Nubra 

Hello all,
I am doing maintenance a wonderful older tall NIshiki for a client, and he would love to have compact ring,in the low 30s, on this bike to make the hills a little more tolerable. Still running the 5 speed freewheel.with Suntour VGT lux derailleur (love it!)
Crank is a 50/40 and 171 length. Would just switch out the 40 ring, not try and add a ring.

Or do I just have to sacrifice the all original bike and and replace the crank with 5 bolt?






.

bark_eater 

I think a 106 BCD Max's out at 33 or 32 teeth. I'd look for a freewheel or cassette cog that has a 6 arm symmetry and enough "meat", and drill 3 holes.

Nubra 

Intriguing! Not sure what you mean by six arm symmetry? Can you elaborate?

droppedandlost 

There has to be metal where a hole would be drilled.

Nubra 

Right, got that part, but I was wondering what he meant about "six arm symmetry"? Thanks for reply though.
Nubra

bark_eater 

Your crank has 3 arm symmetry....

Nubra 

Ah ha!!! OK got it. Thanks. I am lucky enough to have 32 tooth aluminum TA chairing that was given to me after I did some work on a TA Crank bike for a friend. But I hate to ruin it if it doesn't work!
Here is the 32 TA with 3 of the arms lined up with the 3 bolt Sugino. I think I will have to take it to a machinist (and/or a bicycle builders here I kinda know) and have them drill the holes for me. I don't trust doing it with hand held tools. That is a $30-$40 ring there, sigh.

But it would be well worth keeping the bike with the original crank. As you can see, it has minimal wear. Maybe I can sell this 40T ring here to offset the cost of the TA ring.
Anyways, thanks for the idea bark_eater. Cheers!

kroozer 

Can you get a bigger freewheel?

Nubra 

It already has a 32 freewheel

oneclick 

It's not clear to me if you want new holes in the ring, or new holes in the arms.
Sheldon says a 32t ring should clear your arm's existing holes, so holes in the ring is the simplest route, and a doddle to do:
Clamp them in the correct position.
Drill one hole, use a bit exactly the size of the existing hole and use that hole as a guide.
Put one of the existing bolts through the new hole and just snug it down, check position of the other two undrilled holes, and clamp them AND tighten the bolt.
Drill your other two holes.

If you instead want new holes in your arms (for aesthetics or when that 32 wears out) -
If you drill 10mm holes for standard bolts there won't be much left of the arms.
Drill holes for the existing bolts, I think they are 5mm, and you'll need three sleeves, 5mm id and 10mm od, and three 12mm washers.
If that sounds good, pm me and I'll make you the sleeves nc (and I'll look for some washers).

You probably can drill the holes well enough, you need a decent screw-clamp or vice or locking pliers or similar.
Place and position the six-hole ring (put the ring on the frame-side, so the measuring below is correct.
Clamp it and check that it's still placed correctly.

Mark the centres of the holes as best you can with whatever pointy thing you use, then take the ring off.
I draw a circle around the bottom corner where the holes meet the undrilled arm, take the ring off, then put the mark in the middle of that circle.
Measure all your marks' radius-to-the edge of the swage and re-mark your holes using the average of your three measurements, making sure they are centrered on the arms; make the marks as a pair of lines forming an X so when you drill the hole and loose the mark you can see after if you got it right.
Place the six-hole ring back on to double check.

Centre-punch the marks.
Fix the crank to something sturdy and drill your first hole, with a bit smaller than what you'll finish with; this give you a chance to check if you got the hole in the right place before it's too big to fix (and to check/refine your drilling technique if necessary).
A hole in the wrong place can be fixed with a jeweller's file.
If it's good, drill the other two, smaller drill bit first and check location after each.
Once they are all good, make them the right size.

Nubra 

Thanks! Wow offer to machine up the sleeves for the crank is awesome, but I am going to wimp out and put on a modern crank, using a sugino triple, changing out the spindle to s shorter drive side (lots of used spindles in the drawer in the bike co op) and set the derailluer to run only the 48 and the 38. I tried to include the tiny 28 but I cannot position the suntour Comp V to run all three and really don't want to take off this front Mech.

I am going to place the crank on sale here for shipping cost only. There are a lot of members doing restorations, and this crank has NO mileage on it. Really clean.
Again really appreciate your help. If you want the crank lmk, you have first refusal.
Cheers,

JohnDThompson 

Several companies made 3-arm 106mm BCD cranks that should have interchangeable rings, but none have been in production for several decades, so sourcing replacement rings can be a challenge.

Nubra 

Thank you very much Sir John.

Great diagram!
Sourcing is indeed a problem. I will keep working on it and if you have read all the thread replies, you will see that I wimped out and put another crank on it. But I am going to keep the original crank, and If I can find a six arm cassette ring with 32 or 34 tooth count, I will definitely try what bark eater suggested. I just don't want to risk that TA ring.
Thanks again, Nubra

clubman 

Have a look at this sale just down the list. Buy it! (for the rings)

Nubra 

Thanks clubman, but I have those rings in excellent condition. I was looking for a compact (ring with 30's count).

clubman 

Ah, likely rare as hen's teeth.