Grinding sound in lowest gear.

[MarcusT]

So, I do light repairs and tune ups for friends. After cleaning a tweaking my friends mountain bike, he said that while doing a steep uphill, he was in the lowest gear (smallest chain ring, largest rear cog), the crank started to make a grinding noise and was hard to pedal. When he told me this, I went to look at the MTB. I put the bike in every gear and pedaled all over town to see what the problem was and could not get that problem to occur. It could have been user error, but I take pride in my work and want to make sure the bike is 100%. Any idea?
The bike has a front derailleur with a bottom bracket mount.

[Heltor Chasca]

On one bike of mine, with 2.35s, the chain skims the tyre when the chain sways in the most extreme gear which makes an odd noise. Grinding muddy tyres maybe?

[Brucey]

one possibility is that the shifter was set to the smallest chainring (as per the indicator on the shifter), but the chain hung on to the middle ring instead. This makes a terrible noise, and on a steep climb, the chain may not derail if it has enough tension in it at all times.

Other possibilities are that

- the chain was part-way off the lower pulley in the rear mech. If this is the case there will be odd scrape marks on the mech)

- that the chain was touching the front mech; this may happen only under load (eg via flex in the chainset), so may only manifest itself when actually climbing a steep hill, and may vary with rider.

cheers

[NATURAL ANKLING]

Hi,
I like your commitment to riding bike, that's what I would do with motorcycles on the same course as owner.

As said it could be rider error or chain suck due to wear or faulty derailleur.
I had a problem recently with a bent front derailleur which I failed to spot

[MikeF]

the crank started to make a grinding noise and was hard to pedal.

one possibility is that the shifter was set to the smallest chainring (as per the indicator on the shifter), but the chain hung on to the middle ring instead. This makes a terrible noise, and on a steep climb, the chain may not derail if it has enough tension in it at all times.

Most likely answer I think.

[peetee]

+1
Wear in the chain and chainring, the chain likes it where it is, the downshift doesn't happen and the outer cage-plate on the front mech scrapes the chain.

[MarcusT]

So after a number of experiments and rides, I could not find any problem. I will conclude user error and leave it at that.

Thank you for the input

[NATURAL ANKLING]

Hi,
When a worn chain 0.75 - 1.0 % goes dry in use it will struggle to shift I have found, bit of oil revives it but its on the way out soon.
You did check the stretch even with a cheap gauge, how it sits on the large front chain wheel in a good indicator, can you pull chain off the teeth in middle run on the chain wheel?

[MarcusT]

Hi,
When a worn chain 0.75 - 1.0 % goes dry in use it will struggle to shift I have found, bit of oil revives it but its on the way out soon.
You did check the stretch even with a cheap gauge, how it sits on the large front chain wheel in a good indicator, can you pull chain off the teeth in middle run on the chain wheel?

Oil is definitely not the problem. This guy puts oil on his chain like a watering flowers.