Bicycle Mechanics - late-80's 105 cranks: forged or cast?

I've got a 105 road double crankset, came with 52/42 Biopace rings, that came on my 1988 Centurion Ironman Expert. 6-speed indexed (pre-HG cogs) 105 drivetrain, down-tube shifters. I'm curious as to whether this 105 crank is forged or cast.

Also, how much does it matter, and in what ways, whether a square-taper crank is forged or cast construction?

I have this same crank (i think) on my Bianchi. The arms are labeled "Bianchi" but it is also a 42/52 105 from the same era. You can usually see the seam on one side which is a clue as to the manufacture method.

I'll look tonight.

I want to know if I can keep the crank and slap a couple new 52/42's on the guy. The 42 isn’t that low and pretty much kills me going up the big hills here.... but hey... you can only get stronger.

Justus

justuspost - wouldn't be any trouble to slap a 39 on that crank either. That's what I'm running on my 105 crank. I'll see if I have any uber close up shots of my 105 crank to post and see if anything can tell if it's forged or cast....

... this is the best I've got on my webserver...

http://thecuda.com/tn_P6241649.JPG

http://thecuda.com/tn_DSCN1721.JPG

Probably not enough detail to show, but maybe...

justuspost - wouldn't be any trouble to slap a 39 on that crank either. That's what I'm running on my 105 crank. I'll see if I have any uber close up shots of my 105 crank to post and see if anything can tell if it's forged or cast....
Yup, with any 130mm-bcd crank, you can fit 39t and even 38t (though they're rare) chainrings.

a 39 would be nice. I doubt there is much difference between a 38-39... Any recommendations on decent rings for this change out purpose?

Justus

check out loosescrews.com for individual rings. Just about any 130BCD alloy ring will work well for you. Nashbar also has some decent home branded rings which are usually TA made.

Lickbike.com has some cheap Salsa chainrings, too $20 for 38 or 39t. And you can always find stuff on eBay pretty cheap.

So, anyone know about that forged crank issue?
Mine is the FC-1050.

ah, lickbike.com, another good source for parts. :) I've used them several times, especially for their price on the Tektro R200A brake levers.

Anyways, back on topic, any inspection to determine, forged or cast? I can get some close ups of any part of my 1050 model crank if anyone wants to tell me what part to photograph in order to determine. ;)

sometimes people don't seem comfortable voicing an opinion on matters such as this unless it's in oposition to another opinion. So to start:

FORGED !

- Joel

sometimes people don't seem comfortable voicing an opinion on matters such as this unless it's in oposition to another opinion. So to start: FORGED !
Do you mean that forged is better (which I don't think you'll find anyone to dispute) or that the Shimano 105 FC-1050 crankset is forged? If the former, how much better do you think a forged crankset is? The main problem of cast construction would be breakage, flex being a lesser problem I think.

I would think if you've been riding that long and there's not hairline cracks anywhere it's probably forged. Most Japanese components in those days were forged except for the real cheap stuff.

he can also slap a 38 on there. that's what i used.

ed rader

I would think if you've been riding that long and there's not hairline cracks anywhere it's probably forged. Most Japanese components in those days were forged except for the real cheap stuff.

hot forged probably. the good stuff was/is cold forged.

ed rader

hot forged probably. the good stuff was/is cold forged.

ed rader

Forgot about that difference. I bought in 84 Suntour Superbe components and was told their cranks were cold forged which supposely Suntour was the only Japanese company to cold forge. Maybe someone can shed more light on that stuff because I'm going on faded memories.

Tim, I was offering an opinion on neither the 105 cranks mentioned nor of the forging process itself, simply getting the ball rolling with a random choice :)

- Joel

I've got a 105 road double crankset, came with 52/42 Biopace rings, that came on my 1988 Centurion Ironman Expert. 6-speed indexed (pre-HG cogs) 105 drivetrain, down-tube shifters. I'm curious as to whether this 105 crank is forged or cast.

Also, how much does it matter, and in what ways, whether a square-taper crank is forged or cast construction?

Casting and Forging are different technologies, so it's possible that it's both.

Casting, a mould is made the shape of the part, liquid metal is poured into the mould and allowed to cool to some degree, then the mould is removed, it is then machined to finish the job. Another way to do this, is to take a solid block of metal larger then the part, and then machine down to the proper shape and size.

Forging, the part is heated then immersed in a forging material, and then rapidly cooled, for example steel parts can be forged by dropping them into a bucket of carbon powder, and then cold water. The carbon powder adds carbon to the steel making it much stronger. Not sure about forging other materials like AL or Ti. In shop in highschool we made a steel tackhammer, and the head was forged this way, that was 30 years ago, and I still have it, and it still works quite well.

For cast parts, there may be a ridge that looks like a joint in one or more places, from where the two parts or the mould fit together, but those can be machined away as well. I would expect that most cranks are cast, as the machining is much less that way, and they can produce them by the hundreds. As for forging, if it's AL probably not -- AL is strengthed via alloys. If it's steel, then it could be forged before being chromed, not sure cranks really need it though.

Read up on forging here - http://www.forging.org/facts/faq9.htm

A useful explanatory article is on Sheldon Brown's site:
www.sheldonbrown.com/dp-forging.html

I'm guessing that the FC-1050 crank is forged, but still no one knows, or has the specific advantages of a forged crank over a cast crank. This is one of the times where I practically miss Sydney.

A useful explanatory article is on Sheldon Brown's site:
www.sheldonbrown.com/dp-forging.html

I'm guessing that the FC-1050 crank is forged, but still no one knows, or has the specific advantages of a forged crank over a cast crank. This is one of the times where I practically miss Sydney.

I think each of the advantages of forging discussed in the last paragraph under "forging" of Sheldon's article (increased density, increased strength especially at the surface, and the ability to design tools and dies that will put the most strength where needed) can be applied to cranks..........All I can do is guess about the 105 cranks being forged, but even lower-end Sugino cranks I've got laying around have "forged" stamped on the back of the crankarms-

Casting and Forging are different technologies, so it's possible that it's both.

Casting, a mold is made the shape of the part, liquid metal is poured into the mold and allowed to cool to some degree, then the mold is removed, it is then machined to finish the job.
This is basically correct


Another way to do this, is to take a solid block of metal larger then the part, and then machine down to the proper shape and size.
This is neither casting nor forging. These days it is done on CNC machines and is generically known as "machined from billet". A lot of boutique cranks were made this way a few years ago by people with a better eye for style than knowledge of material properties. Breakage was a chronic problem.


Forging, the part is heated then immersed in a forging material, and then rapidly cooled, for example steel parts can be forged by dropping them into a bucket of carbon powder, and then cold water. The carbon powder adds carbon to the steel making it much stronger.
This is an incorrect description of forging. What you describe here is "case hardening" and it doesn't matter how the part was initially shaped. It's also limited to steel parts.

Forging is done by taking a piece of hot metal (steel, Al or Ti can all be forged) and literally pounding it to near net shape using either a power or hand hammer. Commercial forging is usually done using power hammers and a die to establish the initial shape but it can be done freehand. The result is a strong part with the "grain" oriented directionally for the best strength.

Forged cranks are considered superior since they can be somewhat lighter for the same strength as the metal is better utilized but it is a more expensive process. Cast cranks are less expensive and will typically be a bit heavier though plenty good and durable.

Forged cranks are considered superior since they can be somewhat lighter for the same strength as the metal is better utilized but it is a more expensive process. Cast cranks are less expensive and will typically be a bit heavier though plenty good and durable.
Yeah, that was my sense of it - as long as the part was well-designed and -tested, forged is better mainly because it requires less material. Thanks.

Shimano (http://corporate.shimano.com/publish/content/corporate/en/shimanocorporatesiteen/about_shimano/company_history.html)invested heavily in cold forging in the 1960s and uses the technique for pretty much all its Al components, fishing and cycling, auto parts etc.
Cold forging produces items with good grain, high precision shape and excellent surface finish, minimising the amount of hand finishing required.

From what I can gather, Campy uses an outside contractor for their forging (the same as TA). This is std practice in N Italy where each company specializes in a certain sector or technique and there is a large concentration of precision engineering outfits.

Shimano (http://corporate.shimano.com/publish/content/corporate/en/shimanocorporatesiteen/about_shimano/company_history.html)invested heavily in cold forging in the 1960s and uses the technique for pretty much all its Al components, fishing and cycling, auto parts etc.
Cold forging produces items with good grain, high precision shape and excellent surface finish, minimising the amount of hand finishing required.

From what I can gather, Campy uses an outside contractor for their forging (the same as TA). This is std practice in N Italy where each company specializes in a certain sector or technique and there is a large concentration of precision engineering outfits.
I'm quite certain that Shimano doesn't forge all of their aluminum components. Often some of the higher-level components will be described as "forged aluminum", while lower-level verions of the same component will just say "aluminum" - see this thread (http://www.bikeforums.net/showthread.php?t=230440) where I note the diff in hub shell manufacturing. I'd heard in the mid-90's when I was working in bike shops that Shimano didn't forge all of the 105 cranks at the time while Ultegra were forged. (Although I don't know the verascity of that statement.)

I inspected the cranks on the Bianchi last night. The arms were only marked with the bianchi label and stamped on the back as 9/16x20F. This bike has a collection of components and I didnt see anything noting the BB. the chain rings, hubs are Ofmega. the rear cassett is made in italy Extra BX (and something else)

The brakes are all Modolo america and it has a campy FD. There was no seam on the AL/alloy crank arms. They are very light and smooth. They are polished, but not chromed.

I had strong thoughs of putting shimano on my bike, but not my thought run towards campy..... :D

Justus

This is an incorrect description of forging. What you describe here is "case hardening" and it doesn't matter how the part was initially shaped. It's also limited to steel parts.


I stand corrected:D

Cast from memory but I've been wrong before.

By the way, there are other manufacturing options including 'melt-forging'. http://www.bikepro.com/products/cranks/crankover.shtml gives some more details.