Spark Plug Troubleshooting

[Marauder]

Want to get your opinion on what I am seeing. Went to fly tonight and had a rough mag that I couldn't clear. The JPI indicated it was the #2 cylinder, right mag. If i remembered the cylinders orientation correctly, this should be the front left cylinder on the pilot's side. Since the JPI was indicating an issue on one mag, I pulled the lower plug. I found a very small amount of lead in it (I lean aggressively so seeing lead fouling is unusual for me).

I decided to pull both plugs on this cylinder. The top one had no lead. I pulled out my trusty ohm meter and found the article Daver posted last year with the Champion plug changes that addressed the high ohm readings. I always carry a couple of new plugs with me and pulled one of them out and measured the resistance. The article said it should be between 800 and 1200 ohms. The new plug was exactly in that range (keep in mind this is a 24 year old plug).

Put the ohm meter on both plugs I pulled and found them both wide open!

So, obviously these plugs are toast. Right? Since I have two new ones, is there a gap spec that I need to set for them? It is clear the old plugs are getting worn. The new plug:

[Hank]

I do 0.018-0.021 (I think). The red double-ended gap set, use the smaller ones. But then again. I have a carburetor, O-360, not an IO.

[Marauder]

And BTW -- these plugs have been in there FOREVER! I asked my mechanic every year about changing them out (along with the spark plug leads) and he kept saying they were fine to fly with. I will pull my logs tonight and see how long they have been in there.

[carusoam]

The moment you have been waiting for has arrived!

You either get new fine wire plugs or a new fluke meter.

Best regards,

-a-

[Marauder]

Just now, carusoam said:

The moment you have been waiting for has arrived!

You either get new fine wire plugs or a new fluke meter.

Best regards,

-a-

After dropping a pretty penny on new strobes, I was hoping to get back to my cheap bast#$d ways.

[Marauder]

Well, it appears these have been in there since my last overhaul. Looks like 940 hours. Could that be? If I were to replace them with Tempest, what are the recommendations? I have Champion REM-38E massives. I see from the Tempest chart 37s, 38s and 40s can be used. Why would I pick one over the others?

[milotron]

Marauder, I just swapped my 800 hour old massives for fine wires and measured the Unisom plugs that came out. Initially I was getting the same readings as you and really had to scratch at the electrode surface to get any reading less the megohms. After getting through this high resistance layer, the plugs came out on the 900k ohm range. Mine were terribly eroded explaining my high altidude and lean misfires, but the resistance was fine after all of that.

 

The fine wires are soooo much smoother and lean so much farther.

[carusoam]

Sanding the plug to get a better resistance reading could make some sense. Use caution to not get any abrasive material left behind in the plug.

how oblong is the center post.  They turn a bit oval shaped with time.  They start out as cylindrical and erode to the shape of a football.

What is the coating left behind?  Soot, lead oxide, oil or carbon?

That would be an interesting find if some form of lead oxide coating is causing higher electrical resistance.

PP ideas, not a mechanic...

Best regards,

-a-

[milotron]

Mine were very oval. The gap was well beyond spec also. I was already committed to the fine wires for their inherent benefits.  

The residue on the electrode was not significant; virtually no lead as I lean aggressively to reduce this. The on cylinder running warmer had some minor soot, but all others were a healthy tan color.

 

I had this conversation with the local flying club where I am based. The C172s use massive that never get replaced. They typically run so rich all the time, and are rarely at altitude that they only get replaced when they are actually cracked or broken; it doesn't matter how eroded they are, they go back in. Mechanic said that most of the plugs have 1500 hours or much more on them and they never have ignition related issues. They use a hotter range on the bottom to reduce fouling, but that is it.

[Marauder]

36 minutes ago, milotron said:

Marauder, I just swapped my 800 hour old massives for fine wires and measured the Unisom plugs that came out. Initially I was getting the same readings as you and really had to scratch at the electrode surface to get any reading less the megohms. After getting through this high resistance layer, the plugs came out on the 900k ohm range. Mine were terribly eroded explaining my high altidude and lean misfires, but the resistance was fine after all of that.

 

The fine wires are soooo much smoother and lean so much farther.

Thanks for sharing that. I will clean them up a bit and see what I get.

[Marauder]

After cleaning, the top one is showing 2.02M ohms, and the bottom is now 38k ohms. According to the video I watched, 5,000 should be the limit. Hmmm....

[milotron]

I had to really scratch into the electrode tip with the test prove to get a reading; I didn't really clean anything, but had shiny metal exposed where the probe scratched in. I was only going to keep these plugs as spares anyways, with the fine wires going in.

You have real numbers now at least, but still are over the recommendations.  With that higher resistance, and the wear, it certainly couldn't hurt to swap the plugs.  Not sure on the gap value, but for the most part they are pre gapped out of the box.

Edited September 23, 2016 by milotron

[jetdriven]

Not to mention that high resistance contributes to the breaking down of Slick magneto coils.  This often turns into a breakdown and a 1500$ bill for a new mag and the R&R 

[Guest]

7 hours ago, Marauder said:

Well, it appears these have been in there since my last overhaul. Looks like 940 hours. Could that be? If I were to replace them with Tempest, what are the recommendations? I have Champion REM-38E massives. I see from the Tempest chart 37s, 38s and 40s can be used. Why would I pick one over the others?

The UREM37BY plug works well.

Clarence 

[Hank]

2 hours ago, M20Doc said:

The UREM37BY plug works well.

Clarence 

I don't remember if I changed from 37 to 38 or the other way around. Whatever plugs Byron received with his new engine and took out to replace with Tempest fines.

[Marauder]

1 hour ago, M20Doc said:

The UREM37BY plug works well.

Clarence 

So, it looks like you are recommending massives instead of the fine wire. Any reason? I started looking at Mike Busch's video on spark plugs. He said if you needed a 3/4" wrench to remove the B nut, I have the waterproof harness. So this means I should be looking at the URHM38E (massive) or the URHB38S (fine wire). There are no 37s for the 3/4" harness. Did I read that correctly?

[Marauder]

9 hours ago, milotron said:

I had to really scratch into the electrode tip with the test prove to get a reading; I didn't really clean anything, but had shiny metal exposed where the probe scratched in. I was only going to keep these plugs as spares anyways, with the fine wires going in.

You have real numbers now at least, but still are over the recommendations.  With that higher resistance, and the wear, it certainly couldn't hurt to swap the plugs.  Not sure on the gap value, but for the most part they are pre gapped out of the box.

Busch's video recommended 0.016" gaps on them.

[jetdriven]

1 hour ago, Hank said:

I don't remember if I changed from 37 to 38 or the other way around. Whatever plugs Byron received with his new engine and took out to replace with Tempest fines.

i think yours are URHM38E but the -BY plugs are very different, they are the extended electrode plug for the O-235 engines which was approved for most models.  I've heard they run LOP about as as good as fine wires.  But I haven't verified that. 

[Oldguy]

1 hour ago, Marauder said:

So, it looks like you are recommending massives instead of the fine wire. Any reason? I started looking at Mike Busch's video on spark plugs. He said if you needed a 3/4" wrench to remove the B nut, I have the waterproof harness. So this means I should be looking at the URHM38E (massive) or the URHB38S (fine wire). There are no 37s for the 3/4" harness. Did I read that correctly?

I have Tempest massives and regularly run LOP without a problem. Cold and hot starts are all fine as well.

[Bob_Belville]

1 hour ago, jetdriven said:

i think yours are URHM38E but the -BY plugs are very different, they are the extended electrode plug for the O-235 engines which was approved for most models.  I've heard they run LOP about as as good as fine wires.  But I haven't verified that. 

 I installed UREM 38S (Tempest fine wire) in my IO360 A1A over 4 years ago, shortly after buying this E. Never have to even think about the plugs... running LOP, starts, idle, etc. I believe that fine wire plugs are better and in the long run cheaper. Current ASpruce is ~ $76. ea.

http://www.tempestplus.com/Portals/0/PDFs/ProductLiterature/p4871-TempestAppGuideV324x36.pdf

[ArtVandelay]

1 hour ago, Marauder said: So, it looks like you are recommending massives instead of the fine wire. Any reason? I started looking at Mike Busch's video on spark plugs. He said if you needed a 3/4" wrench to remove the B nut, I have the waterproof harness. So this means I should be looking at the URHM38E (massive) or the URHB38S (fine wire). There are no 37s for the 3/4" harness. Did I read that correctly?

I have Tempest massives and regularly run LOP without a problem. Cold and hot starts are all fine as well.

Ditto, but I do take care not to run rich, severely lean during taxi ops and always cruise LOP.

[Bob_Belville]

3 hours ago, Marauder said:

So, it looks like you are recommending massives instead of the fine wire. Any reason? I started looking at Mike Busch's video on spark plugs. He said if you needed a 3/4" wrench to remove the B nut, I have the waterproof harness. So this means I should be looking at the URHM38E (massive) or the URHB38S (fine wire). There are no 37s for the 3/4" harness. Did I read that correctly?

What is the number of your current (Champion massive) plugs?

My plugs are UREM38S

U: Tempest           (blank: Champion)

          R: resistor

                        E: 5/8"  24 thread                        (H: 3/4" 20 thread)

                                            M: 18mm mounting thread; 1/2" reach; 7/8" hex   

                                                                        38: the higher the number the hotter. Range is - 26-50

                                                                                                      S: fine wire              (E: massive) 

[bradp]

IO-360 engines either take UREM38S or URHM38S depending on whether you have 5/8 or 3/4 spark plug leads to the plug.  

Double check the tempest application chart. 

Easiest to look at the current spark plug part number and match it up to the corresponding tempest fine wire.

From your picture I can read "REM3" in which case you probably need UREM38S.  

Take care

 

B

[Guest]

6 hours ago, Marauder said:

So, it looks like you are recommending massives instead of the fine wire. Any reason? I started looking at Mike Busch's video on spark plugs. He said if you needed a 3/4" wrench to remove the B nut, I have the waterproof harness. So this means I should be looking at the URHM38E (massive) or the URHB38S (fine wire). There are no 37s for the 3/4" harness. Did I read that correctly?

I put a set of 37BY plugs in an A1A, the owner was happy with the performance.  At the price of S plugs they aren't for everyone.

Clarence

[rbridges]

On September 23, 2016 at 5:45 AM, M20Doc said:

The UREM37BY plug works well.

Clarence 

I did some digging on Mooneyspace and came across another thread that recommended these. My IA said my plugs were getting pretty worn but they were running fine. Anyway, just installed them with .015-.018 gap. I thought about fine wires but I'm at 1100 smoh and figured massive would get me close to the next oh.