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Help Setting Up Drivetrain - 8 Spd Barends, 6 Spd FW, Bit Of a Franken

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Help Setting Up Drivetrain - 8 Spd Barends, 6 Spd FW, Bit Of a Franken

Old 05-02-12, 10:58 AM
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jyl
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Help Setting Up Drivetrain - 8 Spd Barends, 6 Spd FW, Bit Of a Franken

I'm setting up the shifters on the boy's bike. Narrow 6 speed freewheel, Suntour I think, 14-26 if I recall right. Front chainrings are 50-34, just plain old rings I found used (no fancy ramps/pins, but not worn out). I measured cog spacing at 5.0 mm which is 7 speed spacing. Shimano 600 tricolor RD and FD. Shimano Ultegra BS64 8 speed barend shifters. Origin8 BMX crank on 121mm spindle. From reading, I think this should work if I use the alternate cable routing for the RD.

Here's what I did for the RD:
- Shortened chain so that, when on the big-big combination but not threaded on the pulleys, I had 1 full link (1 inner + 1 outer) overlap. (I can lengthen if needed, have an un-used master link)
- Set high and low stops for the RD to line the pulleys up with the small and big cogs.
- No idea how to set the B screw, so I left it alone.
- Put right shifter in the "smallest cog" position, i.e. lever pointing straight down.
- Placed chain on smallest cog (call it #1).
- Screwed downtube cable stop fully in (clockwise).
- Set RD cable adjuster to middle of range.
- Pulled cable tight and fastened to RD using "alternate cable routing".
- Fiddled with the RD cable adjuster until shifting was as good as it got. Which is okay, but I still have three problems.

Problem 1: Starting at the smallest cog (#1), I have to pull the lever 2 clicks to get to cog #2, the first click doesn't do anything. Ideally I'd like to shift to cog #2 on the first click, because . . .

Problem 2: To get to the biggest cog, #6, I have to pull lever all the way to the extreme end of its range, past horizontal and pointing a bit "up". This requires a bit of hand strength, and might be hard for my son. Ideally I'd like to get the cog #6 with the lever still pointing a bit "down", that being the best leverage position for little fingers.

Problem 3: When the chain is on the big chainring, it is hard to get into biggest cog #6. I know you're not supposed to use this combo anyway, but should a well-set-up drivetrain got there easily anyhow?

For the FD, I did:
- Set high and low stops on the FD.
- Adjusted FD clamp so that cage just clears the big chain ring and, viewed from top, is lined up w/ chainrings (rear of cage not pointing to right or left)
- Screwed downtube cable stop fully in (clockwise).
- Put left shifter in the "smallest ring" position, i.e. lever pointing straight down.
- Pulled cable tight and fastened to FD.
- Fiddled with all of the above, shifting is okay, but I still have one problem.

Problem 4: Getting to the big chainring - it works, but the chain doesn't "leap" right up there, it takes maybe 1/2 to 1 revolution of the crank for the chain to catch on the chainring teeth and start moving. I'd like the FD to shove the chain onto the big ring with more authority, but the FD appears to be at the limit of its range. Having the cage as low as possible seems to help. I tried angling the cage outward (rear end further out than front end) which didn't do much. I think a narrower spindle would help by bringing the chainrings inward, but the selection of square taper spindles that fit old French cups is limited at the bike coop. If needed, I could mount both chainrings on the inside of the crank spider, would look like uck and might be tough to find the longer chainring bolts, so I'd rather not.

Do you have any suggestions? I don't know much about setting up or fine-tuning a drivetrain. All my life, my knowledge of bike mechanics has been of the "get you home" variety, so I'm trying to learn new stuff here. I also don't know what to expect from this set-up - how good is "good enough", how good is "whaddya expect with a franken bike".
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Old 05-02-12, 11:50 AM
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Problems 1 and 2: Tighten the cable tension and you should be able to hit the 2nd smallest cog in the back on the first click. This should also solve the issue of bringing the lever past horizontal to get into the biggest cog. If the hand strength of your son is an issue, have you considered thumb or grip shifters instead? They exist in Shimano-compatible 8spd and are affordable.

Problem 3: Make sure the setup is supportable using your RD (sum of number of teeth differential on the smallest/biggest cogs front and rear). If the RD isn't designed to handle it, you will have issues. Next, make sure chain is long enough for Big-Big. Next, screw in the B-screw to pivot out the body away from cogs a little so the top pulley with chain has clearance to shift onto the big cog in the back. Then check the chainline. If the middle chainright is not riding aligned fairly close to the middle rear cog, you need to get a different BB spindle of sorts. Lastly, check the limit screws on the RD to make sure you have a little extra room to over shift needed with Suntour FW. Install a spoke protector for the reason that you're going to need to slightly over shift.

Problem 4: If you have older crankset, w/ no ramps or pins, the chain will take longer to get up there. Clack, clack, clack, clack, hop, and up. That's the nature of the beast. Just make sure your FD cage is within 1-2 mm clearance over the big ring and the cage is aligned toward the rear cogs. Height and pivot alignment of the cage can depend on the cage shape and crank teeth combination. Read owner's manual if you can find it for alignment, otherwise, trial and error with height and pivot keeping cage about 1 - 3 mm above big chainring will usually result in the best shifting you'll get.
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Old 05-02-12, 12:57 PM
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Ultra 6 is a 5 speed width, is that what you got.

life is simpler with friction-shifting,

only my Internally Geared Hub bikes klick shift.
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Old 05-02-12, 04:25 PM
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Great, thanks gyozadude. I'm going to work on it again tonight.

The 28-tooth wrap is right at the limit for the RD, and 50-34 is a pretty big jump, so I expected this to need more than one try.

fietsbob, yes the FW is a 6 speed in a 5 speed's width.

I am happy with either index or friction, personally. With indexing I shift more often and am in the "optimal" gear more of the time. Like when accelerating I will stay seated and spin as I click up through the gears. With friction I find myself in a higher gear, standing up and mashing until I get closer to cruising speed, then I sit down.

This bike is for my son, it is his first "ten speed" so I decided to let him keep his hands on the bars rather than reaching for the downtube. Found the indexed bar ends NOS for the same price as well-used Suntour friction bar ends, so the decision was made.

I've never had an internal gear hub bike, but would like to sometime.

Last edited by jyl; 05-02-12 at 04:33 PM.
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Old 05-02-12, 05:31 PM
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Maybe a lot of lateral slop on the guide pulley will make up for some of the mismatch.

pretty much what shimano does any how, ..

and because freewheels in general, have a bit more planar wobble
of the cogs, than cassettes. that is another factor.

add shift happy hyperglide tooth profiles ..
and the closer spaced cogs want to ghost shift.
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Old 05-02-12, 09:53 PM
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Originally Posted by fietsbob View Post
Ultra 6 is a 5 speed width, is that what you got.

life is simpler with friction-shifting,

only my Internally Geared Hub bikes klick shift.
+1

With your setup, you're going to pull your hair out trying to get the DT to index. Just set the RH shifter to Friction
and leave it at that. Besides... if it's your boy's 1st 10 speed he'll learn how to shift, just like all of us had to before
Indexing came around; he'll be a better rider because of it.

Question... what is this 'alternate cable routing' you refer to?

Alan

Last edited by oldskoolwrench; 05-02-12 at 09:56 PM.
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Old 05-02-12, 10:38 PM
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Originally Posted by jyl View Post
Narrow 6 speed freewheel, Suntour I think, 14-26 if I recall right.
Many Suntour freewheels (made before indexing) are impossible to index. It's not that the spacing issue cannot be overcome, but on many of the ST freewheels the spacing is actually different depending on which cogs you're looking it! For friction shifting this is a non-issue but for indexing is literally impossible on some of the old ST freewheels. Suggest you get a Shimano 6S freewheel if you want this thing to index, they are cheap enough.

Can't get to the 28T cog? That could be a b-tension screw issue. Once you actually get there, then how does it spin? If the upper pulley of the RD is interfering with the 28T when you're using it, you need to turn in the b-tension screw (clockwise) to give the RD more clearance.
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