new bb/crank on retro mtb help

[backontheroad]

Hi

I recently decided to fix my old mtb from the early 90s. Changed all the gearing on it with new stuff

Seem to be having problems with the front crank derailleur and bb set up

Old gearing was shimano ct-90 altus crank 38t /derailleur - bb 116mm spindle

New gearing fc-m131 crank with recommended un55 122.5mm spindle with fd m190 as a result the chainline is way off

Anyone here can help with their knowledge?

 

[NeilM]

Re:

Welcome to the forum.

Have you changed the bottom bracket? If not, that is where your problem is.

If you have, then something else is amiss.

 

[backontheroad]

Re: Re:

Welcome to the forum.

Have you changed the bottom bracket? If not, that is where your problem is.

If you have, then something else is amiss.

Thanks

Yeah I put in the 122.5 recommended by the crank manufacturer, it throws the chainline angle way off

Going back to the original 116mm bb bottoms out the FD

Not sure what to do

 

[FluffyChicken]

By way off, what do you mean?
You may need to alter you front mech limit screws and realign the indexing.
It could have moved to the modern 50mm chainline (the old wide chainline)
So everything is just ~2.5mm further out.

Though the tech docs say this shouldn't be the case and it should be at 122.5

which leads me back to ..
By way off, what do you mean?

 

[backontheroad]

By way off, what do you mean?
It could have moved to the modern 50mm chainline (the old wide chainline)
So everything is just ~2.5mm further out.

The chain line angle is parallel from the front to the back on the old original 116mm bb sitting around 45 mm region from seat tube to middle rings

On the 122.5 bb , the crank from the middle crank ring is sitting around 50+ mm mark

"way off i mean" - chain has a a fair amount angle and stepped out from the front relative to the rear resulting in fair bit of grinding noise on the teeth when on the outer crank ring

Yeh sounds like the fronts stepped out to the new 50mm chainline

Should i space the rear freeehub extra 2.5mm?

Or i could try in between 118mm bb?

 

[spike3]

We need pics