I'm bouncing around to all sorts of FWF tasks these days. Something I purchased a while ago and need to install is the crankcase vacuum modification. As a standard approach, Van's has you route a rubber tube from the oil breather port back to the firewall, connect it to a large aluminum tube, then terminate that tube just above the exhaust. The idea is that oil that is blown out the breather will drip onto the exhaust and be burned up. In reality, people find that while it may mostly burn up, it still creates a huge mess on the belly of the plane. One option to fixing that is to put an air/oil separator in the loop to remove the oil from the air and send it back to the crankcase. I chose to go with kind of a hybrid between the two approaches. Antisplat Aero has what they call a crankcase vacuum kit. It's supposed to be used in conjunction with an oil separator, but is commonly used on its own. It takes that rubber tube from the oil breather port on the engine and connects it to a one way valve that is piped directly into the exhaust pipe. This essentially serves the same function as the Van's approach, but because it goes into the actual exhaust stream, the oil is truly burnt up. Pilots say that this alone keeps the belly clean, even without an oil separator in the mix. The other advantage to this is the slight vacuum that it creates in the crankcase (hence the name). It keeps a slight negative pressure in the crankcase, and people say that it essentially stops oil leaks from happening. Many people have commented that they had leaks around the crankcase that went away completely after installing the vacuum kit. So that's what I'm going with.
This does come with a maintenance gotcha though. You need to pull the valve off of the exhaust during oil changes to make sure that burnt oil is not clogging up the tube. You don't want the passage to get blocked, which would then cause pressure to build up in the crankcase and potentially blow out seals. As a safety measure, Antisplat provides a second .25 psi pop off valve that gets T'd off of the main rubber hose. If the exhaust port were to get blocked, the safety valve would open to keep pressure from building up.
I couldn't fit the saddle mount fitting and valve right by the firewall exhaust exit, so I moved it upstream a bit. Antisplat said the valve can sit anywhere on the pipe as long as it's at least 45 degrees or less from vertical. I drilled the hole to accept the tube that sets down into the exhaust.
The saddle mount fits fairly closely, but not close enough. For now I used a piece of fiberfrax heat barrier material as a gasket to keep any exhaust gasses from leaking out (although so close to the cowl exit, I'm guessing they would be sucked right out anyway). I may switch this over to some gasket material at some point, but the thickness of the fiberfrax made filling the gap easier than a thin piece of gasket material would. I thought about silicone gaskets, but silicone can't withstand the extreme heat of the exhaust pipe. Once I'm done sorting some of the other wires in the area I'll connect the oil breather tubes.
Next up, I routed and connected the oil cooler lines.
There is a bolt that goes through the engine block, through a 7/8" aluminum spacer and into the rear baffle. You can barely see it to the right of the pushrod down by the cylinder fins. The fit of the baffle was bugging me because it was being distorted in a weird way here. I pulled out the bolt and made a slightly longer spacer. Just getting the bolt back in took me a solid hour of course. Real estate for hands is getting hard to come by behind the engine! But the longer spacer made a huge difference and made the baffle fit much more evenly across the cylinder.
The mechanical fuel pump has a drip line that comes off of it and has to be dumped somewhere. This is essentially a plastic tube that gets connected to the fitting on the pump, then also connected to a small aluminum tube that exits under the engine mount. I bent the aluminum tube to fit around the mount. I don't have a final picture, but it then got safety wired to the plastic tube. There is no space on the engine mount to put an adel clamp, so a zip tie is the only way to hold all of this (although it's pretty solid anyway since I also put RTV around the aluminum tube where it exits the firewall). I don't want to have a bare zip tie attached to the engine mount since they have been known to be able to saw into the steel over time though. I've ordered a few grip lock zip ties to replace this one. The grip locks are ridiculously expensive for a zip tie, but they have a rubber pad on the back side.
On to wiring routing! Since the spark plug wires are the bulkiest, I started there. The wires for Pmags have to be kept separate. I use high temp zip ties with a chunk of rubber hose as a separator. I did both left and right side the same way. After I took this picture, I also added an adel clamp to the engine mount to keep the wires from bouncing around. I haven't figured out how to handle the top wires yet. The are longer than they need to be (these cross over to the opposite side Pmag for redundancy) so have more slop to deal with. I could cut them down, but I'm hoping I can make them work without having to do that.
