Whether or not WD-40 will keep your chain's O-rings happy or ruin them is one of the most controversial topics in motorcycle maintenance. Supporters say WD-40 is great for cleaning your chain and won't harm a thing. Critics say WD-40 – or more specifically the petroleum distillates in WD-40 – will dry our the O-rings, displace the grease, and ruin your chain.
What's the truth?
To begin, 'WD' stands for Water Displacement, and the '40' stands for the 40th formula to be mixed up. The safety sheet for WD-40 says that it's mostly Stoddard solvent, a petroleum product similar to kerosene. So for all intent and purposes, WD-40 is mostly kerosene. And most motorcycle owner manuals actually recommend using kerosene to wash your chain.
Okay, but WD-40 isn't 100 percent kerosene, and there might still be something in that secret formula that will cause your chain's O-rings to swell up and die. So, to find out just how damaging WD-40 might be we disassembled a motorcycle chain an dropped some O-rings into pure uncut WD-40 and let them stew for a week.
And? They were fine. Compared to the control I-rings, the parts in the WD-40 bath were the exact same size and consistency.
WD-40 won't ravage the O-rings, but some people are still worried about it penetrating past the seals and diluting the grease around the pins. To test that theory we submerged a single assembled link in fluid for several days. After cleaning and drying the link was disassembled. The grease was thick and gooey, and there was no evidence that the WD-40 had even made it past the first lip of this particular chain's three-lip XW-ring seal. To be fair, we were working with a section of brand-new motorcycle chain and the chain was stationary, not in use on a motorcycle.
Our experiments show that WD-40 will not harm those little O-rings. However, one of the chain manufacturers we contacted for an opinion warned against using WD-40, saying 'we cannot recommend it, out of an abundance of caution.' Not a particularly strong admonishment, but with so many products available specifically for cleaning O-ring motorcycle chains, there's no reason to use WD-40 if you're even slightly concerned about iut shortening your motorcycle chain's life.