Failed blow-by on Cylinder 5

The Jabiru Engine which is used in many other aircraft.

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Shaunus
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Failed blow-by on Cylinder 5

Unread post by Shaunus » Sun Oct 13, 2019 8:32 am

Morning all

So alas my 500hr 3300 engine failed its blow-by on the 5th cylinder, reading 40/80. All others were fine, and no other issues to date. So currently getting a ring replacement at Diepkloof AMO north of Malmesbury. Anything I should be aware of anything going forward, any of you had similar issues?

Cheers
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Re: Failed blow-by on Cylinder 5

Unread post by Chalkie » Sun Oct 13, 2019 10:34 am

If a blowbye is that low, the air can only leak past the rings, or past an inlet or exhaust valve or in the case of your engine past the cylinder head gasket. Considering you are changing piston rings this will indicate that you did remove the dipstick to confirm air leaking past the rings?
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Re: Failed blow-by on Cylinder 5

Unread post by Shaunus » Sun Oct 13, 2019 12:20 pm

Chalkie wrote:
Sun Oct 13, 2019 10:34 am
If a blowbye is that low, the air can only leak past the rings, or past an inlet or exhaust valve or in the case of your engine past the cylinder head gasket. Considering you are changing piston rings this will indicate that you did remove the dipstick to confirm air leaking past the rings?
Hi Chalkie. Yes as far as I am aware, Pieter did confirm that the leak was via the rings using the usual listening techniques at the oil filler.

Am sure I will get a full run down from Pieter, keen to see how many other people have had to replace a ring here and there on the Jabbie and if this is a cause for concern at the 500hr mark.
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Re: Failed blow-by on Cylinder 5

Unread post by Chalkie » Sun Oct 13, 2019 12:43 pm

If you over heated that cylinder the rings can be annealed and lose their tension, causing the blowby.
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Re: Failed blow-by on Cylinder 5

Unread post by Antman » Sun Oct 13, 2019 6:50 pm

Want to learn more about piston engines, read Mike Busch’s articles and books. Very Informative!!

https://www.savvyaviation.com/home/resources/

This article is about blow-bys
https://www.savvyaviation.com/wp-conten ... ndancy.pdf

Here’s the continental SB he talks about.
https://www.aircraftspruce.com/catalog/ ... lletin.pdf
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Re: Failed blow-by on Cylinder 5

Unread post by Shaunus » Wed Oct 16, 2019 7:33 pm

Thanks, wish I had read that earlier!

New rings have been put in and all seems good, will monitor and see how it goes. Apparently I need to fly relatively hard for the next 3 hours for the new rings to take properly, mainly just circuits and landings.

Cheers
Shaun
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Re: Failed blow-by on Cylinder 5

Unread post by TOFFS » Thu Oct 17, 2019 9:00 am

Hi Shaun

Reading this and the comment of circuit work for initial break-in did peak my interest as the stipulated break-in procedures for type certified engines is very different and low power settings as used in the circuit are counter productive to the run-in procedure in that +75% power is called for, for a period of 2 hours. Low power settings are blamed for the varnishing of cylinders and no bedding in of the rings.

Here is an excerpt from the Jabiru Manual:

"CIRCUIT WORK is possibly a good sequence for initial run in work. Abbreviate circuits initially, step climb, climb shallow. No glide approaches. Gradually reduce power. Avoid sudden heating up and sudden cooling down."

Within the Maintenance Manual it does recommend a non-detergent oil for the break-in period.
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Re: Failed blow-by on Cylinder 5

Unread post by Flooi » Thu Oct 17, 2019 2:00 pm

I once wrecked a newly overhauled Conti in 40 hours
because I nursed it.... so leer mens.🙄
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Re: Failed blow-by on Cylinder 5

Unread post by Shaunus » Sat Oct 19, 2019 9:31 am

Have done 4 hours circuit work on the new ring, temps looking really good. Using Phillips 66 X/C Aviation SAE 20W-50 to run it in. Apparently can continue using this oil after the run in period.

Holding thumbs for a long ring life! On the side, also used the circuit work time to adjust the fixed trim tabs by shaving a bit off, biggest improved to my Jabbie in 5 years. Have posted in the J430 trimming post.

Happy flying all, and thanks for the advice to date
Cheers
Shaun
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Re: Failed blow-by on Cylinder 5

Unread post by JvTonder » Sun Oct 20, 2019 3:22 pm

TOFFS wrote:
Thu Oct 17, 2019 9:00 am
Hi Shaun

Reading this and the comment of circuit work for initial break-in did peak my interest as the stipulated break-in procedures for type certified engines is very different and low power settings as used in the circuit are counter productive to the run-in procedure in that +75% power is called for, for a period of 2 hours. Low power settings are blamed for the varnishing of cylinders and no bedding in of the rings.

Here is an excerpt from the Jabiru Manual:

"CIRCUIT WORK is possibly a good sequence for initial run in work. Abbreviate circuits initially, step climb, climb shallow. No glide approaches. Gradually reduce power. Avoid sudden heating up and sudden cooling down."

Within the Maintenance Manual it does recommend a non-detergent oil for the break-in period.
Sorry for the Hi-Jack, TOFFS when breaking in a newly overhauled motor, Conti, for said two hours must it be flying or can it be done on the ground?

Thanks
J
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Re: Failed blow-by on Cylinder 5

Unread post by TOFFS » Mon Oct 21, 2019 10:55 am

"Sorry for the Hi-Jack, TOFFS when breaking in a newly overhauled motor, Conti, for said two hours must it be flying or can it be done on the ground?"

Continental talk about a "Break-in" and a "Run-in"

A break-in would be conducted on the ground in a cell with a test club fitted so therefore the engine would not be installed in the airframe.

A run-in would be during a flight in accordance with the Service Bulletin relating to engine run-in's. I'm not sure of the number off the top of my head, but within it, it will give you time periods and engine settings conducted during the flight.
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