Ash deposits on 912ULS spark plugs

[3kdscf]

Is this what ash buildup looks like? It doesn't match any of the "reading your spark plug" charts but the ash looks the most similar. There are globs of buildup that scrape off easily with the lightest pressure from a knife. If it is ash, the cause listed is leaking valve seals - how could that happen on an engine on a 400hr engine? Is it just fouling because my front cylinders are too cool?

The spark plugs in the photos were changed 100 hours ago. The plugs on the back two cylinders look fine but the plugs on the front cylinders definitely do not look normal. On previous plug changes, the front plugs have always been much darker than the back plugs but this is the first time it's looked this ugly. I have always used the NGK DCPR8E plugs gapped to 0.025" and I change the plugs at every 100hr inspection. My EGT sensors are on cyl 2 and 3 and run about 1200F with about 50 degrees difference between the two of them. I have always used 100LL with Decalin in every tank. Oil used is always Aeroshell Sport Plus 4.

Any suggestions what to do?

Thanks!

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Note: Although it appears that there is thermal paste around the first thread on the Cyl 3 plug, I dont think that is what it is. This is how I always put the paste on the plugs:
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[rv9ralph]

That looks more like lead. Are you using Decalin in the proper ratios?

[Dave S]

Dan,

That is somewhat less cruddy than I would expect if you are running 100LL for 100 hours (maybe the decalin helps a little). The gunk is mostly lead deposits but mixed in with some carbon residue. The guck in the thread of the one plug is likely lead residue collected on the edge of the plug. The guidance photos leave a little to be desired.

Significant oil leakage past the valve guides would be normally accompanied by measureable oil consumption.

It seems the ULS usually runs a little richer on the front two cylinders.

Not sure there is anything to do:confused:

[3kdscf]

Significant oil leakage past the valve guides would be normally accompanied by measureable oil consumption.

It seems the ULS usually runs a little richer on the front two cylinders.

Not sure there is anything to do:confused:

Thanks Dave,

That makes me feel a lot better! I have never had to add any oil between 50hr oil changes so I guess that does eliminate leaking valve guides.

[3kdscf]

That looks more like lead. Are you using Decalin in the proper ratios?

I have been using the Decalin at the rate they recommend but upon looking at the label again, the "1/2 oz per 10g" is a minimum. Given this issue, I think I will try increasing to 1oz per 10g on this new set of plugs.

[Delta Whisky]

Is there any chance your flight habits changed in the last few hours? Maybe shorter flights and/or at lower power settings? Scenic or passenger demo flights? Are you keeping the RPMs at 5200 or higher? I ask because you say this is the first time they look "this ugly" and the front plugs have definitely been running cooler. The ash pictured is what I see when running Decalin. Are the plugs pictured all from the top or bottom of the head(s)? Once the work (I assume an annual) is complete you might want to take at least a 30 minute flight at 5400 or 5500 RPM and then take another look.

[3kdscf]

Actually this was totally different operation as I did a 80 hour cross country trip with this set of plugs rather than short local flights. On my xc trip I ran about 5250rpm much of the time because of headwinds. Also, my local flights are in the desert where its always hot compared to the cool weather on the cross country flight.

Both the top and bottom plugs up front were equivalently ugly. Good idea to pull the plugs again now that my 200hr engine service is done and take another look!

[Slyfox]

here is a picture of one of my plugs, this is the one closest to the firewall, the ones at the front looked just a nice, maybe nicer. I had been running with a super rich condition previous and did nothing to the plugs after it started running good31038. Now the engine is running super nice. I removed the plugs to regap for winter and to clean thinking I needed to do it. I didn't clean them just regapped for smaller gap(.022) for winter. Anyway I was quit surprised on how they looked. I feel the plugs looked so good because I put a cross over of 1 inch on, from hal Stockman. I will say not only was the plugs very clean but now the engine runs like a top with NO miss what so ever from idle to full rpm.31039

[Slyfox]

I run mainly 91 oct auto gas no alki. At one time about a month ago I filled both tanks with 100ll ( no decaline) because I was having an issue and thought I was having peculation problems. Ended up being a carburetor with a bad seat for the needle and seat. Got a different carb and problem fixed, at the same time put on the cross over. I really feel the cross over stopped the black plugs in the front because that was a problem since new on the engine.

[3kdscf]

Update. So I did an experiment since the last spark plug change. I used 2x the recommended amount of Decalin per tank and I also increased my cruising oil temperature from about 160F to 200F by temporarily taping over my oil cooler. Wow! The difference is incredible. My guess is that its the increased Decalin that cleaned my plugs.

I know this, I will continue to put in twice the amount of Decalin that the label on the bottle suggests.
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[Dave S]

Dan,

Not bad! Looks so much better that the first photos you showed with the grunty plugs.

If I recall, Decalin states the recommended amount as a minimum.

Maybe this is a legitimate example of "Mores Law"....If some is good, more is better and too much is just right.

I think you convinced me to increase the amount of Decalin I use when occasionally burning 100LL.

Good work.

[3kdscf]

Maybe this is a legitimate example of "Mores Law"....If some is good, more is better and too much is just right.

.

LOL! By the time I zero in on precisely the right amount of Decalin, we will have lead free aviation gas at all our pumps. In the meantime, on this next plug change my experiment is to use 50% more than recommended rather than double the recommended amount.