 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
bvthomas(at)bigpond.com
Guest
|
 Posted: Sat Jul 29, 2006 2:58 am Post subject: M14P misfiring |
 |
|
Hi All,
I have a problem that I will tell you about in the hope that somebody can throw some light on it.
Last Wednesday Garry Mitchell of Australian Air ferry and myself took off from White Waltham Airfield In the UK in my newly acquired Yak 18T.
We were bound for Genoa Italy as the first leg of a long trip which was to end in Melbourne Australia.
After 30 minutes flying we cleared English airspace and were handed to Paris control and were given clearance to climb to 8000 ft. from 2500ft over the English channel, shortly after passing through 3500ft the motor at climb power,82%, the engine gave one cough as if power was completely turned off then instantly back on.
This concerned us, but it continued to run well and smoothly, Ok as smoothly as a M14P can , then about one minute later all hell broke loose; It began coughing and popping and loosing power. The fuel and oil pressure gauges were oscillating to zero then almost instantly back to full pressure again ( I don't know if this was a cause or an effect ) however it continued to run albeit without much power, Garry tried various minor adjustments without being too adventurous as we were over water at this stage and didn't want to kill what power we had.
.
We declared an emergency and London control vectored us back towards Shoreham airfield at Brighton, about 12 miles back, luckily we made it having lost about 2500ft.
As we dropped the gear and flap then went to full fine pitch prior to landing, the banging and backfiring stopped and we were able to land normally, the motor ran well during taxi and also ran cleanly at 65% for 30 sec, at shut down.
We rang Russian engineering at White Waltham and ran the symptoms past Genna and Atur
and they thought it was magnetos, and bought two new units to Shoreham next morning and fitted them. Did comprehensive run up checks and pronounced it cured,
Alex Berry , the previous owner, then flew her back to White Waltham, without incident, to be dissembled and packed into a container to be shipped to Australia as both Garry and I at this point decided that we didn't have the confidence to attempt another 12000 mile trip again.
On reflection we are inclined to think that it was fuel starvation, rather than magneto's that caused the problem, and will disassemble the entire fuel supply system when it gets here.
This is where I am looking for assistance, has anybody out there had a similar occurrence,
or has any suggestions on what it may be and how to cure it once and for all.
One other point, I fitted an ignition harness from Dennis prior to the flight and the engine checks
at the 100 hourly indicated smoother running, however this is not the cause as it has done the same thing previously, but was put down to carby icing, a reason that I accepted at the time but which I now do not believe. Incidentally at the time it was CAVOC and 30o C so icing was impossible on this day as it was on the previous occasion. I have since found out that the last time it was 24o C and fine.
Sorry about the long winded explanation, but it has me stumped and I hope some of the vast knowledge available on this list will point me in the right direction to avoid repitition when she arrives home.
Kind Regards Bruce Thomas
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
 |
dsavarese(at)elmore.rr.co
Guest
|
| Posted: Sat Jul 29, 2006 3:27 am Post subject: M14P misfiring |
|
|
Bruce,
I have seen this problem several times before. When it happens, it typically happens somewhere between the initial 20 and 35 minutes of flight. It has always been a bad coil breaking down in one of the mags. The symptom is an engine "cough" which feels like a complete engine shutdown for a half second or so. It DOES get your attention. You will have fly the airplane over your airfield for 20 - 40 minutes hoping the engine cough will show up again. When it does, switch to one mag then the other. Whichever mag coil has failed will definitely be discernable. Remove the suspected mag and replace the coil. Bench testing the coil will show the coil as normal. But do not use this coil again because under heat and load, it will fail again.
To access the front mag hold-down nut, (a real pain to get to) purchase an inexpensive 14 mm combination (box end/open end) wrench. Heat the wrench shaft with an acetylene torch and put a bend in the shaft of approximately 120 degrees. Use the box end wrench to loosen and tighten the front hold down nut. That is the easiest way to access the front nut. If you put 3 vertical marks between the base of the mag and the accessory case using a Sharpie pen or similar marking device, you should be able to remove and replace the mag by lining up the 3 marks and not have to retime the magneto.
Dennis
[quote] ---
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
|
viperdoc(at)mindspring.co
Guest
|
| Posted: Sat Jul 29, 2006 2:52 pm Post subject: M14P misfiring |
|
|
Bruce,
Did you say you bought two new mags and it continued to misfire. The incidents Dennis speaks were indeed a bad coil. I happened on my YAK-50. The loss of engine power comes a sphinter tightening silence for a heartbeat. The reason for the loss of power is pressumed to be a misfire that is like a backfire that consumes all the aeosolized fuel in the intakes and supercharger. After it does this, then it begins to run correctly again. If the flight continues for about 10-15 min, then it starts to run rough and only jockying the throttle will give enough power to land. When it cools down, then it will run normally for about 20 minutes then the process starts all over again,
An airborne mag check will identify the offending mag. As Dennis says, it takes changing out the coils to fix this particular problem. That was the way my engine misfires went. This does not sound completely like a mag problem though, unless you got M9 F mags with an advancing dwell (found on the 52 W and TW). If you have the standard M-14, then the centrifigal advancing magnetos will be next to impossible to get tuned. You will have uneventful runups but will find yourself riding a bucking bronco after coming up to 100% and generally passing about 1500 feet. By retarding the power, the engine runs more normally much like a fuel flow problem. Been there, got the T shirt and do not want another!
The reason I ended up with the wrong mag, was that the case had had the embosing sanded off.
Just to confuse a little more.
Sorry, hope all works out. Keep us informed.
Doc
[quote] ---
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
|
dsavarese(at)elmore.rr.co
Guest
|
| Posted: Sat Jul 29, 2006 3:21 pm Post subject: M14P misfiring |
|
|
When Bruce said "the engine gave one cough as if power was completely turned off then instantly back on", I was fairly certain it's the mag coil and it doesn't matter if it's a pair of M9F mags or a pair of M9-35 mags.
What Doc is talking about is his airplane had the same symptom. We replaced one of the mags (the one we suspected to be bad) with one we received from across the pond that had just come out of overhaul. The data plate on the mag was clearly marked as an M9F. So we timed it as an M9F. The damn engine simply would not run on the ground without misfiring. We replaced wires, plugs, cap, points, but no change in the problem. Then I just happen to notice that under the cover on the boss of the mag was stamped a "36", just like on a centrifugal advance mag like the M9-35 used on the Romanian 400 HP engines. Humm I said to myself, I wonder if this mag's data plate was removed and replaced with an M9F marked data plate. After careful examination of the area around the data plate, one could see circular grinder marks in the area around where the data plate was affixed. We replaced this same mag with a known good M9F mag and bingo, problem solved.
Why is this a problem? Mixing one centrifugal mag (M9-35) which is suppose to be timed at 5 degrees AFTER TDC with an M9F mag which is timed at 15 degrees BEFORE TDC just ain't going to work when the mag switch is in the 1+2 position.
But Doc's original problem was exactly as Bruce described. As Doc said. It really does get your attention.
Dennis
[quote] ---
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
|
richard.goode(at)russiana
Guest
|
| Posted: Tue Aug 01, 2006 8:42 am Post subject: M14P misfiring |
|
|
This type of problem is common0 M14 engines. It is very typical to fly 20/35 minutes and then hit0 problems. The impression is of a fuel problem, but inevitably it is high0 tension electrics.
As Denis says inside the0 magnetos; magneto caps, and very often short circuiting between the ignition0 leads.
Again it is typical that it0 works fine for a test flight, and only seems to breakdown when the engine0 becomes hot.
Richard Goode
Dictated by Richard Goode but0 sent in his absence.
Richard Goode Aerobatics
Rhodds0 Farm
Lyonshall
Herefordshire
HR5 3LW
United Kingdom
Tel: +44 (0) 1544 340120
Mob: +440 (0) 7768 610389
Fax: +44 (0) 1544 340129
www.russianaeros.com
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
