Mag and plugs....rough mag question

[btbell]

Hello everyone,

I have a '46 BC12D with a A-65. I have a rough mag (~2-300 RPM drop) which improves in flight. Does anyone know offhand which plug wires are on the R vs. the L mag? I think the top plugs are on one mag and the bottom plugs on the other?

I have M41E plugs installed in the top cylinders inside Ercoupe cups and shielded plugs installed on the bottom (I think REM37BY or REM40E...can't remember off the top of my head). The engine has about 60 hrs SMOH and has been switched to standard oil.

There have been some thoughts on this problem offered to me so far:

1. The REM37BY/REM40E plugs are too cold and are not burning off deposits??
2. Bottom plugs are still getting wet and are not burning off the fluid/deposits??
3. Problem with the connection inside the Ercoups cups??
4. Bad mag (however mags were new at OH)??

Anyway, the mechanic and I will be looking at this on Sat...any thoughts on the forum??

Thanks,
Brian

[fredaustin]

Re: Mag and plugs....rough mag question

Brian,

Right Mag fires the top plugs. Left Mag fires the bottom plugs.

Fred

[btbell]

Re: Mag and plugs....rough mag question

Right Mag fires the top plugs. Left Mag fires the bottom plugs.

Thanks Fred!

Since I have not flown the plane in several months I cannot recall with certanity which mag it is. Unfortunately I was not the last to fly it when this problem developed. Will find out when we run it up on Sat morning.

So based on this, this is where I am at....any thoughts?

If right mag (top plugs):
1. Problem with the connection inside the Ercoups cups?? The spring leads are just compressed against the side of the spark plug head (is this correct)??
2. Bad plugs? (however they were brand new at time of installation about 15 hrs ago)??
3. Bad mag (however mags were new at OH)??

If Left mag (bottom plugs):
1. The REM37BY/REM40E plugs are too cold and are not burning off deposits??
2. Bottom plugs are still getting wet and are not burning off the fluid/deposits??
3. Bad mag (however mags were new at OH)??

Any comments or experiences on any of these potential causes or anyone have any other suggestions?

Thanks,
Brian

[Howard Wilson]

Re: Mag and plugs....rough mag question

Brian,

I'm betting on a bad plug. See if you can determine which mag is rough at or near idle. Once you determine top or bottom, that leaves you with 4 possible culprits. The safe and sane way to do it from there, if you don't see an obvious problem, is to replace 1 at a time with a known good plug, run the engine, and see if the problem goes away. I have seen other people start the engine with the cowling off (tail tied down!) With one hand holding on to a strut at all times use a long insulated handle screwdriver and short out each of the suspected plugs one at a time. The rpm will drop drastically when a good plug is shorted and there will very little or no change when the bad plug is shorted. The Lycoming split exhaust is even easier, you can narrow down the suspects to two plugs by holding your hand near the end of the pipe and 'feeling' the miss. I bought 8 new plugs and had 3 of them go bad within 5 hours! Talked to an IA friend of mine and he said somebody probably dropped them while in the box. His old adage was "You can drop a spark plug twice; once on the floor and once in the trash."

[3Dreaming]

Re: Mag and plugs....rough mag question

If you have access to a infrared temperature gun you can run the engine on the rough mag 30 seconds to a minute then just shut the engine off. Check for the cold exhaust stack or cylinder. If there is a cold cylinder it is a plug, wire ,or in the cylinder itself. If there is not a cold cylindr I would lean towards a mag. I have also seen a sluggish valve represent as a mag problem. Tom

[fredaustin]

Re: Mag and plugs....rough mag question

Alternate method of cold plug check is to start the engine on one mag run it on that mag only for a couple of minutes. Then shut the engine down most of the time the non firing plug will be cool/cold to the touch. Then to make sure it's the plug and not the lead switch the cold plug with a warm one and repeat the check.

[astjp2]

Re: Mag and plugs....rough mag question

Its probably an oil fouled plug and when it burns off, then it starts to run like it should. Since the engine is fairly new out of overhaul, some oil may be seeping past the rings, pull your bottom plugs and see if they are wet after the engine sits overnight. If you are real worried about it, get some fine wire plugs, they will fire in oil. Tim

[Greasemonkey]

Re: Mag and plugs....rough mag question

Brian,
When I bought my tcraft it had the same problem. I looked at the mags, the plugs, the timing, and what I found was that two of the spark plug wires were switched around. After looking at a schematic I placed the wires on the correct spark plugs and my problem was solved. This may not be your problem, but it was not mentioned yet, so I thought I would throw in my two cents worth.

Greasemonkey

[btbell]

Re: Mag and plugs....rough mag question

fine wire plugs

Thanks Tim,

Looks like Autolite has the UREM38S and Champion with the REM38S (roughly $35-40 each). Anyone have any thoughts on the differences between these companies?

If it turns out that this is the problem, I will probably switch my bottom plugs over to fine wire and leave the top plugs as the Champion M41E plugs installed inside the ercoupe cups. Thoughts?

Thanks,
Brian

[btbell]

Re: Mag and plugs....rough mag question

Thanks to everyone so far for their thougths!!

I will be sure to post what the mechanic and I find tomorrow when we look at the issue. If anyone else has thoughts, please keep them coming. This group is always great!!

Brian

[Guest]

Re: Mag and plugs....rough mag question

I once had a similar problem, last fall actually, I found two gaskets on a lower plug.

Apparently that resulted in a setback in the plug's position in the cylinder and made it "catch" more oil.

Removed one gasket, problem gone.

That's the true series of events, I can only speculate what was happening.

Dave.

[tawadc95]

Re: Mag and plugs....rough mag question

anybody here ever use factory rebuilt bendix mags as a replacement?
they as good as new?

[Buell Powell]

Re: Mag and plugs....rough mag question

I have a pair of Bendix S4RN-20s that I had completley rebuilt by Arn-Air(712-651-2255) in 2004 and so far I have not had any problems at all with them.

[astjp2]

Re: Mag and plugs....rough mag question

Well I just spent 2 weeks looking for S-20 series mags, most places are on back order for the one with impulse coupling, there are no cores available and to buy new is $2281.00 from TCM, that was my IA price. I am going with slicks and fine wire plugs. For less than 1400.00 for both mags, gears, wires and plugs. Spruce has a special on the kits, fine wires for massive prices. the left over money will buy a nice set of VG's and a new windshield...Tim.

[Guest]

Re: Mag and plugs....rough mag question

Tim,

Check out Fresno Airparts , they used to a have a good deal on pair with wires and plugs.

I just looked, they still do, $775, two OH mags with harnesses & new plugs.

Dave