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
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
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 ..
 

linklemming

Well-Known Member
In a last ditch effort to fix my drivetrain side loosening crankarm problem, I decided to try blue 242 loctite. I see lots of pros/cons on its use for crankarm bolts but figured what the heck. After 200 miles I had planned on reporting success tonight.

Wasnt going to be, about 12 miles from home the left pedal felt really weird and I looked down and could see it was REALLY loose. Tightened it several times and it got to the point that I couldnt even go a mile. At one point while tightening, it suddenly got easier to tighten (Im guessing the crankarm split). At that point, I couldnt use the crank at all without loosening and focused all my weight on the right side. The left side crankarm never had any issue up to this point.

Throttle saved me today, only way to get home. That being said, neither of my brose mid drives would fail this way as they are not using the obsolete square taper BB design. I hated the ride home using the throttle only.

Lucikly I ordered a second erider BB with crankarms so I will try those tomorrow. I am also going to try a set of crankarms for a shimano 6100 mid drive which look compatible.

So I decided to come home and replace the rear tire and true rear wheel on my iZIP moda E3 with 4k miles. Rim had fractures in several spots focusing around spoke holes but also further towards the outside of the rim like possible fractures from less than perfect hopping up curbs which are steep out here in CO.

I bought a park truing stand/dishing gauge and spoke tension gauge in anticipation of going to wider 27.5 wheels on the GMAC build. Looks like this was a wise choice as trying to find a quality 27.5 built rear-wheel at a less than $500 price seems pretty hard. New spokes, nipples and a WTB bikepacking rim cost about $140 for one wheel (I bought parts for 2 wheels though).

So 2 ebikes down, glad I have 2 more
 

Spaghetti888

New Member
Region
United Kingdom
You might be able to convert to disc brakes, I did it on my Zaskar about 10 years ago.

For the front, just buy a new fork with disk mounts. When my zaskar wasnt my primary MTB anymore I put on a rigid disc fork. I bought a suspension fork awhile back (rockshox reba) that had both canti and disc brake mounts.

For the rear, you could use the A2Z adapter. I used this for over 9 years on my Zaskar. Its big, bulky and fiddly but works
View attachment 68199

I knew this could cause problems with a hub motor so I recently got an adapter specifically for the Zaskar
View attachment 68200

I still might have fitment issues, we will have to see
Hi,
Is this adapter custom-made? I'm interested in exactly this thing as I have non-disc frame too. The A2Z looks tempting - I have a rear hub conversion on an aluminium frame and I use the eyelets to mount torque arms. How is yours working? If it's a viable option, I may see about getting one made up that also functions as a torque arm. Yes, I could get a new frame, but I really like this one.
 

linklemming

Well-Known Member
Hi,
Is this adapter custom-made? I'm interested in exactly this thing as I have non-disc frame too. The A2Z looks tempting - I have a rear hub conversion on an aluminium frame and I use the eyelets to mount torque arms. How is yours working? If it's a viable option, I may see about getting one made up that also functions as a torque arm. Yes, I could get a new frame, but I really like this one.
I originally had the a2z adapter. It was pretty commonly used back when I bought it in 2007ish, Its very fiddly to get setup/aligned but I used it for 13 years. It only has a hole sized for a QR skewer so you would have to drill it out.

Depending on your skills and patience, you could likely even use it as a torque arm.

I felt it would be too much work so I used the other adapter that I found on ebay (the black adapter on the silver frame). That design while frame specific was soooo much nicer and simpler. In the end, it interfered with the GMAC torquearm
 

Spaghetti888

New Member
Region
United Kingdom
I originally had the a2z adapter. It was pretty commonly used back when I bought it in 2007ish, Its very fiddly to get setup/aligned but I used it for 13 years. It only has a hole sized for a QR skewer so you would have to drill it out.

Depending on your skills and patience, you could likely even use it as a torque arm.

I felt it would be too much work so I used the other adapter that I found on ebay (the black adapter on the silver frame). That design while frame specific was soooo much nicer and simpler. In the end, it interfered with the GMAC torquearm
Thanks for the info - very useful. On the Zaskar, did you have to drill the mounting holes to the dropout plate? The A2Z looks quite secure with the four bolts - I'm a bit unsure about whether two eyelets would hold a caliper well? Mind you, they're good enough for a torque arm so in assuming it wouldn't have too much issue. This is the torque arm I'm using. The way the dropout space was cut into it means I have to mount it in a weird way which covers up the second eyelet. The mudguard struts are quite far out which pinches the mudguard itself up top. I'm looking to devise an all-in-one solution.
If I have a plate cut, it would be secured in the two eyelets above the dropout, plus the nut on the axle itself - should be fine right?!
Sorry for the threadjack...
 

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linklemming

Well-Known Member
So Im at about 700 miles now so its time for some updates.

Overall absolutely loving the bike. Definately my most powerful bike and so far has taken everything I have thrown at it. I mostly ride it at 1.5x assist averaging about 200human watts although the extra power is nice when required like today when a cold front blew in and I just wanted to get home as fast as possible using 5x assist.

Ironically, Im not much of a throttle guy but find myself using it alot to make downhills faster. No waiting on gravity to speed up :cool:

Finally got all the parts/tools to build my own wheels and glad I did as I noticed rear wheel rim stress cracks on 2 of my other ebikes so at this point, the tools have pretty much paid for themselves (assuming $100 for a wheel build).

So upgraded wheels from 26inch to 27.5 inch (it was always the plan)

Going from 26x2.35 to 27.5x2.6 smartsams was quite a noticable change in ride quality(both at 30psi although I will ride the 2.6 at 25psi eventually). The tire clearance was just about perfect and didnt require the 'monkey nuts' shown in post #84. There was a 3/4 inch bb height increase but thats fine since the bb height was pretty low with the 26inch tires at 11.8inches.

Put on some new miranda crankarms since the previous set became toast due to loosening. About 6 rides on these new crankarms and they seem to require tightening after every ride. I initially marked the bolt/crankarm with paint and have had to increase them about 3/4 of a turn at this point (note that the bolts dont unscrew). Im torquing them to 35ftlbs which on the high side for a square taper crankarm bolt.

Also bought a set of bafang bbs02/bbshd crankarms (super cheap) and a set of shimano FC-E600 crankarms to try in case the miranda cranks dont work out. All these crankarms have about the same q factor.

So, all is perfect except for loosening crankarms. Hopefully I can get this working soon as well.

Ordered a second throttle to play with regen and ordered a battery powered light that will connect to the CA easily.
https://ebikes.ca/shop/electric-bicycle-parts/lights/roxim-x4-ebike-light.html

For the price, the SPL-01 is likely a better light but I dont need a primary light that bright(I have several 850 lumen offroad lights in my camelback) and wasnt sure if the daytime running leds were always on (sometimes I want total stealth)
https://ebikes.ca/shop/electric-bicycle-parts/lights/spl-01-1900-lumen-ebike-light.html
 
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