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Peter H
Joined: 20 Mar 2007
Posts: 197
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 Posted: Tue Jul 29, 2008 10:38 pm Post subject: Barrel Nuts |
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Clive,
I got the response below from Jabiru engine engineer Doug Smith.
It looks as if the barrel nut mod is for another issue and not for the tight engine.
The tight engine for me is an issue only when the engine stops and the barrels cool faster than the pistons. When running the tolerances appear to be OK and it will idle down to 800RPM.
Peter
From: Doug Smith [mailto:dougs(at)jabiru.net.au]
Sent: Wednesday, 30 July 2008 2:10 PM
To: 'Peter Harris'
Subject: Barrel Nuts
Dear Peter,
There is a mod, much as described, which we have informed our engine specialists about. However, it is not necessary on all, or even many, engines – it is a fix if a low-hour engine is using excessive oil, has poor leak-down results, high blow-by etc. It is basically a tolerancing issue – on some engines the nuts ride slightly up on the radius of the barrel but on the majority of engines they do not. The mod does not affect the tightness of the engine. I’d add that it is a very dangerous task to undertake in the backyard – it is far too easy to over-torque an engine through-bolt which will result in an engine failure down the track. If it is to be done it must be done by an approved Jabiru engine man, and it’s not worth thinking about unless the engine has the symptoms mentioned above.
Regards,
Doug Smith
Engineer, Jabiru Aircraft
This email message and any accompanying attachments may contain information that is confidential and intended only for the use of the addressee named above. It may also be privileged. If you are not the intended recipient do not read, use, disseminate, distribute or copy or take any action in reliance on it. If you have received this message in error please notify the sender immediately and delete this message. Before opening any attachments, check them for viruses or defects.
[quote][b]
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Clive J
Joined: 03 Nov 2007
Posts: 340
Location: UK
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| Posted: Fri Aug 01, 2008 10:24 am Post subject: Barrel Nuts |
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I was at ST again today and spoke about your case. Roger says it will be a contribution if not the cause. He said the distortion is amplified by the heat. I've seen the strange looking strike marks on my brand new engine. Roger heated a barrel up with a hot air gun and the tightness came in as he did it. Hardly normal if the tightness is shrinking barrels. If you can get it done or can do it your self yours would be an ideal engine to try it on. Imagine free power less fuel consumption.....
I'll be running my modified engine this weekend, I'll ley you know.
BTW what engine do you have in what?
I have a 2200 in a Jabiru and a 3300 in an Esqual.
Regards, Clive
________________________________
From: owner-jabiruengine-list-server(at)matronics.com on behalf of Peter Harris
Sent: Wed 30/07/2008 07:34
To: jabiruengine-list(at)matronics.com
Subject: FW: Barrel Nuts
Clive,
I got the response below from Jabiru engine engineer Doug Smith.
It looks as if the barrel nut mod is for another issue and not for the tight engine.
The tight engine for me is an issue only when the engine stops and the barrels cool faster than the pistons. When running the tolerances appear to be OK and it will idle down to 800RPM.
Peter
________________________________
From: Doug Smith [mailto:dougs(at)jabiru.net.au]
Sent: Wednesday, 30 July 2008 2:10 PM
To: 'Peter Harris'
Subject: Barrel Nuts
Dear Peter,
There is a mod, much as described, which we have informed our engine specialists about. However, it is not necessary on all, or even many, engines - it is a fix if a low-hour engine is using excessive oil, has poor leak-down results, high blow-by etc. It is basically a tolerancing issue - on some engines the nuts ride slightly up on the radius of the barrel but on the majority of engines they do not. The mod does not affect the tightness of the engine. I'd add that it is a very dangerous task to undertake in the backyard - it is far too easy to over-torque an engine through-bolt which will result in an engine failure down the track. If it is to be done it must be done by an approved Jabiru engine man, and it's not worth thinking about unless the engine has the symptoms mentioned above.
Regards,
Doug Smith
Engineer, Jabiru Aircraft
This email message and any accompanying attachments may contain information that is confidential and intended only for the use of the addressee named above. It may also be privileged. If you are not the intended recipient do not read, use, disseminate, distribute or copy or take any action in reliance on it. If you have received this message in error please notify the sender immediately and delete this message. Before opening any attachments, check them for viruses or defects.
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Peter H
Joined: 20 Mar 2007
Posts: 197
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| Posted: Fri Aug 01, 2008 3:07 pm Post subject: Barrel Nuts |
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Thanks For the feedback Clive. Very interesting. Although these engines are
basically good I am not surprised by what I hear from you on this subject.
I will be interested to hear the outcome of your next flight.
I have a 3300 in a Quickie now designated a Q-200.
I have conducted many trials to overcome the tendency to run rich above 2700
and discovered that the carb as supplied is fitted with a large float needle
seat 2.25mm which is released by Bing for use with gravity feed. I got
advice from the Bing engineer in Germany. I tried the Bing recommended 1.5mm
seat and it was too lean but got rich when I started the electric boost pump
ie even the smaller seat was leaking under pressure from two pumps. The carb
power needle was selected by Jabiru to provide a compromise performance
setting using the 2,25 seat. I also noted that EGT varies with engine load.
According to Doug Smith it is intentional by design to run the engines over
rich above 2700 even to use up to 40LPH. That is a conservative way to
protect the engine from burnt valves. I was using 36LPH.
Now I have fitted a single barrel twin injector throttle body (Jenvey) and
can over ride the ECU injector dwell time (mixture) with a potentiometer but
EGT still varies. It is even at top of climb then goes to 10deg variance as
the aircraft accelerates. When the EGT is 100degC or more variance the
engine starts to run rough due to unequal boxing power strokes and I would
not be surprised if this contributes to broken flywheel bolts. The factory
told me they often find the RH side is 100degC hotter (like mine) and they
recommend playing with the scat hose intake.
I blame the lack of a plenum. The carb is fitted direct to a collector which
is very restricted inside. Even the entry is restricted.
I have made a 6 port plenum in fiberglass (pic attached) and hope that this
will improve the fuel/air distribution. Ideally it would be an updraft
design but I don't have the space.
I am getting 170KTS CAS at 3000 ft ( 4mph true) at 3000 RPM WOT. My prop
is a Sterba 55X72" pitch and is a bit over pitched but I think the engine
has more potential and of course it is not really fully run in and is tight.
I suppose the Esqual performance will be close or better than the Q-200.
Good luck with the barrel nut job and I look forward to hearing from you.
Cheers
Peter
Queensland
OZ.
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