Oil fouling

[zephyr]

Anyone ever experienced a problem with oil fouling on a plug associated with a weak mag? I've had a cylinder iraned twice and both times it was given a clean bill of health. The mechanic thinks it might be a mag problem.

[aaronk25]

Tested the ohms on the plug that fouled?

[mike_elliott]

Hi zephyr

 

Oil getting into the combustion chamber comes from only a couple of places

   1) From the crankcase via the cylinder

The rings are not doing their job and letting oil into the combustion area. Is the offending cylinder chrome, by chance?

Have you listened for a hissing sound from the oil filler spout as you moved the prop thru the compression stroke of the offending cylinder? And while your at it, listen to the exhaust pipe for a hissing sound as you travel thru a compression stroke of the offending cylinder.

   2) From the valves. Have you checked the valve guide clearance via a wobble test or micrometer when it was apart? what did the valve seats look like?

While it is possible that a weak mag wouldn't provide enough spark to clear an oil fouled plug, the cause of the oil fouled plug should be drilled down to. Are you sure this is not lead fouling vs. oil? What are your leaning practices while taxiing and at idle?

 

Just a few random thoughts for you to chase. Good luck in getting it cured

[zephyr]

Aaron and Mike,

Thanks for the reply.

Aaron I don't think its a plug. I've rotated them with the same results at the same location.

Mike, I believe its the nickel cylinders. I know they aren't chrome. I haven't listened to the hissing as you mentioned but the compression checks are all good. It's definitely oil fouling and not lead. Also I lean agressively while taxing and run LOP.

David L

[BigTex]

Might be the spark plug lead. Have you checked that?

[zephyr]

Leads have checked out ok Bigtex. Thanks

[aaronk25]

I just developed a oil issue 2 on my #2 cylinder on my j. I run 400 hours a year and normally burn a quart every 10 hours or so but about 2 oil changes ago it stated burning a quart every 3.5 hours. I thought it might just be the rings lined up bad but the problem is continuing. We're going to pull the #2 cylinder on Monday and I suspect were going to find a broken oil control ring in which we will just re-ring it.

Btw the compressions are all 75-76 and I run peak egt or lean of peak everywhere and run camguard too.

Anyway I'll post the results but I'm pretty sure it's not a valve guide.