Introduction.
Since the advent of the motor to 85 HP Jabiru 2200A backlash hydraulic valves, motors are affected by breaks of exhaust valves, to date over 20 cases were reported in France, engines equipped "economy kit" would be particularly affected by these problems.
- FOR THE FIRST TIME use, oil consumption is important (1 liter per 20 to 25 hours).
- lubrication chambers rocker is sometimes insufficient or uneven.
- Oil return chambers of rockers to the crankcase is defective.
- The exhaust valve guides wear out very quickly.
This results in fractures of valves in a period which is very variable, but that could average between 300 to 400 hours (sometimes less, sometimes more).
Over time, Jabiru (source JABACHAT) a:
- canceled the service bulletin "economy kit", JSB 002-2, 018-1
replaced by JSB - published a service bulletin "vent chambers rocker "JSB 014-1
- indicated that the low level of the dipstick became the top level, (April 4, 2008),
- which changed the flywheel screws broke
- perhaps changed the oil circuit in yokes?,
- perhaps changed the valve guides?, and changed the spacing of valves,
- changed the profile of the tree cam (designed originally for a mechanical adjustment of valve clearance)
- modified the hydraulic lifters (version reduced leakage)
- modified the fins of the cylinder heads,
- enlarged the oil pan and modified dipstick.
JABIRU AUSTRALIA has never "officially" considered among its clients, the design of the valve guides and lubrication thereof, could be blamed, blaming problems with fuel quality, improper use, inadequate propellers, etc. ... ... parameters certainly affect the holding of the engine, but explain no recurring problems break valves.
Drilling vents in the rooms of rocker (as JSB 014), has sometimes led to large splashes of oil from the engine. Background
staff.
I have a Jabiru SKYRANGER purchased new, commissioned in 2006 and in October 2008 which totals 230 hours.
A friend also has a SKYRANGER JABIRU who broke in flight at just over 300 flight hours (broken exhaust valve).
At 200 hours, I found
- engine oil that darkened quickly (despite the renewal due to high oil consumption),
- traces that appeared suspicious and were advancing in the chambers of rockers.
After installing a latch on the valve stem, I then measured the comparator (valve semi-depressed), the game guides exhaust valves result
- 1, Game 2 mm (up / down) on the cylinder the most affected,
- 0.8 mm on the cylinder the less affected.
I sent these pictures and information JABIRU France, and I asked the management of the replacement valve guides under the warranty. Refusal
formal JABIRU France who, while recognizing that this series of engine is affected by breaks in the exhaust valves, seems to operate under the guarantee that when the case is converted! ! Yet
JABIRU announcement ensure TBO of 1000 hours on the top motor! !
Resellers U.S. or UK (source Jabiru-engine-yahoo-group) seem to perform the operation preventive Warranty! !
So I started to disassemble it myself at my expense, cylinder heads for repair guides.
The following comments are the result of my own observations and interpretations.
Game in the valve guides.
- I have seen dismantling the game initially measured on the engine block, was representative of the actual game in the exhaust valve guides, I also noticed significant play in the valve guides of admission.
- I found that the magnitude of brown marks in the chambers of rocker are proportional to the wear guides exhaust, since it seems that some of the fuse burned gases through the game in the exhaust guides.
Lubrication of cylinder heads.
The small amount of oil (when it comes to cylinder heads! Source Contrails) feeding guides and rocker flows through the first hole (d = 4 mm) of the oil boom in the room rocker it lubricates the fact that the first guide to the law of the intake valve and nothing came DIRECTLY on the exhaust valve except that the projections of Reciprocating valve spring admission.
Results: exhaust valves and guides poorly lubricated and cooled especially badly.
oil consumption.
The cons-pressures in the chambers of rockers (hydraulic lifters unsuitable), impede the return of oil in the sump, vents in the rocker covers enhance oil return, but does not significantly affect consumption ; oil.
My observations lead me to believe that oil consumption is mainly due.
- Has a Gambling at the outset in the intake valve guides.
- In the presence of a lubrication hole in the valve guide (s = 4 mm) facing up to a valve stem (d = 7 mm), decreasing virtually sealing the guide and causing retention oil just waiting to be drawn at admission.
- In the absence of valve stem seal (useless anyway with the hole in the guide).
- A design gallery lubricants which can be seen above supply power that the intake valve.
Result: oil consumption and large deposit of carbon on valve seats, inlet side!
Breaking exhaust valves.
The origin of these failures seems to be the direct result of wear and excessive play (I think from the beginning), the valve guides and as shown above to a lack of lubrication these guides.
- In light of the gambling, the valve seat Exhaust is deformed, since the seat is not tight, the valve "oar" on the seat, the hot gases amplify the damage, and eventually break the valve effect of repeated stress by fatigue, and what to especially as the camshaft and hydraulic lifters seem inadequate.
- As can be seen in the photo above, only 200 hours, laid, side exhaust valves and seats are so distorted that it took deep milling seats to regain a proper scope.
- Finally I observed that the material component guides is very different nature of guides to good quality found in automobile engines, hardness, machining chips:
- chips guides JABIRU break up into smaller pieces, like a cutting brass?,
- chips of a guide bronze automotive type form filaments that wrap behind the tool.
Remedies.
Insofar as I was doing the restoration of cylinder heads on my own at my expense, there was no question of putting the same configuration as the original (same causes, same effects). So I was brought
- To change the guides for guides bronze quality automotive-style, without oil hole and equipped with valve stem seals on admission as to the exhaust,
- in light fabric restrictors to ensure a sufficient flow of oil in each cylinder head material (for lack of money, I have not measured the speed).
- to change the oil gallery of the cylinder heads to get a flow of lubricant directly on the two valves in each cylinder head,
- to replace the exhaust valves that had undergone too many constraints to be raised without risk.
course to this day I do not have sufficient perspective to judge the merits of these interventions.
I do not pretend that this substitution guides is the solution because, as mentioned here, many factors may contribute to failure of valves: cinematic rockers, camshaft, springs, cooling, etc. ... I can say
however:
- that oil consumption is now very small,
- the pot breather collects only very little oil,
- the cylinder head temperature dropped from -5 to -10 ° C in cruising
- As if I had not intervened proactively engine would probably have broken into the following hours (the question is how??)
Current.
Installing vents on the covers of sprinkler heads and the richer developed by Jabiru France, are actually in the right direction (back oil, reduced exhaust heat stress). If these provisions allow
probably extend the life of valve guides, the initial default seems to be induced by a design flaw that JABIRU AUSTRALIA never really admitted, leaving the customers to get by themselves.
Read JABIRU (source JABACHAT)
- The Client should make clear lids and check and enjoy himself, that heads are properly supplied with oil,
- the Client should need to re-machine the restrictors ducts oil supply to cylinder heads.
- Customer should replace the bearings rocker who took excessive play by lack of lubrication.
- Customer should install EGT on each cylinder.
- The Client (at least in France) must bear the cost of preventive replacement of defective valve guides.
Applying these recommendations is the Customer not even the satisfaction of having an engine fully operational since the critical engine components remain inadequate (camshaft, hydraulic lifters, flywheel, cooling and lubricating the cylinder heads ...).
This means that the hydraulic versions of Jabiru 2200 A 85 HP, sold only two years ago are now completely obsolete compared to the current definition of the engine, which indeed I have no idea reliability ..
Conclusions.
JABIRU begun, with earlier versions mechanical push to become a credible alternative engine ULM.
Since the release of the versions to hydraulic lifters, Jabiru, seems to have no duty, no liability with respect to its Customers.
JABIRU long overdue, develop technical solutions (improved cylinder heads, engine replacement) for Clients versions affected by such failures of valves.
This is particularly regrettable that these engines are fun to use and relatively light compared to other engines ultralight on the market.
The result of these changes at 400 hours:
http://jabiru-engine-inspect-400.blogspot.com/
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