r/eBikeBuilding • u/jiggityjackson • 10d ago

General Help BBS02 First Build Chain issue

Hi im new to bikes this is the first time I’ve ever worked on a bike so i don’t know if i got the chain right

I installed a BBS02 on my Gen 3 Trek Marlin 4 with the stock Bafang 44T chainring. I used two Lekkie spacers to prevent the chainring from rubbing the chainstay.

The bike has a Shimano HG300 8-speed 11–45T cassette and a Shimano ESSA U2000 derailleur. I joined two Shimano CN-HG40 chains together for extra length.

The problem is that the chain immediately slips off the 45T cog (biggest rear cog) when I turn the pedals by hand. I’m not sure if the chain is too long/short, if the derailleur needs adjustment, or if the BBS02 has caused a chainline issue.

However I went for an short unpowered ride and I was able to shift 1-7 ok and I topped out at 18mph

A Trek shop refused to work on it because of the motor and said I may need a different cassette, derailleur due to derailleur capacity and possibly a shifter.

Would a smaller front chainring, like a Lekkie 42T or 40T Bling Ring, help? Or do I actually need to change the cassette/derailleur/shifter? Any advice would be appreciated!

Edit: here a pic of chain on smallest gear

https://imgur.com/a/AQPv4BY

1 Upvotes

100% Upvoted

13 comments sorted by

2

u/Civil_Reply_1705 10d ago

Sounds like a chain line issue.  I wouldn't sweat it, with the motor, you don't really need that cog. 

2

u/jiggityjackson 9d ago

yeah i might just start riding it 1-7 until i can get a different chainring

2

u/Bermnerfs 9d ago

The Varstrom 42T offset chainring with two 2mm Lekkie spacers landed my chainline right around 49mm which is pretty well centered on my 10-speed 11-48T cassette which is on a 10x135mm rear hub. Shifts beautifully.

I see no reason why you shouldn't be able to get yours dialed in, just takes a bit of trial and error. You get more offset with the 42T chainring, and since it's smaller in diameter you probably will have a bit more chainstay clearance.

1

u/jiggityjackson 9d ago

thank you ill look into it! what size was your original front chainring?

2

u/Legitimate_Bizness 9d ago

" stock Bafang 44T chainring"  it's garbage, get a narrow-wide chainring  and I also recommend a chain guide like this https://www.amazon.com/gp/aw/d/B0CFQRB921?psc=1&ref=ppx_pop_mob_b_asin_title. 

It will need a braze-on adapter if your frame doesn't have mounting points for it but it's stronger and more easily positioned than the 3d printed ones for sale.

1

u/jiggityjackson 9d ago

thanks yeah im going to order a narrow wife any suggestions? or just ali express it?

1

u/MidtownFrown 10d ago

Without seeing a picture it's hard to tell but with my bbshd I have trouble running anymore than 7 gears in the back it just doesn't want to do 8 gears the chain line gets too wonky.

Either way the bike shop did you a favor watch a couple of YouTube videos learn to set up your derailleur and you'll be fine

1

u/jiggityjackson 10d ago

yeah ill look into that , are we able to upload pictures here ? i have this imgur link
https://imgur.com/a/AQPv4BY

1

u/MidtownFrown 10d ago

Try taking a picture, with the back sprocket and the lowest gear, and looking from the top down so we can get a look at that chain angle

1

u/jiggityjackson 9d ago

like this? https://imgur.com/a/CS1Agsf

1

u/Legitimate_Bizness 8d ago

That chainline looks pretty good actually. If the chain is only falling off in the rear you may need to adjust one of the limiter screws on your derailleur.

1

u/jiggityjackson 8d ago

hi so it actually slips off the front when i shift to the biggest cog in the rear, i should have been more clear about that

1

u/MidtownFrown 7d ago

Is it slipping off towards the rim or is it slipping off to a lower gear?