The International Cessna^® 170 Association

Well, after several delays and rescheduled attempts, I finally started the move of my '48 from San Diego to Norfolk, VA. Made it about half-way and ended up leaving the airplane with an A&P friend in Mineral Wells (MWL).

Pardon the long story, but hopefully some of the details will help.

Background: after flying the airplane for a year, an average of 3 times per week doing mostly pattern work, the airplane sat on the ground with no use for about 6 months. Just had the annual done a month ago.

Left San Diego and the first leg to Phoenix was just fine. Departed early the next morning headed for Albuquerque. Runup was normal....although static RPM seemed a little low as I went to full power on the runway (normally airplane has always made 2230 at sea level, that morning it was more like 2175). I completed the takeoff and everthing seemed to be performing fine. Climbed just fine over the mountains east of Phoenix and everthing seemed normal so I proceeded on.

Runup at Albuquerque was again fine. Static RPM was better: 2200. Took off again and had a smooth flight to Plainview, TX.

When I went to leave Plainview, the engine suprisingly didn't want to start. Turned over fine and caught, but seemed to sputter and cough and quickly died (acted like a fuel or mixture problem). I re-adjusted the mixture and throttle and it started fine the second attempt. Runup was normal, but again static RPM was back to around 2175.

Takeoff normal and I continued east. Had to duck down under the overcast layer that was hanging out across Northern Texas this weekend and ended up cruising around 1-2000' AGL and just below the layer. I was cruising at 2450 RPM, but noticed that I needed close to full throttle to get that. Then I experienced a brief drop in RPM - slowly dropped about 100 RPM and then went back up. Seemed like it was running slightly rough, but that may have in my head. I started to think about carb ice and tried playing with partial carb heat which seemed to help, but the problem kept returning. Then I tried a mag check - when I selected the right mag....it was dead. Went back to the left mag and decided to divert to MWL where my friend's hangar is.

What was interesting, was that I was still experiencing RPM issues and occasional roughness on the left mag and continued to play with the carb heat the rest of the way until I arrived at MWL. Landing uneventful, but the engine quit completely on the rollout and would not restart.

Obviously the right mag is a problem, but any ideas what was going on with the left one? My friend checked the p-leads and didn't see any issues. He suspects it is in the mags themselves.

Anyone else experienced similar symptoms? Any thoughts?

Similar experience when my mags oil seals leaked due to chronological age.
Cleaned mags up, new oil seals, cured problem.

Check for severe lead clogging on the spark plugs.

gahorn wrote:Similar experience when my mags oil seals leaked due to chronological age.
Cleaned mags up, new oil seals, cured problem.

Well....I was hoping this was the case.

However, my A&P friend just sent me photos of the right mag.....there is a whole tooth missing from the gear. It is somewhere inside the accessory case of th engine......this is not good!

He is going to bring out the video broscope and send it into the accessory case tomorrow to see how bad things look.

This is sounding very very bad to me. Any ideas what I'll be up against?

Check the scavenge screen....chances are thats where it'll be found.

It might have dropped right below the cam gear. If it was my machine, I would remove my accessories and examine each gear to ensure it didn't foul itself on something else. I guess if it did you'll find some smaller evidence in the screen. I'm just wondering if a strong magnet wouldn't coax it out of hiding, if it doesn't revel itself right away.

Well, just got the call from my friend...it's bad.

Wasn't able to find the tooth with the borescope, but was able to confirm that the accessory gears on the engine are pretty badly damaged. Sounds we'll have to pull the engine off and do some work on the accessory gears.

This is a new one for me.....any ideas what this might cost me???

It sounds like what happened is that the mag became loose and with all the extra play caused the tooth to break off and then it just got worse from there. What I don't understand is how the mag came loose. The mag was last removed for IRAN over a year ago for the first annual. Since then I flew the airplane with zero problems for close to 75 hrs. The shop that did the most recent annual (a month ago) said they didn't touch the mags. Thoughts?

Well I am horrified that they didn't check you mags on a annual. I would change shops . if they checked I your mags a month ago you might not have the problem that you have now. I always check point gap and lub the point cam ,check for leaky seals ,burning or pitting marks internally , check the resistance and continuity and insulation of the coils.And the internal timing of the mag and the mag to eng timing .

You may not really know yet whether the mag was the originator of your problem, or a casualty of the original problem.
It's not always easy to figure out the chain of events in a failure.
Your mechanic needs to keep his mind and eyes open for clues.

One has to wonder....if they "didn't check" the mags last annual because they failed to performa complete annual which may have prevented this problem.....
...or if they "didn't check" the mags last annual because they don't want to be blamed for leaving them mounted loose.

You're in for an expensive ride. None of those gears are cheap, and there may be additional damage.

I'd explore options here before the total tear down, as in removing all accessories and then pulling off the back case. Never know you might find the bits your looking for. If there's a whole bunch of metal made as in fine metal that's been circulating around then you are in trouble. Any pics?
You never know, some cheap gears may be available.

gahorn wrote:...or if they "didn't check" the mags last annual because they don't want to be blamed for leaving them mounted loose.

That isn a concern. They said they did time them, but didn't 'touch' them. I left a message with the shop asking how they timed them. FWIW, so far, the shop that did the last annual only knows I had a mag failure. They don't know the extent of the Mag failure.

I'm not looking for a "scapegoat" in this matter. I"m just very disappointed this event has occurred at all.
The 100 hour inspection of the engine should have inspected for "security and condition" of the mags and accys.
Even checking the "time" (timing) of mags requires a degree of disassembly (perhaps "in situ") but nonetheless it requires
that gear backlash, impulse wear, point-cam wear, etc., be removed (which changes virtually every few hours of operation.)
It is very unlikely that from year to year no need to loosen, adjust mount-angle, and re-tighten the magneto mounting nuts is not required.

HOwever, it IS possible perhaps on operations which involve few hours each year, I suppose. (Comparatively speaking, I only fly my airplane about 65 hours per year, yet my mags have never undergone an annual inspection without adjustment requiring loosening/re-tightening the mounting bolts. If, perhaps, for no other reason than the fact that it's difficult to exactly determine where 26/28 degrees btdc is using a mirror/etc. without feeling I can get it a bit "closer".... especially coupled with the magneto point-check operation.)

Of course, in "not looking for a scapegoat.... I also have to admit it's almost as likely the loose mag is a result of the broken gear as it is causative.

I'm just hoping the last inspector learns a lesson from the possibility-matter, and will futuristically double-check mags during inspections...but you'd have to inform them of the problem you've experienced before that will occur.

I have a couple of mag gears still attached to mags I acquired as spares from a fellow Member here. I bought the set not for the magnetos/harnesses in the set, (although those mags are good, if for none other than cores) but I bought them purely because the cost of those gears is scary and I thought I'd feel better having a good spare set.
Chances are that used gears are widely available for you*...just be certain to have them all re-certified (8130-3 tags) before installation.

*EnParts, Lancaster, TX sells used engine parts from salvage airplanes. I have had excellent experiences with them, at very fair prices.

I have slicks, new since my last overhaul and the timing has not changed in the last 350 hours. I would have thought that a loose mag would have caused an eventual decay in timing accuracy but not cause a gear tooth to be liberated, until it was at the point of coming out of the case. What happened during the annual ? Well even though my timing hasn't changed there's only one way to know if its slightly out by hooking up the buzz box and you would think that if the mag was anything but tight it would be discovered then.