Q: I have a 1979 Arrow IV with an IO-360-C1C6 200-hp engine. My #3 cylinder EGT runs about 120° higher than the other three. I lean to accommodate #3 at about 1,400°, which makes the rest of the engine run pretty rich.
Today I took the spark plugs out of #3 and found some light colored deposits between the insulator and the barrel of the spark plugs. Both had the deposits. Both were black around the electrodes. I took the spark plugs out of cylinder #1 and they were also black, but had no deposits.
I need to add oil every three or four hours of flying. Compression on #3 was 80/80 at the last annual in June. That was actually up from the previous annual (bad measurement?).
Am I leaking oil into #3 or do I have a partially clogged injector nozzle, defective fuel distributor, or injector? What do you suggest?
Bob Wert
A: From the information you provided, I’m suspicious of a partially blocked #3 cylinder fuel nozzle.
The typical indications of this are a richer fuel mixture on the other cylinders, which would be what you are seeing on the three spark plugs with the black color.
My suggestion is that you remove all of the nozzles and flow check them. This can be done by disconnecting the fuel line at each nozzle, then carefully removing the nozzle from the cylinder.
Use caution because, depending on the age of the engine, you may have a two-piece nozzle installed and the two pieces must be kept together at all times. Do not mix the pieces of these nozzles because they are a matched set, but are much easier to clean than the one-piece nozzle.
If your engine has the one-piece nozzles, then my suggestion is to check for any foreign material in the nozzle prior to cleaning them. This can be done by holding the nozzle up to the light and looking carefully in the hole while you slowly roll the nozzle between your thumb and forefinger. What you are looking for is a tiny piece of foreign material that may be lodged between the air side and the fuel side of the nozzle. By rolling the nozzle, you may observe something drop across the hole the fuel passes through.
Do not, under any circumstances, put a wire or anything in the nozzle to clean it.
Assuming you see no foreign material, then I’d suggest you soak the nozzles in some Hoppes #9 gun oil, which is a great solvent to clean the nozzles.
Once you’ve allowed the nozzles to soak, you may then remove them and blow “clean” shop air through them in the direction the fuel flows.
Once you’ve completed the above, it’s now time to reattach each nozzle to its respective fuel line. Locate four equal quantity containers, such as baby food jars, and put each nozzle in a jar. With the master switch on, turn on the boost pump and put the throttle and mixture full open and observe the flow pattern from each nozzle. They all should show a nice even pencil point stream of fuel.
If you notice one or more of them having a wiggly erratic flow of fuel, that is probably your problem nozzle. You may try cleaning it again or, better yet, replace it.
This entire process shouldn’t take more than 30 to 40 seconds.
Now you can turn off the boost pump and master switch.
The next step is to take all four jars and set them on a flat level surface and check the total quantity of fuel in each jar. They should all have an equal amount of fuel. If one jar has less fuel, then that’s the bad nozzle and should be replaced.
With regard to your oil consumption, I’d say you have no problems there and this is probably a rather normal consumption with an engine that has a decent amount of time on it.
” Do not, under any circumstances, put a wire or anything in the nozzle to clean it. ”
https://www.mscdirect.com/browse/tn/Holemaking/Chucking-Reamers?navid=4287924615+4288237227&searchterm=Reamers#navid=4287924615+4288237227&searchterm=Reamers
This will likely will never get passed the A&P overseers, but
there are commercially available reamers made to the tenth of a thousandth.
regular gage pins will tell you where you are to the nearest thousandth, usually .027 go .028 nogo
open up the one that is too hot compared to the other three and you will be able to lean those other three properly without burning up the cylinder that runs hot due to the
” flawed design of the upper cowling ”
ask yourself, how do the GAMI guys get their nozzles so precise ? Luck ?
very lucky guys, huh.
It is all too common for 4 cylinder PA28’s to have #3 run significantly hotter than the other cylnders. I have a 1968 PA28-180 with a Lyc O-360-A4A and I spent several years trying to chase down issues with a hot #3 cylinder. In that time I had replaced all baffling chased down induction leaks from the intake tubes as well as loose primer lines, I even changes the carburetor for one with a larger nozzle to increase fuel flow during take off and climb out. I have practically become an expert on baffling and have discovered just how many little details pertaining to baffling are missed by even the most seasoned A&Ps. Yet despite being able to bring down CHTs significantly, #3 is still the hottest. It is actually unavoidable but I currently understand why it happens so here are the major factors:
1) On most PA28s with the xO-360-xxx variant, the oil cooler hose attachment comes from the rear baffle behind cylinder #3. This very large opening robs #3 of some cooling air. You may notice that in the winter when you install the winterization plate that #3 temp will be much closer to the other cylinders (expect #1 which is always cold.
2) The design of the cylinders on this engine has the more massive bulk of cooling fins on the exhaust port side of the cylinder. This means that for #3, the bulk of the cooling fins rests in the middle of the engine and does not benefit from very good air flow. Some people have also reported issues with their #2 CHT being higher than desired. #2 suffers from the same issue, but at least benefits from ram air cooling.
3) The design of the PA28 cowling is about as inefficient as you can get. I am not an expert here, but I have learned from those who are experts in aerodynamics that the intake ports are too large and result in lower pressure than needed in the upper cowling. I have also heard that the shape of the intake opening are inefficient, but I do not know enough about fluid mechanics to understand the reason for this.
4) For carbureted engines, the mixture distribution is highly variable with throttle plate position. At FT, the rear cylinders run considerably leaner that the front two cylinders. I have had success pulling the throttle back just enough to maintain full throttle MP to slightly cock the throttle plate to even out distribution.
5) Baffles, baffles, baffles!!! It is critical that baffles are not only in good shape, but positioned properly. For example, the front lower baffles are almost always mis-aligned after re-installing the cowling. They need to be bent forward to provide a seal against the lower cowl. And be sure that baffle seals overlap properly. ALL baffles seals should overlap in a manner that ram air will push them together rather than lift them apart.
As I said, despite all these points, you will likely never get #3 CHT down to where you want it. It’s the result of a flawed design of the upper cowling. But with some work you can get it down to an acceptable level.
Just a minor…the text mentions Hoppe’s No 9 “gun oil”. The pic shows Hoppe’s No 9 Bore Cleaner. To avoid confusion, Hoppe’s No 9 is bore cleaner. Don’t use oil to clean the injectors.
And as a bonus, Hoppe’s No 9 is some of the best smelling stuff on the planet.
Correction…Hoppe’s No 9 is the brand. Get the bore cleaner.