Tap and Die Size - Dragster

[Sommer79]

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.

[rkelsen]

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.

[GraemeK]

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

[Mulger bill]

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]

.......Beware that the left hand side is left hand threaded to prevent it coming undone.......

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.

[rkelsen]

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]

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?

Challenge you to go out to your bike. Slacken of the pedal so its not tight. Mount the bike in a stand so you can pedal it. Now leave the spanner on the pedal or somehow grip the pedal shaft amd slowly turn the cranks forward as if pedalling keeping the shaft static (as if the pedal had seized on it). Keep turning until the pedal unscrews itself from the crank and falls into your hand (careful not to damage the crank thread). Note that the pedal thread and BB thread (for an English BB that is) are opposed for the reasons I stated already.


To answer your questions, over 35 years and a few way back in the day when pedals had adjustable bearings, cup and cone fashion and were not as realiable as pedals today. Hope that is satisfactory enough for you.

[rkelsen]

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.

[Oxford]

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.

Precession may help keep them tight when pedalling, but the setup of the threads will cause them to go loose if the bearings seize, which as I have said is moot with the designs of BBs and pedals currently.

[Wild Turkey]

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 CRC. 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!

[rkelsen]

Precession may help keep them tight when pedalling

Thankyou!

[Sommer79]

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?

[Mulger bill]

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.

[Sommer79]

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.

[Mulger bill]

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.

[Sommer79]

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

[Oxford]

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.

[Sommer79]

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.

[Hodaddy]

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