Model RM-20 Frame Details

The bare bones

Even before I bought my Sekine, I knew that any used bike would probably require a complete re-build. An overhaul would both ensure reliable long-term function of the bicycle, and bring it to a riding standard I'd be content with. Happily, a re-build is work that I enjoy doing, and I was eager to get into the details.

Tange 1" threaded fork, chrome-plated

Warning: bike nerd/mechanic stuff ahead!
As soon I had the chance I stripped the frame almost completely, leaving in only the press-fit headset cups and crown race. A bare frame is much easier to clean, although there were some thick streaks of hockey tape residue that required a lot of elbow grease to remove. A thorough cleaning gave me opportunity to look closely over the entire frame, and I examined where an old kickstand mount had slightly crushed the rear chainstays, and discovered a dent at the base of the downtube. Some quick sprays of Frame Saver into the 30 year old frame & fork tubes to slow any unseen rust seemed prudent.

Shimano LF dropouts, 130mm rear spacing

Frame laid bare (and leaking Rust Check) I took the opportunity to weigh it and get some photos. I present, for your Sekine-nerding enjoyment, specs for the RM-20 frame & fork:
Seat Tube: 53cm/ 21"
Top Tube: 56cm/ 22"
Chain Stays: 435mm
BB Drop: 60mm
Wheelbase: 1040mm/ 41"
Seatpost: 26.4mm
Brazed-on cable-guides and stops, DT water bottle bosses
Frame Weight (incl. steel headset cups): 5lb 10oz/ 2.56kg
Fork Weight (incl. steel headset race): 1lb 14oz/ 0.84kg (fork is chrome-plated)
I do not currently know the head/seat tube angles, nor the fork rake (anyone..?)

Inside the BB shell. Shimano cable guides brazed on top.