My new Custom GMAC build

linklemming

Well-Known Member
Well, Im guessing the drive side crankarm is toast as even when the crankarm bolt is torqued down to 390inlbs, it loosens up. It took 60 miles before it started making noise and sure enough the bolt was loose.

I used square taper BB and cranks for over 10 years back in the day and never had this issue. I did have an old suntour crank get so used that the tapper got enlarged so that the bolt would bottom out before the crank was tight enough but that was over 3 years of hard offroad use and constant removal/mounting as I wore BBs out alot in those days due to excessive bike washing getting dirt in the BB. Even the 'known to be soft' bafang crankarms I used for my for my TSDZ2 to get a lower q factor held up fine (at least until the TSDZ2 bearings became junk).

Im guessing the extra paint or powder coating on the inside of the square taper hampered me getting them good and tight

The miranda 0 qfactor cranks sold with the erider kit dont seem to be easily available in the US so I just decided to order another torque sensor from grin. Probably not a bad spare part to have anyway. Supposedly they are a good part as they are used on alot of bikes. Might order a spare set from england although Im still researching other options.

I also noticed that the chainring had a bit of runout (inside/outside wobble). I thought I had fixed this earlier but Im guessing I didnt mount the spider the same way. While it could be a machining issue, the easiest answer would just be uneven powdercoat/paint.

Pretty sure Im going to remove the powder coat or paint on the new spider just to be safe.

So new order from grin for the spare erider torque sensor and a set of spokes for a 27.5 wheel if I decide to use those wheels on this frame.
 
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AHicks

Well-Known Member
I have that same issue with the drive side crank arm loosening on my new Ultra powered bike - it's only taking about 10 miles to start making noise after tightening. It's been tightened 3 times now. Your mention is the first I've read about any issue like that. Interesting. Wondered about paint or some other contaminant on that taper too. That, or maybe the arm is cracked or something. Sounds like I'm going to have to take it apart now....
 

linklemming

Well-Known Member
Decided to do a whole ride in the 'legal' preset on mostly paved bike paths. Basically only up to 3x assist, 750watts and 20mph. I wanted to keep the watts high in case I really want to put in some human power if need be.

A very pleasant bike to ride, basically silent(smart sam tires were louder). I basically felt like I was riding a regular bike, only faster. About 11.5wh/mile at 1.5x assist 90% of the time. Avg speed of 16mph is pretty good for the wh/mile, total mileage of 25.3 miles. If I dont turn up the assist, this would be good for just over 40 miles.

Whats really notable is the behavior as you reach 20mph limit, no feeling of hitting a brick wall, you just dont seem to go much over 20mph unless you really try

Probably a good thing today as I hit a deer tonight on a section where I am usually really flying. I see deer in this area every now and then and they look like they are watching traffic to figure out when to cross (they seemed focused on the other side on the 4 lane highway with concrete center divide). Because of all the car lights, I dont think they can distinguish my lights (the bike path parallels the highway). They always seem surprised. So I came up on this deer about 20mph, I slowed down to about 10mph and when my handlebar was about even with his rump, I yelled at him as he didnt seem to notice me. He was on concrete and decided to try to take off and go across my path (like they always do). Of course he had no traction like a dog running/stopping on a slick tiled kitchen floor, so he was trying with all fours to go but was just wasnt. Of course I was maximum braking with the rear wheel just sliding a tad and I tagged him on the rump at about 5mph. No harm done but its a funny vision I will remember for awhile.

Good news is that my monkey brain maximum braking skills are spot on, all the mental gymnastics required for regen just seems like it would change this
 
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linklemming

Well-Known Member
I was able to test fit a 27.5x2.6 smart sam on a 24mm inner width rim/wheel. Definately not the best rim in actual use though but all i had lying around. The tire measured only 2.3 mounted on this rim. A true 2.6 tire would be a really close fit with the wheel all the way forward in the dropout.

Luckily being a horizontal dropout, you can just move the wheel back. Surly sell monkey nuts to make alignment easy.
surly-monkey-nuts-v3.jpg

With this nut, its apparent I could have a much bigger tire as the 2016 redesigned troll can take a 26x3.0 tire so 27.5x2.6 or even 27.5x2.8 tires are in my future. The cantilever brake mounts do get in the way but 1 minute with a dremel and they are gone.

Forgot to mention, I bought a second torque arm from grin so I will make a nicer cleaner torque arm mount.

The GMAC moto does push the rear brake rotor out as far as the spec probably allows. The caliber was at the limit of in/out adjustment so a minute with a file on the caliber bolt holes and the disc is now centered between the pads.
 
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linklemming

Well-Known Member
I put the smartsam 27.5x2.6 on a 35mm inner width rim and it only measures 2.42 so it will likely work without the monkeynut mentioned in the previous post
 

drewberz

Active Member
Well, Im guessing the drive side crankarm is toast as even when the crankarm bolt is torqued down to 390inlbs, it loosens up. It took 60 miles before it started making noise and sure enough the bolt was loose.

I used square taper BB and cranks for over 10 years back in the day and never had this issue. I did have an old suntour crank get so used that the tapper got enlarged so that the bolt would bottom out before the crank was tight enough but that was over 3 years of hard offroad use and constant removal/mounting as I wore BBs out alot in those days due to excessive bike washing getting dirt in the BB. Even the 'known to be soft' bafang crankarms I used for my for my TSDZ2 to get a lower q factor held up fine (at least until the TSDZ2 bearings became junk).

Im guessing the extra paint or powder coating on the inside of the square taper hampered me getting them good and tight

The miranda 0 qfactor cranks sold with the erider kit dont seem to be easily available in the US so I just decided to order another torque sensor from grin. Probably not a bad spare part to have anyway. Supposedly they are a good part as they are used on alot of bikes. Might order a spare set from england although Im still researching other options.

I also noticed that the chainring had a bit of runout (inside/outside wobble). I thought I had fixed this earlier but Im guessing I didnt mount the spider the same way. While it could be a machining issue, the easiest answer would just be uneven powdercoat/paint.

Pretty sure Im going to remove the powder coat or paint on the new spider just to be safe.

So new order from grin for the spare erider torque sensor and a set of spokes for a 27.5 wheel if I decide to use those wheels on this frame.

One thing to check for are the bottom bracket shell faces, which typically need to be cleaned up on new frames (from paint and some aren't square :confused:). Paying a LBS with the proper tool is well worth it:


@AHicks worth considering too.
 

linklemming

Well-Known Member
One thing to check for are the bottom bracket shell faces, which typically need to be cleaned up on new frames (from paint and some aren't square :confused:). Paying a LBS with the proper tool is well worth it:


@AHicks worth considering too.
What would the advantage be if your BB bearings spin fine? Of the 5 bikes I have built from a frameset, none have needed this. I understand the need, I just havnt needed it.

FWIW, I have been subscribed to Hambini on youtube for awhile (the youtube BB misalignment guru)

Surly recommends using a boxcutter to get the paint off mating surfaces, My surly troll didnt require this
 

E-Wheels

Well-Known Member
The GMAC kit looks to be of high quality and would be a good fit to the host bike I’m considering to use for a home build project
Anyone know if Grin still ship their kits internationally (i.e. Australia)
I have emailed them directly on several occasions but they never reply
 
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Timpo

Well-Known Member
The GMAC kit looks to be of high quality and would be a good fit to the host bike I’m considering to use for a home build project
Anyone know if Grin ship their kits internationally (i.e. Australia)
I have emailed then directly on several occasions but they never reply

"We will gladly welcome orders from pretty much anywhere in the world. The map below shows where some of our recent customers ordered from; all over the USA, Canada, Europe, Australia/NZ, and even South Africa and Korea. Interest in ebikes is poised to be a global phenomenon but hasn't caught on in many places, and if you can't find a local source for your parts yet we'll be glad to help you out."
 

E-Wheels

Well-Known Member

"We will gladly welcome orders from pretty much anywhere in the world. The map below shows where some of our recent customers ordered from; all over the USA, Canada, Europe, Australia/NZ, and even South Africa and Korea. Interest in ebikes is poised to be a global phenomenon but hasn't caught on in many places, and if you can't find a local source for your parts yet we'll be glad to help you out."
Thanks Timpo
I saw that page but didn’t know if it was still relevant given things have gone crazy in this COVID age, hence my reaching out to them
However I’m not comfortable placing an order until I get some acknowledgment of my enquiry
 

Timpo

Well-Known Member
Thanks Timpo
I saw that page but didn’t know if it was still relevant given things have gone crazy in this COVID age, hence my reaching out to them
However I’m not comfortable placing an order until I get some acknowledgment of my enquiry
Ah I see. Yeah I don't know how covid will affect their shipping ..