Timing Chain stretch - Food for thought

[zKars]

The other day a friend and I were discussing our respective commuting bicycles (stay with me here, it gets better).

I mentioned how my latest bike seemed SO much easier to peddle, feeling almost friction free compared to my old cruiser. It mentioned how the old one seemed to be down right hard to pedal compared to this new one in the same situation. Different tires? gearing? newer bearing?

He immediately piped up and asked if I had ever changed my chain and/or sprockets? (see where this might be going?). He was not surprised at all, and offered this (to him) well known detail of bike maintenance. Change your chain and sprocket every year or two!!

Seems we often talk about timing chain stretch here, but so far, I've only ever heard the discussion in terms of how it adds extra length, and "slack" and how that affects cam timing and ultimately how that's bad. Or how its getting weaker as a result of fatigue and may fail.

But as I have come to understand, there is another side to this we have not been considering! Let me explain.

What is it that actually changes when a chain stretches? Not only the entire length, but the spacing between the holes in each link increase!

At the same time, what does NOT change? The spacing between each tooth on the cam and crank sprocket!!!! So what is the result??

The ever increasing mis-match between the sprocket teeth and chain hole spacing increases FRICTION between these components, which increases WEAR on the teeth, etc etc and the whole things gets worse quickly.

This is why my poor old commuter has gotten progressively harder and harder to pedal after 150,000 miles (well, feels like it...) and why that new one just about pedals itself!

It also may be very good reason to consider changing your timing chain on the ol' Z perhaps a bit more often then the NEVER, that most of do except at rebuild time.

Just food for thought. Comments welcome. Not evening claiming the resulting changes in friction are robbing more than a 1-2 HP, but you never know. Maybe its a tuners secret....:stupid:

[carrott]

Maybe the fact that the new bike chain is well lubricated when it is new , unlike a car that is constantly oiled , not a good comparison , but none the less as a chain wears (not stretches) it does alter the cam timing , but you will find that if the timing chain was that worn out so would the rest of the engine , in fact the rings and bearings ect would be worn out much sooner than the chain in most incidences.

[Z train]

Maybe the fact that the new bike chain is well lubricated when it is new , unlike a car that is constantly oiled , not a good comparison , but none the less as a chain wears (not stretches) it does alter the cam timing , but you will find that if the timing chain was that worn out so would the rest of the engine , in fact the rings and bearings ect would be worn out much sooner than the chain in most incidences.

THe chain does stretch.Hence hole numbers 2 & 3 in the cam sprocket.

[sblake01]

wear/stretch are essentially the same thing. As it loosens over time due to wear it also becomes longer.......