I was taught do the mag-check to see if there is a diffs in RPM drop. Well, finally there was today. Right drops 50 rpm / Left drops 125 and runs real rough. So I turned her around and brought it back into the hanger AGAIN. So Now What?
The last time I flew (15 mins with a mech) that mag was dropping more rpm. I caught it and told the mech, but he thought it was OK, it wasn't as rough sounding and the RPM diff wasn't that much. Any advice, before taking it to the Shop.
Magneto Problems
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David Laseter
- Posts: 156
- Joined: Sun Oct 13, 2002 11:24 am
Magneto Problems
Last edited by David Laseter on Tue Mar 04, 2003 3:05 pm, edited 1 time in total.
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jon s blocker
- Posts: 217
- Joined: Tue Apr 23, 2002 1:56 pm
rpm drop
David,
There are several reasons this could be happening, but it sounds like you have it narrowed down to one mag. when your engine is cold, take a crayon and put a mark on each of the exhaust pipes coming down from each cylinder, (just below the flange on the cylinder head). Start your engine and run on only the weak or rough running mag for a couple of mins. If you have a dead cylinder' the crayola mark will not change in texture or color. If you have a dead cylinder you will be able to determine quickly that you do and which one it is. (You can also do this just by touch, but even a dead cylinder will heat up somewhat). You can then start trouble shooting that cylinder by checking the plug, (you can swap them with a known good plug to see if that evens out the roughness). Check the wire going to that plug, and BASICALLY, you have checked all that will go wrong with one certain cylinder. Make sure you check this through a range of RPM, as the roughness may change at different RPM. Next check your timing, remember one mag has different timing than the other and this DOES make a difference. Check your points, make sure they are gapped properly and clean, (also check for wear). Check the wires to the mag for condition and ground. Check ignition switch. And finally it may be a mag coil, but that normally shows up after the coil heats up, then begins to break down. Hope that gives you a couple of options before you spend alot at the shop that will do basically the same trouble shooting.
Jon
There are several reasons this could be happening, but it sounds like you have it narrowed down to one mag. when your engine is cold, take a crayon and put a mark on each of the exhaust pipes coming down from each cylinder, (just below the flange on the cylinder head). Start your engine and run on only the weak or rough running mag for a couple of mins. If you have a dead cylinder' the crayola mark will not change in texture or color. If you have a dead cylinder you will be able to determine quickly that you do and which one it is. (You can also do this just by touch, but even a dead cylinder will heat up somewhat). You can then start trouble shooting that cylinder by checking the plug, (you can swap them with a known good plug to see if that evens out the roughness). Check the wire going to that plug, and BASICALLY, you have checked all that will go wrong with one certain cylinder. Make sure you check this through a range of RPM, as the roughness may change at different RPM. Next check your timing, remember one mag has different timing than the other and this DOES make a difference. Check your points, make sure they are gapped properly and clean, (also check for wear). Check the wires to the mag for condition and ground. Check ignition switch. And finally it may be a mag coil, but that normally shows up after the coil heats up, then begins to break down. Hope that gives you a couple of options before you spend alot at the shop that will do basically the same trouble shooting.
Jon
Magneto
One other item to check is the nylon drive gear in the Bendix Mag. I had one fail on takeoff. One of the teeth broke off and succeed in shearing off a few of the others. Needlees to say it was randomly firing plugs. I subsequently change that gear at 500 hrs during the AD check
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David Laseter
- Posts: 156
- Joined: Sun Oct 13, 2002 11:24 am
Jon & N1277D, thanks for the trouble shooting techniques. They will be easy to locate under Magneto Problems. The answer to my problem is located under the subject ENGINE ROUGH ON TAKEOFF. Today was a good day! I got a lesson on fuels (100LL) from the owner of our local maintenance shop. This included history of aviation fuel and all the changes before my time. Most of you already know were this is going!
Here’s what he had me do:
-Ramp it up to 2000 – 2200 rpm’s and lean it out as lean as possible.
-Use my watch and time it for 2 minutes. By heating the deposited lead back to liquid phase, the engine was able to burn it off. Hope that’s an, in the ballpark, explanation? After this, I dropped back to 1800 rpm’s and checked mags. That did the trick! So, my wife and I flew for 15 mins and kept leaning it hot until downwind on landing. After landing, leaned all the way to the hanger. He said he keeps his planes leaned after starting, until take off. Gave the same exact method as garybcollins, which I’ll be using from now on. This is the second tank of 100LL that I’ve bought in Arkansas since leaving Alaska, where in 9 yrs I never had this happen. I’m wondering if there is a difference in fuel or something? Elev is 400 ft here, was 232 ft in Palmer, AK.
[quote="garybcollins"]
I lean it until it gets rough and then go back rich until smooth while it warms up on the ground. You can't hurt it by leaning at low power settings while taxiing etc. I keep it so lean that I get a BIG mag drop when I check the mags and that reminds me to go rich for the take off. I also try to remember to lean it again after landing as I taxi in.
Here’s what he had me do:
-Ramp it up to 2000 – 2200 rpm’s and lean it out as lean as possible.
-Use my watch and time it for 2 minutes. By heating the deposited lead back to liquid phase, the engine was able to burn it off. Hope that’s an, in the ballpark, explanation? After this, I dropped back to 1800 rpm’s and checked mags. That did the trick! So, my wife and I flew for 15 mins and kept leaning it hot until downwind on landing. After landing, leaned all the way to the hanger. He said he keeps his planes leaned after starting, until take off. Gave the same exact method as garybcollins, which I’ll be using from now on. This is the second tank of 100LL that I’ve bought in Arkansas since leaving Alaska, where in 9 yrs I never had this happen. I’m wondering if there is a difference in fuel or something? Elev is 400 ft here, was 232 ft in Palmer, AK.
[quote="garybcollins"]
I lean it until it gets rough and then go back rich until smooth while it warms up on the ground. You can't hurt it by leaning at low power settings while taxiing etc. I keep it so lean that I get a BIG mag drop when I check the mags and that reminds me to go rich for the take off. I also try to remember to lean it again after landing as I taxi in.
I'd avoid (relatively) high power settings while sitting on the
ground with the mixture heavily leaned. If the plugs get fouled,
in my opinion, it's way easier on the engine to just pull them and
clean them.
Aggressive leaning on the ground (at or just above idle, whatever
it takes to move around on the ground) and taking care not to
over-prime on startup can keep the plugs from fouling in the
1st place.
All that being said, I'm glad to hear you just had a fouled set of
plugs, and not a bad mag!
Bela P. Havasreti
'54 C-170B N170BP
ground with the mixture heavily leaned. If the plugs get fouled,
in my opinion, it's way easier on the engine to just pull them and
clean them.
Aggressive leaning on the ground (at or just above idle, whatever
it takes to move around on the ground) and taking care not to
over-prime on startup can keep the plugs from fouling in the
1st place.
All that being said, I'm glad to hear you just had a fouled set of
plugs, and not a bad mag!
Bela P. Havasreti
'54 C-170B N170BP
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David Laseter
- Posts: 156
- Joined: Sun Oct 13, 2002 11:24 am
Oh I just can't resist...somebody HAS to say it....so here goes. Us mogas users don't have to worry about this 
Can't wait until April and I can burn the nasty 100LL out and get back to my less expensive mogas for the warm flying season. I am glad you found your problem and learned a bit about the pitfalls of 100LL....price and lead.
Can't wait until April and I can burn the nasty 100LL out and get back to my less expensive mogas for the warm flying season. I am glad you found your problem and learned a bit about the pitfalls of 100LL....price and lead.John, 2734C in Summit Point, WV
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David Laseter
- Posts: 156
- Joined: Sun Oct 13, 2002 11:24 am
It's extremely unlikely you had a lead fouling problem. You most likely had an oil fouling problem. A high power ground run would likely cleared things up just as well. What happens is that after shutdown, oil leaks down past the valve-stems and pools in the cylinder and "well" of the lower spark plug. This causes shorting/non-firing of that plug until a high power run burns it off.
Lead fouling, if very severe may cause plug misfire, but when it becomes that bad, a power run will not clear it. It takes a plug cleaning to do that.
The mag difference you experienced was also only a 75 rpm difference. That is acceptable for takeoff, if the engine is running smooth. (A fouled plug would not likely run smooth as you discovered, however.)
Also, be especially careful about marking exhaust components. Never use a graphite or carbon marker such as a pencil. Heat will build up at that spot and result in a crack.
Lead fouling, if very severe may cause plug misfire, but when it becomes that bad, a power run will not clear it. It takes a plug cleaning to do that.
The mag difference you experienced was also only a 75 rpm difference. That is acceptable for takeoff, if the engine is running smooth. (A fouled plug would not likely run smooth as you discovered, however.)
Also, be especially careful about marking exhaust components. Never use a graphite or carbon marker such as a pencil. Heat will build up at that spot and result in a crack.
Howdy All,
A couple of days ago, had a rough engine on mag check prior to departure. I discovered it was the left mag....lower plugs,
and a drop of about 200 RPM's. I did a search on the "Forums" and found this thread. I had cleaned and rotated, top to lower, the plugs about 30 hours ago. I was really dreading a "Mag" problem 
I followed Jon Blocker's advice (posted 4-23-02) and quickly found that I had a bad plug. THANK YOU JON !!! 
and THANK YOU to all who post questions and answers on this Forum.
Should I replace the one plug, or all six? They have approximately 500 hours of service.
Richard....
A couple of days ago, had a rough engine on mag check prior to departure. I discovered it was the left mag....lower plugs,
and a drop of about 200 RPM's. I did a search on the "Forums" and found this thread. I had cleaned and rotated, top to lower, the plugs about 30 hours ago. I was really dreading a "Mag" problem I followed Jon Blocker's advice (posted 4-23-02) and quickly found that I had a bad plug. THANK YOU JON !!! and THANK YOU to all who post questions and answers on this Forum. Should I replace the one plug, or all six? They have approximately 500 hours of service.
Richard....
Richard Haydon
'49 170A
Ducote Airpark TS65
'49 170A
Ducote Airpark TS65
500 hours is about the max for massive electrode plugs. Look at your center electrode. Is it pretty egg-shaped? It's worn out. (Fine wire platinums will usually go to TBO but are expensive.)
I switched over last year from Champions (REM40E) to Unison/AutoLite's (UREM40E) and have really liked them. They don't lose their external appearance due to high-nickel construction. (They work as well as Champions, in my experience.)
I switched over last year from Champions (REM40E) to Unison/AutoLite's (UREM40E) and have really liked them. They don't lose their external appearance due to high-nickel construction. (They work as well as Champions, in my experience.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
Although, the chapions, previously installed, went about 500 hours.....Re: Magneto Problems
HI ALL, I AM WONDERING WHO CAN ADVISE ME ON THIS QUESTION, IAM NEEDING TO REBUILD THE MAGS & REPLACE THE HARNESS ON MY 1953 170BBUT THE PRESENT HARNESS IS NOT WIRED RIGHT MAG TO TOP PLUGS LEFT TO BOTTOM IT IS A C 145 PLEASE ADVISE.
Re: Magneto Problems
Shouldn't be too difficult to correct unless the harness you have is too short. Just re-route the leads. Left mag fires the bottoms (and is timed 28-degrees BTC) and Right mag fires tops and is timed 26 -degrees.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
Re: Magneto Problems
DOES ANYONE KNOW WHY THE C145 IS SET UP TO FIRE RIGHT MAG TOPS &LEFT MAG BOTTOMS?????