# Bottom Bracket help



## broady (30 Aug 2014)

I'm new to the forum and new to bike maintenance. 
I need to replace my bottom bracket. I've removed everything and taken the bb out. The markings on it are-
RPM
BB 7420
BC1.37x24T
73

What does this all mean?
And what replacement do I need to buy?
Does the screw thread part get removed from the BB? The other side came off quite easy.

Many thanks for any help


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## Rickshaw Phil (30 Aug 2014)

Hi and  @broady

Not sure about all of it but I'll decipher what I do know:
RPM I suspect is the make of bottom bracket.
BB 7420 I don't know but this is probably the model number.
BC1.37x24T tells me that this is a standard British threaded bottom bracket
73 is most likely to be the width of the bottom bracket shell

The important information which is missing is the axle length which can be measured using a vernier caliper if you have one available While at it I'd also measure the shell width (not diameter) to confirm it is 73mm.

I'd suggest a Shimano replacement as they are pretty good. The UN55 (LINK) is high quality and will last for ages.

In answer to the other question, I presume that you mean the other cup by "screw thread part". Yes it does get removed and the new bottom bracket will come with a replacement.

I hope this all helps.

Edit: Just seen a link to the same BB but cheaper: HERE


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## broady (30 Aug 2014)

Thanks for your help. 
But what is a vernier caliper?


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## Paulus (30 Aug 2014)

This is a vernier caliper,


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## broady (30 Aug 2014)

Does the length of the spindle have to match perfectly? 
And I don't have one of those tools.


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## vickster (31 Aug 2014)

Perhaps get advice from your LBS?


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## cyberknight (31 Aug 2014)

vickster said:


> Perhaps get advice from your LBS?


Indeed, is the bike a road or MTB and was it shimano or campag gears ?


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## Tim Hall (31 Aug 2014)

It doesn't need to be an exact match. A millimetre here or there won't make much difference. The old one can be measured with a ruler, IMO.


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## broady (31 Aug 2014)

Its for a hybrid bike with shimano gears. The crank is suntour.
I'll get it measured and have a look.
My lbs is closed by the time I finish work and Halfords is my only other real alternative and my friend didn't find them particularly helpful.


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## Big_Dave (31 Aug 2014)

I'm afraid you are going to have to measure to bottom bracket, RPM is the Brand, BB7420 just refers to it being a bottom bracket cartridge type and not a specific size, 1.37x24 is English thread. bottom brackets come in either 68mm wide shell or 73mm shell so yours is 73mm you can measure it with a tape measure or ruler. Spindle lengths vary (square bit where the crank arms fit) again measure with ruler/tape measure, yours appears to be fairly long, probably in the region of 118mm or 122.5mm. Depending on what yours measures you need a bottom bracket the 3 things you need is shell (73) spindle (eg 118) and thread type (English)
eg. 73x118, english thread,as previously mentioned Chain reaction cycles are the cheapest, shimano UN55 bottom bracket is the one to go for one you know the size required. if you don't 100% trust your measuring order a two or three different sizes (over £9 is free delivery) then match up the one you need once they arrive and send the others back (also free returns)


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## broady (31 Aug 2014)

Thanks for your help. I think the spindle was too long before it started to go, so I might order the same length and one a bit shorter.
Thanks again


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