New Chain Rattling.

[Smokin Joe]

As the problem only started when a new chain was fitted, I'd go with a stiff link as my first port of call.

 

[Ajax Bay]

Frequency of rattle (see OP) is associated with crank (ie cadence). How would a stiff link (in the new chain) mesh with that?

 

[silva]

Could it be that the chainring shows some lateral movement at a max at its circumference (flexing) under tension, causing chain links engaging then under a less straigth chainline?

 

[nmfeb70]

Hi again, just took the bike out on a smooth & safe road and looking down I noticed the rear mech cage seemed slightly bent (as suggested by @Mike_P) and the chain was rattling and jumping. I also checked the bolts on the front chainring and while three were tight, the other just kept turning.
So I'll start with a new rear mech and see what happens.

 

[Ajax Bay]

a rattle occurs when the drive side pedal reaches the downward position.

The symptom described suggests a slightly misaligned chainring. As well as checking that, I'd check that all the chainring bolts are tight.

that suggests the problem is with the chainrings, or something at the front. Possibly bent / misaligned chainrings as above,

Frequency of rattle (see OP) is associated with crank (ie cadence).

I noticed the rear mech cage seemed slightly bent (as suggested by @Mike_P) and the chain was rattling and jumping. I also checked the bolts on the front chainring and while three were tight, the other just kept turning.
So I'll start with a new rear mech and see what happens.

The rear mech is nothing to do with the symptom you describe in the OP. Think about it.
What do mean: oneof the chainring bolts "just kept turning"? Did you get it tight? That loose one is the cause and aligns perfectly with the symptom described in your OP (I have emboldened the text above) and commented this 6 days ago. Once you get that or its replacement secure: job done: ride on, rattless.

 

[nmfeb70]

The rear mech is nothing to do with the symptom you describe in the OP. Think about it.
What do mean: oneof the chainring bolts "just kept turning"? Did you get it tight? That loose one is the cause and aligns perfectly with the symptom described in your OP (I have emboldened the text above) and commented this 6 days ago. Once you get that or its replacement secure: job done: ride on, rattless.

I thought you would come back with a reply along those lines. I hope to prove you wrong.😁🚴

 

[nmfeb70]

The rear mech is nothing to do with the symptom you describe in the OP. Think about it.
What do mean: oneof the chainring bolts "just kept turning"? Did you get it tight? That loose one is the cause and aligns perfectly with the symptom described in your OP (I have emboldened the text above) and commented this 6 days ago. Once you get that or its replacement secure: job done: ride on, rattless.

Ok, so the rattling is now happening around every 1/2 to 3/4 rotation and the chain & jockey wheels are bumping around. Could a double threaded chainring bolt cause this?

 

[Ajax Bay]

It's your rattle: keep it if you want. The chainring bolt are there for a reason: all 4 (or 5) or them. When you install the replacement, use thread locker on it.

 

[nmfeb70]

Ok guys, returning to the rattling chain and going on the advice given by @Ajax Bay, I'm going to replace the chainring as there are no bolts to tighten, just what look like welded pins? The aforementioned bolt which I said kept turning in my previous post was holding the chain guard in place.
It's a 24/34/42T so do I simply replace it with another part with the same number of teeth or do I have to consider other factors such as the BB? I haven't replaced this part before so I'd appreciate your advice.

 

[DaveReading]

It's a 24/34/42T so do I simply replace it with another part with the same number of teeth or do I have to consider other factors such as the BB?

As you will have noted from the post prior to yours, some chainrings have 4 bolts, some have 5. Make sure your new one matches the old.

 

[Ajax Bay]

Sounds as if this is a 'normal' MTB triple with all the rings rivetted to the cranks (OP threw us off track with the 'replace the chainring' and then the loose chain bolt wheeze). Looking from above, can you see any variation in the chinrings, moving a little from side? That'd link with the symptom (chain touching FD cage at one point only, per revolution).
If that's the issue, new chainset required: they are quite cheap (for the vintage and spec (assume square taper given age)) you have now.

 

[nmfeb70]

Hi all, due to an accident and an illness I haven't logged in for a while so I thought I'd let you know the outcome of the above problem.
It seems @Ajax Bay was correct, the problem was a worn/misaligned chainwheel refusing to play ball with the new chain. The bike then required a new freewheel in order for all three components to work in unison. Apologies for the late reply. Thanks again for the responses and hopefully this will help anybody who encounters a similar chain rattle.