Estuche

Hi All, I am considering buying some lightweight Topline cranks for a featherweight single-speed project. I know they use a JIS bottom bracket type. However, I am having a hard time finding information about chainline. For example, what length would the BB need to be for achieving a 42mm chainline?

Chombi

I have a Topline "road" crank, and the previous owner did mention to me that he thinks that I will need a JIS tapered BB to use it as a road double.
Unfortunately I have not used the crankset on a bike yet, and neither did the PO, so I cannot say the the JIS spec for the BB is definitive.....
If you have not noticed yet, the Topline crank only has shoulders to support a chainring on the outside faces of its spider, hinting at single speed crankset design, so there's a possibility that it would require a different taper than usual on its spindle to get the correct chainline for a double chainring setup. But whether that means that it should be a JIS tapered BB, I'm not so sure either.......

Estuche

Yeah I've heard about the lack of shoulders, though I am luckily using it as a single speed!

I wonder if there is a way to measure chainline just with measurements from the cranks, and then making assumptions about BB length...

Chombi

I wish someone here that has a Topline cranset already on their bike would chime in to help you out, and I am curious too on what is the final word on the required BB spec for it....but as you might already know, these cranks aren't so common out there.
One other note I have for you is that what ever pedals you end up using on these, you will need to make sure that they have flats on the pedal axle to install and remove them with a wrench, as the pedal threaded holes do not go through the crank arm like they typically do on most cranksets, so there will be no access to the usual allen head wrench hole you see on most newer pedal sets, to tighten and remove the pedals from the crank arms. I've seen Toplines with their pedal holes drilled through, by their owners to make it possible to use pedals without the flats on their axles, but I would not suggest doing so as there is not that much material on the ends of the crank arms (for lightness) and you might structurally compromise the crankset if you do so....

Bandera

I've had a Topline crankset on my Vitus since '94 installed on a Dura Ace BB from whatever the 7spd groupo was.
Fits fine even for re-rofit to it's current 10 spd incarnation.

Just eye balling compared to my FG road bike, which runs the chainring on the inside position, the chainline of the Topline, which would only fit a single ring on the outside, would require a much shorter BB spindle right side to work for FG.

Look up the specs on the DA BB and see what's available for your requirments.
Good luck.

-Bandera

YoKev

No experience, but my gut (for what that's worth) says 102 or 103...somewhere in that neighborhood.

gaucho777 

FWIW, according this (astronomical) ebay auction for a matching set of matching NOS Topline cranks and BB: "The cranks come with 127mm Titanium spindled Topline Bottom bracket." Seems awfully wide, but what do I know? Maybe this is the BB length for a 3-ring setup?

Topline SLS Crankset w Titanium Bottom Bracket Tools etc in SEALED Package | eBay

Bandera

Good thing I sorta cleaned mine up when I installed new chainrings, they being so unicorn-like & all.

-Bandera

Estuche

Thanks for the heads up, this is valuable to know!Is this the BB you are using?:VeloBase.com - Component: Shimano BB-7400, Dura-Ace so it would be ~112mm. Can you please measure your chainline with a ruler or similar? See Sheldon for instructions:https://sheldonbrown.com/chainline.html Here is an excerpt:Simply hold the ruler against the seat tube or down tube and measure the distance from the middle of the seat tube to the middle of the chainring teeth. In the case of triple chainwheel sets, measure to the middle chainring. In the case of doubles, measure to the halfway point between the two rings.Thanks for sharing this link. I asked the seller but s/he seems clueless about it.

Bandera

Looks like 44mm to the centerline of the chainrings, that is the BB-7400 I'm using.
It's 115F in the garage, not going to measure the distance to the outer ring right now.

PS
There is a "weight limit" on the Topline cranks, at ~160Lbs I still ignore whatever it is/was.

PPS
Now that I think about your project, my experience of decades riding FG on the road and my familiarity with the Topline crankset I would not use one for a FG regardless of chainline issues.

-Bandera

Estuche

Many thanks!!

According to Sheldon, if the chainline is 44mm to the centerline of a double, then with the typical 5mm separation between rings the outer one should be at about ~46.5mm.

So...for a ~42mm chainline I would probably need a 103mm BB (112mm - 4.5 - 4.5)!

I am 140lbs so should it work for me, right? I don't have any intentions of skidding on this bike. Is the crank strength what makes you have reservations about it?

Unless my calculations are really off, your gut estimate appears to be right on the money

dddd

I have SL series Topline double cranks on my Cannondale CAAD3, running on a 107mm Shimano BB iir.


On my XC/CX race bike, I have standard series Topline triple cranks mounted on a 113mm Real-branded BB.


I prefer using the shortest spindles that will fit and allow running clearance for the chainrings as well as staying within the travel limits of the front derailer, so that's what I probably did with these. Both installations were many years ago.

Bandera

Exactly, strength/toughness is the issue.
FG bikes really take a beating compared to geared road bikes.
Even with a supple high cadence style one still has to put the stomp down to climb, the drivetrain takes unintentional shots on rough roads and back pressure adds an unusual stress.

This is very light, even spindly gear, the construction is not forged but machined from billet aluminum and so softer than a forged unit.
In all not really suitable for FG in my opinion, but it will stay in service on my Vitus where I can shift down for hills and get my butt off the saddle and FW over the worst rough stuff.

edit: I just looked & as I remembered the right side crank arm is swaged/pinned in place onto the spider, not all one piece as w/ a conventional forged crankset. Not what I'd require for the stress of FG riding but fine for light riders on geared bikes who don't expect extreme durabilty.

-Bandera

miamijim

I think 127 would be for installation as a triple. I'm not up to speed on TopLine cranks but they're clearly not 'low profile' like the DA 7410 which requires a 103mm BB. It probably takes a 113+/- like most other standard profile cranks.

Ex Pres 

Used a 115mm Shimano cartridge UN-xx BB on my installation with a double ring, but I don't recall the exact chainline I achieved. It was certainly close enough to run the bike like that for a while. I only took it off to match up the entire rest of the DA group. So while still a little bit of a guess, I'd start with a 113mm running a single ring.

FWIW, I'm well over any 160# limit, and didn't break it.

Pics of mine with well-scarred rings are on Velobase HERE

Bandera

That would not give the OP the 42mm chainline he needs for FG/SS, but he has it figured out:

"So...for a ~42mm chainline I would probably need a 103mm BB (112mm - 4.5 - 4.5)!"

-Bandera

Ex Pres 

Give it a whirl, but at 103mm I'd bet the inner portion of the arm near the spindle rubs on the BB cups. I tried a shorter spindle Stronglight and that's what happened to me. But I didn't measure chainline as it wasn't rideable.

Bandera

Actually the whole project is ill-advised in my opinion, Topline & FG are not good idea but I'm not going to ride it......

-Bandera

Estuche

I appreciate the insights that everyone has kindly offered. I'll side with wisdom and find other cranks for the fixie. However, it was still useful to document the elusive Topline chainline for my and others' future projects. It is still a fine looking, lightweight, and cheap crankset

devinfan

Toplines are fantastic cranks, actually my favourite overall crank. I love the fact that you can't see the wrong side of the pedal from the backside of the crank, it's a great finishing touch. I'm running a double chainring on a white industries titanium bottom bracket, but it has an adjustable chain line which makes things easy. I'm not a 100% sure but I think it is 111mm? Anyway I think the reports of them being delicate come from people using them in an off-road application.

dddd

There were two different Topline arm versions (SL and standard, for weight-limited and unlimited use, respectively).

Failures I saw were of the left-side arm splitting open at the spindle, reportedly from riders habitually tightening the bolts.
The correct way to keep the bolts tight was to torque them once, either using Loctite on the bolt threads or (as I did) using a cap over the bolt, one that seated against the bolt head.

I bought my standard arms in 1995 in a visibly well-used (off-road) condition, and have since done well over 100 races on them, both on-road and off, plus much training mileage, during the ensuing 16 years.

Even after I had the left-arm bolt somehow come loose under the cap at the start of the last lap of a cx race two years ago, and after the arm then fell off half-way through that last lap (glad the pedal didn't stick to my shoe!), I later re-seated the arm using Loctite on the bolt threads and then raced virtually the entire season on the somewhat-chewed crankarm.

As for the SL version arms on my Cannondale, I've not put many miles on them.
I'm light (150's), so expect to get good, long use out of them eventually.

Here's the really well-used ones, having of course been re-polished many times over the years:

Bianchigirll 

I thought these were lightened and rebranded Avocets? If so wouldn't they require the unique tapered Avocet/Ofmega BB?

Bandera

If memory serves, no markings of country of mfg on mine, Topline machined cranks in California as a by product of the downturn in the Aerospace industry in the early 90's. Mounted on a DA BB 7400 they still spin happily away 20 years on.

Topline road cranks serve well in an appropriate role on my Vitus and add a "what's that" factor as well.

-Bandera

AAZ

[h=4]An alternative to the DA-7410 is Sugino CBB-103
[/h]

notenoughdaylig 

[/QUOTE]

Can we see a photo of the rest of that bike? The cranks aren't the only unique feature.