This one is a thinker...I'll try to keep it short while giving as much information as possible.
So a few months ago the weather was perfect for flying my dad's RV 7 to and from work. I was flying it every few days. It's an RV7 with an IO360 with P-mags and about 400 hours TT (I think). Mags had never been overhauled until recently. More on that later.
So, to make this post a little less boring, I'll include some pictures. Here is the plane freshly washed in Roanoke, VA minutes before heading home.
Flying home...beautiful flight.
It's running pretty **** good if you ask me. The true airspeed is a little lower than you might think, but that's because of the composite 3 bladed prop.
Now for the fun part. I park the plane at Lake Norman airport just north of Charlotte, NC for the night. The next morning I hop in and fire it up. I do my mag check and when I turn the left P-lead off, it bangs and pops in the worst way I've ever heard. Sounded terrible. EGT's went through the roof when I turned it off for any length of time. When I turned the right off, the RPM smoothed out and increased.
Fortunately there were some very nice mechanics on the field. After a full day of trouble shooting, they found that the right P lead was out of timing. They retimed it and all was well. I picked the plane up a few days later, flew it a short flight back to our home base and put it in the hanger. We sent the P mags out to be checked and they really didn't find anything wrong. Their suggestion was to have the left one rebuilt ($85) and the right one rebuilt along with a new circuit board just to rule out this happening again ($450).
We got them back and decided to install them today. We've never done this before but it seemed simple enough. We followed the instructions. Installed the mags, connected the proper plug wires, connected the plug. We set TDC by pulling a plug on #1, gently inserting a screwdriver to feel the piston movement, and rotating the prop till it stopped. We also found the TDC mark on the flywheel lined up with the seem in the case. We timed the mags by blowing into the tube. Got the green lights like we should.
We cranked up the engine and all seemed well, until we turned one mag off. 90 RPM drop on the left, 170 on the left with about a 150 degree increase in EGT. It also sounded bad with one mag off. We retimed the mags 3 times to make sure we had it right. No real change. The odd thing is that with both mags on, it sounds great. Smooth, no popping, nothing. It sounded like a perfectly happy engine.
So, to summarize....
Engine ran great
Overnight, right P-mag lost timing, but once timed, ran great again.
Mags rebuilt, nothing found wrong. Company has no idea what happened.
Now both mags have an unacceptable drop during mag check after rebuild.
We are confident that we set TDC correctly. But the tech guy even said if we were a couple of degrees off that we wouldn't even be able to notice it, implying that even if we missed it just barely, it would still be fine. But we didn't, we had the marks lined up.
We are at a loss. Why would they both have such a big drop? Before the rebuild, they would maybe lose 10-20 RPM. Almost no drop at all.
The tech guy insists that we have something else going on, like a fuel problem. I call BS on this because NOTHING changed. All we did was remove the mags and then reinstall the rebuilt ones. We didn't even remove plug wires. I am very confident that we have a timing issue, but I don't know why.
I'm sorry for such a long post. It's tough to keep it short and provide as much information as possible. If you guys have any insight as to what might be wrong, we are all ears. The good thing about this experience is that we are learning a lot about the airplane and how the systems work. The other good thing about getting stranded that one day in Lake Norman Airport is I got to see this...
Anyone redneckinize this old barn? Remember the barn scene in "Days of Thunder"?