Mag drop---no-go?

deyoung

deyoung

Line Up and Wait
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Chris
Recently I've been fairly consistently seeing a mag drop out of limits on one side (200-225 rpm or so) when starting out. Suspecting that I just have a plug that's getting fouled a bit, I've tried a few times going ahead and flying for a short while, staying close to the airport just in case, and every time when I land after 20 minutes or so and check again it's now fine, only about 50rpm drop. But, half the time the problem will be back the next time I go out.

Since it seems to consistently clear after running for awhile my inclination is not to worry too much about it, but is that stupid?

And, am I just not leaning enough on the ground, or should I suspect something else?

Thanks!

This is a Lycoming O-540 with Champion massive electrode plugs.
 
Did you try leaning during the runup for a minute or so? That will usually cleanup the plugs. Pull the mixture back until it misses then increase slightly. I'm sure someone else will chime in with better instructions for that engine.

I wouldn't try flying with a 200 rpm drop.
 
Sounds like you got the lead out ;)

yea, I won't go unless I get the mag drop within the POH limits. 200 is much more than I've ever seen - but maybe someone with a O-540 will correct me if I'm wrong.

Just need to lean more.. Much fewer issues now that I'm running MOGAS mostly...
 
I lean the crap out of my o-360. General consensus on mooneyspace is to lean aggressively on the ground.
 
In your case I'd agree you're looking at lead on one plug that probably clears out on your takeoff roll. Ground leaning, MoGas, and new plugs are all options. I found on the 310 that plug fouling basically went away once I put in new plugs.
 
I know one particularly crazy fool who has flown more than once with very high mag drops and an engine running rough on mag check.

This was discovered because I was talking about running the engine at higher RPM to help clear the fouled plugs, because I've had the rough mag check. Sometimes for me it takes a few minutes of running to clear it up.

I mentioned this and he said something along the lines of "I know its just a fouled plug that will clear later so I say F it and go". I tried explaining how that was a bit on the crazy side but he didnt want to hear it.
 
Ted DuPuis said:
In your case I'd agree you're looking at lead on one plug that probably clears out on your takeoff roll. Ground leaning, MoGas, and new plugs are all options. I found on the 310 that plug fouling basically went away once I put in new plugs.
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Same exact experience with my Arrow. New plugs took care of the mag drop and the grey box starts much better now.
 
deyoung said:
And, am I just not leaning enough on the ground, or should I suspect something else?
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Look at the logs and find out when the mags were last inspected internally. If it's much more than 500 hours, I'd be concerned. If it's past 1000 hours, I'd be really concerned. If the mags are Slicks and the serial numbers fall within those affected by three service bulletins issued since 2008, they should come off immediately.

200 RPM drops, unless there's significant roughness accompanied by it that could indicate a fouled plug, is most often due to internal mag trouble or timing way off.

Dan
 
Dan Thomas said:
200 RPM drops, unless there's significant roughness accompanied by it that could indicate a fouled plug, is most often due to internal mag trouble or timing way off.

Dan
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Thanks -- it is noticably rough when the mag drop is large, so probably fouled plug?

I have a box of Tempest fine-wire plugs that I was going to put in at the next annual; sounds like I should just do it now...

Thanks!
 
brian];1783838 said:
Sounds like you got the lead out ;)

yea, I won't go unless I get the mag drop within the POH limits. 200 is much more than I've ever seen - but maybe someone with a O-540 will correct me if I'm wrong.

Just need to lean more.. Much fewer issues now that I'm running MOGAS mostly...
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I've seen drops up to 400RPM. The engine wasn't happy about that one. During the summer one of our planes likes to run way lean and I'll see drops of around 250 if it's not left leaned. Sometimes I'll just do a run up with the mixture pulled out until the temps get upper midrange. That will normally fix a bad plug for a flight or two.
 
Lycoming's recommendations on running with 100LL in low-octane engines may be helpful in preventing recurrence. Even if you're running a 91/96 engine like the 180HP O-360's in 180 Cherokees and Grumman Tigers rather than an 80/87 engine like the 150HP O-320-E's in many Cessna 172's and 140 Cherokees, these recommendations are still a very good idea.
 
Mike5250 said:
Did you try leaning during the runup for a minute or so? That will usually cleanup the plugs. Pull the mixture back until it misses then increase slightly. I'm sure someone else will chime in with better instructions for that engine.

I wouldn't try flying with a 200 rpm drop.
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This is exactly what my instructors showed me. Do that, then check it again.
 
deyoung said:
Recently I've been fairly consistently seeing a mag drop out of limits on one side (200-225 rpm or so) when starting out. Suspecting that I just have a plug that's getting fouled a bit, I've tried a few times going ahead and flying for a short while, staying close to the airport just in case, and every time when I land after 20 minutes or so and check again it's now fine, only about 50rpm drop. But, half the time the problem will be back the next time I go out.
Click to expand...

Dan Thomas said:
Look at the logs and find out when the mags were last inspected internally. If it's much more than 500 hours, I'd be concerned. If it's past 1000 hours, I'd be really concerned. If the mags are Slicks and the serial numbers fall within those affected by three service bulletins issued since 2008, they should come off immediately.

Dan
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I had identical to the OP start occuring and it progressively got worse. As Dan suggested, check the mag inspection times ... somehow mine weren't for 1400 hours. I just replaced them with new and problem solved.

For those of you new to ownership your question of, "how are the mags and when is the next inspection due" to a mechanic translates to, "did you have to advance timing" which you are not asking. Inspection means pull them and send them out if they don't have the ability/experience there to open and examine.
 
Ron Levy said:
Lycoming's recommendations on running with 100LL in low-octane engines may be helpful in preventing recurrence. Even if you're running a 91/96 engine like the 180HP O-360's in 180 Cherokees and Grumman Tigers rather than an 80/87 engine like the 150HP O-320-E's in many Cessna 172's and 140 Cherokees, these recommendations are still a very good idea.
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The O-540 is not a low octane engine. Rated for 100/100LL.
 
docmirror said:
The O-540 is not a low octane engine. Rated for 100/100LL.
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According to my POH, it's happy down to 80/87. (Not sure what's 80 and what's 87, that's just what the book lists... I always use 100LL anyway.)
 
deyoung said:
According to my POH, it's happy down to 80/87. (Not sure what's 80 and what's 87, that's just what the book lists... I always use 100LL anyway.)
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Well that's interesting. Piper derating the octane on Lycomings' engine. They say 100/100LL on the type cert. Hmmmmm
 
Ah, now I get it. Piper puts a special carb jet in and derates it to 235HP, and allows 80/87 at that setting. My mistake.
 
Has your mechanic recently checked your plugs and your mags, etc?! Are you familiar with leaning the engine during run up? If you answer no to both, better check into things. Many aircraft are lost on takeoff , killing lots of people.( any decent mechanic should know how to check mags.)
 
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Jimmy cooper said:
Has your mechanic recently checked your plugs and your mags, etc?! Are you familiar with leaning the engine during run up? If you answer no to both, better check into things. Many aircraft are lost on takeoff , killing lots of people.( any decent mechanic should know how to check mags.)
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I'll bet the A&P only sees this aircraft once a year, and probably wouldn't if it didn't need an annual.
 
Tom-D said:
If they did that it would be a different designation.




It will anyway.
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Lyc says even the 7.2:1 C/R is rated for 100/100LL, which is what caught me up. Piper puts some special sauce in the carb to allow 87.

And yes, pretty much any engine of those compressions will load up with little prompting. Lean a lot except for take off and climbout.
 
docmirror said:
Ah, now I get it. Piper puts a special carb jet in and derates it to 235HP, and allows 80/87 at that setting. My mistake.
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There are many versions of the 540. About the only similiarity between many of them is the number 540.

Dan
 
Dan Thomas said:
There are many versions of the 540. About the only similiarity between many of them is the number 540.

Dan
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That, and they're all rated for 100/100LL(except in a Piper) :cheerswine:
 
Tom-D said:
If they did that it would be a different designation.
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The 80/87-certified 235 HP O-540 in the Archer does indeed have a different designation than the O-540-series engines which require higher octanes. It's the same as with the 80/87-required 7:1 compression 150HP O-320-E and the 91/96-required 8.5:1 compression 160HP O-320-D's. The basic series designation (e.g., O-540 or O-320) doesn't change when compression ratio changes, but the suffixes do.
 
Ron Levy said:
If you check Lycoming's SI on fuel requirements, I think you'll find that isn't so.
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I'll pass. Already said it was my mistake for not checking with Piper's special sauce.
 
weirdjim said:
That's because 100LL is an abbrvtn. The proper name is 100/130LL.

Jim
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Never, in my 42 years of flying, have I ever heard it called that. I believe (and might be wrong) that the double designation was dropped a long time ago. 80/87 became 80. Same fuel. 100/130 became 100. I think 100LL came out after the designations changed.

Dan
 
Dan Thomas said:
Never, in my 42 years of flying, have I ever heard it called that. I believe (and might be wrong) that the double designation was dropped a long time ago. 80/87 became 80. Same fuel. 100/130 became 100. I think 100LL came out after the designations changed.

Dan
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Well, sonny :goofy:in my 60 years of flying I haven't either. But there has never been a formal double designation drop so far as I know. As a matter of fact, you can buy fuel filler decals that still say 80/87 and 100/130. It is true that since its inception 100LL has always been called 100LL but that is not to say that its true designation is the lean/rich octane rating with both numbers.

And, my 182 type certificate data sheet still shows 80/87 and 100/130 as the approved fuels. You would have thought that if there was a formal change, that all the TCDS would have changed, wouldn't you?


Jim
 
Ron Levy said:
The 80/87-certified 235 HP O-540 in the Archer does indeed have a different designation than the O-540-series engines which require higher octanes. It's the same as with the 80/87-required 7:1 compression 150HP O-320-E and the 91/96-required 8.5:1 compression 160HP O-320-D's. The basic series designation (e.g., O-540 or O-320) doesn't change when compression ratio changes, but the suffixes do.
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Like I said
 
weirdjim said:
And, my 182 type certificate data sheet still shows 80/87 and 100/130 as the approved fuels. You would have thought that if there was a formal change, that all the TCDS would have changed, wouldn't you?
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Changing TCDS is a pain. I was in contact with Cessna last week about some omissions on the 185 TCDS and they told me that getting them changed is like pulling teeth.

The TCDS for Cessna 172's up through the N model show the dual designation (80/87 or 100/130, depending on engine). 172P and onward (1980 and newer) show the fuel grade as being 100/100LL, which is not a dual designation since 100 and 100LL are two different gasolines. The Cessna 182 TCDS shows the same sort of thing.

I take that as a strong hint that the dual designation was dropped somewhere late in the '70s.

Dan
 
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Dan Thomas said:
Changing TCDS is a pain. I was in contact with Cessna last week about some omissions on the 185 TCDS and they told me that getting them changed is like pulling teeth.
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When it comes to MY expenses on MY aircraft, the FAA doesn't seem to give a hairy rat's a$$ about how much it costs to fix it, but somehow the manufacturers get a pass when it is their ox being gored.

Jim
 
deyoung said:
Recently I've been fairly consistently seeing a mag drop out of limits on one side (200-225 rpm or so) when starting out. Suspecting that I just have a plug that's getting fouled a bit, I've tried a few times going ahead and flying for a short while, staying close to the airport just in case, and every time when I land after 20 minutes or so and check again it's now fine, only about 50rpm drop. But, half the time the problem will be back the next time I go out.

Since it seems to consistently clear after running for awhile my inclination is not to worry too much about it, but is that stupid?

And, am I just not leaning enough on the ground, or should I suspect something else?

Thanks!

This is a Lycoming O-540 with Champion massive electrode plugs.
Click to expand...

Lean hard on the ground and run the engine up over 2000RPM for a minute or two. I'll bet the problem goes away. I wouldn't fly with a drop like that.
 
WhiskeyPapa said:
Lean hard on the ground and run the engine up over 2000RPM for a minute or two. I'll bet the problem goes away. I wouldn't fly with a drop like that.
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lower the float level in the carb, and set the idle mixture to a leaner setting. 10-50 RPM
 
How you shut off your engine? If you get fouled plug every start you may not doing the shut off procedure for your engine, on my 360 I have to follow to the T shutoff procedure or I will have mag drop next time. Usually I lean the crap out fart the plug back to life.
 
deyoung said:
Why do you say that?
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Either, because of the fact that you went ahead and flew the airplane knowing there was something wrong and are showing that you will ignore problems OR he knows you have an outstanding airplane that is never in need of repair. I'm leaning in one direction. ;)
 
Re: the cessna 195 I bought which was not as advertised. Among other problems was a miss that showed up sometimes on run up. The mechanic at home base..said...l." Aw ....l.it just needs runnin, it's just fine!" I climbed it to 4000 feet above the runway and after a bit , flew it to a much better mechanic. After searching for an hour he took the ring off the engine which housed the wiring harness. (It had been sold to me this way ) the harness literally fell out in pieces , ( 1953 harness!) it was shot. Trust no one and find a mechanic that knows what he's doing. Some do not.
 
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