Forum menu
Hi All,
Please can any BMX experts help me out? I've never worked on one before (familiar with MTBs and Road bikes). Picked a Haro up off ebay for my 10 year old son to try out, but the bottom bracket and possibly chainwheel are shot.
[url= http://flic.kr/ps/Ae638 ]Pictures here[/url]
I took it all apart and the bearings just dropped out on the floor. They are cage type bearings - maybe 1/4 inch? cage is about 45mm or 1 3/4 inches diameter. i think this should be pretty cheap and simple to replace.
The cranks are Primo, on a round 8 splined axle (isis/octalink??), pinch bolt fixing at the side with a preload via end cap into the end of the axle.
The chainring is Voxom. I beleive it should have been splined in the middle to fit on the axle, then there is a single bolt on the crank arms to support it. The centre of the chainring appears to have worn away becuase everything was allowed to loosen up. Is that correct? Are these type of chainrings still available and if so where from please?
Many thanks
not isis/ octalink. the axle is part of the cranks - splines are proprietary.
BBs come in american (traditional) mid, spanish, and euro (same as mtb)
EDIT: this link is much better http://www.profileracing.com/ht_crank_install.php
Chainring - Voxom, felts parts brand doubt you'll get the chainring again, but you will get a replacement that works. The bore in a BMX chainring is 15/16" (though 22mm bore is becoming common now), then a top hat spacer is used to accommodate the various axle diameters (19,20,22mm) and to get a snug fit on the axle. You just need any old BMX chainring, measure your axle diamter (i rekon it will be 20mm) and the appropriate top hat spacer. The chainrings are never really splined, just a nice hole with a snug fit on the axle.
BB - By the looks of the age of things, the bike will have a US bb, is the bb shell massive? If so, halfords or any big bike chain should have the bearing in store to compare the old cage against. There is a chance that the bb is Mid, but i doubt it, but that will complicate getting bearings further a little because mid tend to be cartridge bearings. We'll just see if your bb shell is "massive" first, but up the diamter of the shell, that will help..
Chainrings on bmxes aren't splined. I think the way I used to do it was tighten up the bearing preload bolts on the sides of the axle, then tighten up the crank arm bolt. Never had any issues with it coming loose.
Thanks for all the help guys. Glad I was wrong about the chainring having splines. You learn something new every day!