Raleigh71

For the life of me, I can't get the front derailleur adjusted on the bike so that I get to use all 3 chainrings. I'm not exactly a neophyte at this but I'm about to give up and just use the 2 chinrings and forget about the granny gear.

The crank is slightly warped I'm aware, but this seems to be some other issue.

I tried moving the derailleur up and down the seat tube, which didn't seem to help.

I tried angling it a bit in or out in addition to perfectly parallel, which didn't help.

I used the fine tension adjustment on the grip shifter to no avail.

I have the 2 stop screws all the way out so that's not the issue.

The only thing I can think of is: I replaced the original Shimano FC M16 crank with a newer Shimano FC M410 crank. Is it possible there's some incompatability??

operator

So what you're saying is that the derialleur doesn't drop the chain to the granny. Is that correct? Othwerise i'd say you're adjusting it wrong if you have both the limit screws backed off. That won't ever shift properly. https://www.parktool.com/repair/readhowto.asp?id=75

Raleigh71

That's correct: either I get the granny gear and the intermediate gear or no granny gear and the 2 larger chainrings. Can't get all 3. It's close but no dice. And BTW: I'm doing all the adjustments on a repair stand.

operator

No hits came up for your original crank so i'm going to assume that the new crank may have required a different bb length - throw the chain in the middle chainring and into the middle of the cogset. Chainline should be straight in this combo. If someone actually has the BB specs for both cranks you can verify this rigorously.

Raleigh71

Thanks! I'll give it a try.

Before mounting the new (actually new to me but used) crank, I measured it very, very carefully and it seemed identical but the tolerances on these things are so tight.

Raleigh71

The straightest chain line seems to be on the largest freehub cog when using the middle chainring. That tells me the chainrings are set in a little closer into the frame, and mebbie this crank was designed for a slightly longer crank axle.

operator

Here is the tehdoc for those cranksets: https://cycle.shimano-eu.com/media/te...9830667768.PDF

It's supposed to tell you what length you have to use but it doesn't for only *your* crankset there. Someone should investigate this more thoroughly - also note the recommended front derailleurs.

Raleigh71

Thanks for the info!

My crank axle is LP-26 which is 113 mm long with 68 mm internal. I think it's the right crank.

I'll mess with it a little more...

Raleigh71

Success!!