Recumbents and all feet forward machines
8 posts • Page 1 of 1
I am in the process of building a recumbent tadpole (full suspension) from plywood-yes that's right-plywood. The bottom bracket is giving me headaches. I have purchased (stupidly I now think) a VP sealed cartridge hoping to fit it to a salvaged BB shell from a mountain bike. Not so easy, in fact - impossible, the shell I have, I now realise, is threaded for a BB with separate cups and the cartridge will not fit. I need a BB shell into which a VP BC73 127mm BB will fit. Can anyone tell me which shell to purchase-please?
Thanks, in advance.
Sounds like you managed to buy a 73mm bottom bracket (based on the numbers) - standard is 68 mm which may explain why it doesn't fit. Most BBs these days are english thread although you may have been unlucky enough to rescue one from the odd bike that had italian threads? Failing that if you are just working with the BB shell just check you haven't accidentally installed it in your frame upside down so your left and right threads are reversed. Also a 127 mm BB is very wide for a recumbent boom, it will leave you with a wide chain line and probably shift problems with your front derrailier - normally 113 - 118 will be plenty.
Not too sure I follow what the problem is, the BB unit that you bought is a two-piece, the righthand cup remains fixed on the BB unit and the lefthand cup slips off so that you can install the BB unit from the righthand side of the BB shell. You then screw the lefthand cup into the corresponding side of the shell. Some bikes have a plastic cable guide under the BB and the bolt fixing this on may protrude into the BB enough so that you can't get the BBunit in, you have to remove that bolt first. The threads on the left and right cups are different, if you've reversed your BB shell so that you can use part of the downtube to bolt the BB onto your trike then you'll have to reverse the BB. Hopefully this helps.
My concern would be maybe getting the mounting post for the front derailleur right. A 127mm axle is fairly wide and although a recumbent's long chain means that the chainline is less critical for the rear gears you might find that your front derailleur hasn't got the swing to get across to the big ring - you need to check this. And the angle that the front derailleur is mounted at, therefore the angle of the mounting post coming up from the BB, will help the derailleur perform properly. Are you using a recycled BB shell with some of the seattube still attached or are you going to attach a derailleur post later? If the latter you can cheat a little by positioning the post more to the right to help with the derailleur swing. More on that later maybe.
Where roughly are you located? Perth?
Thanks for the responses guys. - Nessbike - the threads are fine, the trouble is that the cartridge needs to go all the way through, it cannot be separated as in separate cups and ballraces. The cartridge includes sealed bearings.
Just4tehhalibut - the BB unit is one (1) piece, it's a cartridge with sealed bearings. I was working with just the BB shell, no frame or anything else attached, just the BB shell itself.
BTW I am located near Wollongong, NSW.
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