A Deore chainset with chain guard?

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

• Deore XT RD-735
• Chainring bolts – super size me, please!
• Chains, chainsets, and links

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

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