I'm always curious when I hear of folks getting 4000-5000 miles from a Diamond chain. My last one went over 40,000 miles and had worn ("stretched") to the 2nd adjuster notch on the swingarm (it started out on the front edge of the first notch). The current one has over 10,000 miles on it: this one is a 102-link version (Diamond Powersport plain-Jane type) and it started at the 2nd notch on the swingarm adjusters: so far it is barely past the notch.
Chain care (and lube choice) is vital, and not just on the SOHC4 bikes. I wash mine with the hi-pressure carwash, bike on centerstand, let it have it until it spins the whole wheel 'round and cleans the rear sprocket, about once a month (or about 1,000 miles). Then I ride about 2-5 miles at 40-70 MPH to fling the water away and warm the chain up, and immediately lube it warm and let it cool down. When on a long trip, it gets new lube once a day, on the centerstand, when the chain is warm. I usually do this at night or when stopping for the day, lets the lube soak in and set up. When the slack reaches more than about 1.5" I adjust it back to 3/4"-1" slack.
Every 8K miles or so, I flip the front sprocket: every 10k or so the rear one. This 'evens-out' their wears, too. I usually get about 20K miles from the front sprockets and about 50k from the rear: I have just installed the 4th rear sprocket on mine, at 140k miles.
The OEM Honda RK chain lasted less than 4000 miles, was stretched to nearly the center of the adjusters and jumped and rattled like a grasshopper on a hot summer day. This was in 1972, April. Diamond had just intro'd their new-for-CB750 Diamond XL chain, so I installed that: by the next April I had 15k miles on that chain (19k miles on the bike) and it had adjusted just 1/2 notch on the swingarm. I was 'sold' on the Diamond then: in the meantime, all the other 750 riders who hung out with our shop had gone through multiple RK (or other) Japanese chains. The only exception was a guy who switched to Renolds chain when his OEM wore out: he had adjusted his a full swingarm notch in about the same mileage as mine, or about twice the 'stretch'. It was still silky smooth, and he ran it another year after that.
At 38k miles I was heading out for a round-the-West trip of 10k or more miles (which became over 12k in the end) and Diamond had intro'd their "improved" XDL version of this chain. It has Oilite bushings for every pin, hardened pins and sideplates, shot-peened sideplates to boot, and the 1-piece machined rollers are also hardened and have extra clearance between the sideplates and them to let the oil move about easier. The first one of these I used went 38k miles, the second went over 40k miles (I still have that one) before they stretched 1% (5/8", or one link on the 100-link chain). I switched to the new one when I started using the 102-link version: by then Diamond renamed it the 'Powersport' chain, but it is still the same as the older XDL series. That's what they call it today.
The main advantage of the "O-ring" or "X-ring" chains is the lack of need for lubing the pins. But, the sprockets and rollers still need all the lube they ever did, or they will wear, and quick! These 'sealed' chains suffer drag: they are about 93% efficient (say their builders) while the "bare" chain is 95% effificent with good lube: Powersport technology takes this up another notch to 97%. These actual dyno tests are (or WERE) found on the Diamond website, circa 2006, when I was writing my book, and were done by an independent lab. I know from working on the Baby Fours that installing a "bare" chain in place of the O-ring type most definitely improved hiway throttle response, which meets with those numbers.
