Singlespeed chain & freewheel- what am I missing

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CliveyT
Posts: 290
Joined: 13 Jun 2012, 2:55pm
Location: Cambridge

Singlespeed chain & freewheel- what am I missing

Postby CliveyT » 12 Dec 2019, 11:55am

OK my singlespeed commuter needs a new chain (and almost certainly a new freewheel as well- I've been a bit lax about it). Got a new KMC 1/8" chain and a generic 16tooth freewheel from LBS (which is actually 3/32"). The new chain fits around the chainwheel perfectly. Measured out same number of links as the old chain, checked on the bike and this looked right so cut and joined chain, but it simply won't engage properly with the freewheel teeth. It either rides at the very top of the teeth or, if I put a link where it's meant to be, the adjoining link is forced right off the cog. It's not chain tension, I've moved the wheel fore and aft to no avail, and even taken the freewheel off and still can't get the chain to engage properly. It also doesn't engage with the old freewheel - exactly the same problem.
It's almost as if the pitch of the chain is wrong- but why does it fit around the chainwheel so well?
It's a cheap freewheel, but surely standards aren't that bad? And why do I get the same problem with the old freewheel? (it's worn, but not that worn)

I've almost certainly done something stupid, but for the life of me I can't see what

hamster
Posts: 3314
Joined: 2 Feb 2007, 12:42pm

Re: Singlespeed chain & freewheel- what am I missing

Postby hamster » 12 Dec 2019, 1:24pm

I don't think you have done anything wrong.

Are you sure its not the other way round, with a 3/32" chain and 1/8" freewheel? It sounds like the chain is too thin and the inner link pair cannot engage on the freewheel. Otherwise, it sounds like the chain is defective and the inners too small. It needs to be a 7 or 8 speed chain maximum.

Brucey
Posts: 37280
Joined: 4 Jan 2012, 6:25pm

Re: Singlespeed chain & freewheel- what am I missing

Postby Brucey » 12 Dec 2019, 4:42pm

16T freewheels are often built on the largest possible sized body which means that not every chain will fit; some of them will have side plates which are too tall and prevent the rollers from hitting the valley in each tooth.

You can buy 1/8" chains which are bushingless and these are shallower than fully-bushed 1/8" chains but both can be deeper than 3/32" chains which are meant for derailleurs and have side plates that are barely any taller than the rollers.

If you bought a 17T (or larger) 3/32" freewheel you would be able to use almost any chain with it, but 16T ones are the exception. Often there is a shallow groove either side of the teeth, without which no chain would work.

hth

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Brucey
Posts: 37280
Joined: 4 Jan 2012, 6:25pm

Re: Singlespeed chain & freewheel- what am I missing

Postby Brucey » 13 Dec 2019, 12:10am

you can see the grooves in this picture; not every 16T freewheel has them but plenty do

Image

even with the grooves not every chain will work

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

hamster
Posts: 3314
Joined: 2 Feb 2007, 12:42pm

Re: Singlespeed chain & freewheel- what am I missing

Postby hamster » 13 Dec 2019, 8:22am

Wow, never knew that!

Brucey
Posts: 37280
Joined: 4 Jan 2012, 6:25pm

Re: Singlespeed chain & freewheel- what am I missing

Postby Brucey » 13 Dec 2019, 9:39am

On a similar note, for the last few years BMXs have often had tiny sprockets mounted to a (special) tiny freehub. Half link chains have been popular in BMX circles too. Well, guess what, if you have the smallest sprocket not every chain will fit and half-link chains are amongst the most likely to behave in this way. I've seen experienced bike mechanics baffled by this; the transmission often runs OK on the workstand, but incredibly roughly when under load. Only if you have seen the exact fault a few times before would you suspect that new parts could create such a circumstance.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

mig
Posts: 2153
Joined: 19 Oct 2011, 9:39pm

Re: Singlespeed chain & freewheel- what am I missing

Postby mig » 13 Dec 2019, 9:49am

CliveyT wrote:OK my singlespeed commuter needs a new chain (and almost certainly a new freewheel as well- I've been a bit lax about it). Got a new KMC 1/8" chain and a generic 16tooth freewheel from LBS (which is actually 3/32"). The new chain fits around the chainwheel perfectly. Measured out same number of links as the old chain, checked on the bike and this looked right so cut and joined chain, but it simply won't engage properly with the freewheel teeth. It either rides at the very top of the teeth or, if I put a link where it's meant to be, the adjoining link is forced right off the cog. It's not chain tension, I've moved the wheel fore and aft to no avail, and even taken the freewheel off and still can't get the chain to engage properly. It also doesn't engage with the old freewheel - exactly the same problem.
It's almost as if the pitch of the chain is wrong- but why does it fit around the chainwheel so well?
It's a cheap freewheel, but surely standards aren't that bad? And why do I get the same problem with the old freewheel? (it's worn, but not that worn)

I've almost certainly done something stupid, but for the life of me I can't see what


not riding it fixed :!: :wink:

CliveyT
Posts: 290
Joined: 13 Jun 2012, 2:55pm
Location: Cambridge

Re: Singlespeed chain & freewheel- what am I missing

Postby CliveyT » 13 Dec 2019, 10:02am

mig wrote:
not riding it fixed :!: :wink:


25+ years of Rugby and too much cycling in town I'm afraid. Emergency stops on these knees are to be avoided :cry:

Thanks all,
Too dark in the garage to see what was happening this am. Will pop to and may just buy chain and freewheel together. I'll use up the parts I have at home some other time.
C

Brucey
Posts: 37280
Joined: 4 Jan 2012, 6:25pm

Re: Singlespeed chain & freewheel- what am I missing

Postby Brucey » 13 Dec 2019, 10:14am

If you want to test for this kind of problem, it is simply a matter of offering the chain up to the freewheel and seeing that there is clearance between the sideplates of the chain and the body of the freewheel. If you can't see a gap then I would suggest that you test if a piece of paper can get trapped in the would-be 'gap' or not.

I have seen a few setups where it ran OK but there had been some contact rather than none between the chain and the freewheel body, enough to wear the chrome off it.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Brucey
Posts: 37280
Joined: 4 Jan 2012, 6:25pm

Re: Singlespeed chain & freewheel- what am I missing

Postby Brucey » 14 Dec 2019, 4:39pm

FWIW I did some measurements and if a 16T freewheel is to accept the strongest-built 1/8" chain (which includes KMC B1 and some others) then the body needs to be ~54.5mm dia or less if the sideplates are to clear it . The diameter measurement needs to be taken in the grooves (if there are any).

If the body is between ~54.5mm and ~55.9mm diameter then you need to use a less deep chain. This category includes both derailleur chains (nearly all of them) and some (but by no means all) bushingless 1/8" chains. Some 1/8" bushingless chains are built using sideplates that are identical to those used in 3/32" chains. Unsurprisingly these chains are exactly the same depth as one another.

Modern derailleur chains are typically about 8.3 to 8.5mm deep whereas the strongest built 1/8" chains are at least 9.5mm deep.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~