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Hot rear cylinder example Jabiru 3300A-2575 and plenums


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Part of getting to know my new old plane, is pulling it apart. 

Plenums need work on this beast. 

Here we have burned oil on the rear cylinder exhaust valve spring seat (#5 here) , and cyl # 1 for comparison. head bolts on exhaust side also discoloured.

oil is 22 hours old.
Going to pull all the bores off, new rings, new head bolts, and get the guys next door to do a penetrating dye check on the pistons for cracks.

-glen

image.png.07c187d53868cc21de25ce8db62bbcba.pngimage.png.e50b14401684ab0165e76578e6a26b11.png

 

 

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Yep, the old molasses trick is well known amongst the car, truck, and machinery restorers. Another thing you can do, is round up all the rotting citrus fruit from your local fruit and vegie shop.

Had a mate that used to restore vintage cars. First thing to do was remove the motor, empty any oil that may be in there, then place the whole thing into a drum with a mix of fresh water and molasses,

I've seen plenty of really dodgy repairs done by so called professional lames especially electrics with poor joins and a bit of insulation tape, a Mooney engine installation the flange was almost touc

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That looks like overheating. I doubt that rings and head bolts will fix the problem and why would you suspect that the pistons are cracked.

Do you have CHT info for all cylinders?

How do the tappet clearances stack up if they are not hydraulic. The clearance could be different from the other cylinders, less clearance due to stretching of the valve due to overheating.

Have you checked head bolt tension, especially the bolt nearest the exhaust valve?

Can you get a borescope in to have a look at the inside of the cylinder, especially the exhaust valve seat area?

Do you have a problem with the runnning of the engine? Are temps and pressures good?

I would recommend that you don't pull anything apart, unless there is a very good reason to do so.

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Hi Yenn

I posted  the pics for people to see the sort of bad things that go on if hot running is permitted...

The main thing is, I want to know EXACTLY what condition this engine is truly in . So doing rings and a hone   and crack test the pistons is the way for me to get piece of mind....   I have quite a bit of local assistance .

 

I have CHT EGT on all cylinders, these rear ones always run hotter. Jab suggest cylinder head bolts during a top end. 

There was some corrosion in #2, #4 cylinder , some pitting,  and spotting as seen with a boroscope. Need a better 'scope to look at seats. 

head bolt torque on the weak pots was fine.  Torque on CYL5  the exhaust head bolt- required about  1/6 turn  approx  of a turn to meet torque.....

The other hot one around the other side #6 had its exhaust lapped 50 hours ago.  I have not looked/touched  at that one  yet. I think it was low 70s.  The Plenum problems and cooling on this cylinder 5 relate to cooling plenum mechanical problems. (and of course there is a volume and volumes about this issue elsewhere)  CYL5 was running about 15 degC CHT hotter than the others- like 185-190 on climbout (OAT ground= 32C)  way way way too hot. others mid 160s etc. CHT probes are all good.  That's OK, I have the cooling issues in hand.

 

Hydraulic lifters. Last Gen3 engine (#2575 late 2013) has most of the desirable mods in it. Service book record excellent. ..

..corrosion most likely due to it sitting around for a few months (Moree) . cyl 2,4, they have a high blow-by on leak down.  others are mid 60s on average

service record shows slow decline in leakdowns since install .  Previous engine (2010) lost a flywheel in flight. 

The weak  pots might improve with a few good hard long climbs (overhead  strip in case something breaks....) with garbage burned out of ring grooves..maybe. ,

but I need to get the cylinder temps down  in any case.

 

The plenums are all dicky and misfitting an dleak  at the rear cyls. I'm onto the plenum issues and improvements, that's OK I have  that in hand. 

 

I've read the overhaul manuals several times. .... (on gen3 and 4) and every SB on earth..
 

 

 

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OH, and engine is 370 hours, which, from what I can gather up from all the information everywhere is a pretty common figure for needing a top end overhaul.  Jab recommend new head bolts  when doing a top end.  Jab parts are cheap.

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1 minute ago, RFguy said:

OH, and engine is 370 hours, which, from what I can gather up from all the information everywhere is a pretty common figure for needing a top end overhaul.  Jab recommend new head bolts  when doing a top end.  Jab parts are cheap.

Surly you jest!😲

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here is another good one for you, this  hot pot #5  is leaking at the CC interface . 

and here is the burned up fibreglass- note this is the plenum from the ORIGINAL engine - so this plenum is 750 hours old.

you can see the cool end on the left, and the hot end on the right.

it lived in a hot place.

 

 

cyl5_crankcase interface.jpg

burned plenum.jpg

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Not sure where you get your info Glen, but it's wrong. With respect, I think you're suffering OCD or something. What did the leak-down checks reveal? Top end overhaul at 370 hours - bollocks.

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Hi Kevin

happy to know where I am wrong, which bit ?

last leakdowns 4 @ mid 60s  and 2 x fails  (blowby, not valves) . 

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Howdy. It just seems to me you're expecting a shiny clean engine with no signs of ever running. Even my engine at 160 hours shows most of the stuff your on about, although my leak down tests are all in the high 70s.

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it's more the high temp tell tale signs around the exhaust valves springs in the rocker. I bet yours would look like my right hand (clean) photo..

 

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Topend at 1000 hours is the right amount. If the cooling has been poor that will contribute to a much reduced headgear life and even oval cylinders. The hottest cylinders in my engine are  Nos 3 & 4 but not by much. Are there any baffles in the plenums? I glassed in these to aid with forcing the air down. I use the old style with the plug leads on the outside as the newer ones are too tall for my top cowl. My engine runs cool all the time even on a prolonged climb.

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Hi KG. 2200 or 3300 ?

Not a complete top end.... heads and cyl off, hone, rings....  guides check , valve seat check...

 

it is just amazing how fast this is on a Jabiru engine. about 15 minutes and it is down to the bones !

and the parts are inexpensive. 

 

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Hi KG. yeah this one had a hot life. we'll see how it comes up.  Do you get an oil analysis done ?

 

Kevin- your airplane engine is carefully flown and well looked after...

 

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No. The oil stays relatively clean between 25 hourly changes. I do not top up between changes. Each oil change I use 3 quarts of Aeroshell W100+. My leakdowns are all 75/80 or better.

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On 18/01/2021 at 8:16 AM, RFguy said:

Part of getting to know my new old plane, is pulling it apart. 

Plenums need work on this beast. 

Here we have burned oil on the rear cylinder exhaust valve spring seat (#5 here) , and cyl # 1 for comparison. head bolts on exhaust side also discoloured.

oil is 22 hours old.
Going to pull all the bores off, new rings, new head bolts, and get the guys next door to do a penetrating dye check on the pistons for cracks.

-glen

image.png.07c187d53868cc21de25ce8db62bbcba.pngimage.png.e50b14401684ab0165e76578e6a26b11.png

 

 

Valve guide ok?

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My temperatures were evened out and lowered by doing a lot of tweaking with the ducts. It took years. Examples include blocking off holes or gaps where cooling air could escape without coming close to the metal surfaces of the engine and joining left and right side ducts with a pipe, as well as adding rivetted aluminium duct extensions. This was experimental stuff and not everything worked at first. But it was fun and satisfying.

I also added a smallish skirt to the lower cowl and baffled the oil cooler so as to avoid any higher than necessary lower cowl pressures.

If you think about the physics of air flow and heat transfer you will get things better and you should do this before putting new engine bits in to suffer the same fate as the old bits.

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valve guides will be checked, I have the tools... although I really need to get a tool gauge that can measure tiny holes in different directionas, as apparently they wear oval.

 

The community thinking is they get full of lead compounds, and carbonized oil... and then you get a valve sticking.  too hot  and the oil burning is a problem, too cool and you dont burn up the lead compounds. 

 

 

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Possible some oil additives as well with the guides. Using the aero oil should cover that. Lead doesn't help guides. It's effective at valve head temps but in the Rotax it doesn't get hot enough for it to lubricate the seats and is therefore not recommended as it builds up and then sometimes a piece dislodges and compression suffers. You can measure valve guide wear/clearance with a dial gauge setup at  right angles to the rocker pivot axis. Turn the engine till the valve JUST opens then measure how far you can move it Yes they wear oval. Nev

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thanks Nev, I  will do that . 
Have been reading about effects of  temperature, time on 4032 cast alloys.
Are their any engines that use copper inserts into ally or steel heads around the exhaust seats (to heat spread) ?


 

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2 hours ago, RFguy said:

valve guides will be checked, I have the tools... although I really need to get a tool gauge that can measure tiny holes in different directionas, as apparently they wear oval.

 

The community thinking is they get full of lead compounds, and carbonized oil... and then you get a valve sticking.  too hot  and the oil burning is a problem, too cool and you dont burn up the lead compounds. 

 

 

You must do in my opinion; because how does the chocolate colour get to where you are seeing it???  The terms I use for assessing that area is clear, honey and chocolate; chocolate being the dark colour that says look into to this soon / now.  Look forward to your findings.

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Hi Blue. yes, hence the reasons for posting it, it is significant.  It's why I am pulling it apart (and also to know where I am at- piece of mind). Bottom end will be likely fine. Wont touch that unless I see soemthing bad when looking through the holes....will have a look at the insides soon enough (boroscope on oil filler) (with bore soff, right in the holes...) 

It is not uncommon, by other accounts.  got to get temps down in that area. 

 

 

 

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 So what happened to crack testing the pistons? You say the low pressures were due to blow by, rather than leaking valves, but this all started about oveheating, which would make valve problems more likely.

How did you do the leak down test? Did you have the correct gear for the Jab engine?

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Hi Yenn

leakdown  yes, had and have correct gear.  

some pots are due to valves leaking , 2 are due to blowby.  Brains trusts say they might come good with a couple of hard full power long climbs. But,  I want to know where the insides are at, so I will pull it down...

 

yes, going to crack test the pistons. no biggie. have some new circlips also for the gudges.

 

BTW : there is a new improved piston for the Gen1,2,3 out, .apparently the what was adopted for the new HD pistons for Gen4 updates have trickled down  (but I am not installing them unless i have cracked pistons AND my bores are nice and round and not worn oval,  and meet tolerances at the 3 heights in the bore etc etc etc)  

:-) glen

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