I will start this blog entry by revealing the ending. My Zodiac XL is happily flying again powered by its smooth-running powerful Jabiru 3300 engine. Saturday I flew 126 miles with the overhauled engine.
Now back to the beginning…
My Jabiru 3300 engine is serial number 1,256. It is about three years old and has 600 hours on it. Since it was manufactured several improvements have been introduced by Jabiru to address high oil temperatures in the cylinders. They are:
1) The oil cooler size has been increased by 50%
2) The fiberglass air ducts have been made wider and now cool substantially more of the cylinders
3) A defect in the cylinder base and through-bolt nuts has been revealed which affects some engines. The defect distorts the cylinder and allows blowby resulting in hot exhaust gas heating the oil
4) The recommended oil has been changed from Aeroshell 100 to Aeroshell 15W 50. The newly recommended oil is 50% synthetic and is better able to withstand high temperatures
5) The pistons have been changed so that the ring grooves are wider. This reduces the chance of the rings sticking in there grooves.
Now you may say “I don’t have high oil temperature”. I would say “how do you know”? Your oil temperature gauge tells you the temperature of the oil in the pan, not the temperature of the oil on the piston rings. If engine oil is exposed to temperatures above about 450 degrees the oil will change into a tar-like substance. These high temperatures can be found in the cylinders where all the heat comes from.
I am no expert on oil and oil temperatures. What I can tell you is my stock Jabiru 3300 engine required an expensive early engine overhaul because the piston rings had become stuck in the piston ring grooves which resulted in reduced performance and excessive oil consumption. So if your Jabiru engine lacks the above improvements you might want to look into some modifications before you encounter a similar fate.
I replaced the pistons, rings, cylinders and rod bearings. I had the heads and valves reworked. Essentially this is the 1000 hour top-end being done at 600 hours.
So what do the engine parts cost? Here is a picture of my parts invoice.
I did all the disassembly and reasonably myself with the aid of the Jabiru manual and an occasional phone call to Jabiru Pacific. I took a few pictures along the way.
The following picture shows a piston without rings, a wristpin and connecting rod. Notice the wristpin end of the rod is discolored. That is from the heat of machining to the larger diameter needed for the new piston's larger wristpin.
The next picture shows the dot on the scraper ring. The scraper ring is the second one down from the "top" of the piston. The dot goes up. The top ring does not have a dot nor an up or down.
The next picture shows the three-piece oil-control ring which goes in the wide bottom groove. This is a sandwich with the bronze-colored ring in the center.
Here you can see the cylinder and the head. There is no head gasket. That is why it is important to keep the 6 head bolts correctly torqued.
Here is a view "down" the cylinder to the head.
I chose to install the rings on the pistons, connect the rods to the pistons, insert the pistons into the cylinders and insert the rod bearings into the connecting rods all in the comfort of my office at home. There are a number of tricky steps here. Keeping the parts correctly oriented and labeled will help. The pistons have a forward and backward relative to the front of the engine. They have markings for this. Half of them end up "right-side up" and half end up "upside down". The rings need to be oriented correctly relative the the top of the engine. The instructions that came with the rings are marginal. I made numerous internet queries for additional information. Here is a picture of all 6 finished assemblies.
Next I took the assembled parts out to the hanger and started several days work putting things back together. I installed the cylinders in order starting with #1 and working back to #6. Here is a pilot's side view of the engine with the number 2 cylinder in place.
It was a bit of a trick to get the connecting rods back in place on the crankshaft. In the next three pictures you can see how I did it. I oiled the rod bearings to help them stay in place. I also used safety wire to keep the cap from sliding out of place and falling down into the motor. Screw this up and you get to take the oil pan off.
Here you can see the safety wire holding the cap so it does not slip into the abyss.
Next I used a long head bolt, which happens to be the same diameter and thread as the connecting rod bolts, to mate the rod to the cap. Once the rod and cap are mated, you can remove the safety wire, screw in the top rod bolt then replace the long head bolt with the rod bolt and torque them both both.
The Jabiru manual indicates that the rod bolts be primed with loctite 7471 primer and "glued" in with Loctite 620. Expect to pay about $20 for each of these. I ordered them off the internet because I could not find these items locally.
Here is a picture of the ends of the push rods. Notice the scoring on the ends. (The three on the right are normal looking.) This is a sign of oil starvation - a design flaw which Jabiru will soon be addressing with yet another modification.
The next picture shows the worn out and damaged motor mount rubber (lower on pilot's side). Its close to metal on metal. In 600 hours and two years the engine had sagged about 3/8 of an inch. This was affecting engine pitch and clearance around the oil cooler.
I bought much stronger rubbers from here
If I were writing a manual there would be many more steps and pictures here. But because I was working alone, stopping to take pictures with oily hands did not seem to happen - sorry. There were a few challenges like getting the two nuts, one on each end of the through-bolts, to end up in the right place - arrrgggg..
Skipping ahead a few days and a few busted knuckles, its time to do the ground run-in of the engine. Two identical 46.5 minute run-in sequences are spelled out in the Jabiru manual. There are specific RPMs to be held for a specified number of minutes. I built a spreadsheet to make following this sequence easier. I used a stopwatch to stay on-track.
The manual forbids doing this with the standard cooling ducts. Far more cooling is needed to prevent over-temps. Here is a picture of the shroud I made from a sheet of galvanized steel. Notice the band of aluminum for a bit of extra insurance. I did not want this chunk of metal to go flying!
The above shroud worked quite well but I was not able to run the three-minute high-RPM segments without inserting a one minute cool down period.
The engine fired up right away. It seemed a bit rough and the #5 cylinder was too cold. I shut it down and started to investigate. The sparkplug wires were OK so it had to be compression - dang! I pulled the valve cover on #5, rotated the prop and watched the rocker arms. At the top of the compression stroke I checked for clearance. There was the problem; no play in one of the rocker arms. The tappet end of the push rod was not properly seated in the center of the tappet so the valve could not close all the way. Sloppy mistake! A little tweaking with a screw driver and she is all fixed. That was easy...
After the run-in I finish by putting the standard air ducts and the cowling back on. Too late to fly it today.
Next day, after the morning fog cleared, it was time for the first flight. I told the tower I had a newly overhauled engine and wanted to climb in a circle over the airport. They kindly agreed. Of course the engine ran hot just like I expected. After one minute of full throttle climb I pulled back to 2300 RPM and continued a slow climb up out of the KSTS airspace. At 3,000 feet with the engine working well I said goodbye to the tower and head off to the QSP open house in Cloverdale a happy camper as they say...
P.S. You can read additional information in my prior blog post