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avidflyer01
Joined: 07 Jun 2007
Posts: 9
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 Posted: Sun Aug 19, 2007 8:36 am Post subject: insufficient rocker chamber greasing ????? |
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hi guys, I would like to share some very worrying facts about my engine (2200 w/hyd lifters) and maybe get some answers from those who have already been there.
I have just completed reassembling my engine after replacement of all valve guides (both of N°2 were completely worn out at 100hrs, others were replaced as precaution). Today I started it and run for 5 min at 1200-1500rpm, then stopped and made a close inspection. When I removed tapper covers, I discovered there was some oil, as it should be the case, in rear rocker chambers (N°s 3 and 4) but the forward ones were AS DRY AS PRIOR TO ASSEMBLY.
The airplane was sitting almost level, with tail slightly lower, maybe 5°. Oil level was slightly above minimum, as per SB 013-1. The oil pressure was (as always both in flight and at idle) at 35psi.
After checking that the T junctions on oil feed line were not blocked and some more thinking, I tilted the airplane more on the nose (3° nose down), cleaned rocker chambers and run it again for 1 min at 1200rpm.
This time forward rocker chambers were correctly flooded with oil while the aft ones were virtually dry, except a few drops.
I sincerely hope that at a higher power setting the amount of oil carried thru the feed tube from under the cylinders is sufficient to spread it correctly in the T-junction to grease both rocker chambers (I have so far always seen oil in rocker chambers, although there was always more of it in the rear ones – my plane is a taildragger).
But the worrying truth seems to be that when warming the engine or taxiing at low rews (and even more so in a taildragger, although already 5° tilt seems to make a difference), there are good chances that fwd cylinder rockers and valve guides run dry!!!! My guess is that the quantity of oil delivered is insufficient and it only runs “down the slope”, towards the cylinder that is lower.
This could be by the way one of the possible explanations why my valve guides were ruined after 100hrs and that my rocker bushings also show some premature wear.
Has anybody any comment on these facts? Pete, Andy, do you guys consider it normal that the whole rocker chamber is not bathing in oil????? Any similar problems found/cured????
Once at that subject, the SB 013-1 explained to us that vent holes and correct routing of the sump breather were supposed to enhance the return of oil from rocker chambers back to the sump, as if too much oil was delivered to the heads. Seemingly, I have the opposite problem (or at least I do have it on lower revs) – isn’t there a restriction between the main oil galley and the two tubes feeding oil to rocker chambers, that could be increased????
I don’t like the idea of running idle with no oil in my rockers/valves….
Any input, guys????
Martin
Avid flyer w/Jab 2200
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johnl(at)loram.org
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| Posted: Sun Aug 19, 2007 10:25 am Post subject: insufficient rocker chamber greasing ????? |
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Martin:
What you've encounter is a documented problem with Jabiru engines in tail-draggers, and has been discussed in the past on this list.
Simply described; when the tail is down and the oil is thin (hot), the oil flows up the oil tubes to the heads and then, at the 'T' it flows 'down hill' to the rear cylinders with the forward cylinders running dry.
Colin Hales, the English aeronautical engineer who's 'epic' flight from England to Australia in a Jabiru 2200 powered Rankin KR2 is mentioned in the December 2002 JabaChat, describes the problem thusly: "... But there is one problem that we had as a tail dragger that happened to us and Jabiru knows about, but don't tell. We had to taxi for half an hour after landing. With hot, thin oil at idle, all the oil that is supplied to the rockers through the supply tubes runs to the back cylinders and the fronts run dry. Normally there is enough oil floating about to do the necessary lubrication and the oil when cool and thick gets everywhere. But do not run your engine for long after landing. The front rockers will run dry and heat up and damage them selves. Happened to us in Bali. ..."
Buy the way, if you can find Colin's auto-biography of the trip, it's a fascinating read. He had it published on a website that I have lost track of. He describes the above problem in much greater detail.
Regards, -john-
[quote] --
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avidflyer01
Joined: 07 Jun 2007
Posts: 9
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| Posted: Sun Aug 19, 2007 11:47 am Post subject: Re: insufficient rocker chamber greasing ????? |
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thanks John.
Taildragger configuration makes it certainly worse, but my remarks concern the airplane that is as level as an airplane can be ( +5° or -5° from horizontal keeps fwd or rear cylinders dry....).
They also concern cold oil (engine just started); hot oil is probably worse.
I am tempted to think (but no proof to that) that keeping higher rpm while warming up or taxiing could help.
martin
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t_fogelson(at)yahoo.com
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| Posted: Sun Aug 19, 2007 12:47 pm Post subject: insufficient rocker chamber greasing ????? |
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A bandaid that will help is a preoiler. Certified
ones are expensive, but if you adapt an auto one they
are reasonable. http://www.autoenginelube.com/ is one
that uses engine oil pressure to charge an accumulater
and then it traps the pressure after the power is shut
off. one to three quart accumulators.
Terry
--- avidflyer01 <vegayacht(at)club.fr> wrote:
| Quote: |
"avidflyer01" <vegayacht(at)club.fr>
thanks John.
Taildragger configuration makes it certainly worse,
but my remarks concern the airplane that is as level
as an airplane can be ( +5° or -5° from horizontal
keeps fwd or rear cylinders dry....).
They also concern cold oil (engine just started);
hot oil is probably worse.
I am tempted to think (but no proof to that) that
keeping higher rpm while warming up or taxiing could
help.
martin
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=129846#129846
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Park yourself in front of a world of choices in alternative vehicles. Visit the Yahoo! Auto Green Center.
http://autos.yahoo.com/green_center/
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andy(at)suncoastjabiru.co
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| Posted: Mon Aug 20, 2007 9:24 am Post subject: insufficient rocker chamber greasing ????? |
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Martin,
Thanks for the information - I find it very interesting. However, as a Jabiru dealer having sold several hundred engines over the years I can't tell you it's a problem I have either personally experienced, or had heard about from others until now. It's true to say there are probably a greater number of tri-gear Jabiru-engined airplanes out there, but equally true that there are a significant number of taildraggers too. I'm sure your observations are correct for your installation, but in my experience we don't see higher valve guide or rocker bearing wear in heads at the front of taildragger installations. So we must assume that the stem and bearings retain sufficient lubrication both before and after flight.
However, we are educated by your posting and will look for particular signs or trends in future. Thanks again.
Andy Silvester
Suncoast Sportplanes, Inc.
39248 South Ave, Zephyrhills, FL 33542
Tel: (813) 779 2324 Fax: (813) 779 2246
www.suncoastjabiru.com
--
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Thu Aug 23, 2007 5:36 am Post subject: insufficient rocker chamber greasing ????? |
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Martin-
Go back and look at the archives of this list (around May 8 of this
year) and you'll see my write-up of the problem I had with my rocker
arm bushings. I always had oil when I had to pull my covers for valve
clearance adjustment, which seemed to be too often. One day I noticed
flakes of a brass-color inside the covers. During some research of
the problem, it was suggested that I drill out the restriction in the
tube you mentioned (at the oil gallery) to the next size number
drill, which I did, but I don't recall what the size was right now,
but the next size drill was only 3 or 4 thousands of an inch larger.
Lynn Matteson
Grass Lake, Michigan
Kitfox IV Speedster w/Jabiru 2200
flying w/369+ hrs
On Aug 19, 2007, at 12:36 PM, avidflyer01 wrote:
| Quote: |
<vegayacht(at)club.fr>
hi guys, I would like to share some very worrying facts about my
engine (2200 w/hyd lifters) and maybe get some answers from those
who have already been there.
I have just completed reassembling my engine after replacement of
all valve guides (both of N2 were completely worn out at 100hrs,
others were replaced as precaution). Today I started it and run for
5 min at 1200-1500rpm, then stopped and made a close inspection.
When I removed tapper covers, I discovered there was some oil, as
it should be the case, in rear rocker chambers (Ns 3 and 4) but
the forward ones were AS DRY AS PRIOR TO ASSEMBLY.
The airplane was sitting almost level, with tail slightly lower,
maybe 5. Oil level was slightly above minimum, as per SB 013-1.
The oil pressure was (as always both in flight and at idle) at 35psi.
After checking that the T junctions on oil feed line were not
blocked and some more thinking, I tilted the airplane more on the
nose (3 nose down), cleaned rocker chambers and run it again for 1
min at 1200rpm.
This time forward rocker chambers were correctly flooded with oil
while the aft ones were virtually dry, except a few drops.
I sincerely hope that at a higher power setting the amount of oil
carried thru the feed tube from under the cylinders is sufficient
to spread it correctly in the T-junction to grease both rocker
chambers (I have so far always seen oil in rocker chambers,
although there was always more of it in the rear ones my plane is
a taildragger).
But the worrying truth seems to be that when warming the engine or
taxiing at low rews (and even more so in a taildragger, although
already 5 tilt seems to make a difference), there are good chances
that fwd cylinder rockers and valve guides run dry!!!! My guess is
that the quantity of oil delivered is insufficient and it only runs
down the slope, towards the cylinder that is lower.
This could be by the way one of the possible explanations why my
valve guides were ruined after 100hrs and that my rocker bushings
also show some premature wear.
Has anybody any comment on these facts? Pete, Andy, do you guys
consider it normal that the whole rocker chamber is not bathing in
oil????? Any similar problems found/cured????
Once at that subject, the SB 013-1 explained to us that vent holes
and correct routing of the sump breather were supposed to enhance
the return of oil from rocker chambers back to the sump, as if too
much oil was delivered to the heads. Seemingly, I have the opposite
problem (or at least I do have it on lower revs) isnt there a
restriction between the main oil galley and the two tubes feeding
oil to rocker chambers, that could be increased????
I dont like the idea of running idle with no oil in my rockers/
valves.
Any input, guys????
Martin
Avid flyer w/Jab 2200
|
| | - The Matronics JabiruEngine-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?JabiruEngine-List |
|
_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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