Left pedal won't stay tight?

[mjr]

My left pedal won't stay tight. This isn't the first time it's happened to me on a bike. Would anyone like to suggest what I might be doing wrong? Shall I just use a bigger wrench and/or lean on it more?

[531colin]

Pedal washer? (stops pedals with spanner flats gouging the crank.....with the left pedal being a left thread, precession should tighten it)

[Brucey]

on few occasions where I've seen a pedal that comes loose in recent years, it has usually been a pedal which doesn't have a full base circle to it where it abuts to the crank. The pedal flats have gouged into the crank (leaving a visible mark) and this has seemingly then prevented the pedal from tightening further in service via precession as it should do.

As Colin says, using a pedal washer often helps.

cheers

[borderghost]

This is a problem i am slightly having on my carrera, after a week of use i decided to give it another quick check over to make sure all nuts/bolts were still tight, all was fine accept for the left pedal needed tightening, Did not think to much of it and went for a good 15 mile ride, when i got back i decided just to give it one last check but again it needed tightening, I was wondering if maybe I applied to much grease to the threads, I say grease but I actually used vasaline, I do have grease but it is dark grey and easily stains were as Vasaline is much clearer so i used that to lubricate the threads instead. What I am trying not to do is start checking it everyday as i can see myself getting into a never ending circle.

I have a pedal spanner in my lidl/aldi style tool kit, using this tool one handed can i give it pretty much all my strength in tightening or do i risk damaging the threads?, i used generous one handed force but did not strain myself so could put a bit more might into it if need be.

[Brucey]

pedals should self-tighten in use.

They won't do this if they cannot turn easily, and the #1 reason they won't do that is that the pedal bears badly against the crank arm. I would wager that in most such cases the pedals (if tightened correctly to start with) are ones which don't have a complete shoulder on the spindle but instead have flats that extend to the crank.

Good pedal;



less good pedal;



If you have the latter type of pedal spindle and the spindle has sharp edges, they gouge into the crank and raise a burr that prevents the pedal from precessing (self tightening) as it should do.

cheers

[mjr]

Yes, the problem pedal hasn't a shoulder. Pedals are such a flaming compromise between features that I never seem to find ones perfect in every way.

I've attached it with a longer wrench for now and will get a washer, as I doubt this will be the last similar problem.

[borderghost]

Mine was lose again today after approx another 70 miles, I though about how the pedal shoulder must get held in place by friction just like any other bolt,, i wonder if it is because my pedal shoulders have excess grease on from when i greased the threads, I removed the pedals and removed all the excess grease from the shoulders and crank, thinking that if there is grease between the shoulders and crank then this would cause a lot less friction and allow the pedal to work loose.

On my previous bso i never used grease at all on the pedal threads and never had a problem with pedals coming loose. Do nearly all others use grease on there pedal threads? I wonder if the likes of halfords bother applying grease when they assemble bikes.

Also I can understand that precessing will stop the pedal from unscrewing but surely it would not actually tighten a pedal with any force, If that was the case would that mean that someone who only tightens there pedals by hand could then go on a 50 mile ride and by the time they had finished the pedals would be nice and tight, surely precessing only has enough force to stop the pedal from unscrewing.

[PJ520]

In my experience you can't overgrease pedal threads, you certainly can under grease them and leave your pedal almost impossible to remove. I go along with those suggesting a washer.

A bit of trivia here. The LH thread on the left pedal was thought up by the Wright Brothers Scrroll down to "Cycling Innovations"

[[XAP]Bob]

Precession will actively, and strongly, tighten a bolt.

Similarly if fitted backwards (on a bodge tandem maybe) it will loosen even tightly fitted pedals (hence frequent use of thread locking compound in such cases)

[Brucey]

Mine was lose again today after approx another 70 miles..... i wonder if it is because my pedal shoulders have excess grease on from when i greased the threads...

Also I can understand that precessing will stop the pedal from unscrewing but surely it would not actually tighten a pedal with any force, If that was the case would that mean that someone who only tightens there pedals by hand could then go on a 50 mile ride and by the time they had finished the pedals would be nice and tight, surely precessing only has enough force to stop the pedal from unscrewing.

Grease doesn't hurt any. Precession does indeed tighten pedals; anyone who has flown with a bike will have experienced the 'incredibly tight pedal' syndrome after a week or two's touring/training.

However there are conditions that will reduce or even inhibit precession;

1) the 'barrier burr' thrown up by flatted pedals as described above
2) too much sliding friction in the screw thread (which is why grease helps, not hinders, and why chrome plated pedals self tighten more than others; they have very low friction)
3) a bad fit in the screw thread, or a damaged screw thread
4) an unusual pedalling technique eg where the power is low, and the weight of the leg is on the pedal on the upstroke as well as the downstroke.

Generally a steel-on-steel interface is fairly tolerant of all kinds of things but a steel pedal in an aluminium crank is rather less so. Often if the pedal has been ridden loose for any distance, 3) applies and after that you may have more trouble regardless. In extremis, use threadlocking compound on the screw thread.

BTW that the Wright bros may have invented the LH pedal thread is not widely accepted; I think that there are numerous examples that predate them.

cheers

[borderghost]

Could the paint on the crank are also be a problem? When i removed the pedal to remove some of the excess grease, i noticed some of the paint had been scraped away were the pedal shoulder makes contact with the crank.

[Brucey]

Could the paint on the crank are also be a problem? When i removed the pedal to remove some of the excess grease, i noticed some of the paint had been scraped away were the pedal shoulder makes contact with the crank.

kind of; this might well make a 'barrier burr' type situation too. Anything that removes paint unevenly certainly won't help...

cheers

[borderghost]

Could the paint on the crank are also be a problem? When i removed the pedal to remove some of the excess grease, i noticed some of the paint had been scraped away were the pedal shoulder makes contact with the crank.

kind of; this might well make a 'barrier burr' type situation too. Anything that removes paint unevenly certainly won't help...

cheers

Is this were a washer is the answer? Do most bike shops have pedal washers in stock, or should i be returning to halfords and get them to resolve under warranty as i have only had the bike a few weeks?

I wonder why as the original poster this seems to be more an issue with the left pedal, is there maybe slightly less precession on the left pedal or some other mystifying cause?

[Brucey]

definitely a warranty issue on a new bike.

Why the left pedal? Well my theory is that the pedal spindles are more likely to have a bad burr on one side than the other, and for whatever reason it seems like the left side is more likely to be that way right now.

You can buy pedal washers and this will fix it if the threads are not damaged, but you shouldn't have to do that on a new bike.

cheers

[borderghost]

Hi Brucey, this is the pedal in question, hoping you can see in the image what i mean about the pedal shoulder contacting the paint first, as i have had to tighten the pedal a few times now it has started to scrape/chip some of the paint away.
I have now tighten the pedal to my very near max strentgth using 1 arm on the pedal spanner and the other holding the crank still, if it continues i shall take it up with Halfords. How much strength do others put into tightening there pedals assuming you do not have a tourqe wrench to fit?