Chainwheel Ramps and Pins

[Mick F]

I have a 61t outer on my Moulton with a 34t inner and a 42t middle.
The 61t outer has no pins or ramps - just plain.

The gears change ok, but sometimes going up from middle to outer, it grinds away for a while before climbing up. Other times, it climbs silently and immediately.

I was wondering the other day, of DIY fitting pins to the 61t. Ramps would be impossible perhaps.

How could I fit pins?
What would I use?
Where would I fit them?
How many should I fit?

Is it a stupid idea?

[meic]

I have been considering doing this for years.

You just use a ramped and pinned chainring as your template and try and recreate its number and positioning of the pins.
Drill a small hole and insert a rivet. My plan was to use pop-rivets because I have them, they are very easy to install and could be replaced later with something better if it works.

As your existing chainring is changing fairly well without them they will not be required to do much at all to help things work properly.

Another option is to abandon the indexed changer and you will automatically over-shift and return the lever if using a friction type lever. I used (cheaper) pinless rings in this way for years, it was only moving to an STI that made the rings become troublesome, though I have learned how to overshift with them too.

[Norman H]

I can't see any harm in trying. The best bet would be to salvage some pins from an old chainring and copy the spacing as closely as you can.

I'm not sure a pop rivet would have a well enough defined square edge to pick up the chain

[Brucey]

you can make your own pins by reshaping the heads of M3 12.9 capheads, fitting them to drilled and tapped holes in the chainring using strong threadlock. You will lose the socket in the caphead if you make the head shallow enough, so if necessary, cut slots in the heads so that they can be worked with a screwdriver.

Be wary of the heads of your 'pins' clashing with the chain when running cross-chained onto small sprockets though; I suggest you check the clearance here first, it may put the kybosh onto the whole scheme.

cheers

[meic]

Be wary of the heads of your 'pins' clashing with the chain when running cross-chained onto small sprockets though; I suggest you check the clearance here first, it may put the kybosh onto the whole scheme.

My daughter's standard double chainset on her Isla bike does this a tiny bit on small-small.
I havent really looked into it any further as a triple will replace it as soon as I get around to doing the job.

[Mick F]

Thanks guys, it's not a stupid idea after all!
I was thinking of drilled and tapped holes rather than pop rivets. Good idea about copying another chainring, so I'll have a shufti at one.

The front changer is friction. If I let the stop out any more to allow a bigger overshift, I could inadvertently get the chain right off.

[mig]

as a matter of interest - is the 61 a standard issue? or have you had it made and fitted it later?

[Mick F]

The Moulton WAS as TSR30 - 10sp triple.
Now a TSR90 by addition of a SA 3sp.

Came with 11-25 cassette and 34/42/58 Stronglight Z triple chainset. Shimano Tiagra STI.
First thing I did was to fit 11-28 cassette, and second to fit a 61t outer chainwheel.
All this, to extend the woefully narrow gear range, though the 61t only increased the top end a bit - but at least it got the top gear to over 100 inches.

Bought from Spa.
http://www.spacycles.co.uk/m2b0s113p969 ... ter-60-61t
Sold the 58t to help pay for it.

If I had my time again, I'd have stuck with the original 58t outer and gone straight to the Sturmey Archer idea.
Can't remember if the 58t outer had ramps and pins, but the middle ring does have them.

[Mick F]

Some photographs. Click for bigger views.

It would seem that the pins are "recessed" in the thicker part of the alu, so it would't be very easy to machine them like that.
Note that the pins are slightly off-centre of the tooth peaks.
Also note that the Campag 53t has two separate groups of four pins.

Not sure I can do this effectively.

Advice?

[mercalia]

those pins are very close to the teeth?

[meic]

Note that the pins are slightly off-centre of the tooth peaks.

I dont know if they are positioned there for shifting purposes or because that will be a part of the "tooth run" which is put under compression by the resistance from the chain but a few millimetres back and it will be in a part which the chain is trying to open up.

I must mention that when you originally bought up "DIY-pinning" I was thinking in the context of a £10 chainring, possibly even part worn. Not a pristine ring which cost over £70! Things going wrong at that expense changes the gambling odds a little.

It may be worth having a trial run on something cheaper. On the bright side there should be less driving force on the teeth with it being such a large ring, compared to you grinding just as hard with a 39t ring.

[Brucey]

pins in that position only work in conjunction with cutaways in the 'shoulder' of the chainring, as per that one in the picture.

It is, (I think) not the only way it is done; worth looking at a few others before making your mind up how to try.

cheers

[meic]

Here is a pinned but not ramped ring, similar to the sort which I was thinking of using as my template, they do however seem to have a greater expanse of metal to drill into.

http://www.spacycles.co.uk/m2b0s149p399 ... cral-Outer

[Mick F]

That photo is from the outside of an outer.
If there are any ramps, they'd be on the inside.
Also, the pins are smaller on the outside, with the heads - being bigger - on the inside.

[meic]

You are right, that website is not a good source for a picture of what I wanted to show.

I have such rings and the view from the other side is not much different. The heads are indeed larger but there are no ramps, just the same slight shoulder as on the rings sold as inner rings.