XP-360 Mag Check problem

Fellas, I could use some help with this one. I'm deployed right now and my wife is trying to get our brand-new RV-6 into the air and fly off the test time. Unfortunately, she's having a problem with the engine.
1. Immediately after start, she is checking the mags by shutting down the Lightspeed ignition. The mag checks fine at this point with only a small rpm drop.
2. When she gets to the runway, she re-checks the mag and gets a 300 rpm drop, with one cylinder dropping off line, showing a large EGT drop. This cylinder is running 200 degrees hotter (at 1150) than the others during ground operations, and is tied for the hottest CHT during ground ops.
3. This has been repeated on at least 3 different days. Tried replacing the spark plug to no avail.

Other data:
1. Aerosport Power XP-360 (180 hp).
2. Airflow Performance Fuel Injection
3. Lightspeed II+ on the right side, magneto on the left.
4. Hartzell Blended Airfoil CS prop
5. Brand new - less than 2 hours on the engine. It has flown 1 time.

Any ideas on how to run this one down?

Thanks a million,

Jordan Grant
RV-6 at home, trying to fly...

If I understand what you are saying, when running OK on the ground the temp is higher on the one cylinder. Then when you get a big drop in rpm at the runway the cht for one cylinder drops also. If I've understood this correctly I would have tried the spark plug also, but since that didn't fix the problem it sounds like possibly you are getting a stuck valve. Probably an exhaust valve.

You didn't say how many hours are on the engine. But you can get a stuck valve at any time. This is most likely a valve guide clearance issue but could also be that the rocker is not being oiled sufficiently or has the wrong bushing. I believe that if it is the guide it is fixed by droping the exhaust stack, removing the plugs. Remove the rocker cover & rocker arms. Remove the offending valve spring and slide the valve into the cylinder but not all of the way. Ream the valve guide. I would suggest that you have someone with a lot of experience with these engines do the work as apparently there is a lot more to it that I've explained. I'm just trying to give you a general idea that if it is the problem that I've described, it can be done on the airplane.

I should have pre-empted this message by stating that I am in no way an expert on engines especially the Lycoming or clone type engines. I am simply passing along the answer to this same question that it turned out to be on a couple of other engines of friends I know. Maybe an expert will jump in here and give his/her opinion or thoughts. I wish you the best of luck and I'm sure you will get to the bottom of the problem.

You say that you have checked the plug opn that cylinder, but what about the plug wire? That would be my second check. You also don't mention which cyl it is. Number 3 typically runs hot on the ground in an RV.
Mel...DAR

mag drop issue

One other thing I would check on a new airplane is to make sure that all of your instrumentation is labeled correctly.

In other words, take a heat gun and heat the EGT probes one at a time, and make sure that when you heat the probe for cylinder #1, the corresponding gauge moves. It's easy to miswire and not notice.

It's possible, but not likely, that she is replacing a plug in the wrong cylinder.

James Freeman

Mag trouble??

JordanGrant said:

2. When she gets to the runway, she re-checks the mag and gets a 300 rpm drop, with one cylinder dropping off line, showing a large EGT drop. This cylinder is running 200 degrees hotter (at 1150) than the others during ground operations, and is tied for the hottest CHT during ground ops.


I had a similar problem with my engine.

Turned out the internal timing of the mag was off. It took about 50 hours for the rotor to fail because it was firing so far out of sync. Engine temp seemed to effect the mag drop also.

Click to expand...

Whatawife

JordanGrant said:

Fellas, I could use some help with this one. I'm deployed right now and my wife is trying to get our brand-new RV-6 into the air and fly off the test time. Jordan Grant
RV-6 at home, trying to fly...

Click to expand...

Ok, now there has been lots of talk about wives that don't like to fly, wives that put up with it, wives that like to fly and those wonderful women that make the building process easier (either by allowing it, being understanding, shelling out cash or general Rosie type help).

Now here is a real gal. She does the test flying while her hubby is deployed!

I can see it now: "I'm a SWM with an RV kit, looking for a F to build and test fly for me. Please send a photo of riveting and priming samples."

Jordan, what's your wive's phone number and when will you be home?

Jekyll

Loosing a Cylinder?

If it seems like you're dropping the cylinder, changing the plugs doesn't help, timing is right, and everything is wired properly as per the above suggestion, might try checking the fuel injector nozzle on that cylinder. Could be something coming thru the system that has it partially blocked, especially since it's a new plane. Of course, I'm assuming the injection system you're using has the injector nozzles in the cylinders!!
Good Luck!
Bill Waters