Preamble
Following on from Deore XT RD-735, I’d like to replace my FC-TY33 chainset with some Deore XT FC-M730 cranks and generally the chainrings on the M730’s come without a chain guard. However, I would like to have a chain guard, to save oiling up my jeans. So, what’s the solution?
See also
Related Links
- Replacement compatability for Shimano Mountain LX Chainring and or Crankset
- Differences between Biopace and Rotor cranks
- To Calculate BCD, see Bolt Circle Diameter
- Biopace Video: [demo] How to install the old 1990’s biopace chainring so that it actually works!
Solution
It would seem that a hybrid is called for.
I found a ideal set up in Italy, Guarnitura crankset SHIMANO DEORE FC-M730 vintage retro MTB 1980 1990 XT, £??? (auction was ended early)
This is a pair of FC-M730 crank arms, with Biopace-SG chainrings. Biopace are elliptical chainrings, or rather, in Shimano’s ownwords, follow a “point-symmetric egg curve”.
There are two chainrings that support a chainguard, Biopace-SG A-46, and B-48, which also fit the FC-M730 cranks (BCD110). They have a set of five holes around the perimeter of the outer ring, for mounting a chain guard.
From Shimano Biopace Replacement
I swapped all my Biopace rings for round ones years ago.
IIRC the BCD is 110 & 74. My rings are 46-36-24T.
From Shimano SG Biopace B-48/38/28 MTB Kettenblätter Silber BCD 110mm BJ 1990 RAR ALU, €67.90+€14.90
From Shimano Biopace-SG MTB Chainring and Chainguard 48 teeth with 110 BCD from the 1990s
Important note about BCD
As stated here, only a FC-M730 will support this hybrid idea (M737 and M739 have different BCD), Differences between various XT groups?
No the 5 bolt chain rings from the M730 will not work on the M739 as they have different BCD’s (bolt circle diameters). The M730 are 110/74mm with the mid and outer rings being 110mm and the inner ring being 74mm. In 1993/4 when Shimano switched to the Hyperdrive-C cranks and chainrings the BCD’s became smaller 94/58mm that the FC-M739 uses. You need to find middle and outer rings that are 94mm BCD and an inner with 58mm BCD.
Chainrings
Biopace-SG A-46
Shimano Biopace-SG 46T Chainring 110mm BCD Silver, £8.47+£10.78 (see also Shimano Biopace-SG 46T Chainring 110mm BCD Silver, $9.99+$13.99)
Biopace-SG B-48
chainring Shimano biopace SG alloy 48 t bcd- 110, £14.40+£4.30
And stupid prices too, CORONA SHIMANO BIOPACE-SG A-46 VINTAGE, €49+€20
Chainguards
There are at least a couple of chainguards:
- MT60-46T
- MT60-48T
- MT60-48TS
- M450-48T
- M650-48T
Shimano Biopace-SG Bicycle Chain Guard Protector MT60-46 (794), $22+$8 £
Shimano Deore MT60-48 Biopace – SG Kurbelschutz Hosenschutz BJ 1990 TOP Zustand, €29.90+€14.90
Shimano Biopace Bicycle Chain Guard Protector MT60-46/MT60-48T/M450-48T/M650-48T, $29+$8
Chainguard Dimensions
From Shimano Biopace Bicycle Chain Guard Protector MT60-46/MT60-48T/M450-48T/M650-48T
MT60-48T
MT60-46T
MT60-48TS
Biopace M450-48T
Biopace SG M650-48T
A cheap alternative
However, instead of buying the chain rings and the chain guard separately, it is probably cheaper to buy them on a different set of cranks and swap them.
FC-M500
For example, Shimano Exage 500 Kurbelgarnitur Biopace-SG -3fach- FC-M500 – 28/38/48 – 170 mm, €35+€15. However, there appear to be a crack in one (bottom right) of the chainring guard mounts.
FC-M550
There is another crankset with a chainguard, the chainring is not a A-46 nor B-48, but 50T, Shimano Deore LX FC-M550 crankset 50/40/30 175 mm bcd 110/74mm steel chainrings, $35+$20. This has a chainring guard with mounts that do not appear to be as study as those on the M500 above.
1990 vintage MTB crankset Shimano Deore LX FC-M550 VIA Japan 48/38/28 T 170 mm, $50+$10, from Poland, which has the same sturdier looking chainring mounts as the M500 above.
Something to note is that the left arm does not:
- Have Deore LX printed on it
- Have FC-M550 stamped on the inside
Both of which make the left hand arm look fake, but it is not. To illustrate:
and
This set was sold, and now is for sale in Germany with an outrageous P+P price, Shimano Deore Lx FC-M550 Kurbel 28/38/48 175mm, EUR 55.00 Approximately £48.97 + EUR 75.00 (approx. £66.77)
Most annoyingly, I missed out on an identical but cheap set from Glasgow, Shimano Deore LX triple Cranks 170mm FC-M550, £18 +£3.50
1990 crankset Shimano Deore LX FC-M550 made in Japan for MTB 48/38/28 T 175 mm, US $49.00 Approximately £38.94 + US $10.00 (approx. £7.95). From Poland.
After some offers and counter-offers, I got the price down to US $49.00 (approx. £38.94), but after reviewing the price of the Glasgow set I thought that I would wait to see if a better deal arose elsewhere. Who knows?
FC-M560
Another chain guard, on a SG-X, from Shimano Deore LX crankset FC-M560 170mm 28/38/48 – perfect condition, £38.59+£9. BCD 110
FC-M730
Some lovely cranks, Shimano Deore XT FC- M730 Kurbel(Retro kult Vintage xtr dx Classic, EUR 24.09 Approximately £21.45 + EUR 20.00 (approx. £17.81)
However, I ended up purchasing these, Shimano XT FC-M730 Kurbel Set (crank set) Retro Mtb Vintage, €17+€15.50 – 48-38-24 Biopace, 175 mm
FC-M737 Crank
From Shimano Deore XT FC-M737 94BCD 175mm Crankset GOOD, this two ring, as the bash board takes the place of the outer ring. crankset looks good. Pricey though, at $117.75+$15.73+$32.29!
The Marin bashboard below should also fit it.
FC-M739 Crank
These would seem ideal from 1990s SHIMANO DEORE XT FC-M739 ALLOY 170MM VINTAGE MOUNTAIN BIKE MTB CRANKSET.
but it is likely that the BCD is incompatible. The BCD of this five bolt mount is 94/58, if it is the same as the cranks in this link, FC M739 5 arm 177,5 mm cranks + 44 chainring SOLD
BCD 94/58
There is a chainguard available for the FC-M739, see the Small Parts list for after market for the FC-M739 [PDF:EV-FC-M739 5-Arm-1648]:
However, this lovely Marin bashboard, currently on a FC-M36, would fit a 94 BCD, from Deore XT RD-735
FC-M560 – removable spider
As an aside, it is interesting to note that whilst the FC-M560 generally has the spider integrated into the arm, there is a version of the FC-M560 which has a similar crank arm to the FC-M739 above, with the removable spider, Shimano Deore LX FC-M560 crankset 175mm, 42/32/22 (relisted)
FC-M570
Likewise the FC-M570 also has a removable right hand crank arm, see Retro 5 Arm SHIMANO FC-M570 Chainset. although it does not have the notched arm base (which the photos of the FC-M560 chainsets above clearly show):
Random
A nice Dual SIS chain guard,from BICYCLE CHAIN WHEEL GUARD COVER BICYCLE 5 BOLTS, VARIOUS SIZE, £5.50+£2. However, the dimensions appear to be different from that of the SG A-46 and B-48 chainring
Conclusion
I ended up getting this, SHIMANO / Deore XT / FC-M730 / 175mm length / right crank arm, $33 in total, with the high price due mainly to the outrageous $20 import charges imposed by the eBay tax machinery.
The arm is rather dirty but it should be possible to clean them carefully (see polishing crank arms). I polished them up when they arrived:
I also purchased a single chain ring, with chain guard (although it is the more skinny type – useful as a spare), Retro Shimano Deore LX – FC-M560 – Crank Arms – 170mm, £12
[images??]
and a lovely FC-M730 pair, quite reasonably priced, Shimano XT FC-M730 Kurbel Set (crank set) Retro Mtb Vintage, EUR 17.00 (£14.90) + EUR 15.50
blah
I’m hoping you can help me regarding a Shimano mountain bike I bought used, it did not come with a chain guard and I’m having a tough time matching up the sizes to what I see available. It is 48T and a 5 hole mount. The distance is roughly 98-100mm between 3 of holes and roughly 87-90 mm between 2 of the holes. I’m using a ruler centered between the holes so that’s why there’s a range, I could be off by a little bit. In looking at the models you show online (MT60-48 or M450-48), there does not appear to be 3 longer sides and 2 shorter sides, at most 2 sides are identical width apart. The only other info on the bike is that on the crankset and arm it says SR Suntour XR11 and 170. Not sure if that helps but would really appreciate any guidance. Really cannot ride the bike as is. Thank you very much.
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