BBSHD - Luna Eclipse offset adapter idea

I moved the Luna BBSHD motor kit and parts over to another bike

Everything was great except the Luna Eclipse 42 tooth chain ring was hitting the chain stay
It needs about 6 mm reverse/positive offset to make it clear

Shimming the motor out away from the BB is not an option with my 120 mm BB and 120 mm BBSHD motor
Shimming the chain ring out 6 mm with spacers will not work
The chain ring would be hanging out in the air without any center support

The chain ring is only a couple weeks old and I really want to be able to use it again
In the mean time, I am using a Luna mini 30 tooth chain ring
It's a great chain ring, but not enough offset and not enough top end with an 11 tooth cassette gear.

So I came up with an idea to make an adapter to add 6 mm positive offset to the motor-chain ring
6 mm lets the chain ring just barely clear my frame

I made a mock up adapter out of plastic to test the concept
It looks to me like this idea will work if made from 7075 aluminum.
I would have to find a machine shop with a lathe because I only have a small hobby lathe

Or maybe Luna thinks this is worth a look?

Here's the mock up and how it works

The video has a full explanation and shows detail of how it looks on the bike

[youtube]u04NICHEQ5Q[/youtube]

Hi you made the job harder then you need .

Just take out 6 mm from chianring it take 1 min on lethe

It look like 2 part chian ring.
Sould cost $10 for that mod.

Best of luck

aCeMadMod said:

Hi you made the job harder then you need .
Just take out 6 mm from chianring it take 1 min on lether.
It look like 2 part chian ring.
Sould cost $10 for that mod.

Best of luck

Click to expand...

Hard to tell what you are suggestion with all the misspelled words?
If you are suggesting to machine the chain ring itself, that's not an option because of the way it is constructed

You cant spit chian ring ? Into 2 parts
Upload pics

Did you try ?

aCeMadMod said:

You cant spit chian ring ? Into 2 parts
Upload pics
Did you try ?

Click to expand...

Yes the chain ring splits apart
Both half's have a ridge and a groove that fits into each other
they are not two flat surfaces
It's more complex that you realize

I've never seen how those chain rings go together. My first thought would be to separate the parts and flip over the hub, but I guess that won't work. Your spacer idea should work if everything fits.

fechter said:

I've never seen how those chain rings go together. My first thought would be to separate the parts and flip over the hub, but I guess that won't work. Your spacer idea should work if everything fits.

Click to expand...

The Luna chain ring is machined in a really clever way.

The outer ring and inner hub have a groove and a tongue that fit together perfectly
This keeps the two parts perfectly aligned in a perfect circle
The 7 screws just pull the two half's together

Without that tongue and groove fit, it would be possible to pull the outer ring out of round away from the hub body when under a large amount of stress from the chain

Plus, the outer chain ring is replaceable, so I would not want to alter the inner hub or the outer ring
The replacement chain ring would not fit on the hub

And you could not remove enough material from both half's in order to get the offset I need.
The 7 screws would not have enough screws threads left to hold the two half's together properly any more

There's a bunch of reasons machining the Luna chain ring is not an option.

I will fool around with the adapter idea some more
No hurry on that, I am using the Luna 30 tooth chain ring for now

Ok, here is the adapter, fresh off the lathe

I have to get some longer 5 mm bolts today and then I can test it with the 42 tooth Luna eclipse chain ring

Does the crank arm still fit with the adapter in place. Good pictures, but the last one made me wonder.

E-HP said:

Does the crank arm still fit with the adapter in place. Good pictures, but the last one made me wonder.

Click to expand...

Good eye!
I had to put it back on the lathe this morning and chamfer the inside area where the crank arm goes.
It was touching just a bit, and the chamfer did the trick

I went to Lowes and got some longer 5 mm bolts

I'll be doing a test ride tonight

Here's what it looks like mounted

I ran into another issue when trying to shift to my lowest gear
My 9 speed chain is too short for the 42 tooth chain ring and a 34 tooth cassette cog.
The 9 speed Chain and cassette were from a bike I had many years ago
They were used to test this setup only
I used to shorten the chains quite a bit when I have mountain bikes with multiple chain rings up front

I need that 34 tooth cog for the big climbs here in the mountains
Actually, I could use a bigger cog than 34 teeth

I have to get a new chain anyway, so the test run will have to wait
And a new cassette if I can find the right one

Came out nice. Which cog does the chain line up with for an exact straight chain line?

E-HP said:

Came out nice. Which cog does the chain line up with for an exact straight chain line?

Click to expand...

Loos like the 5th cog up from the smallest 11 tooth is a straight chain line

I can probably go back to 9 speed now
I did have it set as a 7 speed because of the bad chain line with the 30 tooth Luna mini

I ordered a 9 speed KMC chain with 116 links
And a Sun Race 11-40 tooth 9 speed cassette

It will be a couple days before I can test out the 42 tooth Luna ring

I put the 30 tooth ring back on for now

I got to get out and test the 42 Tooth Eclipse ring with the adapter shown above.

Did 28 miles with 2000 feet of climbing.
Everything went smoothly.

The new 11-40 cassette had enough low end on the steepest stuff I did.
The 11 tooth had enough top end for my fat bike.

I tested the top speed into a strong headwind on a flat section
It hit almost 36 mph which is more than enough speed for me.
So I consider this project a success.

Good day, I’m having the same issue with my Luna chain ring, would you make a few spacers to sell? If you will I would gladly pay for one. My email is razored52.gh@gmail.com. Thanks.

Razored said:

Good day, I’m having the same issue with my Luna chain ring, would you make a few spacers to sell? If you will I would gladly pay for one. My email is razored52.gh@gmail.com. Thanks.

Click to expand...

Sorry, no can do
That was a huge amount of work to make that one.
My lathe is not large enough to do easily