Doing an annual on my 1999 RV-6A and I found the above when the cowl came off. Wow! I know it was not like that at the last oil change, 26 hours ago. (About 650 hours total time) There would have been no way to miss those.
If you look just above the upper right mounting hole, you can see the 1/16" dia. hole drilled for the tab type lock washer that were supplied with the kits at that time. It appears that that was the origination point of all the cracks, that one had not progressed too far or the airbox would have just fallen off.
I ordered a new plate and a set of drilled head bolts that Vans uses now.
What concerns me is how rapidly this progressed from not visible to complete destruction. The failure mode would have the airbox fall off and most likely not block the air into the carb, but you cannot be sure.
I would suggest anyone with a very early airbox take a very careful look for these types of lock washers and their small hole right next to the mounting bolt. If you have one, replace it with a new and drilled head safety wired bolts. This one came with a finish kit in 1998 or so, but I don't know when they changed the lock mechanism on the four mounting bolts.
Problem with Pre 1999 airbox mount plate
Linear Mode
