My Jabiru 3300 is undergoing a major overhaul

At 600 hours I am replacing all 6 pistons, cylinders and rod bearings. The heads are being overhauled.

My engine is almost 3 years old and has been flying for 26 months. It is serial number 33A 1256.

A few months ago I replaced a burned valve. Recently oil consumption has been going way up. Last Saturday the engine used 2 quarts in 5 hours. It was time to find out why.

When I did my annual a few months ago I performed a leak down compression check. All cylinders came in between 65 and 75 which is acceptable. The instructions that came with the gauge suggest that compression be checked at TDC. I can tell you now; that is not good enough.

Last Sunday I did another test. This time I checked compression not just at TDC but also before and after. What I found on some cylinders, and one in particular, is that shortly after TDC, the values dropped off quickly from 70 to 45. Wow that’s way wrong. What is that? Must be some problem with the rings or cylinder. That hissing noise coming from the oil filler tube can’t be a good sign.

I pulled the head and cylinder off on #5, the worst cylinder, and found that the rings were completely frozen in their grooves, in the compressed state. Because the cylinder is a bit tapered, as soon as the piston started down the cylinder, the rings lost contact with the cylinder wall.

I pulled off the other cylinders. Four out of six pistons had one or more stuck rings.

Time to call Jim McCormick. I bought my engine from Jim. Jim owns and operates Jabiru Pacific which is based in Fresno California. He has has helped me before. One day I was flying past Fresno on my way to Arizona. I did an in-flight mag check and was astonished to find I was flying on one magneto. I called Jim on my cell phone, while I was flying, and he told me to come on in, so I diverted to Chandelier field. He had me fixed up in no time and I was on my way.

This time I drove to Chandelier field with three boxes of parts. Jim and I went over them. The heads are not too bad but since they are off the engine, we decided to give them the full treatment to get them back into shape. It should be noted that one more exhaust valve was showing early signs of leaking. Also one of the heads had been leaking. I have been careful about torquing my head bolts, especially when the engine was new, but I guess I was not careful enough.

There is an improved piston design with wider ring grooves. I will be upgrading to these. The cylinders have odd wear patterns. Jim is contacting the factory about them.

My oil pressure is down to 26 PSI. The rod bearings look warn and they are not expensive so I am replacing them.

It’s important to note that the rings are stuck with carbon deposits. This is the result of oil oxidizing. The oxidizing has occurred because of high operating temperature. I am replacing the oil cooler which came with the engine with one that is twice as large but bolts into the same place and does not require major cowing rework. I am also going to switch to Aeroshell 15W-50 year round. This oil is over %50 synthetic and stands up better under high temperatures. I had been using Aeroshell 100 Plus in the hot summer months and the 15W-50 in the winter.

I love the way my Jabiru engine performs; its smooth, powerful and light weight. It has powered my plane safely all over the United States. I hope after these repairs I get more than 600 hours out the engine before my next major overhaul.


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Comment by Mark Ertz on March 24, 2013 at 8:43am


Are you up and running now.  I'm in same boat, Overhauling top.  Also Buying the rotec TBI.  Bing out.  I want primer and mixture control.

Comment by Stephen R. Smith on September 30, 2009 at 10:39am

Here is AVDALSR050-1.PDF which is titled "Procedure - Engine Through-Bolt Nut Installation". It details how to correct the through-bolt nut problem which is presumed to have caused my engine to fail.

I also like the following description which I found on this web page.

If the pistons/cylinders/rings are not doing their job (sealing), you have a problem called "Blow-by". Blow-by occurs when hot combustion gasses leak past the rings and into the crankcase. Besides the obvious loss of power and efficiency, many people aren't aware of another consequence, which is the damage caused by hot exhaust and flames into the crankcase! You are literally heating your engine's oil with a blowtorch. Yet another complication is the contamination of the lubricating oil with exhaust and gasoline. Based on these negative side affects alone, blow-by should be avoided - the added incentive of increased engine power will be a bonus!

Obvious signs of blow-by are carbon build up (nasty hard, black chunky stuff) and/or heat discoloration on the piston land (between the top and second ring). Bad cases of blow-by will even discolor the piston skirt to a black/brown color.

Let me explain even further, so you'll be totally convinced. Ideally, as the piston is beginning to move upwards on it's compression stroke, the air/fuel mixture is compressed above the piston and rings. The rings are sitting on the bottom of the ring lands as the piston drags them upwards. As the pressure increases, the rings (especially the top one) are pushed downwards even more against the ring land. The combustion pressure spreads across the upper ring surface and down behind the ring, and forces the ring out against the cylinder wall. The radial pressure of the ring tension is only used to START the sealing process, and cylinder pressure is what really pushes the ring outwards against the cylinder wall. For this to occur, the ring gap and piston to ring contact surface must be perfect.

There are multiple problems that can result when the piston and ring mating areas are ignored. Excessive clearance between the backside of the ring and the ring groove in the piston results in pressure building too slowly behind the ring, and leakage occurs because the ring is not being pushed out against the cylinder. This gap should be as small as possible.

Also, if the ring is not sealed against the bottom of the ring land, the pressure will leak past this area. Once the ring is leaking, the hot gasses from the chamber are like a torch to the metal surface of the piston land and the ring itself. This excessive temperature bakes the oil in that area and turns it to carbon, which reduces ring clearance to nothing and grabs the ring solid. Can you say, "ring replacement"? You don't want to have to replace those on a regular basis! Although there is a second ring, it is primarily an oil scraper ring, not a compression ring, and if the top one leaks for any reason, your engine loses power.

I will start a new blog to detail the re-assembly of the engine in the next day or so.

Comment by Stephen R. Smith on September 29, 2009 at 1:06am
I don't have the final invoice yet. I know I received a discount on the parts but it was different then I expected. I should have the invoice tomorrow and will post exact cost information then.

I have not gotten an explanation for the early failure of my engine. Jim at Jabiru Pacific was aware of the following issue which you can read about in the Jabachat News letter. I think it wise to read all the Jabachat news letters. They contain good information. I only just recently learn about them.

"Recently it was found that the nuts of the engine through bolts could run up onto the fillet
at the base of the cylinder and that, when tightened, this had the effect of distorting the
barrel. A dealer information notice has been distributed which gives more detailed information
on this. Symptoms include low compression, high oil usage, poor power and
high oil blow-by. Affected engines can be modified by grinding a small chamfer onto the
base of the nuts to give more clearance from the fillet on the barrel. All overhauled engines
should be modified in this way.

So did my engine have the above problem? Jim thought it did. He told me I would get the cylinders for free; but then I got bill for them anyway. When I objected, the bill for the cylinders was reduced but not eliminated.

I also now have the re-designed pistons with wider ring grooves. This makes the rings less likely to stick. And of course the oil cooler sold to me with the engine was much too small. My new one is twice the size of the original.

So if this engines were being sold to ordinary consumers I think they would take them back to the store and want there money back. I am more inclined to see this as an experimental partnership. Jabiru is not a perfect company. The engine is getting better all the time; that is the good news. The bad news is some of us got engines that were not yet fully improved. If you don't want a Jabiru, what would you use on a Zodiac XL that would give you 120 horse power and weigh 180 pounds. Answer: nothing. So there you go. I like the engine when it works correctly so I am taking another shot at it.

Yesterday I ordered the Rotec TBI-40-S carb. I hope it will even out my EGTs and eliminate the over-temps I get at around 2,000 feet MSL with the Bing.

I also ordered new rubber motor mounts from Sonex. My lower mount on the pilot's side was shot. The engine has slumped about 3/8 of an inch. Sonex claims their rubber mounds are stronger than the stock Jabiru rubber. That would be nice. Replacing the rubber mounts is not a fun job. I don't want to do it every two years.

So that is my rambling update. I will upload some pictures of the new parts. Perhaps tomorrow evening.

Comment by Tim Garrett on September 12, 2009 at 7:45am
Doesn't the Zenith demonstrator have over (way over?) 1000 hours? What is the history with thier early Jabiru 3300?
Comment by Stephen R. Smith on September 10, 2009 at 8:58pm
Hello Ralph,

Jim McCormick thought the nuts were distorting the cylinder base. Apparently the factory agrees.

I did see that the manual calls for withdrawing the pushrod tubes. I did not bother. They come off with the head very nicely. Might be good to make sure neither valve is open so there is no push rod presser to pop the head on the bottom more than the top as you loosen the head bolts.

I also removed some of the intake and exhaust runners with the head. This is possible if you remove the heads in the necessary order. (Loosen and slide down the short hose which joins the two intake runner segments.)

Your going to want to take a good look at the valve seat. For that reason I would remove the head from the cylinder. At a minimum you will need to lap in the new valve - more than that may be needed - you need to get a good look...

The Jabiru engine is quite new vs. others. The factory is still tweaking things. I am quite new to experimental aircraft and still getting accustom to the idea that folks will sell you things that don't actually work without additional modification. So yes, they will sell you an engine, complete with oil cooler that does not actually work in the real world here in sunny California. And yes, if you fly your plane with the engine the way it was sold to you, damage may result. OK, I get it, its my experiment.

Comment by Ralph Sanson on September 10, 2009 at 4:49pm
Thanks for the detailed information.
I'm about to embark on similar remedial work myself, on my 2200A of 300 hrs / 5 yrs I have detected minor exhaust leaking on 2 cylinders and leakdowns in the range 80/ 62 - 68 on all.

The odd bore wear you see might be a result of the cylinder base nuts choking the base, a problem that has surfaced on engines up to last year and described in the Jaba chat bulletin on their website.

I ordered 4 new exhaust valves and a set of machined modified base nuts to be ready for the job.

The overhaul manual calls for withdrawing the pushrod tubes out of the heads prior to removal of head or cylinder. In practice will these tubes slip out when the head is removed or does the angle they are set at require prior removal?
Also because I'm replacing all cylinder base nuts I might avoid disturbing the cylinder-head seal by changing the valve with head in situ- is this likely to be possible? I was going to do the base nuts pair by pair and not remove the cylinders, but seeing you pictures reminded me I could also have rings to look at.
The engine has run well, on Avgas and either Aeroshell 15/50 or lately Castrol Aviator AD100 which I prefer.
Having followed all the maintenance procedures and revisions I was not expecting a problem this early, yet its too soon to plan on an updated model engine because enough field experience has not become available to validate them.
Comment by Stephen R. Smith on September 10, 2009 at 10:48am
Hello Brad,

Apparently the cooler that came with my engine is a TRU-COOL B7B with 12 rows.

The new cooler is a TRU-COOL L7B with 24 rows.

Comment by Brad DeMeo on September 10, 2009 at 10:15am
Steve, Thanks for posting. We all appreciate the very useful information you provide. Good luck with the rebuild. I'd like to see the new oil cooler sometime.
Comment by Chris Sinfield on September 10, 2009 at 3:54am
Thanks for the feedback Please keep us informed as I amabout to buy my new Jab3300 and hope to get more than 600 hours out of it.. Maybe I should ask about the new wider ring groves and pistons..
Chris ..

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