Pressurized Magneto Source ?

KyleTownsend · #1 04-17-05, 10:40 PM

I am looking for a pressurization kit for the bendix mags on my P337.

I know several of you guys have the pressurized mags. Where do you get them? The only source I know of is the Riley kit, and it is pretty expensive.

Thanks,

Kyle

SkyKing · #2 04-18-05, 03:23 PM

Kyle,

If you attend to the preventive maintenance steps in the Cessna Service Manual and TCM recommendations for your engines and magnetos, you'll find you shouldn't ever have a problem. Additionally, in Cessna's infinite wisdom and R&D on this airplane, if it was really a problem they would have addressed the issue. Sort of like the gami game again... not needed.

SkyKing

kevin · #3 04-18-05, 05:17 PM

There is another kit available for Mooney's and such. It is STC'd for the TSIO-360, but not for the 337, so you would have to get it field approved. I don't know the source, I can try to dig it up by asking my (retired) mechanic if you are interested.

My mechanic was of the same opinion as Skyking and (if I recall correctly) Gmas, that regular plug maintenance at 100 hour intervals and magneto maintenance as specifed in the book made pressurized mags unnecessary, and undesireable because the pressurized air "blew junk into the mags" and created maintenance problems.

But once in a while, when I had 95 or so hours since plug maintenance and was flying above 17,000, I would wish for the pressurized mags, because I would get an intermittant miss, and hated to fly lower to make it go away, but knew that I had to or damage the engine. The mechanic that helped me work on mine when last I owned one, who also had 500+ hours in turbo and pressurized 337s flying checks in Oregon and Washington, said he would put the kit on in a second. He said that my old mechanic was opposed to them because he never had been in a situation when he needed every foot of altitude he could get to overfly weather, and the mags started to miss necessitating a lower altitude and slog through the weather, or 180 degree turn due to ice.

Kevin

KyleTownsend · #4 04-19-05, 11:38 PM

Thanks for the lead. I can probably find the source in the STC listings for Mooney.

We discussed this subject at some length in the recent CPA Skymaster Systems and Procedures course.

CPA recommends pressurized mags on P-Skymasters because the bendix mags are too small (physically) for altitude flying. They will cause crossfiring when near the P337 service ceiling because the reduced electrical resistance of the ambient air inside the mags versus the constant (high) pressure inside the cylinders makes this possible.

Cessna solves this problem on all of their other high flying airplanes by using larger mags. This isn't an option on the skymaster due to the limited space.

Crossfiring is extremely detrimental to the engine and even an "occasional hickup" should be avoided. Crossfiring will definitely shorten engine life.

We experience occasional crossfiring above 16,000 despite having brand new fine wire plugs gapped to 16 thousanths, a new magneto harness, and relatively young mags.

I talked to the fellow who designed the pressurized mag system for Riley (no longer with the company). He said that, when they were developing the Riley rocket, they found that they could not reliably avoid high altitude crossfire without pressurizing the mags.

I have heard the concern about "blowing junk" into the mags. There is probably some validity to this. However, we are talking about filtered upper-deck air (the same thing that is going into the cylinders), so I doubt that it is too full of "junk." This problem is further mitigated by using a good inline filter (continental and RAM both have one) on the pressurized air supply line.

CPA reported that the pressurized mags would routinely make the specified service interval, but that unpressurized mags had to be serviced much more frequently if flown at altitude.

I'm not wild about this idea. However, it seems like the only reasonable solution to the problem and, like your frind, I want to be able to use my airplane at altitude when necessary.

Kim Geyer · #5 04-21-05, 10:30 PM

Try Ram Aircraft in Waco Texas. Their pressurized mags had an inline filter with a clear case so you could see if anything was going through the lines. There is not much air flow with pressurized mags, like blowing a coke bottle,
Kim

kevin · #6 04-22-05, 12:01 PM

Kyle,

I used my airplane for hundreds of hours at altitudes between 16 and 20K (every time I flew east from home). I did not have pressurized mags, and except when I got close to 100 hours on the plugs, and even then not very often, I did not have crossfire or missing problems. When I did, I went to a lower alititude immediately, as yet, it is bad for the engine.

I was using mass electrode plugs, not fine wire, maybe that is a difference. But FYI, it is possible to run unpressurized mags without high altitude miss, so if you are getting a miss, pressurized mags may not be the only possible solution. Might be the best solution though.

Kevin

KyleTownsend · #7 04-24-05, 12:48 PM

Kevin:

I do believe that it is possible to fly high without pressurized mags if everything in the system is just right. For example, it is much less of a problem on our rear engine than on the front.

The fine wire plugs are actually an attempt to help mitigate the problem. They are supposedly better than massive electronde at altitude. In fact, they did help substantially, but did not solve the problem completely.

I have decided to take Skyking's advice, pull the front mags, and make sure everything is within tolerance.

My A&P is going to let me pull the mags off myself. Then he is going to inspect, adjust, and put them back on. Any advice on removing the front mags would be greatly appreciated since it looks to me like they are going to be pretty hard to get off.

Thanks,

Kyle

SkyKing · #8 04-24-05, 02:52 PM

Kyle,

How much time is on the magneto in question?

Rather than have and A&P mess around with them, your best bet is to remove them and send them out to a certified TCM magneto speciality shop. AND, if they've got 500 or more hours on them, an even better idea is to exchange them for TCM overhauled and warranted units... that way if you do have a problem with them, at least you've got a back door.

SkyKing

WebMaster · #9 04-24-05, 04:51 PM

Quote:

Originally posted by SkyKing
AND, if they've got 500 or more hours on them, an even better idea is to exchange them for TCM overhauled and warranted units... that way if you do have a problem with them, at least you've got a back door.

SkyKing

Oh, good point SkyKing. I know I would have never thought of that.

SkyKing · #10 04-24-05, 06:04 PM

Hey Dive Bomber,

What's your 'gripe' anyway... did you get up on the wrong side of the bed today? How's the New World Order treating you, hey?

SkyKing

SkyKing · #11 04-24-05, 06:11 PM

BTW there Dive Bomber,

Kyle may NOT have thought about it... and my contribution was specifically directed to him in the first place.

SkyKing

KyleTownsend · #12 04-25-05, 12:13 AM

There is about 300 hours on the magnetos.

I got the mags off without too much problem.

The contact for the #1 top cylinder was very blackened from arcing and so was the end of the plug wire.

I think I will just have the mags overhauled per Skyking's recommendation.

Kyle

PS: There is a small silver cylinder attached to the side of the magneto that connects to the P-lead. I didn't see any mention of this in the maintenance manual. What is this?

WebMaster · #13 04-25-05, 08:49 AM

Quote:

Originally posted by SkyKing
Hey Dive Bomber,

What's your 'gripe' anyway... did you get up on the wrong side of the bed today? How's the New World Order treating you, hey?

SkyKing

No gripey from mee.
just observing that you had a VERY GOOD suggestion.

SkyKing · #14 04-25-05, 04:57 PM

OKay there Larry... maybe it was ME who got up on the wrong side!

Anyway... changing out the mags at 500 hours, especially on the P's and T's, was actually an original thought from GMAs. With the mags being a critical item, other than making normal adjustments for timing, I think it's a whole lot smarter not to let some flunky A&P mess around with them and goof something up. Cheaper in the long run to R & R.

SkyKing

Paul Sharp · #15 05-03-05, 06:14 PM

I used to fly Piper Arrows. For their turbo model they have a presurrized magneto kit (used to cost $250 back in the late 80's). If you didn't have it you'd tend to get missing from the arcing in the mags once you spent 1/2 hour or so over 12K-13K feet. Happened to me once and the dumb FBO said it had nothing to do with the mags. I had been flying at 14,500 and after about 1/2 hour, as mentioned, the missing started.

Called Piper customer support when I got home and the first question he asked me was "Does the airplane have the presurrized mag kit on it?"

All the kit does is would be the same mentioned in this thread - takes a little upper deck pressurized air and feeds it via a tube back into the magneto. Viola. It was a standard thing for the turbo Arrows.