Hi guys, I am unable to install the long (prop hub) oil pressure relief spring. The manual shows a picture of it sticking out about an inch by the looks of it. Mine sticks out nearly 2.5”. I have fully compressed it, and I’m still about an 1/8” from thread engagement. Anyone else had this issue?
The SCAT engine case installation hardware pack I was sent appears to have high pressure springs. I’m curious if this has to do with my case machining.
To follow up: I have a hypothesis the old plunger seized in this hole.
Yes, it appears it is. I bagged and labeled everything. Finally found the bag with the old oil pressure parts and saw that there is a plunger for the flywheel side but no plunger in the bag for the prop hub side.
Thanks for the recommendation, will order.
I’ve worked tight pistons a few ways. I have a center punch set from Harbor Freight, and the biggest one fits inside the piston. A little blue tape on the end of the punch and it’s tight enough to chuck up in a drill and spin it in the case - or to spin it and polish it with scotch brite or something. I’ve also cut slots in one of the pistons in my collection and used that as a deburring tool for the bore.
Wes, that’s a neat tool for pulling the piston. I’ve been using my transfer punch - once you get it in the piston, you can usually yank it out. The oil makes a little seal and when you pull down rapidly the vacuum it creates lets you pull it.
Yeah, there’s discussion online of using a tap and pulling it out.
The issue is that it’s not a stock piston. It’s something like this: VW Oil Pressure Check Valve by Audirac Racing Products
This is a rebuild of a used AeroVee.
Hi again! so tell us a bit more on what you found? a 2nd piston stuck inside the case? And have you polished as suggested the bore and proper piston? just to keep up with things!
Joe, I remember when you came to look at the engine when I was disassembling it. You took one look at the relief mechanism and said, “mine is not like that”. AFAICT the plunger is still stuck in there. I purchased the pin puller tool suggested and I’ll report back after I give it a shot. The Sonex this came off of had several modifications. I just want to rebuild as stock. The new pin slides easily and does not need polishing but I will check again before final installation.
I had to use a puller like the one Wes Ragle linked to. It worked** - though it wasn’t easy to get it out!
Before you put the new one in with the spring, lube it with oil and try to push it gently all the way up in the bore. You may need to use a small rod (recommend wood or plastic) if your fingers aren’t long enough to get it to the end of the travel. If there is any friction going in, stop and use some fine grit sandpaper wrapped around a dowel to polish the inside of the bore (as well as lightly polishing the exterior sides of the plunger). Carefully and gently clean the bore and the plunger after any polishing.
Then once the plunger can slide all the way up, rotate the engine case upright and ensure the plunger will slide back down on its own (albeit slowly… you may need to jiggle the case or lightly rap on the area with a soft rubber/plastic mallet). If it doesn’t budge, gently use the puller tool to get it out (without distorting the plunger) and do some more polishing of the bore and plunger exterior.
Be sure to gently and carefully rinse out the plunger bore and the plunger itself after any work, to get rid of the metal particulates and sandpaper grit. Note that if you blast brake-cleaner or other chemicals up into the hole, it will just shove all that crud further into your oil system!
**I also had moderate success using a properly-sized tap to cut threads into the underside of the plunger, and then pulled it out with a bolt: I put a nut and big washer on the bolt and ran them up to the bolt head. Then I screwed the bolt onto the underside of the plunger by a couple of threads. Finally, I turned the nut down the bolt until it was pressing the washer against the engine case. I then used wrenches to gently hold the bolt from turning while torquing the nut against the engine case - pulling the whole assembly out slowly.
The headflow master relief piston has a smaller inner diameter than the standard plunger., so I’m not able to use the tool.
I’m going to regroup this weekend.
Ok, it seems that hole is bored and the removal of that tube is going to damage the bore. I have no idea what I’m going to do now that I need a new case. Weighing my options. Trying to figure out what’s involved in machining a new case myself.
That system with the ball looks ok. Why not just use it?
Check out this page on the VW oil system:
All you ever wanted to know about those pistons!
The front spring and piston is for oil cooler bypass. I added an extra spring to mine to keep it out of bypass except for very high pressures. I have slightly high oil pressure, and I had oil temperature problems. A stronger spring rate and preload keeps the oil going through the cooler.
In the winter I block enough cooling air to keep my oil between 160-190F depending on OAT, even with all the oil going through my cooler. You could “weld” that forward piston to the top of the bore and have no issues in our application.
The engine came off of a donor plane that crashed on first flight. There were several modifications, so it starts getting tough to figure out exactly what the problem was. In order to avoid the same thing happening again, the solution is to return to stock.
I know there was detonation, which was the ultimate problem, but there was also a lot of wear on components inside, suggesting something wrong with oil distribution.
If you read a few reviews of the guy who supplies the relief valve kit, there’s very mixed reviews. I know there’s mixed reviews for everything, but I’m working on an assumption that VW knew what they were doing. I’ll still read the oil relief explanation when I have some time today, thanks for posting.
What it boils down to is: I just want to start with stock, and then modify.
