Pedal Problem

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Samuel D
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Re: Pedal Problem

Postby Samuel D » 21 Jun 2020, 2:02pm

My brother bought a road bike in the lockdown and despite warnings from the bike shop and me about the importance of fitting the pedals with grease and tightly, had the left pedal fall out after wrecking the crank threads. He did not use a washer, none having been supplied. I didn’t think to suggest washers. I believe the pedals lack a broad, circular shoulder. I’ll try to get pictures and share them here, since the cause may be similar to Tim’s.

Samuel D
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Re: Pedal Problem

Postby Samuel D » 22 Jun 2020, 9:15am

Pictures from my brother:

Image

Image

Image

Image

As I mentioned: new bike, new cyclist, he installed the pedals himself (having been warned to make them tight), grease on the threads, no washers and I didn’t think to mention them, rode the bike a few times, this was the result. He rode home with his big toe on the crank, hence the smeared grease and dirt around the crank’s pedal eye.

He’s a fairly big and strong fellow, if that matters.

It’s interesting that Tim DH says his two instances of this problem happened after a new build and “at least 20 miles since previous rebuild”. New joints appear to be a common theme.

Brucey
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Re: Pedal Problem

Postby Brucey » 22 Jun 2020, 9:29am

FWIW the only marks on the face of the crank appear to be the ones that presumably occurred when the pedal started to move around as the threads gave way. There is no sign of the usual marking that happens when that type of pedal is made even half-tight in a crank of that sort. Not much sign of grease either.

So looking at that, I'd suppose that it is quite likely that the pedal was never much more than finger tight, and there cannot have been that much grease either.

In this case I suspect that the lack of pedal washers cannot have made any difference, else there would be marks/burrs on the crank where the pedal spindle tried to precess but was inhibited.

FWIW if the pedals are not turned smoothly but instead see a brief but violent push for a small fraction of the turn when pedalling (as often happens with some less experienced cyclists) this also mitigates against precession, in addition to the lack of grease, poor spindle design and lack of tightness.

I'd suggest a thread repair insert could 'make good' here. Best to drill/tap out from the back, given the damage at the entry side of the pedal eye.

BTW has anyone got a good idea why FSA 'tempo' cranks are the shape they are near the pedal eye? Just fashion...?

cheers
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NATURAL ANKLING
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Re: Pedal Problem

Postby NATURAL ANKLING » 22 Jun 2020, 11:02am

Hi,
I never use pedals with incomplete shoulders.
You tend to find these in the cheaper end of the market, That is to say that they are easier to manufacture.
Keep the threads clean.
Degrease the crank thread with a solvent like white spirit.
Use a piece of old towels et cetera and wind it into the hole, repeat until it's very clean.
Wipe off the pedal threads And make sure they are nice and clean.
Use a wire brush if necessary
You should then be able to assemble the pedal into the crank with your fingers?
If not inspect the pedal threads for any burrs.
It's common to see a burr on the end of a pedal thread where the pedal has been dropped onto the concrete.
Ease carefully with a triangular Swiss file.
Re-try the pedal into the crank.
any attempt to use a tap on the crank threads, must be accompanied by a cutting fluid/compound.
Aluminium tears terribly if you don't use a cutting agent.
Once you can screw the pedal in with your fingers when it's all dry and clean.
Add grease to the pedal threads.
I have tools that go back about 40 odd years plus, but I find that "silver line "15 mm combination spanner is quality enough for this job.
At around £2 £2.50, You can also buy a spare.
As said they need to be pretty tight but you need to use Grease.
Normally it would never be advised to Grease threads unless the makers manual says so, but bicycles are exceptions in the fact that certain threads do need to have grease on them.
Failure to use grease means that corrosion might make it impossible to remove your pedal.
On pedal cranks, the mounting face for the pedal shoulder is not machined, So it's very common for this face not to be flat or perpendicular to the threads.
If you wind a pedal on to the crank Nip it up then remove and there is a burr on one side Only then the likelihood is it is not perpendicular to the thread.
You need to remove the crank and put it in a vise And flatten carefully with a smooth file.
Re-try the pedal just nip it up and look for witness marks.
Of course if your pedal does not have a continuous shoulder you are likely to see nice crunchy marks instead!
Shoulderless pedals horrible things.
It's prudent to remove your pedals clean and re-Grease at least once a year if not more.
I have never managed yet to remove a pedal from a crank with just the Allen key?
it's very common to see pedals that are just a finger tight from new bikes from the cheaper end of the market, Halfords mechanics is an elite job, but I'm not sure about the vast majority of the recruits........
NA Thinks Just End 2 End Return + Bivvy
You'll Still Find Me At The Top Of A Hill
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Samuel D
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Re: Pedal Problem

Postby Samuel D » 22 Jun 2020, 1:10pm

Shimano’s instructions for installing pedals confirm the grease (page 13):

https://si.shimano.com/pdfs/dm/DM-PD0002-07-ENG.pdf

I agree there doesn’t seem to be much grease in the photos, but when plenty is applied, most is displaced anyway – especially if the pedal is moving radially because it’s not tight. So although it would look better with more grease, would it function better?

There isn’t much sign of torque on the pedal flats either.

This is a new 2018 Giant Contend 2 bought from a bike shop in the north of England and shipped to my brother in the south, since he couldn’t find a bike down there for love nor money.

Brucey wrote:BTW has anyone got a good idea why FSA 'tempo' cranks are the shape they are near the pedal eye?

Could the shape be to distract from their using the same blanks for a variety of crank lengths? These are 172.5 mm.

Brucey
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Re: Pedal Problem

Postby Brucey » 22 Jun 2020, 8:51pm

Samuel D wrote: ….I agree there doesn’t seem to be much grease in the photos, but when plenty is applied, most is displaced anyway – especially if the pedal is moving radially because it’s not tight. So although it would look better with more grease, would it function better?


well I wonder if there was much grease at all, for similar reasons; I'd expect to see a ring of displaced grease at the back of the crank if there had been a liberal quantity on both parts. If there was just a smear on the pedal only then the inboard threads are usually wiped clean by the time the pedal is screwed in. This presumably further reduces the chances of precession.

cheers
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alexnharvey
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Re: Pedal Problem

Postby alexnharvey » 22 Jun 2020, 9:10pm

Is grease better than anti seize for this?

Brucey
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Re: Pedal Problem

Postby Brucey » 22 Jun 2020, 10:09pm

alexnharvey wrote:Is grease better than anti seize for this?


probably not, but I doubt anyone has done a controlled experiment to prove it. In theory precession relies on rolling contact rather than sliding contact alone, so past that some lubricant is better than none, it may not be that important what lubricant exactly.

cheers
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MikeDee
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Re: Pedal Problem

Postby MikeDee » 29 Jun 2020, 4:04pm

Looks like cross threading damage to me (stripped threads, damage to one side of the pedal face...)

Samuel D
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Re: Pedal Problem

Postby Samuel D » 29 Jun 2020, 6:05pm

MikeDee wrote:Looks like cross threading damage to me (stripped threads, damage to one side of the pedal face...)

Are you talking about my brother’s pedal? And by “pedal face” do you mean crank face? The reason for the damage being more pronounced on one side of the eye than the other is that he pushes the pedals harder than he pulls them. He obviously rode with a loose pedal.

I have since walked him through installing new pedals on new cranks with a torque wrench via videocall. He now realises he didn’t tighten the old pedals to anywhere near the right torque. As for grease, they arrived from the bike shop with grease on the threads. That was all the grease involved. No washers were supplied.

Lessons learned the hard way.

Tim DH
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Re: Pedal Problem

Postby Tim DH » 1 Sep 2020, 3:16pm

So here is the solution I've gone with.... Adding to my travelling kit:

An extra long 6mm allen key to drive the pedals in with (50g) AND a pair of sawn off pedal axles, (allen key ends) (22g) just in case I need to drive out alu swarf from the cranks (again) a long way from home. I begrudge the weight penalty, but this seems to be the lightest and cheapest option.

I'm guessing that, since alu cranks are not designed/engineered for frequent/regular pedal insertion/removal, I will encounter problems again sooner or later, and I'll need to replace the cranks ... My hope is M U C H later!

Thanks for all your thoughts/suggestions

Tim DH
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rjb
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Re: Pedal Problem

Postby rjb » 1 Sep 2020, 7:03pm

It might help to cut a couple of slots across the threads of your "tap" with a hacksaw. .ie in line with pedal axle. This may help it to cut its way past any imperfection :wink:
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin, Raleigh 20, Falcon K2 MTB dropped bar tourer, Longstaff trike conversion on a Falcon corsa. :D

Brucey
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Re: Pedal Problem

Postby Brucey » 1 Sep 2020, 7:22pm

playing devil's advocate here, is there really much benefit in carrying the pedal ends? IME the pedal spindle threads need to be cleaned of any swarf regardless of the state of the crank. Once cleaned the pedal spindles can also be chasers; they are so much harder than the crank is.

The crank can nearly always have the pedal inserted from the back side (indeed this is the direction you should use any chaser from too) and the thread can be cleaned/chased that way; provided the pedal spindle isn't much shorter than the crank thickness, the crank thread can be treated that way.

FWIW if the crank threads are not badly damaged, a non-cutting chaser is probably the best thing; a cutting chaser (or tap) will always remove material which is not always ideal if you have not got much to start with.

cheers
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Tim DH
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Re: Pedal Problem

Postby Tim DH » 4 Sep 2020, 9:21pm

Ah Brucey!
That was my original problem!! … Out on the road I discovered that pedals DON'T travel through Alu cranks far enough from the backside. The thread on the pedal can’t reach the abused thread in the front side of the crank to straighten it out. Hence, as an insurance policy, I’ve reluctantly added the two sawn off pedal ends to my travelling kit.
To save people scrolling back, our tandem deconstructs, allowing it to fit into a suitcase, which permits us to use public transport. Taking pedals on and off is a regular thing!
Anyway, it is now about three months since the last pedal failure, so here’s hoping…….

Tim DH

Brucey
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Re: Pedal Problem

Postby Brucey » 4 Sep 2020, 10:43pm

mad thought; because the thread on the pedal spindle is undercut near the shoulder, the first couple of threads in the crank don't actually do anything much. This being the case, you could counterbore the cranks to about 1-2mm depth and lose nothing in the way of threads; this might then be enough to allow the pedal thread to reach the other side from the back...?

Just a mad thought anyway.

cheers
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