Monday, September 6, 2021

Completing Service Bulletin 16-08-24

Van's Service Bulletin 16-08-24 for the RV-12 involves inspecting the condition of the rivets attaching the WD-1204 left and right engine mount brackets to the F-1202B panel base. I’m very late to the party on this one, but decided to complete it while I’ve been in the mood as of late to get caught up on service bulletins. According to the service bulletin, two RV-12 owners reported seeing signs of lose rivets at the aft edge of the WD-1204 engine mounts. The inspection involves looking for any indications of wear including a smoky or greasy appearing film around the rivets. Any signs of rivet wear requires the removal and replacement of twelve LP4-3 rivets using a much stronger CherryMAX CR3213-4-2 rivet.

Ongoing inspections are to be made during annual condition inspections and if no loose rivets are found, log book entries are made indicating compliance with the inspection portion of this service bulletin and re-inspect at every annual condition inspection until the rivets in question have been replaced.

Service Bulletin 16-08-24 was issued just prior to my first flight, so did not act upon it and figured I would just keep an eye on the rivets and change them at my convenience … later down the road. Well, later down the road finally hit a dead end … because, although the rivets on the DOG Aviation RV-12 still looked pristine, decided since the F-1240 upper forward fuselage skin was already removed to replace the upper engine mount standoff, this seemed like the perfect time to complete Service Bulletin 16-08-24. Below is a screen shot from the Van’s document showing the locations of the affected rivets.

Screen shot of Service Bulletin 16-08-24 showing the locations of the twelve LP4-3 rivets that need to be removed and replaced with CherryMAX CR3213-4-2 rivets.

Admittedly, I have been putting this service bulletin off for quite some time because I knew it was going to be a totally uncomfortable and somewhat of a painful job … I was not disappointed, it was painful. To gain good visual and physical access to the heads of the LP4-3 rivets on the underside of the F-1202B instrument panel base requires being all scrunched up in the cockpit with feet on a seat, torso all twisted to get around the control stick so head and shoulders could slide into the leg wells. Unfortunately, I did not get any photos of myself all scrunched up inside the cockpit with the canopy closed on a 95°, 85% humidity day … but I was told my face got quite red while upside down drilling out the LP4-3 rivets. I can assure fellow builders the actual task of removing the LP4-3 rivets is a piece of cake if you plan ahead …. however, performing the task is just totally uncomfortable.

Here is a poor view of the heads of the heads of rivets on the right side of the F-1202B instrument panel base that need to be replaced. The aft two rows of three rivets closest to the nut securing the fan are the rivets that need to be removed … same rivets on the left side also need to be replaced.

Not wanting to climb in and out of the cockpit a bunch of times, figured I would amass all the tools necessary to complete the job … and set them up ahead of time. Also decided to use the pneumatic rivet puller so I would not have to set the CherryMAX rivets using a hand rivet puller in such uncomfortable conditions. A .090" piece of scrap aluminum was used to set a couple of spare CherryMAX CR3213-4-2 rivets into it using the ATS pneumatic rivet puller. This was done to verify it was set up correctly … I used 50 pounds of air pressure which seemed to work nicely.

Aircraft Tool Supply pneumatic rivet puller … this rivet puller has probably pulled well over 10,000 rivets and still works great! It has been a true workhorse.

Next a couple of LP4-3 rivets were set in the scrap aluminum and a drill stop was positioned on a #30 drill bit so the drill bit would only drill into the rivet head just barely enough to break it off.

This photo shows the two CherryMAx rivets set with the pneumatic rivet puller to verify it was setup correctly. Looking closely, just below the two CherryMAX rivets is a LP4-3 rivet that has had the factory head drilled off using the #30 drill bit and drill stop adjusted as shown.

In addition to the pneumatic rivet puller, the tools used to complete the Service Bulletin consisted of a trouble light, long hemostats, a powerful shop magnet (in case one of the ball/mandrels gets away), sticky tape of choice, a #30 drill bit with drill stop, hammer, and a finishing nail set used to pound out the rivets. I prepped a few rivet mandrels on the ScotchBrite wheel to smooth and slightly taper the ends so they fit easily in the center hole of the rivets (they bend easily, so you will likely need at least two or three). The mandrels work well to pound out the ball/mandrel from each rivet prior to drilling the head off.

Photo of tools used to complete Service Bulletin 16-08-24.

In order to provide better access for my helper to easily collect all the rivet pieces, felt it best to close the canopy … doing this allows unobstructed access to the backside of the instrument panel and the upper side of the instrument panel base. The air hose for the pneumatic rivet puller was run through the right air vent and a power cord for the trouble light run through the left air vent … this was done because I did not want the canopy frame to close onto the air hose or power cord which could easily bend the thin fragile canopy skirt which extends down from the canopy frame.  To complete the job, Bob (a fellow pilot who hangers a C-172 across from me) volunteered to give me a hand collecting all the rivet pieces. Thanks Bob!

The plan, which worked out perfectly, was to keep the canopy closed so Bob could have wide open access to the WD-1204 engine mounts and be able to easily collect all the rivet parts. To remove the ball/mandrel from each LP4-3 rivet, a prepped mandrel from a rivet was used as a pin punch and pounded into the center hole of each rivet from inside the cockpit, thus forcing the ball/mandrel out the backside of the rivet to be collected by Bob with the sticky tape wrapped around his fingers. The sticky duct tape worked quite well. We did need to use the magnet once because I told Bob to collect the ball/mandrel from the wrong rivet and ended up pounding out the ball/mandrel from a rivet he did not have his fingers on… totally my fault, but hey, I was looking at the panel upside down.

Next the 12 rivet heads on the bottom of the instrument panel base were drilled and removed using the #30 drill bit and preset drill stop. Prior to punching each rivet out, Bob attached a long pair of hemostats onto the shop head of the rivet … then from inside the cockpit, a finishing nail set was tapped with a hammer to remove the LP4-3 rivet body from the WD-1204 engine mount.

After briefly opening the canopy to get some fresh air and cool off a bit, it was time to get all scrunched up again to complete the job. The twelve CherryMAX CR3213-4-2 rivets were installed using a pneumatic rivet puller to set the rivets. The pneumatic rivet puller completed the job quickly and fortunately anticlimactically. I say that because when a CherryMAX rivet screws up, one has a real problem on their hands … safely removing them is far more challenging, so was very relieved their instillation went smoothly.

Photo showing the bottom of the right side of the F-1202B instrument panel base where the six CherryMAX CR3213-4-2 rivets were installed.

Photo showing the right WD-1204 engine mount where the aft two rows of rivets are now CherryMAX CR3213-4-2 rivets.

The actual task of drilling out the twelve LP4-3 rivets and replacing them with CherryMAX CR3213-4-2 rivets to complete Service Bulletin 16-08-24 is not at all difficult if a little advanced planning is used … but completing the task is truly uncomfortable.