New Chain Rings - help please.

What is the part number of the crank (should be stamped on the back of the arms)? With that you should be able to look up the chainrings on Shimano's tech docs website.

thanks frogstomp. stripped off and cleaned and they are stamped AF12 and 170517510. I am now not convinced they are Shimano. There is nothing stamped on the rings unfortunately.

OK, from this it looks like the chainset is a Samox AF12 but I can't find much info about them (even on the Samox website!).

You could try measuring the PCD/BCD yourself or your LBS should be able to and advise suitable replacement chainrings (if available). At the end of the day though, a new crankset (complete with rings) may work out cheaper.

Help I am getting desperate now. LBS cant source a 40 - 28 chain rings and Samox have said they are out of stock and postage from TW would be too much anyway.

The Vagabond uses a standard Shimano mtb BB so I think it will have to be a new chainset. I don't believe Shimano do anything as close to 40 - 28 as they are all smaller for mtb's. Typically I have already fitted a new cassette (11 - 36) and chain to fit the same chain rings so i would like to get as close to the original 40 - 28 as possible.

Failing that what 10 speed sprocket will I need to buy to fit the new size chainrings to get the ratios as close as possible to the existing gearing.

thanks ever so much in advance

I think your cranks will be 64 pcd for the inner and 104 pcd for the outer. The new 28t you have should fit and then you'll just need a 40t 104pcd ring

Eg the ones in this link

https://www.actionsports.de/en/shimano-xt-fc-m785-10-speed-chainring-26/28/38/40-3982

Or this one

Shimano Y1P098030 - Double Front Chainring 40T (AJ for 40-28T), 2 x 10s, 104mm https://amzn.eu/d/bZ7k9UH

I don’t believe Shimano do anything as close to 40 – 28

Define close to?

SJS Cycles have all sorts sorted by BCD so you should be able to find something similar;

https://www.sjscycles.co.uk/chainrings/

equally may be sensible to get a new crankset for the price - eg: Deore 38/28 would be slightly lower top gear (how often do you use 40-11 really?)

https://www.wiggle.com/p/shimano-deore-m6000-10-speed-double-chainset?color=black&chainringTeeth=38%2F28T

If you're able to share some close up photos of your cranks, it would help to be sure.

40t 104bcd cheap at wiggle/chain reaction at the moment.

https://www.wiggle.com/p/shimano-xt-fcm785-10-speed-double-chainring?chainringTeeth=40T+%7C+104mm+BCD+%7C+AJ+Type

Thanks everyone sounding more promising. Here are the existing cranks and chainrings.

https://imgur.com/gallery/PbjzMBx

at a guess I'd say 104/64 BCD - on the basis I have an old 42T chainring on my bench currently and a bit of measuring the diam of that vs the apparent diam of your 40T on my screen and a bit of maths.......but get a ruler and you'll soon work that out, then on to SJS and get ones to suit.

Looking at pics, I reckon that the inner might still work, but they're pretty cheap anyway. But maybe try with the CRC link above for now and see if it is OK?

And as inner has no shifting pins and ramps, I've found any brand outer will go with it, all the shifting work is done by the inside of the larger chainring so nothing to match to.

Thanks. The inner ring is 64 pcd, the teeth line up but the bolt holes don’t!

Eh?

You said you had a new 64 BCD. The teeth don't have to be exactly the same alignment as your old one, you'll still be meshing the chain with about half the ring at any time. Just, will it go onto the cranks. Can you take a picture of old and new inner rings showing what you mean?

The larger ring does need to be on in the right orientation as the shifting ramps and pins are (so I was told, may be BS) put to match the powerstroke as you pedal. There'll be some way of knowing, some have a pin that goes behind the crank arm, others have an obvious V on the chainring - your old one has a V at 9'o clock in the top picture above, this aligns to the crank arm.

Am I going mad? New overlaid on the old one

https://imgur.com/gallery/JuC9FdN

The chain ring crib sheet from Sheldon Brown may help.
https://www.sheldonbrown.com/cribsheet-bcd.html
It looks as though there is 64 BCD with both even and uneven spacing used on different Shimano cranks. Your old ring looks even and new uneven (you can measure to check).
I had the really annoying one a few years back where a Deore chainring had an extra lug on it that prevented it fitting an LX chainset because of not standard standards.
Stronglight or TA chainrings are available in most sizes and generally wear well.

Looks like the new one is the newfangled asymmetric BCD whereas what you want is a good old 6-bolt MTB granny ring.

n.b. I suspect 28-40 was chosen as the max capacity of the front mech, so you can go slightly higher if ones available, but not <28 unless you also go <40 by the same amount.

To conclude

New Fangled FFS!

Thanks for all your help girls and boys.  In the end SPA cycles were able to offer some advice on what to buy, I needed to buy a new inner and outer.  The inner was a standard 9 speed which works on 10 speed and the outer was actually a mid ring.

All fitted and good to go! Might treat myself to some new inner and outer cables and complete the job properly as well as adding the dysfunctional rings to the never to be used parts bin!