Refit Original Chain Same Way - Or Backwards?
 

Apologies in advance for the basic question.

I took the chain off my old MTB for a quick degrease and clean. It's the type where you push the pin out with a removal tool. Now, am I best in putting the chain back on to run the same way as it was? Or, would it be better to put the chain on the other way around?

My thinking is that the forces and wear will be in different parts of the links and rollers if I put it on the other way. I'm presuming this would equalise wear and make the chain last longer. Or, as the chain is well used (but not worn), is it best running the way it always has, as it is bedded in this way, and will be happier?

You could be onto something. The rollers are always spinning and shouldn't be affected by chain direction. However, I think the pins don't spin freely, so the pressure and wear on the pins would affect them mainly on one side. Flipping the chain front-to-back would cause pins to wear on their opposite side, possibly extending chain life. I'll be interested to read what more knowledgeable people think.

The tension loads on the pins are the same forward or backward, so reversing the chain will have no effect.

However, if you think about it, you'll see that on the loaded part of the chain (top section), the chain only flexes in one direction, so the wear zone on the pins will be below the center line, with the most wear being roughly 5° below end on. So flipping the chain over will have wear happening in the less worn area on the other side of dead on.

Just keep in mind that the difference is marginal in practical terms.

[Edit: I see now that what I wrote below basically just restates what you posted. Sorry.]

I follow you (I think). The pressure/wear on the pin will be approximately on its lower rear quandrant when it passes over the top of chain ring. It remains on that quadrant as it continues around the chain ring. But, visualizing the pin on the top of the driven gear, I believe the pressure is now on the lower FRONT quadrant. The top two quadrants (those that always face outward from either the chain ring or the driven gear) receive the least wear. Or such is my impression. Is this uneven wear really negligible, or am I debating how many angels can dance on the end of a (roller) pin? I think there may be some slight benefit to flipping the chain, not front to rear, but inside out. I'll keep thinking this over on my Sunday morning ride.

Chains are cheap compared to the more expensive freewheel or cassette cogs. Replace your chain! Hopefully the cogs are not worn so much that they need replacing as well. When you replace the chain often your cassette will last a few years at least.
Cheers