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Thruster87
Joined: 16 Apr 2008
Posts: 193
Location: Australia
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 Posted: Sun Oct 17, 2010 11:21 pm Post subject: Jabiru Engine mods |
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Most of the problems in Jabs is due to overheating ... sticking rings, worn guides, exhaust value pitting/breakage, broken through bolts (detonation) etc etc is all heat related.
The new fine fin heads have 50% more surface area along with a wider setting between the valves .. there is also a lot more finning material around the exhaust port which make quite an improvement in terms of getting heat away from the top end. Additionally the new hollow push rod and rocker gear has greatly improved lubrication system and will help extend the rocker gear life many times. One mod I have come across and have implemented into my own engine is to use K-line valve guide inserts, whilst I haven't done enough hrs on them yet to personally give them the thumbs up, the South African Jab Distributor has done thousands of hrs and say they are the bees knees.
The new piston and ring set up provides more clearance in the ring groves which should help stop ring sticking and the new piston have larger drain slots in the oil ring grove too ... this combo is a good step forward to reduce ring and bore wear. Jab have also changed the cylinders in the last few months; these are now 0.5m longer to lower the compression to overcome detonation and stop thru bolts breaking.
As I said, most problems in Jab engine relate to getting too hot ... the biggest factor to fix over heating is fuel mixture. It is imperative that you have the latest jetting (including needle) in your carby .. Without the right jets you will most certainly run lean and do damage. Fuel distribution in the 6 cylinder is a problem and has also claimed the life of many engines ... however there is a simple fix for the 6 cylinder (not the 4). In the induction track of the manifold there is an aerofoil which acts as a divider to direct flow inside the manifold … this aerofoil doesn’t work. The factory has discovered if you remove this and simply replace it with a 12mm round tube it improves fuel distribution and EGT becomes balanced across the cylinders… it really does work!
There is another mod to the Bing Carby, although I have not done this myself, .. the South African Jab Distributor has increased the emulsion air induction size and drilled the emulsion tube air holes to 4mm … I believe this as improved things in terms of better atomisation. I know Jab in Bundy have verified this and suggest you talk with them to get the exact details.
I have also tried exhaust wrap for 250 hrs and came to the conclusion that this didn’t provide any real benefit .. it reduced the inside cowl temp but think it may have put heat stress on the exhaust valve.
Lastly, fly them hard, particularly during run-in to ward off glazing … they love heaps of fuel going through them to cool thngs down.
This is a copy of a post from http://www.recreationalflying.net/index.php
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davgray(at)sbcglobal.net
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| Posted: Mon Oct 18, 2010 2:34 am Post subject: Jabiru Engine mods |
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Wow, all of these issues not worked out prior to release for only $20K?
I am feeling really happy I chose to fly a William Wynne Corvair engine.
Gary Ray, WW Corvair, 0.060 overbore, Roy's 5th bearing, Falcon Heads, 150
hrs TT
davgray(at)sbcglobal.net
--------------------------------------------------
From: "Thruster87" <alania(at)optusnet.com.au>
Sent: Monday, October 18, 2010 3:21 AM
To: <zenith-list(at)matronics.com>
Subject: Jabiru Engine mods
| Quote: |
Most of the problems in Jabs is due to overheating ... sticking rings,
worn guides, exhaust value pitting/breakage, broken through bolts
(detonation) etc etc is all heat related.
The new fine fin heads have 50% more surface area along with a wider
setting between the valves .. there is also a lot more finning material
around the exhaust port which make quite an improvement in terms of
getting heat away from the top end. Additionally the new hollow push rod
and rocker gear has greatly improved lubrication system and will help
extend the rocker gear life many times. One mod I have come across and
have implemented into my own engine is to use K-line valve guide inserts,
whilst I haven't done enough hrs on them yet to personally give them the
thumbs up, the South African Jab Distributor has done thousands of hrs and
say they are the bees knees.
The new piston and ring set up provides more clearance in the ring groves
which should help stop ring sticking and the new piston have larger drain
slots in the oil ring grove too ... this combo is a good step forward to
reduce ring and bore wear. Jab have also changed the cylinders in the last
few months; these are now 0.5m longer to lower the compression to overcome
detonation and stop thru bolts breaking.
As I said, most problems in Jab engine relate to getting too hot ... the
biggest factor to fix over heating is fuel mixture. It is imperative that
you have the latest jetting (including needle) in your carby .. Without
the right jets you will most certainly run lean and do damage. Fuel
distribution in the 6 cylinder is a problem and has also claimed the life
of many engines ... however there is a simple fix for the 6 cylinder (not
the 4). In the induction track of the manifold there is an aerofoil which
acts as a divider to direct flow inside the manifold â?¦ this aerofoil
doesnâ?Tt work. The factory has discovered if you remove this and simply
replace it with a 12mm round tube it improves fuel distribution and EGT
becomes balanced across the cylindersâ?¦ it really does work!
There is another mod to the Bing Carby, although I have not done this
myself, .. the South African Jab Distributor has increased the emulsion
air induction size and drilled the emulsion tube air holes to 4mm â?¦ I
believe this as improved things in terms of better atomisation. I know Jab
in Bundy have verified this and suggest you talk with them to get the
exact details.
I have also tried exhaust wrap for 250 hrs and came to the conclusion that
this didnâ?Tt provide any real benefit .. it reduced the inside cowl temp
but think it may have put heat stress on the exhaust valve.
Lastly, fly them hard, particularly during run-in to ward off glazing â?¦
they love heaps of fuel going through them to cool thngs down.
This is a copy of a post from http://www.recreationalflying.net/index.php
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=316131#316131
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