Harhir

I need to replace the front derailleur sprockets of my recumbent bike. The outer two are worn pretty bad after over 20 years. I have a few questions since I have never done that:
- Are these sprockets universal to fit to the crank arms I have?
- If yes can I just replace the sprockets or do I need to replace the crank arms as well?
- Any brands to choose or to avoid?
They are 52, 42 and 24 teeth sprockets.
And last but not least: is the right crank arm center bolt left or right threaded?
Thanks




Thanks

soyabean

Your chainring is not proprietary. You can find new parts.

Just the rings. Crank arm is good.

Unless you do some sort of extreme enduro olympic UCI racing, any compatible part will do.

Check your LBS. They have these in stock, and yes, your LBS is fine selling parts to DIY

JanMM

I would imagine the bolt circle diameter (BCD) of the two larger rings is 130 and that the inner ring’s BCD is 74. Measure to be sure.
https://www.sheldonbrown.com/cribsheet-bcd.html
You’ll need to source matching middle and large rings. Ramped and pinned for better shifting.
Crank arm fixing bolts should both tighten clockwise.

Harhir

Thanks guys that helps a lot. You learn something new every day. I will do some measurements to get the correct BCD. I should be good from here.
And that Sheldon Brown Website has been a savior to me so many times. I hope it will get maintained going forward.

dedhed

Just to make it clear when you are looking for replacements you are looking for chain rings for a crankset or chainset not "front derailleur sprockets".
Using the term front derailleur sprockets will get zero hits searching or a WTF look at the LBS

Harhir

Yes that was my bad. Lol. I now know what they are called.

soyabean

Just bring your whole bike to your LBS and they will sell you what you need to DIY.

You'll save a lot of time because they will match all the exact parts you need.

It might cost a few dollars more, you agree that is worth the instant service.

cxwrench

"Instant service" and "a bunch of bike parts" don't necessarily go together these days. We have TONS of stuff in stock but I wouldn't be able to put 3 matching triple chainrings together at this time.

soyabean

Sorry, my bad.

Let's not support our LBS and just buy everything on amazon so Jeff can get air miles to outer space

cxwrench

If we can't get the parts I'm not going to just send the potential customer away. I'll have them try to find the parts and we'll do the work. We've been doing this for the whole of Covid. It's a minor inconvinience but their bike gets the work it needs.

70sSanO

Just to back this up a bit. I’m not familiar with a Lightning brand crankset. It kind of looks like a Truvativ/Bontrager ISIS crank, but it could be square taper.

Guessing as others have mentioned a BCD of 130mm for outer and middle, probably a 74mm BCD inner. 5 bolt cranksets are not that popular these days, except lower end. As such it might be in your best interest to look into a higher quality chainrings.

I would look at TA Specialties chainrings. Peter White used to sell them and they can also be found at UK sites.

Occasionally I’ll find older NOS chainrings on eBay, but the prices are becoming outrageous. However, I would look for an NOS Shimano SG steel ring for the 24t as it will last longer than aluminum; which is nice since you’ll have to pull the crank to replace the inner ring.

Finally now might be a good time to re-assess if you really want a 52t/42t outer/middle. You can technically go down to a 38t with a 130mm BCD, a 39t might be more common. Maybe a 48t or 50t if you don’t use the 52t in the highest ratios.

John

JanMM

It’s a Lightning Phantom recumbent bike, which explains Lighting on the crank arm.

Harhir

I measured them last night. Yes these are 130 BCD. I actually only need to replace the two outer ones. The inner one is still good. I think the previous owner only used the two outer ones. I however almost exclusively use the middle one which gets the most wear. The inner one occasionally on inclines but I have never used the outer change ring one so far. It is still as worn as I bought the bike 5+ years ago.
I will check with my LBS today but I doubt they have any. They don't have many parts in store. And last time I ordered a derailleur through them it took two weeks to get delivered to the store and then it took them one week to unpack.

dedhed

If it's just the two outers you can probably replace them without removing the crank arm. You might want one of these.

​​​​​​https://www.rei.com/product/750478/p...B&gclsrc=aw.ds

But if you're going to be doing work you might also want to remove the crank and see if the bottom bracket could use service or replacement

bboy314

If you’re having trouble finding chainrings in stock at shops, you can also check eBay, I’ve had good luck finding a cheap new or NOS triple crankarm or set with the right bcd and tooth counts and just using the chainrings. Something like this may work (double check the specs):

https://www.ebay.com/itm/Nashbar-Dri...-127632-2357-0

alcjphil

Looking at the large chainring in the above photo, I don't believe that it is even close to being worn out. Large chainrings outlast smaller ones by a large margin. That some teeth appear to look different than others is by design to aid in shifting. I would look at replacing only the middle ring which should cost much less than the large one