'94, erm '92..., well '93 Rocky Mountain Cirrus rebuild

foxb13 · Oct 23, 2018

While I was busy adjusting the gear indexing, I noticed something wrong with the front derailleur. It was quite impossible to shift to the granny, despite the front derailleur cage fork nearly hitting the frame. By contrast, it was rather easy to go beyond the outer chainring, despite the limiter screw being correctly set.

Height as well as parallelism of the front derailleur cage fork seemed fine too.

Yet the routing of the derailleur cable didn't look good. @RockiMtn pointed to me that the cable was not sitting within the small grove of the derailleur tab. But even with this fixed and despite other advices from @RockiMtn (thanks again!), the cable was still sliding against the derailleur body when on the granny position.

All this eventually made me wonder whether I was running the correct chainline. Bikepro's Bottom Bracket Compatibility Table [1] lists 122.5mm spindle as compatible with "1993 or earlier" FC-M730 crankset, while also listing 127.5mm spindle for "pre 1994- some chainline applications". Shimano date code PC is etched in my crankset, meaning it was manufactured in March 1991. So both "1993 or earlier" and "pre 1994" apply in my case. Great! So? Should I go with 122.5mm or 127.5mm spindle? And how should "some chainline applications" be understood? Looking at the current setup, the chainline was measured at a mere 45mm with 68 x 122.5mm BB-UN52 bottom bracket. The latter was obviously not an original component, as confirmed by Shimano date code UE (May 1996). Moreover, BB-UN5x references are for Deore LX bottom brackets vs. BB-UN7x for XT.

foxb13 · Oct 23, 2018

It took me quite some time to source a suitable 68 x 127.5mm BB-UN71 bottom bracket.

Once fitted, the chainline was measured at a more conventional 47.5mm. In this configuration, I was able to shift to the granny, yet the frame clearance was reduced to a minimum. And with the limiter screw correctly set, the chain was no more running beyond the outer chainring.

In the end, is 127.5mm spindle the correct length for a FC-M730 crankset? I still don't have a definitive answer and Retrobike information is rather scarce on the subject [1]. All I know is, despite now having a standard 47.5mm chainline, the derailleur cable is still slightly sliding against the derailleur body.

So, if Cirrus/Expérience owners are reading this, I'm interested to have your thoughts on this issue. Sure, replacing the FC-M730 crankset with a Syncros Revolution may be a solution

Perhaps one day...

foxb13 · Oct 23, 2018

What am I still missing? Pedals of course. onZa High Output are my pedals of choice for nearly a quarter of a century. And indeed, all my bikes sport them, even my youngtimer '02 Cannondale F700 and "actual" '09 Cannondale Rize Carbon 2. Plus I only own one MTB pair of shoes

I was thus very happy to find yet another NIB pair, with the original price still stated in French francs!

foxb13 · Oct 23, 2018

Panaracer Smoke II and Dart II 26 x 2.1 tires in great condition completed the rebuild. I have no clues when exactly these tires were introduced to market (they are referenced in '96 Trek Technical Manual [1]), but finding runnable blackwall Ritchey Megabite Z-Max tires as fitted on most '93 Rocky Mountain bikes is unobtainium. As is, my Cirrus weighs 12.8kg, including the pedals. Not particularly light, but not too unreasonable either for a bike with 21.5" frame and suspended fork. All in all, I had a cool pastime rebuilding it and I hope you had a cool moment reading this.

For now, let's go for more additional pictures