are the same as is found on other shimano HG type freewheels such as MF-HG22, MF-HG20 etc., i.e. there is a HG timing spline but the other splines are identical to shimano UG.

cheers
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Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by Brucey »

In the main, my future plans mostly include fitting SunRace sprockets to shimano freewheel bodies. Turns out it is just as well it is not the other way round; I had previously noted that SunRace sprockets are an easy fit on shimano bodies, but it turns out the converse is not the case. The shimano spline is fractionally smaller than the Sun Race spline.

The SunRace large body spline measures ~50.05mm/47.7mm. The shimano body is about 50-100um smaller than that, and the shimano sprockets are between these two sizes, so fit the shimano splined body but not the SunRace body; they start but bind after a few mm, presumably because the body is very slightly tapered. It is a similar story with the smaller spline size.

So if you want to fit shimano sprockets to a sunrace body not only do you have to worry about timing splines, but also the exact dimensions of the spline itself. AFAICT the clash is worse on the minor diameter of each spline, which means in the event of a clash, it is probably easiest to modify the sprockets not the freewheel body.

Oddly enough I do want to fit a shimano sprocket to a sunrace body, in order to make a compact spaced, dish-efficient 7s freewheel; I think I can make one using a sunrace 6s freewheel body and a dished #1 sprocket. However this will probably need a shimano sprocket on the sunrace body.

cheers
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Brucey
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by Brucey »

almost there;

Sun Race 6s freewheel modified to compact spacing and 7 sprockets
Sun Race 6s freewheel modified to compact spacing and 7 sprockets


The freewheel above uses a SunRace 6s body, SunRace 6s sprockets (14-28T), SunRace lockring, spacers from 7s MF-TZ37, and the large sprocket is also from MF-TZ37.

The large sprocket required a fair amount of grinding before it would fit the SunRace body. However it wasn't that difficult to do.

The only remaining operation (apart from painting the large sprocket) is to dish the large sprocket (sprockets 1 and 2 are basically touching one another in the photo above); fingers crossed it doesn't end up all wonky.

If this goes well it this 7s freewheel will occupy the same space as a standard 6s freewheel would. Further to this, it may be possible to respace this arrangement to 8s or 9s spacing, which will result in a further width reduction of about 1mm and 3mm respectively.

Gear ratios with a 30,42,52T chainset are given below;

http://ritzelrechner.de/?GR=DERS&KB=52,30,42&RZ=14,16,18,34,21,24,28&UF=2150&TF=90&SL=2.6&UN=MPH&DV=gearInches

and (with 28-622 tyres) gives a range from just less than 24" to 100"

cheers
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Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by Brucey »

the latest experiment is to try fitting IRD sprockets to other freewheel bodies; they always looked like the splined fitments were based on the Shimano UG/HG designs. But the proof of the pudding is in the eating;

32T (large spline) and 16T (small spline) IRD sprockets, fitted to a SunRace freewheel body
32T (large spline) and 16T (small spline) IRD sprockets, fitted to a SunRace freewheel body


Yep, they fit the SunRace spline! As well as timing spline variations the SunRace spline is fractionally oversized vs the shimano spline. However IRD sprockets fit easily onto the SunRace body, in any one of twelve orientations (the timing spline arrangement allows this). They will also fit other bodies, eg shimano, falcon, DNP etc. This suggests that (with a small modification to the timing spline perhaps) SunRace sprockets can perhaps be made to fit IRD bodies too. However I don't have an IRD body to try this with.

To my surprise the IRD sprockets are only 1.6mm thickness; in my hands they don't feel as insubstantial as 10s/11s cassette sprockets which are also about this thickness. Most other current freewheel sprockets are slightly thicker than this, (e.g. ~1.8mm) so thin shims might be required to get the spacing exactly correct when building a freewheel using a mixture of sprockets.

cheers
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cycle tramp
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by cycle tramp »

Stumbled across this thread whlle looking to find which tool required to undo the little lock ring at the frame end of sunraces freewheel sprocket cluster... the nice thing is that you can buy ird freewheel sprockets separately, which would allow me to convert both my sun race freewheels to 14 - 32 teeth.

I'm also guessing that if sprockets are only 1.8 ish wide - there could be a demanding lazer cut sprockets for 34 and 36 teeth (depending on how may folks still custom build their freewheels)

By the way- If anyone does know the name of that tool, please let me know :-)
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rjb
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Location: Somerset (originally 60/70's Plymouth)

Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by rjb »

This guy stripped his freewheel.

viewtopic.php?t=156109#p1770869
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin X3, Raleigh 20 stowaway X2, 1965 Moulton deluxe, Falcon K2 MTB dropped bar tourer, Rudge Bi frame folder, Longstaff trike conversion on a Giant XTC 840 :D
cycle tramp
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by cycle tramp »

Thinking about it - rather than sprockets - all you really need is a 5 arm carrier with a bcd of 74... and then you could use little chainrings as sprockets...
Or some sort of dual carrier for both 74 and 94 chainwheel sprockets converter... thing... dooberry..
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drossall
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by drossall »

Chain rings are usually alloy and sprockets are usually steel or harder materials. Reckon the rings would wear out pretty quickly.

On the same line though, the time keeper in my first club had reputedly brazed a 13 sprocket to the inside of his chain set to get a really low gear :D I never saw it in person, so would have to report that story as apocryphal.
rjb
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by rjb »

drossall wrote: 11 Jun 2024, 9:05am Chain rings are usually alloy and sprockets are usually steel or harder materials. Reckon the rings would wear out pretty quickly.

On the same line though, the time keeper in my first club had reputedly brazed a 13 sprocket to the inside of his chain set to get a really low gear :D I never saw it in person, so would have to report that story as apocryphal.
My club mate bolted a pair of identical small sprockets to the inside of a chain set to give him low gears on his tandem. The identical pair stopped the chain slipping between sprocket and bottom bracket and the big drop gave the chain a choice of sprockets. :wink:
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin X3, Raleigh 20 stowaway X2, 1965 Moulton deluxe, Falcon K2 MTB dropped bar tourer, Rudge Bi frame folder, Longstaff trike conversion on a Giant XTC 840 :D
cycle tramp
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Joined: 5 Aug 2009, 7:22pm

Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by cycle tramp »

drossall wrote: 11 Jun 2024, 9:05am Chain rings are usually alloy and sprockets are usually steel or harder materials. Reckon the rings would wear out pretty quickly.
Blimey mate- where were you during the late 80's? -you couldn't move for stainless steel 24 tooth, 74bcd chainrings.....
Not sure if that's the case now - but even if you were using alloy for the dinner plates, unlike a chain ring where most of the teeth wear at 90 to the cranks - the load/force is gonna be shared equally over a large number of teeth, plus unlike a chain ring - unless your climbing the alps, you're not going to be using the dinner plate for that long.. and if you made a spider to carry the chain rings which had been covered into sprockets - you could always flip 'em over to get wear outta the other side of the tooth...

..for me, its a question of fasteners- is there enough space ptovided by the sprocket spacer to use your average chainring bolt to hold the chainring/sprocket it's carrier. If the answer is no.. it ain't gonna work.

Anyways for the moment, I'm look for stainless laser cutter type engineering people in the Southwest, see if they can backwards engineer a 32 tooth ird dinner plate, and come up with a 34, or even a 36 tooth one...
Last edited by cycle tramp on 11 Jun 2024, 12:33pm, edited 1 time in total.
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Brucey
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by Brucey »

cycle tramp wrote: 11 Jun 2024, 8:13am.....By the way- If anyone does know the name of that tool, please let me know :-)
I have removed this lockring using a hammer and punch, but I had always intended to make a better tool, which should not be difficult. First you SG a piece of 1/4" steel plate to about 50mm diameter and mark it out for drilling such that you have one drilled and tapped M5 hole centred on every cutout in the lockring that you want to drive with a peg. The pegs are made by grinding the ends of 12mm or 16mm 12.9 grade caphead screws. These are held in place using locknuts. A connector nut can be welded onto the plate; this will allow the tool to be held. If you enlarge the centre hole prior to welding, the tool can be prevented from slipping in use using a length of studding or similar.
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drossall
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by drossall »

cycle tramp wrote: 11 Jun 2024, 11:54amBlimey mate- where were you during the late 80's? -you couldn't move for stainless steel 24 tooth, 74bcd chainrings.....
True, but it's no longer the late 80s, or so they tell me. Not sure how easy it would be to get one to suit now.
Brucey
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Re: Sun Race freewheels, eg 6s vs shimano MF-HG22

Post by Brucey »

BITD several manufacturers (including campag) used repurposed freewheel sprockets as inner chainrings on triples. The great thing about steel (even quite hard steel) is that it can be welded fairly easily. By contrast drilling holes in hard steel sprockets is always difficult. This means the easiest way I know of repurposing a sprocket as a chainring is to weld (thick/modified) M8 washers in place, having carefully ground suitable cutouts to receive them. The marking out is made easier if you choose a sprocket with a tooth count that is a multiple of the number of chainset arms, eg. 25t and 30t are good sizes for a 74mm x5 mounting.
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