How do I get rid of these greyish lines? I'm not sure if I should wet sand them out or if it is an anodization problem? I also think these were polished previously.

If they do not come of with a quick rub with metal polish, they are most like corrosion occuring under clear anodizing. If that is the case, the only way to completely remove those greebly tendril looking stains would be to remove the anodizing through mechanical (buffer when and compounds) or chemical (lye based oven cleaner) means, then polishing the cranks with polishing compound. Just note that if you do so, you will have to maintain the cranks with periodical cleaning and polishing as the bare aluminum will corrode much easier that hwen it had the clear anodizing. It's not really too bad if you do not ride in very salty and wet conditions regularly.

Chombi

Yeah, these are the signs of aluminum that was left outside for a long time. Corrosion ate slightly into the aluminum under the anodizing layer. You have to remove the anodizing layer, and then polish the heck out of it with progressively finer polishing compounds, and then buff it on a good new white buffing wheel with white fine polishing compound. It'll come out shiney as a mirror.

...what about clear coating it afterwards?...would that be workable?...

Yep - Thats right - A good polishing with "Brasso" and then a thin coat of clear laquer will do - But - Don't forget to check out your local gun shop - They have some new super dupper cleaning agents designed specifically for adonised aluminum - They also have a brass cleaning barrel that works great for cleaning smaller aluminum parts making them nice and shinny...

+1
This Gran Sport crank looked like the one your original post. I removed the anodizing with oven cleaner and polished on a buffing wheel, then by hand with Blue Magic. The entire process took less than an hour. This is a terrible cell phone photo (all I have).



P.S. Not my bike. Not my pedals.

Had to laugh at this as I live a mile from the beach.

Thanks everyone for the help! I will try the chemical oven cleaner way because I'm lazy and I was going to polish these anyways so they will get buffed eventually. Is there a way to somehow re anodize them once polished or is that it ? will they still be shiny if anodized or is one or the other? Also, what happens to the cranks once polished and I've ridden them for awhile? will they corrode like rust or something? Sorry this is the first time I've tried polishing something and there are instructions on how to polish stuff but not really any on how to do the up keep on them.

You do the upkeep with metal polish.

^^^^^^^^^ really I would have not geussed. Thanks for the curt reply.

Just polish them again every now and then with a cloth and Mother's Mag & Aluminium polish, Solvol Autosol or your metal polish of choice.

Remember as well, once you remove the anodization and polish them, they will be shiny like chrome and not silky like original. I have not yet found a reliable and straightforward way to get back a silvery finish (on bicycles or motorcycles), so if you like the original look (but cleaner) think twice about removing the coating and polishing.

As for upkeep - I find a regular wipedown with WD40 and an annual (or bi-annual) polish with NEV-R-DULL (easiest), Autosol (harder), or ALUM-I-NEW (hardest) keeps things looking good....

You can get a satin type look if you go over the polished part lightly with some fine Scothbrite, although you will have fine directional "grain" to the finish as you might find on older motorcycle lower front suspension tubes. Alternate the scotchbrite application with polishing again to get to the desired effect. You might be lucky too if the original finsh does have the find directional "grain" to it as I found some components do have so it might actually look as if you never took the anodizing off. all you can do is experiment and find out what you can come up with to most closely match the original anodized finish.
If you really want to, you can also have the part re-anodized. Many metal finishing places have opened up to doing very small projects as the car and motorcycle modders have increased the demand. It will stil cost quite a bit though.

Chombi

There is virtually no upkeep if you have it chromed.

Thanks Chombi - I'll try this as it has bugged me for years....I like the satin finish of original parts but have avoided trying to fix the same situation as the OP because I was afraid of not being able to get a decent end result.

To OP: sorry for the mild hi-jack - hopefully this helps you too.

Mark