Sunday, July 20, 2008

Shimano DX RD-M650 SGS overhaul

This derailleur came with Michelle, my 1991 Bridgestone MB-3. Apart from the replacement / upgrading of its jockey wheels to Control Tech sealed cartridge bearing pulleys, the unit has never been serviced.

A picture of the derailleur in its stock form here.

After an external scrub down.

Somehow, the B-tension screw bent over the years. I replaced it with a generic stainless steel 4 mm x 12 mm allen-head screw.

The steps for disassembling the derailleur are similar to those posted for the Shimano XTR RD-M950 GS overhaul. Exceptions are noted in this post.

The cage arm is secured by a single Philips head screw. Removing it allows the sub-assembly to slide out.

Contrary to the RD-M950, the longer prong of the RD-M650 cage arm spring fits into the cage arm. The factory position (tension setting) is the hole closest to the end of the arm.

The o-rings compressed over the last 17 years, allowing ingression of dirt and water.

Derailleur body.

Fully disassembled and cleaned.
41 parts.

All the o-rings were replaced.

For a little more reliability, I replaced the stock Philips head limit screws with stainless steel variants (4 mm x 16 mm set screw w/ 2 mm allen head). HBC's titanium versions will work too, but are overkill for this application.

Shimano RD-M650 rear derailleur overhauled, re-lubed, and reassembled. Don't forget that the B-tension, lower limit, and upper limit screws are now all out of adjustment.

Total capacity:  38T
Minimum gear:  12T
Maximum gear:  32T (although I gotten away with 34T with some fiddling)
Weight:  320 grams

At some point in future, the derailleur cable clamp nut (which is beginning to corrode) might be replaced with a corrosion-resistant HBC titanium version.


Hon Shin said...

that's some serious shit man. any ancient organisms living inside? LOL

Anonymous said...

Very nice. Thanks for showing this. Makes me think, "hey maybe I can do this."