Can you replace the BB on a bike with BB4000 with a BB30? If yes, how?
Short answer - No.
The BB4000 is an FSA Mega Exo 68mm threaded bottom bracket designed for a crankset with a 19mm spindle. This assumes the frame has a threaded bottom bracket and not some weird adapter for the threaded bottom bracket itself.
What frame is this going in?
cervelo dual circa 200?
That bike has an English Threaded Bottom Bracket, so a true BB30 will not fit.
it is a threaded bb. so I should be able to use an ‘old school’ cartridge BB in there?
So long as it’s English Thread, Yes.
What crank are you going to use?
They make BSA 30 threaded to fit your bike > Rotor
Praxis has BSA30 and their own BSA 30 for their cranks which are 30mm drive side and 28mm non dive side
Whatever cranks I have in the basement. Just looking to make a spring/fall training bike out of it. Nothing fancy. Likely an old set of ultegra cranks with limited use.
Thank you for the help guys.
could he not use a threaded 30mm BB, like from Chris King?
if you are planning to use an old set of ultegra, you won’t be needing any bb with “30” in it
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Technically he could, and the frame would then accept a 30mm spindle, but it would require a BB386EVO (or BB30 Long) spindle crank (I’ll address this below).
A “true” BB30 is a 68mm wide bottom bracket shell with the bearings set inboard of the 68mm width. The BB30 spindle is 68-73mm wide, the slack is taken up with spacers, and the crank arms align your Q-Factor based on the “narrower” bottom bracket shell width.
The threaded English bottom bracket shell itself (think frame width) is 68mm, and the threaded Bottom Bracket sits outboard of the frame, giving you roughly 86mm of width for your crank spindle (this is the typical length of a GXP or Shimano crank spindle).
Now back to my first statement - you could use the outboard Chris King “BB30” bottom bracket, but your installed shell width would now be 86mm. If you swapped spindles on a “true” BB30 crank, you’d have a VERY wide Q-Factor, as that crank is designed for the 68mm bottom bracket width. SRAM wised up and makes a crank with a “Long” spindle and the arms don’t flare out as much as a true BB30.
After seeing his last post, if he’s running an Ultegra crank, just slap a Shimano Hollowtech threaded bottom bracket, throw that Ultegra crank in there and call it a day!
You guys are awesome and thanks again. Slapped in an old sealed cartridge BB and the cranks on and ready to roll. The old BB4000 crank arm had stripped threads so that is why I needed to replace the BB.