Australian Cycling Forums - Bicycles Network Australia

Hi,
I just bought a rusty old dragster and need to retap the part that holds the pedals. Does anyone know the tap sizing for this? Cheers.

It could be one of two sizes: 1/2" or 9/16" 20 TPI. My money's on 1/2".

Beware that the left hand side is left hand threaded to prevent it coming undone. I don't think you can buy pedals with an oversized spindle, so you might have limited options if the threads are stuffed.

It will be cheaper to replace the cranks than buy a left hand tap.

Methinks Sommer might mean the bottom bracket. If so, the LBS should have the tools and be able to knock it off in five minutes.

Oxford wrote:Pedals are threaded left and right to make them come undone, in the same way the BB is left/right threaded (opposite to the pedals) so that if the pedals or BB bearings seize, they will actually unscrew from the crank/frame. Its a throwback to when all bikes were fixed gear, if the pedals did not unscrew to loosen, the fixed gearing would quite literally rip your feet off at the ankle and/or throw you off the bike.

'Tis a brave man who disagrees with Sheldon and Jobst:

http://www.sheldonbrown.com/gloss_p.html#pedal

"Another popular theory of armchair engineers is that the threads are done this way so that, if the pedal bearing locks up, the pedal will unscrew itself instead of breaking the rider's ankle. The left-threaded left pedal was not the result of armchair theorizing, it was a solution to a real problem: people's left pedals kept unscrewing!"

http://www.sheldonbrown.com/brandt/left.html

Couple questions: How long have you been riding? How many pedals have you seized?

Oxford wrote:Note that the pedal thread and BB thread (for an English BB that is) are opposed for the reasons I stated already.

It's got nothing to do with them seizing. It's all about the prevention of loosening by precession. It's the very same reason that cars used to have left hand threaded axle studs for their left wheels, back in the days before engineers discovered the miracle of cone-seated wheel nuts.

The centre lock nut on the left hand side of racecars is a left hand thread, including F1. Simpley so the stresses on it will not loosen it. I seem to remember some commercial vehicals running LH threaded wheel nuts up into the 80s. They may still exist?

I have many NOS dragster cranks. I may sell some off if it helps you out.

You can clean up a thread buy finding a bolt (or pedal shaft) the same thread. With an angle grinder cut 1 or 2 grooves along the length of the thread. Run it in with cutting compound or just c r c. The leading edge will cut/clean the thread. A better result can be gained by coming in from the back of the hole. The thread there will get you started straighter. We call them a thread chaser. Just a thought.

I busted a pedal out of the alloy crank an old ladies bike 13kms from home once. I had to cable tie my foot to the other pedal and ride with 1 leg!

Oxford wrote:Precession may help keep them tight when pedalling

Thankyou!

Looks like I have got myself in a nice mess. The circular metal that locks into the frame seems ok but the internal thread in the frame is not happy. Is there someone in Brisbane I can pay to fix this?

Definitely sounds like the bottom bracket shell now. This bit mate?

Any good bike shop should have the tools for the job, ring around your area.

Yep that's the one I'm after (Thanks for putting the pic up!). What exactly am I chasing to fix it? Happy to try at home. 3 girls, one bike and a few tools should fix it! If not off to a bike shop.

You'd need the right sized taps and chasers. One of which will be a LH thread. (Unless the bike is Italian or old French)
THIS is a handy guide to sizing. In fact the late Sheldon Brown is a great place to bookmark.

Tapping, facing and chasing is one of the few jobs I will let the LBS handle, the cost of the tools for the job is too high for the amount of work I'd give them.

Anyone in Brisbane you guys recommend. My local wasn't impressed that I dragged a rusty old bike into their new shop.

Oxford wrote:what side of Brisbane are you on? if northside try Ridgeways in Stafford, they'd appreciate the old bike, it will fit right in with the shop.

Yep Northside and I work at Stafford Heights so I will give them a call and drop in. Was put off by my local a little when they weren't keen to help. I know a little about retro cars and drive a 73' TA22 Celica but bikes are a new 'toy'. Thanks heaps for advice.

I just came in on the end of the left hand thread debate but couldn't resist backing up Oxford.
From my experience he is correct but I had no idea why they were designed to undo in the pedalling direction.
Thanks Oxford for the logical answer.

Hodaddy