Question on OMAS double lockring bottom bracket
02-12-22 | 02:59 PM
#2
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Joined: Jun 2010
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From: Medford MA
Bikes: Ron Cooper touring, 1959 Jack Taylor 650b ladyback touring tandem, Vitus 979, Joe Bell painted Claud Butler Dalesman, Colin Laing curved tube tandem, heavily-Dilberted 1982 Trek 6xx, René Herse tandem
Drive side's gotta be left-hand threaded unless someone tapped it out for Italian. OMAS made these BBs in English and Italian, and it ought to be marked on the cups. BSC 1.370" x 24 = English = left hand threads on right side. It's probably the venerable "Big Sliding" bb, a timeless choice. There was a Ti version, but even the CrMo axle one was quite lightweight because of the alloy cups.
Tapping out to Italian size was a way to save a frame if the BB threads were stripped and you didn't want to ruin the paint. Pretty rare repair, though. I have done 2 BB thread repairs and my go-to is to mig weld and retap as English, because the left hand threads are a Good Idea and if you're careful with heat it's possible to mig weld on the inside without ruining the paint on the outside.
Tapping out to Italian size was a way to save a frame if the BB threads were stripped and you didn't want to ruin the paint. Pretty rare repair, though. I have done 2 BB thread repairs and my go-to is to mig weld and retap as English, because the left hand threads are a Good Idea and if you're careful with heat it's possible to mig weld on the inside without ruining the paint on the outside.
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Owner & co-founder, Cycles René Hubris. Unfortunately attaching questionable braze-ons to perfectly good frames since about 2015. With style.
Owner & co-founder, Cycles René Hubris. Unfortunately attaching questionable braze-ons to perfectly good frames since about 2015. With style.
02-12-22 | 05:11 PM
#4
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Thanks, I got it off, it was left hand. I have the ti spindle version, 160 grams on my scale. Any tips for getting the bearings off? They seem like a press fit. My plan was to soak them in solvent and then regrease using Phil's.
Last edited by MB33; 02-12-22 at 05:15 PM.
02-12-22 | 05:47 PM
#5
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Joined: Jun 2010
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From: Medford MA
Bikes: Ron Cooper touring, 1959 Jack Taylor 650b ladyback touring tandem, Vitus 979, Joe Bell painted Claud Butler Dalesman, Colin Laing curved tube tandem, heavily-Dilberted 1982 Trek 6xx, René Herse tandem
If the bearings are feeling awful/crunchy (indicating water ingress and pitting), replacing can easily be done. Read the numbers on the bearings and order some up. They should be readily available. I've taken sealed BBs apart using a hammer - I don't like doing that. Screw in a bolt and hammer on the bolt, never the BB shaft directly. I've also done it with a car jack and some large diameter deep sockets. A gear puller or bearing puller, like for car engine/transmission work, works even better and they can be found cheaply at Autozone or whatnot. Or if you have an arbor press or a large vise to use as a press, you can do it the Right Way. But all methods will work! Careful not to mess up the threads of those alloy cups!
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Owner & co-founder, Cycles René Hubris. Unfortunately attaching questionable braze-ons to perfectly good frames since about 2015. With style.
Owner & co-founder, Cycles René Hubris. Unfortunately attaching questionable braze-ons to perfectly good frames since about 2015. With style.
02-13-22 | 05:12 AM
#6
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Joined: Apr 2009
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From: Seattle
Nice! That is lightweight even for a Ti bb. Yeah, I regrease sealed bearings all the time. If you can pop off the rubber seals, that'll work nicely. Even if there's a tiny bit of rust, if you flush it and the bearings look fine, go ahead and regrease them!
If the bearings are feeling awful/crunchy (indicating water ingress and pitting), replacing can easily be done. Read the numbers on the bearings and order some up. They should be readily available. I've taken sealed BBs apart using a hammer - I don't like doing that. Screw in a bolt and hammer on the bolt, never the BB shaft directly. I've also done it with a car jack and some large diameter deep sockets. A gear puller or bearing puller, like for car engine/transmission work, works even better and they can be found cheaply at Autozone or whatnot. Or if you have an arbor press or a large vise to use as a press, you can do it the Right Way. But all methods will work! Careful not to mess up the threads of those alloy cups!
If the bearings are feeling awful/crunchy (indicating water ingress and pitting), replacing can easily be done. Read the numbers on the bearings and order some up. They should be readily available. I've taken sealed BBs apart using a hammer - I don't like doing that. Screw in a bolt and hammer on the bolt, never the BB shaft directly. I've also done it with a car jack and some large diameter deep sockets. A gear puller or bearing puller, like for car engine/transmission work, works even better and they can be found cheaply at Autozone or whatnot. Or if you have an arbor press or a large vise to use as a press, you can do it the Right Way. But all methods will work! Careful not to mess up the threads of those alloy cups!
I also interchanged parts both ways between those and Stronglight's version. The bearings fit both the axle and the cups the same, on OMAS as on SL. The SL bearings I worked with had a wiper seal inside and out, versus the non-contact shield on the cartridges OMAS used. So feel free to sub in some fully-sealed cartridges like SL did, into your OMAS. It adds a little extra friction but that sort of seal friction doesn't go up under heavy load and becomes rather insignificant in the big picture, I believe. Maybe a real bearing engineer can correct me if seal friction is something to fret about. But I liked the little extra protection against water and gunk getting in.
If I recall, the bearings were quite standard and easy to find. Probably still are common though I haven't looked in a long time
