Jabiru circlip issue

[jab430]

Hi.

Wondering if anybody could give me some advise on my Jabiru430.
I had the 1000 hour engine overall done about 75 hours ago and we found pieces of circlip in the drained oil. Upon opening the engine we found that a circlip had failed on the gudgeon pin.
We decided to take all the pistons off and in the process of removing the circlips, another one broke.

Now I know that the Jabiru has had circlip issues in the past but these circlips were from the new batch. Basically what we found was that the ears had broken off luckily the bulk of the circlip had stayed in position so I didn't have massive engine failure. Thank goodness!

The jabiru agent here has mentioned that the only thing that could have caused this is incorrect installation yet I can be nearly sure that they were installed correctly. Apparently this can happen if the circlips are installed with the gap aiming sideways rather than with the stroke of the piston. This I can believe even though I would have thought a circlip would be strong enough to handle this type of incorrect installation.

I have got new parts to install but am obviously worried about a future engine failure because I have not worked out the cause of the problem.
Has anybody else by any chance experienced a similar problem with the 3300 engine (solid lifter)?
If anybody has any knowledge on these issues I would very much appreciate been able to talk to them.

What I also noticed is that the replacement pistons are not identical to the original ones that were installed a few short months ago.

I do have more information than I am including in this thread if anybody would like me to share it. Including pictures and microscope photos of the circlips which came out the engine. Seeing these photos has done the opposite to putting my mind at rest.

Thanks.

[18greens]

This sounds like a question for Mr McBride of the LAA.

You have the material for a whole safety spot article.

[onetrack]

I'm presuming the pistons are grooved and the circlips are internal style? Do the problem circlips have an ear with a hole? Are they fracturing through the hole, or through the circlip near to the ear?
IMO, I would say the circlips are of inadequate strength, and thrust is fracturing them. There are some thrust calculation guides in the linked BSC document below.

I would be looking at the possibility of machining the gudgeon/wrist pin grooves wider, to accommodate thicker, and therefore, more robust circlips.
I would also be investigating the availability of circlips that don't utilise ears with holes, if this is the style currently being used (i.e., plain circlips, that are commonly used on driveshaft universal joints).

http://www.bsc.com.au/sites/default/files/products/manuals/Circlips.pdf

[onetrack]

Here's another thought. Use Spiro-locks, as the high-tech race car engine builders do.

There are considerable forces acting on the circlips. There is thrust, as well as the impact of the piston changing direction completely many hundreds of times a minute.

This is why regular circlip positioning on the gudgeon/wrist pin is crucial, to reduce the impact forces on the circlip, that make it constantly flex.
Many engine assemblers state they will only open and close a circlip once before discarding it.

Thrust on circlips comes from the impact of combustion on the piston, and also from the misalignment of conrods. Excessive crankshaft end float and poor cylinder-to-crankshaft alignment can create conrod misalignment and gudgeon/wrist pin side thrust.

Spiro-locks reduce the possibility of circlip breakage to virtually nil, and I'm surprised that Jabiru aren't using high-tech racing engine technology such as this.

How To Install Spiro Locks - YouTube

[jab430]

The circlips fit in grooves and are of the internal type.
I would attach some pictures but am not sure of how to do this?
They are of the type that have got "ears" with holes in them and broke very close to the ear but not around the hole. This is why they didn't come out but had stared rotating around the groove so wearing the groove out bigger.
If we hadn't noticed this, I believe that the circlip would have failed shortly.

Who is the Mr Mcbride of the LAA that you mention?
You mention, maybe use spiro-locks but I will admit that I hesitate to use anything but original Jabiru parts. Even though they are the parts that failed. I'm a bit between a rock and a hard place at this stage.
I also worry about using non-original parts for insurance purposes.

Interesting that you should mention cylinder-crankshaft misalignment because one thing that was done to the engine was a very slight machining of the two engine block halves and so also a realignment of the crankshaft bearings.
Could this possibly have cause a problem?

One thing that I did notice upon removing the pistons was that the circlips had all rotated a small amount from the direction in which they were installed.
Basically they weren't aiming straight down any more but about 15 degrees off and it seemed they were all aiming in a similar direction. I found this a bit strange at the time. Is it normal?

Thanks for your thoughts and ideas.

[146fixer]

You could try asking the question here jabiruengines : jabiru engines (http://groups.yahoo.com/group/jabiruengines/)

[onetrack]

Let's start with some relevant points.

1. The jabiru agent here has mentioned that the only thing that could have caused this is incorrect installation

This is not correct. There are multiple possible causes for the failure, and this attitude that there is only one possible cause, leads to erroneous conclusions.
Perhaps this answer is due to inadequate knowledge on the part of the person you spoke to - or it could be coming directly from Jabiru. If such is the case, I would be concerned about Jabiru's attitude to engine problems.

2. I also worry about using non-original parts for insurance purposes.

Yes, this is a proper concern. You need to commence dialogue with Jabiru and seek their approval to use Spiro-locks - as it is obvious that the Jabiru-supplied circlips are unsatisfactory and unreliable, to the point of causing engine damage.

3. They are of the type that have got "ears" with holes in them and broke very close to the ear but not around the hole.
This is why they didn't come out but had stared rotating around the groove so wearing the groove out bigger.
If we hadn't noticed this, I believe that the circlip would have failed shortly.

You are describing piston circlips that have suffered from excessive thrust problems. As indicated in the BSC webpage information, thrust levels on circlips are crucial. Excessive thrust must be avoided.

4. One thing that I did notice upon removing the pistons was that the circlips had all rotated a small amount from the direction in which they were installed.
Basically they weren't aiming straight down any more but about 15 degrees off and it seemed they were all aiming in a similar direction. I found this a bit strange at the time. Is it normal?

No, this is not normal. It indicates that heavy thrust has been applied to the circlips and that they have rotated in the pistons. The thrust can come from the alignment problems I mentioned previously, or the thrust could come from gudgeon/wrist pins that are too tight, longitudinally.

The pins should have been ground so that the circlips fit easily upon assembly at room temperature, with say, 0.03mm or 0.05mm (0.001" or 0.002") clearance between the pin end and the circlip.

The clearance is dependent upon pin length, of course - and the clearance should have been calculated so that the clearance is virtually eliminated at engine operating temperature.

However - if the calculations or the grinding have been incorrectly done, and the pin length is excessive (miscalculations in pin expansion rate - miscalculation in piston temperature - mistake in grinding), then the pin expansion due to increased pin temperature at engine operating temperature, may possibly be placing excessive thrust load on the circlips.

A gudgeon/wrist pin that is effectively jammed tight against the circlips at engine operating temperature, will cause the circlips to rotate as the conrod rotates with every engine revolution.

This will eventually lead to the combination of worn circlip grooves and fractured circlips.

The ideal length for a gudgeon/wrist pin is when the calculated circlip-to-pin clearance is around nil to 0.03mm (0.001") at engine operating temperature (check with manufacturer for precise, engine-specific specifications).
This ensures little to no thrust is being placed on piston circlips when the engine is operating at normal operating temperature.

Be very aware, that high EGT's created by a lean mixture will result in high piston temperatures - possibly exceeding the Jabiru engineering calculations.
This in turn will result in increased gudgeon/wrist pin temperatures, which will create the problem of excessive thrust on piston circlips. I need not go into the real possibility of piston failure caused by high EGT.

The other factor is how the gudgeon /wrist pins have been ground on the outside end edges of the pin. If this area has been excessively chamfered, this will create excessive thrust on the circlips as the load is being placed on the innermost part of the circlip, leading to thrust loads that exceed design specifications.

5. Interesting that you should mention cylinder-crankshaft misalignment because one thing that was done to the engine was a very slight machining of the two engine block halves and so also a realignment of the crankshaft bearings.
Could this possibly have cause a problem?

Yes, it could, if the machining work was of an unsatisfactory standard, and all alignments were not checked. To ensure maximum engine reliability, every single dimension and alignment angle must be thoroughly checked.
This means that the alignment of piston bores to crankshaft tunnel, in relation to perpendicularity, as well as longitudinal alignment, must be precisely within the manufacturers designated specifications.

There is one thing that separates a well-built engine from a poorly-built engine - and that factor is, whether every possible specification measurement has actually been physically checked - rather than "presumed" to be O.K.

[146fixer]

Jabiru tell you all you need to know on how to fit circlips to their engines here Jaba Chat & News (http://www.jabiru.net.au/jaba-chat-a-news)
Piston Circlip Installation.

[Talkone]

Just had a total engine failure due to a Circlip being side thrusted out of the groove. (Prop side) Pistons are standard issue from Jabiru. V6 Buick with the later Circlips installed. All correct such as gaps at bottom not compressed excessively and flats to the outside. No 5 failed and broke the Con rod. No 3 was about to fail (also prop side) with others showing side wear of grooves. Ideas anyone please? :bored: I would really like any photos as I also have some I am willing to swap

[magpienja]

How does a part of the circlip break off...and get into the sump without damage to the engine?????

Nick.

[146fixer]

I've been doing a top end rebuild on my jabiru engine. I was given some advice by the company that use to manufacture the engines for jabiru. Their advice was not to replace the plain wire type circlips that were fitted to my engine with the circlips recommended by jabiru as described above. I was told the circlips as described with the ears will break. I've taken their advice and fitted new wire circlips