ramps and pins on double. compatibility issues?
 

I helped a friend of mine build up a road bike and we've been having trouble getting the front deraileur to shift properly. (Double crank)

My friend's a little short so, not finding any good shimano used cranksets in 165, we used the 165 double off of a mixte I've got, I think they're suginos. Anyhow, like I said, I'm having trouble adjusting the front deraileur (shimano 105) with the sti brifters (shimano 105). The difficulty is in setting the limit just so so that it makes it up to the big ring but doesn't fall off the other side. I'm making quarter turn adjustments and I just can't get it right. I don't think it's me, and I don't think it's an sti problem but what do I know?

Looking around a little I've seen a bunch of hooey about ramps and pins so I figure that's just the little bit of help we need to get the chain to climb up to that big ring without the deraileur shoving it too far. So I went to LBS and found a used ring (53 - same size as the one we've got), shimano, ramped, pinned. It's labeled shimano sg b-53. From looking around I gather the B indicates compatibility with a 39 tooth small ring, although Sheldon Brown suggests it will still work quite well with the 42. I can't get a look at the bike at the moment because it's in another state, so I'm not sure if it's got a 39 or 42, but I'm almost certain that it's not a shimano small ring. Will this matter signifcantly? Should I be looking for a 39 ring as well? Or, more specifically, should I be looking for a Shimano 39? Or, will I see significant enough improvement with the big ring to let it go for now? I'm just trying to cover all the bases before dropping this thing in the mail.

Thanks in advance for any advice.

Dan

BTW, I know I should just buy a new matched pair but I don't have the scratch at the moment.

The small ring has no pins any way, it might be ramped..so it might work anyway.
I take triples apart, the first ring is not ramped @ least what I've seen.
The mid ring is ramped\pinned, the outer is ramped.
I THINK the important effect will be ramps on the big, not the small.
Make sure the ramp tab is under the crank arm, this lines the ramps up for the crank.
I have a non-ramped small ring Shimano on a double\ going to biopace Shimano big ring. 42-52, works fine.

I have several setups with non ramped and pinned ring and it works perfectly with STI. The A and B buainess in mostly shimano marketing and makes little or no differenct in actual use.I would not even mess with changing out the inner ring. You sure the Sugino cranks are 130? I've also seem em in 144, 135 and 110 BCD.

yeah, I figured the small ring wouldn't be that special, my only real concern was the alignment of the teeth on the small ring to the pins on the big having an acceptable or unaccetable effect.

The cranks maybe SR? I eyeballed them against an old shimano 600 drive side crank and they looked to be the same. it's entirely possible that I'm wrong, of course.

thanks for the advice, you two.

You might have been looking for pins on the large ring, softer metal 'ramps' riveted to the back\facing the smaller ring.
With lining up the real 'ramps' (teeth angles) the chain lifts @ the right part of the pedal stroke.
The pins are lined for the index shift\crank\ramp revolve but serve a second purpose of being a chain 'lift' when shifting to a larger ring.

I'm thinking? IMO...not a mech.... :o

Excatly; modern front derailleurs don't lift the chain as much as older models; the larger inner cage surfaces are evidence of this. The ramps and pins are intended to make up for it.

Go to the Park web site. Look up front derailleur adjustment. Disconnect your shift cable and start from the very beginning.

My suspicion is that the problem is in the LOW limit screw adjustment. If that's off, you're starting with a little too much cable tension to hold the chain on the small chainring. If your chain tension is a little too high, your STI, which pulls the same amount of cable every time, is pulling the chain right over the chainring.

From your description of the shifting/throwing chain problem I'd be looking at the derailleur adjustment, not the ramps or pins or A B designation. I would check the derailleur height above the big ring and the derailleur alignment. The derailleur should clear the top of the big ring by only 1 or 2 mm and the rails (side plates) should be parallel with the chainline.

Al