Bafang bbshd on trek marlin 6 2022

[Biker3422]

I was wondering if a bafang bbshd would work properly on a trek marlin 6 2022 model because it has 10 speed cassete and a 30t front chainring. It has a 72mm threaded bb. I heard that people that used a 68mm bafang motor on a 72mm bb has had chain line issues and had to use spacers. This is discourging me from getting a bafang motor now. Please help.

[73Eldo]

Modern frame designs with a 1x drive and a 135mm rear hub will often have chain line issues. On these the stock chain ring is usually fairly small and tucked in pretty tight. The BBS and similar mid drives have a gear case that is about the size of a 30t ring. If you are lucky the gear case fits with no spacers but that still leaves the chain ring way further out then stock was.

On older bikes this was solved by using an offset chain ring that went over the gear case. These start at 40t which means you need more clearance on the frame which many new designs don't have. I did note on the 2022 specs they say you can go up to a 42 tooth in a 3x so in theory if you get a 42 tooth offset ring you should be able to get it in the stock location and have a decent chain line.

Which 42 tooth? Good question. The Lekkie has about the same offset as the stock Bafang 46 that comes with the HD's. The Luna Eclipse has another 6mm so that would be a lot of spacers if you only had room for a Lekkie but since here you know you have to be as tight as possible you would hate to be short. If you have the BBSHD in hand the stock and Lekkie the chain line ends up being about inline with the seam in the gear case. The Eclipse is closer to the inside of the case.

[ncmired]

Welcome to the forum - there are lots of (older) Marlin owners here, and I suspect your concern is valid.

Do you own the bike? If so, flip it onto the bars and take a well lit picture straight down at the BB, chain stay and chain ring area and post it here. But I'm guessing you are just thinking about the bike.

Here's some expansion on what 73Eldo posted.

Trek forgot to turn the studio lights on when taking their pics, and I wasn't able to find much of any elsewhere that highlighted the BB - other than this one for a 2021 Marlin 6 (maybe the same frame?):

I'm speculating this 2021 Trek Marlin 6 has a 2x8 drivetrain (with a spiffy loose BB cup). The Trek specs for the 2022 Marlin 8 say, "Max chainring size 1x/2x: 34T, 3x: 42T" - This spec doesn't bode well with the BBSHD's reduction gear case clearance from the chain stay. Especially with big fat chain stays that curve out not far from the BB weld.

There are two aftermarket 40T and 42T chainrings that offset significantly to the left (as much as mechanically possible), but if the reduction gear case can't clear the chain stay, they're for naught.

Here's some reduction gear case / chain stay clearance issues we don't want to see:

[from the knowledge base article]

Frames with flat plate chain stay sections can work well:

And there's this Jones frame designed specifically to clear the BBSHD reduction gear:

[Biker3422]

So what do i need to do exactly? Im more worried about clearance issues and chain line issues.

[Biker3422]

Welcome to the forum - there are lots of (older) Marlin owners here, and I suspect your concern is valid.

Do you own the bike? If so, flip it onto the bars and take a well lit picture straight down at the BB, chain stay and chain ring area and post it here. But I'm guessing you are just thinking about the bike.

Here's some expansion on what 73Eldo posted.

Trek forgot to turn the studio lights on when taking their pics, and I wasn't able to find much of any elsewhere that highlighted the BB - other than this one for a 2021 Marlin 6 (maybe the same frame?):

I'm speculating this 2021 Trek Marlin 6 has a 2x8 drivetrain (with a spiffy loose BB cup). The Trek specs for the 2022 Marlin 8 say, "Max chainring size 1x/2x: 34T, 3x: 42T" - This spec doesn't bode well with the BBSHD's reduction gear case clearance from the chain stay. Especially with big fat chain stays that curve out not far from the BB weld.

There are two aftermarket 40T and 42T chainring that offset significantly to the left (as much as mechanically possible, but if the reduction gear case can't clear the chain stay, they're for naught.

Here's some reduction gear case / chain stay clearance issues we don't want to see:

[from the knowledge base article]

Frames with flat plate chain stay sections can work well:

I do not have the bike. I was planning on buying the bike first and then converting it to electric. With the trek marlin 6 2022 model, it comes with a 10 speed so its a 1x10 and the 2021 model is a 2x8. Im not sure how would i fix the chain line issue.

[Biker3422]

I found a post of bafang mid drive installation on a 2021 trek marlin 6. This concerns me a lot.

[Biker3422]

Im only planning on getting a 42t version as i only wanted to go only 20mph max and im planning and doing daily communting with moderate inclines.

[73Eldo]

That post is lacking all the details it would need to be useful. Which BBS width was he using? Which chain ring(s)? What were the issues and where were the spacers needed?

That last photo with the maroon frame shows that seam in the case I was talking about. In the photo its a 36 or smaller ring. You can clearly see the seam in the gear case I was talking about that the Lekkie or stock rings get you to and how that would improve the chain line. You can also see how much further in the Luna Eclipse moves it in further.

Short of someone doing a build on the exact frame you are considering and sharing all the details you can't be sure about any conversion.

Another observation about that bike is the triangle doesn't look big enough for a decent battery especially the smaller sizes. Yes there are other places to mount a battery but they tend to put the weight up higher and take up places that you may want to use for other stuff.

[ncmired]

You're right, the maroon frame picture has a 36 tooth chain ring, and it will not clear either the 40 or 42 high offset chain rings - doesn't need to 'cause it's a Rohloff build with a 58mm (yeah baby!) chain line.

[ncmired]

Since there are no previous build attempts, you'd have to go look at the bike and do some measurements (see the knowledge base article).

Another kludge used to reduce chain line issues is to rearrange the rear sprockets, moving outward the low gears and reducing the gear choices

[Biker3422]

That post is lacking all the details it would need to be useful. Which BBS width was he using? Which chain ring(s)? What were the issues and where were the spacers needed?

That last photo with the maroon frame shows that seam in the case I was talking about. In the photo its a 36 or smaller ring. You can clearly see the seam in the gear case I was talking about that the Lekkie or stock rings get you to and how that would improve the chain line. You can also see how much further in the Luna Eclipse moves it in further.

Short of someone doing a build on the exact frame you are considering and sharing all the details you can't be sure about any conversion.

Another observation about that bike is the triangle doesn't look big enough for a decent battery especially the smaller sizes. Yes there are other places to mount a battery but they tend to put the weight up higher and take up places that you may want to use for other stuff.

Thats the thing. It would be useful if the person gave more info. I know that the trek marlin 2021 and 2022 model both share the same bb size which is VP BC73, 73 mm, threaded cartridge so the person must have bought a 67mm version of the bbshd to fit a 73mm bb. On the trek website, it says maximum chain size: 1x/2x: 34T, 3x: 42T

About the battery, I would be buying a medium sized frame so It should bit a somewhat big down tube battery. The person had a 17.5 inch frame and was able to put a 17Ah battery and I also asked the supplier said that it should be able to fit a Medium size bike.

[73Eldo]

Modern MTB geometry has the angled top tubes and then a high down tube presumably for front wheel clearance which makes the triangle smaller than on more classic designs so I would not just assume any battery will fit. Different types of batteries use different types of mounts which also effects how much space you need. The popular 'shark' types of packs have to side onto their mounts so need a few more inches of space than something like say a Luna Wolf that has a magnet and can pull sideways.

[Biker3422]

Since there are no previous build attempts, you'd have to go look at the bike and do some measurements (see the knowledge base article).

Another kludge used to reduce chain line issues is to rearrange the rear sprockets, moving outward the low gears and reducing the gear choices

Is there any other build attempts on the trek marlin 6 2021 model? Im sure they are some build attemps on the 2021 version that the 2022 version.

[Biker3422]

Modern MTB geometry has the angled top tubes and then a high down tube presumably for front wheel clearance which makes the triangle smaller than on more classic designs so I would not just assume any battery will fit. Different types of batteries use different types of mounts which also effects how much space you need. The popular 'shark' types of packs have to side onto their mounts so need a few more inches of space than something like say a Luna Wolf that has a magnet and can pull sideways.

The supplier said this should fit on a trek marlin 6 on a 17.5 inch frame.

https://custombuilt-ebikes.co.uk/product/52v-19ah-downtube-ebike-battery/

[Biker3422]

I dont if this helps but the trek marlin 6 and the trek marlin 7, they both share the same frame design.

[Biker3422]

I found this thread. This person did a build on a trek marli 7 not sure which year model but fitted a banfang bbshd and never had any issues with chain line without any spacers on either side and able to use all 9 gears.

link: https://electricbike.com/forum/forum...marlin-7-bbshd