Engine runs rough at high power

Ant CB · #1 10-24-2011, 12:21 AM

Hi all,

I've got an AEIO-360-A1A fixed pitch with 10:1 CR pistons. I've noticed that there is vibration/roughness which is directly proportional to manifold pressure. For example, at 2400RPM in the cruise at half throttle it's a lot less than 2400RPM climbing at full throttle.

At 2000RPM run-up there is an even mag drop of about 125-150RPM.

I've checked and replaced intake gaskets, installed new injector nozzles, had the servo flowed, installed new plugs and today was going to install a new ignition harness when I found oil in the harness cap at the mag end.

I told my engineer and he said the mags might be playing up. I pulled them both off to have them inspected and I found one is a 4271 and one is 4370. The 4271 was made in 1990 and the 4370 was made in 2000. The younger one looks okay to the untrained eye but the older one has some pretty good black buildup on the contacts where the harness attaches. I can't vouch for either's time in service but I'm pretty certain the younger was brand new when installed and has around 450hours on the. The older one, I've no idea.

Has anyone else has similar symptoms with bad mags?

So now I'm thinking, I can:

1. Exchange one Slick and get a p-mag for the other side.
2. Exchange both and have two new Slicks
3. Send them in for service ( I was quoted 6 hours labour per mag plus parts) and see if they can be recovered.

BTW, if I send my old one in for a core exchange, how much of it do they want or do I send the whole thing in? Gears as well?

Lots of questions I know...

RV10inOz · #2 10-24-2011, 04:15 AM

I see you are in Sydney, and travelling around Oz you would be in a better place should you have a problem far from home if you have two mags. Just a thought.

You could send them both to a good mag overhaul shop. I know of one at Caloundra, I think it is Aircraft Components, any way phone Suncoast Airparts and ask Barry who the guy is that does all the engine shops Magneto's up there, he will know.

Also remember if you change to Pmags or similar your AP might want to know about it

. Major modification and all that.

DB

kymjon · #3 10-24-2011, 04:54 AM

that anyone would quote six hours to overhaul a Slick magneto. I recently had one of my Slick magneto's overhauled at 500 hours and watched it done. To take it apart and check it plus clean the points and replace the brush and reassemble took about an hour and a half. There is basically nothing to them with few parts and they just use a press to get them apart.

Ant CB · #4 10-24-2011, 05:09 AM

Nice to hear from some Aussies here, I'm gathering lots of good info.

I think one mag will be pretty straight forward but the impulse mag is 21 years old and I think cactus, although for an hours labour it might be worth having someone open it up to confirm it.

videobobk · #5 10-24-2011, 05:42 AM

I think I might try balancing the prop. You didn't say if it is a FP or CS, but it really doesn't matter is it is off. That vibration is more linked to rpm than power, but it may be what you are seeing. You didn't mention misfiring, only vibration. If it is a mag problem, you might consider going to electronic ignition instead of mags, also.

Bob

airguy · #6 10-24-2011, 08:06 AM

If the vibration is truly linked to manifold pressure and not RPM, then your most likely culprits are ignition or compression. It sounds like you have probably already found the problem - but I would do a compression check as well while you have the engine compartment opened up.

Neal@F14 · #7 10-24-2011, 08:35 AM

Engine roughness at high power settings, with 10:1 compression ratio.... I hope it's not detonation you're feeling.

Tom Martin · #8 10-24-2011, 09:13 AM

I had a problem like this earlier in the year. I chased it for quite a while and since my mag had 500 hours on it I thought i would send it in just to eliminate one more thing. Turns out it had a cracked distributor cap. Occasional misses are totally gone. It was worse in the 2400 to 2500 rpm range.
make sure you check rebuilding costs vs replacement before sending them in.

Ant CB · #9 10-24-2011, 05:41 PM

I was worried about detonation so I backed the timing off to 20 degrees, but I don't that that's the problem. It's been doing it for a while.

I checked the compressions cold and they were pretty good.

Tom, were the symptoms the same as mine? Was there much of a difference after the new mag was installed?

Cheers,