Advice Needed - Pedel Sheared Off Crank Arm - Images Included

[rogerzilla]

Assuming it's a square taper crank, the fitting bolts for the crank to the bottom bracket axle need to be torqued to about 45Nm and re-checked about 100 miles later. Pedals should be fitted to the same 45Nm torque.

A bike shop will have the torque wrench and crank extractor needed to do this properly.

[colin54]

I think this may have been caused by the type of pedals you are using from studying your first picture.
Pedals keep tightening in use by precession forces as you pedal, it's why there is a left hand thread on the left hand pedal, the pedal is always tightening slightly on the crank in the direction of the bike's travel.
Looking at your first picture it appears you have the type of pedal that has the spanner flats on the pedal spindle in contact with the crank arm . What can happen with this type of pedal is that the pedal starts to tighten itself by precession as you ride along, but the flats on the pedal spindle dig into the crank arm and stop it doing this by digging into the arm and raising a burr. These precessive forces have to go somewhere and then start to fret the threads and can cause the problems you are experiencing.
If you continue to use this type of pedal you need to fit pedal washers between cranks and pedals, and also as mentioned up-thread ensure the pedal thread is greased, preferably with a copper anti-seize grease. The alternative is to use a pedal with a full circular shoulder between the pedal flats and crank. I'd never heard of this issue until I read this linked post by Brucey a while back. I subsequently looked out for it on my bikes fitted with this type of pedal. Here's a couple of pictures I took to illustrate the point.
viewtopic.php?p=867213#p867213
Picture 1, burr being caused by edge of pedal spanner flat.

Picture 2, consequent damage.

I filed these cranks flat and refitted using pedal washers and had no further problems (touch wood) ,I have subsequently fitted pedals of the full shoulder type hence rendering the use of washers redundant. I think a new set of pedals might not be a bad idea with your new crankset.
Picture 3,full shoulder pedal.

Good luck.

[Pebble]

I have once had this happen to me and I have often wondered if the fact I had not tightened the pedal on properly was the cause?, it only got tighten finger tight [1] and I thought to my self 'well thats OK as the precession forces will tighten it'. about 30 mile later the pedal destroyed the crank as per the OP.

Do precession forces ever tighten stuff, they certainly can slacken stuff.

[1] i was in a hurry and I could not find the spanner, the pedal tightened fully in (so was not cross threaded),

[Cycling_Man]

I think this may have been caused by the type of pedals you are using from studying your first picture.
Pedals keep tightening in use by precession forces as you pedal, it's why there is a left hand thread on the left hand pedal, the pedal is always tightening slightly on the crank in the direction of the bike's travel.
Looking at your first picture it appears you have the type of pedal that has the spanner flats on the pedal spindle in contact with the crank arm . What can happen with this type of pedal is that the pedal starts to tighten itself by precession as you ride along, but the flats on the pedal spindle dig into the crank arm and stop it doing this by digging into the arm and raising a burr. These precessive forces have to go somewhere and then start to fret the threads and can cause the problems you are experiencing.
If you continue to use this type of pedal you need to fit pedal washers between cranks and pedals, and also as mentioned up-thread ensure the pedal thread is greased, preferably with a copper anti-seize grease. The alternative is to use a pedal with a full circular shoulder between the pedal flats and crank. I'd never heard of this issue until I read this linked post by Brucey a while back. I subsequently looked out for it on my bikes fitted with this type of pedal. Here's a couple of pictures I took to illustrate the point.
viewtopic.php?p=867213#p867213
Picture 1, burr being caused by edge of pedal spanner flat.
P1100322.JPG

Picture 2, consequent damage.
P1100289.JPG

I filed these cranks flat and refitted using pedal washers and had no further problems (touch wood) ,I have subsequently fitted pedals of the full shoulder type hence rendering the use of washers redundant. I think a new set of pedals might not be a bad idea with your new crankset.
Picture 3,full shoulder pedal.
P1130651.JPG
Good luck.

Thanks for getting back to me. I think you are right about the damage being caused by the pedel from your description. I was planning on upgrading the pedels to clip-ins but I literally just got the bike. Got it yesterady and took it out for a 5k little test ride and this happens which is super annoying since I now have to fork out a lot for replace parts and haven't even used the bike haha. Do you happen to know or have a link to somewhere that can explain the pedel differences as I'm not too sure on the difference pedels as I don't want to buy pedels that will do this again. Do you also happent to know how much this will cost to fix. You say you had this issue so was wondering what the damage to the wallet was aswell for you as I just want a heads up before haha.

Thanks for your help, Cycling_Man.

[Cycling_Man]

I have once had this happen to me and I have often wondered if the fact I had not tightened the pedal on properly was the cause?, it only got tighten finger tight [1] and I thought to my self 'well thats OK as the precession forces will tighten it'. about 30 mile later the pedal destroyed the crank as per the OP.

Do precession forces ever tighten stuff, they certainly can slacken stuff.

[1] i was in a hurry and I could not find the spanner, the pedal tightened fully in (so was not cross threaded),

Hi thanks for your reply.

Could you explain to me what you are trying to say what you say

Do precession forces ever tighten stuff, they certainly can slacken stuff.

Because after that sentence you say you were in a hurry so couldn't find a spanner to tighten the pedels and then the pedals got tighetned while riding which would answer what you said above surely that precession forces do tighten things. I might just be reading this wrong so if you could explain it a bit that would be great, thanks.

Also since you have had the wsame issue as me before what did it cost you to fix this, what did you have to get changed/do and how did you stop it from happening again.

Thanks, Cycling_Man.

[colin54]

Most ,if not all Shimano pedals (for instance) have a full shoulder as far as I know. It just depends what type of pedal you require, SPD, clip-in with cleat (requires a special shoe), flat pedals (normal shoes), older style toe clips and straps pedals- (normal shoe).
There are various other types of clip-in pedals as well - more road racing orientated ones. I prefer flat pedals with any old shoe, but that's just my preference. You can also get pedals with SPD fitting on one side and flat on the other.
If you google 'Which pedal cycling uk forum ?' it comes up with loads of threads on the subject. Here's one for example from that search, there are plenty more...
viewtopic.php?t=51785

When fitting a pedal it need to be done up sufficiently tight as any other threaded item, you may notice
precession at work when it comes time to remove the pedal as you may need to use more force or indeed a longer pedal spanner to remove. I think as Pebble unfortunately found out, doing it up finger tight is not sufficient.I imagine the movement between the threads meant the precession forces did not come into play in the same mannner as with a correctly tightened pedal.
In my picture number 1 up-thread, that is the non-drive side, left hand pedal, this has a left hand thread (tightens anti-clockwise ; imagine if it had a normal right hand thread the precessive forces at work whilst pedalling forward would tend to loosen it.

[gaz]

The fix your bike voucher would give you £50 towards a repair. i think this is the best way forward in your circumstance.

The bike fix vouchers are released in tranches, the most recent release was in March. They are taken up at considerable pace and are rarely available after much more than 24 hours. I don't know the date (if any) for the next batch. Not every bike shop/repair service subscribes to the scheme.

The Spa crank arms linked earlier are undoubtedly a bargain and the pictures suggest they are the correct BCD. It seems reasonably likely that the existing cranks and bottom bracket are square taper, neither that nor the existing BB being a suitable length can be guaranteed.

Not every bike shop/repair service is thrilled by the idea of fitting parts you have bought elsewhere, even less so should the new parts prove to be incompatible with the old.

If the OP needs a quick fix, he should take it to his chosen bike shop/repair service as it is for a quote and timescale to get it fixed and back on the road.

If the OP has more time and wants to acquire his own tools and learn how to do the job himself, he should continue to seek advice here.

[peterb]

Just a note about pedal washers - don't buy special 'pedal washers', you'll find they are £2 to £3 each!! Just buy washers of the correct size online. I use alloy sump plug washers.

[colin54]

Not every bike shop/repair service is thrilled by the idea of fitting parts you have bought elsewhere, even less so should the new parts prove to be incompatible with the old.

If the OP needs a quick fix, he should take it to his chosen bike shop/repair service as it is for a quote and timescale to get it fixed and back on the road.

If the OP has more time and want to acquire his own tools and learn how to do the job himself, he should continue to seek advice here.

That sounds like good advice to me. most bike shops aren't in the business of ripping 'people off' I don't imagine (the OP's concern in his first post), but they have to earn a living. At least if a bike shop repairs it, it gets him going for now.

[Pebble]

Because after that sentence you say you were in a hurry so couldn't find a spanner to tighten the pedels and then the pedals got tighetned while riding which would answer what you said above surely that precession forces do tighten things. I might just be reading this wrong so if you could explain it a bit that would be great, thanks.

Also since you have had the wsame issue as me before what did it cost you to fix this, what did you have to get changed/do and how did you stop it from happening again.

Thanks, Cycling_Man.

The pedal was only finger tight and within 30 miles I had destroyed the crank in the same way as in the OP. My guess is the problem arose as the pedal was not tightened fully when fitting ? (I thought it would tighten itself when riding - but it must not of ?)

to fix, I bought a second hand crank from local bike shop for a fiver, and fitted the pedal correctly by tightening it on with a spanner.

[Pebble]

I think as Pebble unfortunately found out, doing it up finger tight is not sufficient.I imagine the movement between the threads meant the precession forces did not come into play in the same mannner as with a correctly tightened pedal.

yes very likely - finger tight will have left a little play, may be a hundredth of a mm in the first 100 yards, but with steel going into soft alloy that play would expand rapidly, and yes precession would not happen.

have found the picture of the damage I done, I probably limped about 10 mile after I knew the pedal was failing, it eventually fell out...


The threads on the pedal were fine and I just fitted it into the next crank

[Cycling_Man]

The fix your bike voucher would give you £50 towards a repair. i think this is the best way forward in your circumstance.

The bike fix vouchers are released in tranches, the most recent release was in March. They are taken up at considerable pace and are rarely available after much more than 24 hours. I don't know the date (if any) for the next batch. Not every bike shop/repair service subscribes to the scheme.

The Spa crank arms linked earlier are undoubtedly a bargain and the pictures suggest they are the correct BCD. It seems reasonably likely that the existing cranks and bottom bracket are square taper, neither that nor the existing BB being a suitable length can be guaranteed.

Not every bike shop/repair service is thrilled by the idea of fitting parts you have bought elsewhere, even less so should the new parts prove to be incompatible with the old.

If the OP needs a quick fix, he should take it to his chosen bike shop/repair service as it is for a quote and timescale to get it fixed and back on the road.

If the OP has more time and wants to acquire his own tools and learn how to do the job himself, he should continue to seek advice here.

Hi thanks for getting back to me.

I actually took it to a few places today and decided this one bike shop would be the best. He was the friendlies and most helpful out of them all and he told me that the BCD is 110 he believes and it is a square tapered bottom bracket. The other bike shops only seemed to tell me that they would have to replace the whole chainset, chain and back gears, which would be costly and said that it would be hard to find the lwrt. Well this guy got back to me like 2 hours later and said that he thinks he found a part for it.

The crank arms you suggested would be good. However the website now states they have stopped shipping to Europe so would be unable to get these. He got back to me quick like I said above a linked a set that looked good. The only downside is that they are silver and not black which is a little disappointing. Maybe you could happen to find some that are black but if I can't find any, which I can't right now then these will have to do o guess.

Here are the ones he linked - https://www.sjscycles.co.uk/cranks/sjsc ... set-170mm/

[Cycling_Man]

Because after that sentence you say you were in a hurry so couldn't find a spanner to tighten the pedels and then the pedals got tighetned while riding which would answer what you said above surely that precession forces do tighten things. I might just be reading this wrong so if you could explain it a bit that would be great, thanks.

Also since you have had the wsame issue as me before what did it cost you to fix this, what did you have to get changed/do and how did you stop it from happening again.

Thanks, Cycling_Man.

The pedal was only finger tight and within 30 miles I had destroyed the crank in the same way as in the OP. My guess is the problem arose as the pedal was not tightened fully when fitting ? (I thought it would tighten itself when riding - but it must not of ?)

to fix, I bought a second hand crank from local bike shop for a fiver, and fitted the pedal correctly by tightening it on with a spanner.

I see. When you say you got a second hand crank for £5 did you get the whole crankset, including the front chain rings or just the crankarm itself. Also did this happen to the left pedel as sadly it happened on my right pedel which is the one with the crank shaft. I took it to 3 places today and am thinking of going with this one guy who was very helpful. Two of the shops I went to said I need a new chainset, chain and most likely rear gears as they wouldn't work correctly. One guy quoted me something saying like "it's going to be upwards of a couple hundred quid". However the last guy I took it too actually spent some time looking at the bike and told me that I would need a new chainset but said there is a chance of finding the crank arms available. He also took a look at the chainset and said that I probably wouldn't need to change the chain yet even though it's worn a bit because the chainset teeth themselves actually looked pretty decent. He also said that I could just swapped over the cogs/teeth from the old chainset and place them onto the new chainset, saving the new teeth/cogs for when I do need to upgrade the chain. I really liked this guy because he seemed like he was actually trying to help and save me money which I thought was really good because as a person who doesn't know much about bikes I could be totally taken for a ride (if you parden the pun).

He then got back to me linking these cranks that would most likely fit the bike from his rough measurements. The only downside is that they are silver and not black but I guess it isn't the end of the world as they aren't too expensive and I can always upgrade the chainset later on if I wanted.

Here are the ones he linked me - https://www.sjscycles.co.uk/cranks/sjsc ... set-170mm/

It's annoying because they would be perfect if they were black haha.

[Cycling_Man]

Not every bike shop/repair service is thrilled by the idea of fitting parts you have bought elsewhere, even less so should the new parts prove to be incompatible with the old.

If the OP needs a quick fix, he should take it to his chosen bike shop/repair service as it is for a quote and timescale to get it fixed and back on the road.

If the OP has more time and want to acquire his own tools and learn how to do the job himself, he should continue to seek advice here.

That sounds like good advice to me. most bike shops aren't in the business of ripping 'people off' I don't imagine (the OP's concern in his first post), but they have to earn a living. At least if a bike shop repairs it, it gets him going for now.

I went to a few bike shops (3 in total) and I'm glad I did. The last guy I went to was further away but I definetly believe I am going to be going with him. He was friendly and actually showed interest in helping. Taking a look at the bike and telling measurements so I could find parts myself. I didn't even say that I would go with him, he just told me the things I needed to know if I wanted to find parts and he could fit it. I didn't even ask this but he stright up said that if I wanted to find my own parts he would be more than happy to fit them. I can run them by him so he can double check if they are the right part too. The other shops I took it too told me that I would need a whole new chainset basically, new front crankset, chain, and rear set and one guy quoted me saying something like "it's going to cost upwards of a couple hundred". I didn't really like this guy much as he wouldn't really let me get a word in to tell him what I wanted. I know he is the expert but I coudln't even tell him something. After he stopped I managed to ask him if I could just get new crankarms to use and he basically said that it would be pretty hard to find this part.

The last guy I took it too was the complete opposite though. He told me that from what he sees the teeth on the front crankset look good and a new one would work with the old chain. He even messaged me two hours later with a crankset that didn't include chainrings and said that he could just place the old chainrings onto the new crankset and wouldn't have to change anything else. I really like the fact that he is working with me and value that he isn't trying to "rip me off".