Dekes Posted June 19, 2008 Report Share Posted June 19, 2008 (edited) So I bougth a new frame and brought it to the bikeshop today to get the headtube reamed and faced and the BB shell faced and tapped. I already bought a cane creek tank jump headset and am looking into buying an SKF bb because both these headset and BB have cromoly cups which I prefer. The SKF BFR600 is twice the price of the 300 because it's made out of stainless steel whereas the 300 is made out of cromoly steel, bearings are claimed to be the same on both versions. Is there a reason to pick stainless steel over cromoly steel? Or any other reason to pick the 600 over the 300? Can I put my older try all ISIS cranks on a new BB? I assume yes since the cranks are made from aluminum and the bb spindle is made from steel. Also at eyesight the ISIS interface on the crank and on my old BB don't seem to have a lot of wear on them. Thanks. Edited June 19, 2008 by Dekes Quote Link to comment Share on other sites More sharing options...
forteh Posted June 20, 2008 Report Share Posted June 20, 2008 Stainless steel is typically no stronger than chromoly, the only advantage is that it wont rust and it will look shinier Quote Link to comment Share on other sites More sharing options...
Dekes Posted June 20, 2008 Author Report Share Posted June 20, 2008 Stainless steel is typically no stronger than chromoly, the only advantage is that it wont rust and it will look shinier actually cromoly won't rust either as it contains chrome but stainless steel remains shinier whereas cromoly has a visible oxide layer. Quote Link to comment Share on other sites More sharing options...
forteh Posted June 20, 2008 Report Share Posted June 20, 2008 actually cromoly won't rust either as it contains chrome but stainless steel remains shinier whereas cromoly has a visible oxide layer. Not the case Im afraid, chromoly is only a low carbon steel with chromium and molybdemun alloying elements (amongst others) it will rust just as much as any other steel, albeit perhaps at a slightly reduced rate. Stainless steel has higher percentages of chromium and nickel which gives it higher corrosion resistance but also slightly lower strength. The current cost of stainless is astronomical compared to mild steel which reflects in the price, I would go for the 300 Quote Link to comment Share on other sites More sharing options...
psycholist Posted June 20, 2008 Report Share Posted June 20, 2008 Once you go over 18% Cr in a steel there's enough to form a coherent oxide layer (Same as what stops Al rusting - Pure Al is pretty reactive, so it repassivates quickly, protecting itself from further damage. There are grades of stainless steel that are stronger than pretty much all other steels (Possibly not quite a match for single crystal superalloys) though - Have a look at Maraging steels... As far as I know Reynolds have a bike frame tubing material based on one of these alloys - it costs more than Titanium but may perform better ... Quote Link to comment Share on other sites More sharing options...
forteh Posted June 20, 2008 Report Share Posted June 20, 2008 Once you go over 18% Cr in a steel there's enough to form a coherent oxide layer (Same as what stops Al rusting - Pure Al is pretty reactive, so it repassivates quickly, protecting itself from further damage. There are grades of stainless steel that are stronger than pretty much all other steels (Possibly not quite a match for single crystal superalloys) though - Have a look at Maraging steels... As far as I know Reynolds have a bike frame tubing material based on one of these alloys - it costs more than Titanium but may perform better ... Pity that chromoly is only about 1% Cr Quote Link to comment Share on other sites More sharing options...
psycholist Posted June 20, 2008 Report Share Posted June 20, 2008 I should have mentioned that of course . CrMo steels do resist rust a little better than some other steels, but they're a long way from stainless - composition of 4130 steel (DMR frames are made of this): http://www.matweb.com/search/DataSheet.asp...7487&ckck=1 Composition of Maraging steel (See average figures for all steels in the database at the bottom of the page): http://www.matweb.com/search/DataSheet.aspx?MatID=81726 Quote Link to comment Share on other sites More sharing options...
PaRtZ Posted June 20, 2008 Report Share Posted June 20, 2008 lol, any guest looking in this thread must be thinking "geez what a bunch of engineering nerds" I wouldn't reccomend the old crank, new bb idea, but having said that I do it every time and it probably would work fine. You just might have a quicker wear rate on the ISIS splines of the crank due to the newness of the BB perhaps Quote Link to comment Share on other sites More sharing options...
psycholist Posted June 20, 2008 Report Share Posted June 20, 2008 Provided the old cranks weren't loose on the old BB they'll be fine with a new BB... Grease up the splines and the crank bolts and tighten it well, checking for tightness after an hour or so of riding - usually once they get the second tightening they tend to stay tight ... Quote Link to comment Share on other sites More sharing options...
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