Interesting Mag Issue

Geico266

Geico266

Touchdown! Greaser!
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Geico
I say mag, but I really have no idea.

When flying, engine warm, 100ll, IO-360, 07' Slick mags with 250 hours. I hear a "rumble" that stops immediately if I switch to R or L mag from BOTH. It also goes away when I run LOP.

25 degree timing is dead on, checked twice. New fine wire plugs.

Remember, it runs smooth on L or R, but not both. :confused:

The mags are coming off tomorrow during some other cold weather mods. What should we look at or for? Worn cam? Points?

Any ideas?
 
Did the 'rumble' start after you changed the plugs? Did you have fine wire plugs before?
 
Howard Wilson said:
Did the 'rumble' start after you changed the plugs? Did you have fine wire plugs before?
Click to expand...

New plane to me, I have 4 hours in it.

What makes no sense is it runs smooth on one mag.

BTW, doing a mag check in the air is not a bad thing. ;)
 
Corrosion on the contact point inside the switch?


-VanDy
 
Geico266 said:
New plane to me, I have 4 hours in it.

What makes no sense is it runs smooth on one mag.

BTW, doing a mag check in the air is not a bad thing. ;)
Click to expand...

I have heard of 4 banger lycomings having some issues if the mag harness wasn't routed correctly. Each mag was supposed to fire two plugs on top and two on the bottom.

Just throwing it out there.
 
Geico266 said:
Great idea, but I've been told they rarely have issues, and it was new in a 2007.
Click to expand...

I agree, it was the first common factor I thought of. But... Rarely doesn't mean never! Easy to ohm out. I also like BNT's suggestion for routing. Do the wires cross at 90degrees anywhere? Plug to plug. Or plug to p lead?



-VanDy
 
...When flying, engine warm, 100ll, IO-360, 07' Slick mags with 250 hours. I hear a "rumble" that stops immediately if I switch to R or L mag from BOTH. It also goes away when I run LOP...


Time for a new Bose Headset? :goofy:


Sorry. What plane?
L & R mag drops correct?
Able to kill the motor with the mag switch?
EGT's acting right?

Last thing is something I saw on an old 172 (O-320)...at full power it sounded like rocks in a dryer but ran great; pull the power back or cycle the mags and the sound went away.:mad2:
It turned out to be the muffler innards were trying to escape and only the full exhaust pressure would cause the banging we heard.

Just spitballin'

Chris
 
Assuming this is experimental...

Have you tried retarding timing a little bit and running it again? Have there been any alterations to the engine or is it a bone stock IO-360?
 
I know this sounds weird -- but is this happening with the electric fuel pump off, or on?

When I turn on the electric fuel pump on my O-360 powered -8 (I presume this is on your new -8, right?) the fuel flow jumps as much as 3 gallons per hour, and the engine runs richer. On a hot-hot day, at idle throttle and the electric pump running, the engine pops like crazy.

As for a rumble, I have noticed something similar, but it goes away as I lean. Thus, the question about the fuel pump.

As Chris said...just spit ballin'. It really could be all sorts of things.
 
In addition to the other suggestions a check of the internal timing of the mags might be in order
 
If you are going through the mags, just follow the champion manual and it will guide you through the whole thing.

Other than that I was with Brian on checking the routing on the leads.
 
If you hear it but do not feel any roughness it could be piston slap. Going to single mag or LOP changes the flame pattern and loads the piston differently. Listen for a knack knack sound at idle to confirm it.
 
bnt83 said:
I have heard of 4 banger lycomings having some issues if the mag harness wasn't routed correctly. Each mag was supposed to fire two plugs on top and two on the bottom.

Just throwing it out there.
Click to expand...

Will check that closer today, but why would it be smoother on one mag than both if timing sync is dead on?
 
Hiperbiper said:
...When flying, engine warm, 100ll, IO-360, 07' Slick mags with 250 hours. I hear a "rumble" that stops immediately if I switch to R or L mag from BOTH. It also goes away when I run LOP...


Time for a new Bose Headset? :goofy:


Sorry. What plane?
L & R mag drops correct?
Able to kill the motor with the mag switch?
EGT's acting right?

Last thing is something I saw on an old 172 (O-320)...at full power it sounded like rocks in a dryer but ran great; pull the power back or cycle the mags and the sound went away.:mad2:
It turned out to be the muffler innards were trying to escape and only the full exhaust pressure would cause the banging we heard.

Just spitballin'

Chris
Click to expand...

:rofl:

Okay, this might be another clue. The mag drop is weird. On both, switching to R, it only drops 30 RPM. On L it stays the same, back to both it rises 30 RPM.
 
mondtster said:
Assuming this is experimental...

Have you tried retarding timing a little bit and running it again? Have there been any alterations to the engine or is it a bone stock IO-360?
Click to expand...

RV-8 :D

Might be an issue. It is set at 26 degree BTDC. Data plate says 25. Might try 23 degrees after inspecting the mags.

Heading to the hangar to pull the mags and have the FBO A&P give them a once over. Maybe the points gap is too small, or the cam is worn?

I'll find it. I love hunting down issues, but appreciate the wisdom of smarter people than me. Thanks for the tips. :yes:

How would I "OHM out" the BOTH setting on the switch? I assume it would be turn it to both and check the P leads for resistance? Then check L or R to see what those values are?

Keep those suggestions coming. :yes:
 
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You would measure the resistance between each p lead and ground when the switch is on both. It should read open. Be sure to wiggle the key. If it is a standard switch they are easy to take apart clean and relube too.
 
Single mag and significant leaning both slow the burn rate and have the same effect as retarding the timing some.
 
Geico266 said:
:rofl:

Okay, this might be another clue. The mag drop is weird. On both, switching to R, it only drops 30 RPM. On L it stays the same, back to both it rises 30 RPM.
Click to expand...

The right mag isn't grounding when you go to L. On the L, the RH mag grounds. on R, the LH mag grounds. Turn the key to off (at idle!) and see if it still runs. You might have a hot prop. Probably a broken P-lead at the mag.

Dan
 
Capt. Geoffrey Thorpe said:
Single mag and significant leaning both slow the burn rate and have the same effect as retarding the timing some.
Click to expand...

Yep, which is why I asked if this engine had been altered at all and where the timing was set. It almost sounds too advanced to me.

To eliminate the ignition switch I'd just pull the p-leads off and run it that way.
 
Mags are good. Cleaned and lubed & inspected.

Pretty sure it is fuel related. I can easily run LOP and the rumbling quits.
 
denverpilot said:
They do feed cartridges better that way.

Oh. Wrong thread. ;)
Click to expand...

:lol:


The more I read the more I think it is a fuel related issue causing the back fireing. It is running too rich. I can get rid of the backfiring or rumble by running LOP.
 
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