Monday, February 10, 2020

Completing Service Bulletin 19-03-22 Replacement Of #2 Exhaust Pipe

Last fall during the condition inspection, I completed a few service bulletins and am just now getting around to documenting them on the DOG Aviation blog. From a safety aspect, the most important service bulletin I completed is Service Bulletin 19-03-22 ... which involves replacement of the #2 cylinder’s exhaust pipe due to some of the RV-12 fleet experiencing cracking at one of the welds and in a couple of cases, a  complete separation of the #2 exhaust pipe.

First a little history about the RV-12’s exhaust system. The exhaust system on early RV-12’s placed the muffler very close to the RV-12’s oil cooler which contributes to high oil temperatures … especially for those in really hot climates.  In an effort to move the muffler a little further aft from the oil cooler, Van’s changed the shape of the Rotax 912ULS cylinder’s exhaust pipes (which are custom welded to begin with) allowing the muffler to be positioned a little further aft. The original four exhaust pipes are part numbers EXH-1201 through EXH-1204 and are not affected by the service bulletin. As a side note, on the original RV-12 exhaust system, the muffler’s exit pipe protrudes through the lower cowling at an aft angle.

The DOG Aviation RV-12 received one of the first shipments of the redesigned exhaust system … which has exhaust pipes numbered EX-00015 through EX-00018. One of the identifying features of this exhaust system is the muffler is positioned a little further aft and the muffler’s exit pipe protrudes straight down through the lower cowling. Also of note, the #2 exhaust pipe is positioned close to the lower cowling and one of the springs is very very close to the lower cowling. The cracking #2 exhaust pipe has a part number of EX-00017.

The cracking or complete separation of the EX-00017 #2 exhaust pipe is a serious safety problem which needs to be taken seriously. In addition to the obvious threat of carbon monoxide, the #2 exhaust is so close to the lower cowling that a separated exhaust pipe could have the potential to easily start a fire.
My finger is pointing to the weld on the EX-00017 exhaust pipe that is cracking/separating.
The old EX-00017 #2 exhaust pipe is on the left and the new EX-00017-1 #2 exhaust pipe is on the right. Looking closely, one can see the new EX-00017-1 exhaust pipe has a few obvious differences …. a doubler plate is added over the weld that was cracking for added strength, the overall shape of the pipe is a little different and the welds are larger.

Not wanting to take any chances, decided it best to not rely on inspections and just go ahead and replace the #2 exhaust pipe with the newly revised EX-00017-1 exhaust pipe along with new copper flange nuts and new springs where the #2 exhaust pipe meets the muffler. Instillation of the #2 exhaust was simple and done in a few minutes … replacing the safety wire I use through the springs is another matter.

After installing the new EX-00017-1 #2 exhaust pipe and attaching the lower cowl, I immediately noticed the new shape of the EX-00017-1 exhaust pipe created more clearance between the #2 exhaust pipe and the lower cowling … which I was glad to see. Unfortunately, I did not have my camera with me the day I reinstalled the lower cowling, so did not get a photo of the completed instillation with the lower cowl in place … will have to try to remember to do that and place the photo here.