Ebike crank arms

General Discussion about electric bicycles.
Post Reply
Philaphlous   1 kW

1 kW
Posts: 431
Joined: Mar 28 2017 7:17am

Ebike crank arms

Post by Philaphlous » Jan 31 2018 9:10am

Hey guys....need some help here.

I've got an electric trek 80C sport (basically an 800) and one of the torque arms is completely destroyed by myself for not being able to screw in the pedal...I know there's a right hand and left hand thread for each. I also destroyed a cheap aluminum pedal when I wrecked my bike last year...like half the pedal is still in tact.

In order for me to ride the bike and actually pedal I need a new crank arm. I believe it's the left one that is not on the side of the sprocket. Id like to replace these and possibly with cheap crank arms...? I'm not sure if I need a square or rhombus hole crank? Does anyone know. And it seems eBay has mostly left crank arms...not right? What gives? The crank arms aren't attached to the sprocket so they're very similar except for the pedal screw direction...

Thanks guys! I'd love to get this fixed because this is the #1 issue why I don't ride my bike right now. Im point to spend under $20 also.

User avatar
MadRhino   100 GW

100 GW
Posts: 5864
Joined: Sep 03 2010 5:28pm
Location: Montreal QC Canada

Re: Ebike crank arms

Post by MadRhino » Jan 31 2018 11:07am

You need the same, ideally. Another might have slight differences in lenght and width, that you will feel and find bothering.

Usually, they are available unless very old. Yet a whole used crank of a better quality can be found pretty cheap.
Make it fool-proof, and I will make a better fool.
Current bikes
Street: https://s20.postimg.org/ewrvugywt/Session_04_2015.jpg
Dirt: https://s20.postimg.org/lbqwr55ml/IMG_0157.jpg

User avatar
efMX Trials Electric Freeride   100 kW

100 kW
Posts: 1387
Joined: Feb 15 2013 4:43pm

Re: Ebike crank arms

Post by efMX Trials Electric Freeride » Jan 31 2018 11:43am

since the bike is made by Trek then you should be able to take it to a trek dealer or your local bicycle shop for repair.. damaged pedal threads on your crank arm can likely be repaired by installing a "helicoil" replacement thread insert.. if the cranks are shimano brand then check the back side of the crank arm for the manufacturer part number.. on a trek 800 or similar level bike it probably has square taper cranks and crank axle spindle.. any pics of the damage??
some ride & sk8 videos:
metacafe.com/channels/NATAS666DAMIEN
http://www.youtube.com/natas666damien
i have nothing for sale.. :)

User avatar
dogman dan   100 GW

100 GW
Posts: 34929
Joined: May 17 2008 12:53pm
Location: Las Cruces New Mexico USA

Re: Ebike crank arms

Post by dogman dan » Feb 01 2018 9:16am

I can only google up trek 80c without motors. A link for exactly what you have would get you more specific answers.

80c appears to be a dirt jumper, while 800 is the common steel mtb that is a great choice for hubmotor conversions.

If its a hub motor bike, you just need to match the type of crank, and can easy enough replace both sides. New or used.

By this I mean mtb type crank for mtb, road crank for road bike, etc, and of course the type of spindle. On less expensive mtb's, almost always a common square taper. You will need the crank remover to properly get it off the bike, or have a shop pop it off for you. Look of course, for the length of crank you want, particularly if you replace only one side. 175mm is common, but some bikes have other lengths, 170,165 or whatever. the length will be stamped on the inside of the crank, facing the frame.


If its a mid drive, then chances are you need a factory replacement part. It could be anything for the spindle, including a crank with internal freewheel.

Philaphlous   1 kW

1 kW
Posts: 431
Joined: Mar 28 2017 7:17am

Re: Ebike crank arms

Post by Philaphlous » Feb 03 2018 9:10am

I'll get a picture up today. I'd rather buy a new one.id probably end up spending more to fix it at a shop in my area. Standard of living is like 60% higher in my area that the rest of the country...gotta love Bethesda Maryland!

Philaphlous   1 kW

1 kW
Posts: 431
Joined: Mar 28 2017 7:17am

Re: Ebike crank arms

Post by Philaphlous » Feb 04 2018 11:26am

Looks like a 170mm length. The threads are totally destroyed. I even tried to drill 2 holes through the crank arm and pedal to keep it attached with no luck...

Image

User avatar
efMX Trials Electric Freeride   100 kW

100 kW
Posts: 1387
Joined: Feb 15 2013 4:43pm

Re: Ebike crank arms

Post by efMX Trials Electric Freeride » Feb 04 2018 1:34pm

Philaphlous wrote:
Feb 04 2018 11:26am
Looks like a 170mm length. The threads are totally destroyed. I even tried to drill 2 holes through the crank arm and pedal to keep it attached with no luck...

Image
looks like it says Suntour / 170
so now you know the brand and length..
next you will need a crank arm puller for square taper cranks in order to remove the crank arm from the bike.. maybe call your local bike shop and ask them for the cost of removing the arm for you verses the cost of the needed tool, probably close to the same price.. assuming that you order the correct tool and crank arm then the tool will only be used once.. whereas if you go to the bike shop then this should ensure that everything fits and is tightened to recommend manufacturers spec so that it shouldn't happen again..
if you decide to fix it yourself then you will need to remove the crank fixing bolt with the correct size socket or allen wrench.. then tread in the puller securely with lots of thread engagement, then screw in the puller bolt.. the puller bolt will then push on the spindle thereby backing the crank arm off the spindle..
some ride & sk8 videos:
metacafe.com/channels/NATAS666DAMIEN
http://www.youtube.com/natas666damien
i have nothing for sale.. :)

User avatar
Chalo   100 GW

100 GW
Posts: 7961
Joined: Apr 29 2009 11:29pm
Location: Austin, Texas

Re: Ebike crank arms

Post by Chalo » Feb 04 2018 2:23pm

Is this a mid drive you're dealing with?

If so, you might have the arms on the wrong sides. RH thread is on the right, LH on the left, which is opposite from the bottom bracket threading. If you switch them around, normal pedaling forces will tend to unscrew the pedals.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

User avatar
efMX Trials Electric Freeride   100 kW

100 kW
Posts: 1387
Joined: Feb 15 2013 4:43pm

Re: Ebike crank arms

Post by efMX Trials Electric Freeride » Feb 04 2018 3:11pm

the pedals are usually labeled R and L, check at the end of the pedal axle for this.. also the pedals should tread into the crank easily most of the way by hand, then require a long wrench to tighten securely.. be sure to grease the pedal threads and crank spindle before installation..
some ride & sk8 videos:
metacafe.com/channels/NATAS666DAMIEN
http://www.youtube.com/natas666damien
i have nothing for sale.. :)

Philaphlous   1 kW

1 kW
Posts: 431
Joined: Mar 28 2017 7:17am

Re: Ebike crank arms

Post by Philaphlous » Feb 04 2018 5:34pm

I have a pulley puller and so I'll use that to pull off the crank. I'll have to take a look to see if its the L or R...they're identical except for one has the left hand turn threads...

Philaphlous   1 kW

1 kW
Posts: 431
Joined: Mar 28 2017 7:17am

Re: Ebike crank arms

Post by Philaphlous » Feb 08 2018 3:59pm

FYI just wanted to update the thread...
I took the bike out this am and was able to confirm I have a square hole. I ended up ordering a 175mm square crank arm. Same brand. Hopefully it fits. Lol. I don't think I'll notice the 5mm difference but we shall see. I also ordered a badly needed suspension seatpost too so I'm slowly upgrading my bike. My biggest upgrade this year will probably be a suspension fork on the front and a neaw rear tire...that is if I end up using this bike this year for my work commute.
I've got another thread open in the ebike technical and if I can enable regen this bike is going to be amazing...just saying.

I'm working on another project at the same time...vinyl wrapping my skis! Oh yea...those will be sweet!

Raisedeyebrows   1 kW

1 kW
Posts: 391
Joined: May 13 2017 1:39pm
Location: Oregon/South Point Hawaii USA back and forth

Re: Ebike crank arms

Post by Raisedeyebrows » Feb 09 2018 12:03am

You want both cranks arms the same length, send it back.
Yuba Mundo w/BBSHD
Specialized Hard Rock w/9c clone, statoraid, hubsink
Trek Fuel 90 w/BBSHD
Above all run on 14s4p 52v li-ion
Ecobike folder 36v
Currie Flyer scooter 24v on 24ah of SLA

Every trip made with electric bike is one less car trip, saves money, no toxic fumes, less noise, less impact on roads.

User avatar
Chalo   100 GW

100 GW
Posts: 7961
Joined: Apr 29 2009 11:29pm
Location: Austin, Texas

Re: Ebike crank arms

Post by Chalo » Feb 09 2018 12:52am

For what it's worth, one of the crank arms of my Bafang BBS02 came loose and the square hole was damaged, so I replaced both with a set of very inexpensive unicycle cranks, which were narrower and shorter (making it easier for me to pedal quickly along with the motor).
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Philaphlous   1 kW

1 kW
Posts: 431
Joined: Mar 28 2017 7:17am

Re: Ebike crank arms

Post by Philaphlous » Feb 10 2018 3:39pm

Dumb....ordered the crank arm. Received it today...it's the wrong one. Picture and description says 175mm and square taper. Ends up being a rhombus and 165mm... Thats crap. Sending that one back and already ordered another one thats definitely a 170mm length square taper... Ugh. Well at least I won't be riding anytime soon.

WoodlandHills   10 kW

10 kW
Posts: 748
Joined: Nov 11 2015 12:27pm
Location: Ortega River, JAX, FL

Re: Ebike crank arms

Post by WoodlandHills » Feb 10 2018 3:58pm

Steel unicycle crankarms are only a couple of dollars each and will never bend. Who cares about weight=it's an ebike!

Philaphlous   1 kW

1 kW
Posts: 431
Joined: Mar 28 2017 7:17am

Re: Ebike crank arms

Post by Philaphlous » Feb 11 2018 7:09am

Funny story...this entire time I thought I had a trek 80C sport.... The sport part covers some of the last 0 so I just always thought it was a C...well I don't think it is. Lol so I've got a trek 800 Sport. Ha. What's strange is I can hardly find any detailed specs on them. I took out my seatpost thinking I had like a 27 or 27.2 post and ended up finding 29.2 on the stock post. Lol.

I'm hoping a little down the road I can pick up a suspension fork for my bike. I've read all the reasons why not to but there's too many compelling reasons why I need to get one...the ride on a hard front end is too nasty if I'm going to be commuting with this. Even a cheap pair of front shocks will be better

User avatar
dogman dan   100 GW

100 GW
Posts: 34929
Joined: May 17 2008 12:53pm
Location: Las Cruces New Mexico USA

Re: Ebike crank arms

Post by dogman dan » Feb 11 2018 7:31am

I had suspected same, you have a trek 800. You will need to figure out the size of the headset to replace the fork.

It will be either 1" or 1 1/8" . Not tapered.

Buk___   10 kW

10 kW
Posts: 750
Joined: Jul 28 2017 5:59pm

Re: Ebike crank arms

Post by Buk___ » Feb 11 2018 9:19am

dogman dan wrote:
Feb 11 2018 7:31am
It will be either 1" or 1 1/8" . Not tapered.
According to the blue book it's 1 1/8".

Post Reply