SonexBuilders.net

Hi all
Yesterday I was going to fly the last 1.5 hrs off prior to my oil change and putting the plane away for the winter. During the taxi out the warning light began to flash from the EiS which as I pulled off the taxiway I also noticed a power drop. I quickly shut the engine down and noticed the CHT and EGT were high for just taxing.
Anyways I ended up pushing the aircraft back to the hangar and let it cool down over the night where the next day I would trouble shoot. I was planning on doing a run up to warm the oil prior to the oil change and winterizing the aircraft. I was planning on doing a compression test as well. Put a heater on the engine to warm up the oil for engine start. As I pulled the props through my heart dropped as on two cylinders there was resistance indicating compression and on the other two not a damn thing.
As the notes from the previous day were indicating that the high temps were on the number 2 and 4 cylinder, I suspected the loss of compression was on those cylinders. Needless to say I was not impressed or happy when I pulled off the valve covers to find that the two pushrods came unseated and caused the issue.
Couple of questions come to mind
Has anyone seen this before?
What what would cause a rod to come unseated. Other then a lifter Valve sticking?

With the solid lifters I know that they are to be checked every 25 hrs when the oil change is due.



Thanks for your time.

Mark

Hi Mark, this would be a good question to ask on the Jab/Camit list.

main+owner@JabCamit.groups.io

Rick
C-GRIX
Yorkton

I would guess that the only way that this can happen is if the valve is sticking in its guide. I had to do some head disassembly a while back and found a couple of the exhaust valves were tight in their guides. The Jab doesn't use valve stem seals and if the head is running hot, the oil could burn in the guide, and this is what appeared to happen in my engine. I ran a reamer through the guides and all was good. I also relocated the CHT senders which I think were indicating low. Not sure if that explanation works for the inlet valve too.

Peter

Wood wrote:Hi all

With the solid lifters I know that they are to be checked every 25 hrs when the oil change is due.

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Thanks for your time.

Mark

But how many hours had it actually been since the valve adjustments were last checked? It once surprised me how little beyond the 0.010" gap it took for the valve stem to drop out of place.

Art,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,Jabiru 3300 #261

Hi Mark, sorry to read of your troubles. Several years ago I had to stand in the 'naughty corner' to attone for my sins of running my previous Jabiru 2200 too hot for too long. The heat causes the heats to distort slightly and tightens up the valve stem to valve guide clearance. It sounds like the valve stuck open which allowed the pushrod to fall out. The pistons are relieved to allow room in case this happens to prevent really expensive stuff happening. The good news is that since we all just love fixing stuff (???) you really need to take the offending heads off and measure the valve guide diameter. This is not nearly as scary as it sounds. Jabiru sells the valve guide reamer and 'go-no go' guages to fix the guides. The only parts required will probably only be the valve guide reamer kit which is not scary. If the head bolts are tight in the head that will prove that it was a temperature problem. If you're mechanically minded I reckon it will take you until lunchtime to fix it, otherwise I recommend getting some help. Good luck.

If that engine is old enough to have been built with solid lifters, then unless the pistons have been recently replaced, they do not have recesses for stuck valves and if a valve gets stuck far enough down, it can be bent and broken by the pistons, or punch holes in the piston, or both. Need to pull the head to have a look in there.

If this problem appeared following a recent valve adjustment, there is a real possibility that it was simply due to the adjustment being made when cam was not in proper position, but the higher temperatures seen point to several other possibilities as well. You have an educational toy to explore.

David A.

Hey everyone. Sorry for the delay in the responses here. First thanks for all the reply’s and advice. I’ve been talking to Nick at Jabiru USA. After sending the two pics to Nick and talking with him it sure seemed that he wasn’t surprised at this happening.
After, seeing this and pulling the pushrods out really did not see any damage to the rod or the valve. After talking with Nick and Saying that a good possibility is carbon build up if the engine runs rich. So, too pull the heads and check for carbon build up.
Had a good friend who’s an AME help me with this. Once we took the heads off which was pretty simple we found that on both cylinders, it was actually the valve seat that popped out ???? which lead to the valve sticking and not closing fully.



Pulled the valve and seems ok but a little damage to the head where the seat goes. Possibly and hopefully get it fixed.


Checked the tops of the pistons and found a scratches which could be dealt with easily. Heckled the walls and all is good there thank god.


So, now my concern is that Jabiru says because it’s an older 2200 they don’t make those heads any longer. So, hopefully they can be fixed.

Mark

Mark,

Sorry for your troubles.

From my almost 10 years with the Jab 22A in my Sonex, I recall that any discussion about these units must start with the engine serial no. The build variatons over time have been so numerous that anything else is meaningless. A mech lifter engine like yours with the black starter motor housing would indicate an early gen 2 unit- serial # something in the early one thousands??

Cooling the wide finned heads on these units, is an absolute requirement for safe operation. Jab suggests a max cht of something around 175C under the plug, and 150C continuous. I am sure that is fine, but it really does not address the critical area, namely around the bottom head bolt (the one under the rocker box plug). Personally I would always tighten my buttock muscles if I saw anything close to 140C max wot there. I know that with the notoriously unreliable cht instrumentation they have foisted upon the flying community, this is opening a can of worms: where to hook up the sensor??

What happens is this: the head is not sufficiently cooled down there, the aluminium in the heads are locally going plastic, and gradually you are loosing clamping force under the head bolts- especially the lower one. Sooner or later you will have a leaking sealing surface evidenced by some (miniscule remnants) burnt lube oil. That is when the shit hits the fan- your cylinder egt creeps up: not much, mind you, perhaps not enough to cause any alarm from gage readings, but enough to heat up your head so much more that placticy increases and the valve seats are loosing their crimp: the seats are on their way out! By the way, IMHO egt limits (680-720C) set by Jab are far too optimistic: 620-650 gives me more ease of mind.

Getting plastic heads back into shape is an almost impossible task- it has been tried numerous times before with disappointing results. Many have turned to a more bullet proof solution- install liquid cooled heads, a radiator and a circulation pump. True, it is a lot of work- but it also gives piece of mind! The final result could be looking something like this:

Hi Kia.
Thanks for the reply. Forgive my ignorance on this. Your comment on this engine been a 2nd generation caught my attention and a bit of a relief.Is there a reference which states what serial numbers fall into 1st, 2nd generations.
My serial number on this is 22A 1130. Which, I hope it is not a1st generation. I’ve been told that you can no longer get heads for 1st gen engines. So if it’s a second gene then that takes a load off. At least until I get the bill on what I need to do.

Thanks again.
Mark

You are correct with your assumptions about the valve seats. But technically speaking, here we go, plasticity is not a metallurgical term. Yield strength comes close to it. That's the strength at which it yields and does not spring back. Aluminum expands four times as much as steel valve seat when it's heated. micro inches/degree C. per inch. That's probably why they put a max on head temp. When an alum head expands the holes get larger not smaller. Valve seats have to be shrink fit when they are installed, by several methods, and pressed into the seat in order to be able to absorb the heat expansion without coming loose. The head goes through an expansion/contraction cycle with every engine run which might also tend to loosen head bolts. It would be a good idea to torque check them once in a while. I need change for my two cents worth.