Is it really oil fouling?

[CBogle]

O.K. Your inputs, as always, have been very helpful on the topics of Autolite plugs and oil fouling, and Top Overhaul vs. Major. Thanks much, I really do appreciate it.

Now, if I could get some guidance in determining if I really have an oil fouling problem. Some questions:

1. If I have an oil fouling problem at start-up caused by oil leaking back through the valve guides after shut-down, wouldn't there be visible smoke from oil burning coming from the exhaust at start-up and wouldn't the plug be already fouled at start-up? The reason I ask is that I see no smoke and the plug never fouls until several minutes into a low rpm taxi.

2. Is my assumption correct that because I'm burning lead free auto fuel, that the fouling can't be caused by the fuel? Or, can unleaded auto fuel still foul plugs somehow?

3. What are some ideas to help me diagnose this problem with more certainty?

Thanks,

Curt - N4288V

[CBogle]

Another question:

4. As I indicated earlier, the fouling always clears up, all other engine operations appear normal, I've noticed no difference on oil consumption, etc. Therefore, is my assumption correct that it is still safe to fly the airplane while I continue to try to identify the cause of the fouling? In other words, if in fact it is oil leaking past worn valve guides after shut-down, this doesn't mean that a cylinder or valve failure is imminent, does it?

Thanks,

Curt - N4288V

[N1478D]

Hi Curt,

Before they introduced eythonal(sp) in mogas, I burned alot of both types, avgas & mogas. I rotate and clean the plugs every six months and the only difference I could see related to gas and plugs was the type of deposits that had to cleaned out of the plug.

So, related to your #2 question, my experience has been that the fuel type doesn't foul the plugs differently.

You should be able to remove enough parts to feel how loose/tight the valves are in the guides fairly easily. Depending on how loose/tight things are would be a indication of how serious of a problem it could be.

[Bruce Fenstermacher]

Curt

Here is what I'd do.

I'd first at the least rotate the plugs from the top to the bottom and see if the "fouling" persists. If not it's a bad plug.

I'd then try to determine which plug/cylinder is fouling and if it's the same plug/cylinder each time. How's the plug wire to that cylinder/plug if I narrowed it down to one.?

What's your starting procedure. Perhaps your fouling the plug with fuel. Try something different. HEY heres an idea. Are you sure your primer isn't leaking fouling a plug after the start?

Once I got it narrowed down and I was more sure it was indeed oil fouling the cylinder I'd inspect the cylinder closer. First with a compression check noting where the air was leaking ie which valve or rings.

If at this point if I suspected a loose valve guide I'd remove the valve spring with the cylinder in place and wobble the valve in the guide to get a feel for how loose it may be. Lycoming actually has a wobble test with tight and loose criteria that can be measured with a dial indicator. I'm not aware that Continental does but they might.

After I ran through all this I'd have more specific information to give to "experts" will seeking their recommendation.

Would I fly your plane given the information you've supplied. I probably would. But then I fly helicopters low level in bad weather at night for a living.

[CBogle]

Brice:

So far this all seems to be happening on the #4 cylinder. The first thing I did a couple of weeks ago was pull the bottom plug, had it cleaned and tested, and exchanged it with the top plug from the same cylinder. My first assumption was I might have a bad plug since this all started immediately after my last annual and the changing from Champion to Unison plugs. By the next two or three flights the bottom plug was fouling again on the same cylinder.

I also thought I might be having an ignition wire problem to that specific plug. Question: how does one check for a bad ignition wire short of replacing that one wire?

The primer fouling is an interesting idea, but, I almost never need to prime down here in Alabama and my starting procedures haven't changed in five years, so there is some other variable at play.

From one of the replys it does appear that plugs can get fouled on auto fuel. This I didn't know. However, this apparent fouling problem that I'm having happens on both 100LL and auto fuel.

Your advice on the sequence of steps to help identify the problem is very helpful.

I think the next thing I'll do is check the ignition wire as soon as someone tells me how to do so.

Next, I'm going to montior very closely whether the fouling is always on the same cylinder. I thought it was but just yesterday, it appeared to be on #2 but cleared so fast I'm not sure.

After that, I think I'll take it to someone who can "get at the inside" to wiggle things as suggested who is a little more proficient than me.

I used to base the plane a the airport in Lebanon, PA. Jay Shearer did my first annual. He was really good...wish I had someone like him nearby.

Best regards,

Curt

[CBogle]

Bruce:

Sorry about calling you Brice! I had corrected that during the preview but it didn't take.

Thanks,

Curt

[Bruce Fenstermacher]

While it doesn't seem like it's the new plugs why not replace those your having trouble with with your old Champions till you find the real problem. Chances are the Champions will foul as well but you will have eliminated the spark plug type as an issue.

Just because you don't use your primer doesn't mean it's not leaking. I'd look there. New primer o-rings are pennies and they don't take more than a few minutes to change.

While it wouldn't be legal to fly you could eliminate the primer question by removing the primer line from the primer nozzle at the manifold. Cap the line and the nozzle and see if your problem goes away.

Plug wires can be tricky. Wires are usually checked by their resistance but I don't know the criteria to be looking for.

Depending on the length of the wires you have you may be able to swap the bottom for the top for diagnostic purposes.

[Bruce Fenstermacher]

OK after further thought you might not want to switch the plug wires because of the difference in timing between the mags. But would that make a difference?

Perhap someone else with a clearer mind might comment on this.

[davevramp]

Bruce brings up a good point. If I may expand, you can use an ohm meter to check for opens in your ignition cables but what you really want to do is check them for electrical insulation value. There is a device that called HIGH VOLTAGE CABLE TESTER (http://www.aircraftspruce.com/catalog/t ... tester.php)
It puts a high voltage in the on the conductor and you can visually see or hear it go to ground if the cable is bad. Kind of a service test. The new plugs could be pushing the resistance over the edge and the cable firing to ground.

dave

[HA]

checking ignition wires- you can pull the wires off of the mag (just remove the whole plate holding all the wires, 3 or 4 screws - the shielding is swaged to the plate for grounding so they'll stay with it) and check continuity of the wires from end to end with a multi-meter. While you're checking it have a friend wiggle the wire along it's length to determine if there is a break somewhere.

if that's good you can borrow a high tension lead tester that will put high voltage into the wire which will "leak out" if there is a problem with the insulation anywhere. you might have to borrow the mechanic along with the tester if they aren't in to loaning tools.

also look along the wires for insulation or shielding breaks that could cause intermittent problems. bottom wires have problems with this right at the plug where they have to make the tight turn and sometimes chafe on the muffler shrouds. also look carefully where wires are tyrapped or clamped, or go through baffling etc.

but in light of your original description, I'd go along with the oil fouling theory anyway. pull the suspect plugs before you start and look for oil in the end, if you have some and can clean it out (use carb cleaner or some such, watch your ) and don't have any fouling problem once you start then you've probably isolated it.

[CBogle]

All:

Went out today and taxi'd out and #4 cylinder was fine, but, #1 fouled slightly, on the bottom plug. Cleared up on run-up.

It may or may not help, but, I'm going to order six fine wire plugs and put them in the bottom of each cylinder. (According to the Champion Web Site, there is no problem mixing fine wire with massive electrode.)

I realize from the input that this may not help, but, it definately won't hurt. My impression that the fouling was always occuring on #4 is suspect...I need to check more closely as most of the time I just cleared the roughness without checking, assuming it was #4.

I really do appreciate all the input and I may indeed have a cylinder that needs attention, but, right now, I'm suspecting these Unison plugs...never, ever had any fouling problems until immediately after switching to Unison. (I'm definately not trying to start any controversy here, such as auto gas versus Av gas...not knocking Unison, but, it is the only thing that changed that I'm sure of.

Thanks again all....I'll report back as to what happens.

Regards,

Curt - N4288V

[N1478D]

Was anything done/adjusted to the mags during the annual?

[Roesbery]

Sometimes you can see if plug wires are leaking by removing the cowling and running the engine at night ( Dark ) and looking at the wires. You should see any arcing to ground, a simple repositioning of the wires can sometimes fix that. Be sure the plane is tied down and stay away from the prop. After a flight let it sit all night and then pull the bottom plugs, you will see if there is any oil fouling in the plugs. How about carb ice, those continentals love to make ice or condensation, or possibliy cold plug condensation from combustion on start, clearing as temps rise. Are you in a humid area? Do you leave the mixture full rich or lean it out to best RPM while the engine warms up? Does the roughness clear up during run up by leaning to almost stopping? Just some thoughts before you tear it all apart.

[CBogle]

We checked the timing but didn't adjust them at all. In addition to the fouling that started immediatly after installation of the Unison plugs, the left mag (bottom plugs) drops slightly more than it used to, but still well within limits. Prior to changing to the Unison plugs, however, the RPM drop when doing a mag check was almost undetectable.

The problems that I'm having are all probably completely coincidental to the installation of the Unison plugs and most likely has nothing to do with them, but, it is the only thing that I know changed. Going back to Champions probably won't help, but, if it doesn't, at least I'll have eliminated the plugs as the cause.

Thanks,

Curt

[Dave Clark]

On the primer leak issue the o-rings just keep the fuel from leaking past the shaft and into the cockpit side. The plunger has a tapered end that hits a seat when closed to shut the fuel off to the cylinder side. There are also check valves in there. This is where it can be hard to detect so you'd want to cap off the line and the plug the other side somewhere in front of the firewall.