Champion spark plugs

[PT20J]

My Lycoming factory rebuilt IO-360-A3B6 came with Champion REM38E sparkplugs which now have a little over 300 hours on them.

Most of us probably recall the problems Champion had with the removable sparkplug resistors. And many probably know that Champion changed the design around 2014 to utilize a molded-in resistor similar to the Tempest design. What I just learned from a former Champion engineer is that another change was made at the same time. To simplify the manufacturing process, Champion also eliminated the cement between the ceramic nose insulator and the center electrode. The problem with this change is that it allows high pressure combustion gasses into the space between the insulator and the electrode which can (rarely) crack the insulator. 

I investigated this because I recently found cracked nose insulators on two of the REM38E sparkplugs in different cylinders. The first sparkplug made me aware of its damage when I had a preignition event during a climb. I caught it promptly and enriched the mixture and reduced power which stopped it. Subsequent compression test and borescope inspection showed no damage. Highest CHT attained was 450 F. The cause was a piece of ceramic chipped off the insulator nose that was held captive by the ground electrodes. Unable to shed heat, the chip became an ignition source. I pulled the other sparkplugs and found another insulator missing a piece which apparently departed the engine through the exhaust valve.

I learned a couple of other interesting things while discussing this with the engineer. First, insulator cracks caused by dropping a sparkplug usually occur at the opposite end of the plug rather than the firing end, unless the plug lands on the electrodes, in which case the damage to the electrodes is pretty obvious. Another way to crack a nose insulator is by putting a wire gapping gauge in the gap when gapping and tightening the tool too tightly which puts a side force on the center electrode. Some maintainers like to gap this way because it reduces the chance of closing the gap too tightly, but Tempest doesn't recommend it because it can damage the plug. So, if you do it this way, be careful.

I'm now trying out eight new Tempest UREM37BY sparkplugs.

Skip

[EricJ]

Interesting. 

Ahg, had to edit this as I'd remembered it wrong.   I had a Champion RHM38E fail a couple years ago with a big chunk missing from the nose which we caught at annual, but I replaced it with another Champion.   This annual one of my Tempest fine wires had a cracked nose.

I haven't noticed any evidence of detonation, so fingers crossed these are both due to other things. 

 

[A64Pilot]

Two things turned me off of Champions years ago before they had problems

1. They rust

2. They cost more, and I don’t believe they are worth the additional cost, same with their filters

[PT20J]

At MooneyMAX someone showed me a picture of a Champion spark plug that had lost it's entire ground electrode assembly. I discussed this with the engineer, also. The barrel and the electrode assembly are separate parts made of different alloys (the electrodes have high nickel content and the barrel is just carbon steel). The electrode part is resistance welded to the barrel during manufacture and then a thin portion of the bottom of the barrel is mechanically rolled over to form a secondary mechanical connection. If the rolling process thins the metal too much it can be weak and if the same plug had a bad weld it is possible for the two parts to separate in service.

Skip

[PT20J]

3 hours ago, EricJ said:

Interesting. 

Ahg, had to edit this as I'd remembered it wrong.   I had a Champion RHM38E fail a couple years ago with a big chunk missing from the nose which we caught at annual, but I replaced it with another Champion.   This annual one of my Tempest fine wires had a cracked nose.

I haven't noticed any evidence of detonation, so fingers crossed these are both due to other things. 

 

I doubt you ever had any detonation. I discussed detonation with George Braly a while back:

QUESTION: I'm curious to know if you have ever been able to get a conforming normally aspirated engine burning conforming fuel to detonate under any condition when the highest CHT is below 400 dF.

RERSPONSE: [GOOD QUESTION.  No at 400dF.    But at 430F, then Yes.  But only marginal detonation and only if the 100LL was lower range or “min-spec” MON 100LL and if the IAT was elevated and the mixture was in the range of  35dF ROP back to peak EGT - - and the MAP was near max S.L. MAP. ]

Skip

 

[Pinecone]

We just trashed a piston and cylinder on a C-182, O-470 due to detonation.

A picture of the piston looks just like the detonation picture in Mike Busch's book Engines.

Not sure what the CHT was, as we only have a single probe, that always reads high (winter, cowl flaps open, it still read over 400).  

[PT20J]

On 7/15/2022 at 3:38 AM, Pinecone said:

We just trashed a piston and cylinder on a C-182, O-470 due to detonation.

A picture of the piston looks just like the detonation picture in Mike Busch's book Engines.

Not sure what the CHT was, as we only have a single probe, that always reads high (winter, cowl flaps open, it still read over 400).  

Interesting. I used to rent a C-182 to fly from San Jose to Truckee to go skiing and I never saw CHTs that high. Wonder what’s causing yours to be so high? Any other C-182 drivers here?

Detonation is the rapid, uncontrolled burning of the end gas (the part of the mixture that has not yet burned) and the end gas is near the cylinder walls (the flame quenches when it reaches the relatively cooler cylinder walls) which us why the pressure spikes damage the edges of the piston.

Preignition actually results in detonation, but since the process starts much sooner, there is more heat transfer to the cylinder components which is why continued preignition tends to melt the center of the piston. 

Detonation requires heat because it is the raising of the end gas to the self ignition temperature that causes it. Heat can come from elevated CHT and/or higher pressure (compression heating). You cannot hear the pinging in a noisy airplane and detonation may not reduce power enough to cause noticeable roughness. According to George Braly, detonation heating can set off catastrophic preignition and the already elevated CHT rises very rapidly in a few seconds. He’s trashed a few cylinders on the test stand this way.

I did notice some engine roughness during the preignition event as the CHT for that cylinder climbed above 400 F.

According to George Braly, if CHT doesn’t exceed 525 F the cylinder generally escapes serious damage, but above 525 F it’s trashed. 

Skip

EDIT: Corrected Braly’s observation of maximum CHT before damage is certain from 500 to 525. 500 number was my recollection, but 525 number comes from a more recent post on BeechTalk

https://www.beechtalk.com/forums/viewtopic.php?f=37&t=186351

 

[Pinecone]

Not sure.  Shop has changed the gauge, the probe, wiring.  

Recently compressions were down and borescope showed glazed cylinders due to improper (low power settings) break in.   So they honed all the cylinders and the breakin was done properly

All was good until this last flight.  About 5 minutes after takeoff, very rough running engine.  Returned to the field.

I have pictures of the piston and cylinder.  But the piston could be the twin of the one in Mike Busch's Engines on page 30

[Yetti]

On 7/14/2022 at 6:23 PM, PT20J said:

My Lycoming factory rebuilt IO-360-A3B6 came with Champion REM38E sparkplugs which now have a little over 300 hours on them.

Most of us probably recall the problems Champion had with the removable sparkplug resistors. And many probably know that Champion changed the design around 2014 to utilize a molded-in resistor similar to the Tempest design. What I just learned from a former Champion engineer is that another change was made at the same time. To simplify the manufacturing process, Champion also eliminated the cement between the ceramic nose insulator and the center electrode. The problem with this change is that it allows high pressure combustion gasses into the space between the insulator and the electrode which can (rarely) crack the insulator. 

I investigated this because I recently found cracked nose insulators on two of the REM38E sparkplugs in different cylinders. The first sparkplug made me aware of its damage when I had a preignition event during a climb. I caught it promptly and enriched the mixture and reduced power which stopped it. Subsequent compression test and borescope inspection showed no damage. Highest CHT attained was 450 F. The cause was a piece of ceramic chipped off the insulator nose that was held captive by the ground electrodes. Unable to shed heat, the chip became an ignition source. I pulled the other sparkplugs and found another insulator missing a piece which apparently departed the engine through the exhaust valve.

I learned a couple of other interesting things while discussing this with the engineer. First, insulator cracks caused by dropping a sparkplug usually occur at the opposite end of the plug rather than the firing end, unless the plug lands on the electrodes, in which case the damage to the electrodes is pretty obvious. Another way to crack a nose insulator is by putting a wire gapping gauge in the gap when gapping and tightening the tool too tightly which puts a side force on the center electrode. Some maintainers like to gap this way because it reduces the chance of closing the gap too tightly, but Tempest doesn't recommend it because it can damage the plug. So, if you do it this way, be careful.

I'm now trying out eight new Tempest UREM37BY sparkplugs.

Skip

at annual.  One of the valves was not closing all the way.  Which resulted in hammering out of the exhaust valve.  and then reaming the crud out of the guide with a .4995 ream.    We pulled the Champion BY plug (longer plug for oil fouling.)   half the insulator for the electrode was gone.    These plugs were replaced about 4-5 years ago so same time frame. Excited to fire the engine up and see how she runs.   There was a tiny bit of morning sickness for a quick period of time.