Nobody wants to replace their feederhouse conveyor chain because they're so expensive. Depending on the brand of machine, it's not hard to drop $1,200 on a new chain. So I understand why customers drag their feet and ask me to explain what justifies spending that much money to replace a chain, "...that looks fine to me."
The process I use to judge a feederhouse conveyor chain (hereafter FHCC) starts with eyeballing the chain in its "natural" condition. Stand in front of the combine and look at the crossbars that run from the side strands to the center strand of chain. Note if they aren't parallel to the floor of the feederhouse, or have a slight "V" across the front of the feederhouse drum. The goal is to identify if one of the strands is slightly longer than the others. If, during last year's harvest ,you "jumped a tooth" and ran the chain crooked for a few minutes or a few passes through the field, one of the strands is probably stretched and it's time for a new chain.
Second, examine the rollers on the links. Are they tapered to one side, or hourglass shaped? If those rollers are worn, then the pins inside of them are worn. How worn is too warn? See the next step.
Third, remove tension from the FHCC and find the biggest pair of slip-jaw pliers you own. Spread the jaws as wide as possible to grab two or three links of chain, and use the slip-jaws to see how much freeplay there is in those two or three links. I talked about the chain "stretching" earlier, but that's inaccurate. Chains don't stretch. What we call stretch is actually wear between all the pins and sideplates. That wear is those pins and side plates getting smaller and thinner. "Smaller and thinner" is a not a good thing for roller chains.
So, if the FHCC has a "smile" across the front of the feederhouse drum, if the rollers aren't cylindrical, and/or you can get more than 1/4" of freeplay between two or three links, it's time to bite the bullet and replace the chain. Or, you can spend a half day and twice as much money during harvest digging that broken chain out of the feederhouse and the front of the combine. It's one of those "Pay me now or pay me later" deals.