Intersting find
Posted: Wed Jul 01, 2015 1:37 pmLast flight out on my Jabiru powered Waiex, I noticed on taxi that the #2 cylinder was showing an out of the ordinary egt at low speed, (1,000rpm). I was showing maybe 1100 degrees and the others were barely registering on the Dynon.
At the 1600 run up speed the egts all pretty much lined up. I made a mental note to check the egt on that cylinder next time I had the cowling off.
On the flight I was watching the egts and chts to see if there was any difference than what I was used to? Nothing out of the ordinary.
Just for reference, the #2 cylinder has aways been my warmest since day one. Number 5 and 6 have always been the most balanced and consistly run within 5-10 degrees of each other. Number 2 out front always runs about 15 degrees higher than the rest.
I began to notice on this last flight that making a couple different climbs and decents of over 3,000" each, the #2 was acting funny and getting hotter than normal. I got it up to 345 indicated on an extended climb. Now it is pretty warm out west but it still was off from the rest and by almost 35 degrees. Much more than I'm used to.
The following day I pulled the cowl and decided to run the valves at their normal 50 hr check and got that accomplished. While I had the shrouds off I decided to pull a "cold" leak down test on #2. Much to my displeasure I found it to run at 80/64. Down significantly from the last inspection. Factoring in the cold check it still seemed too much of a change for me. I pulled the head to look hard at the exhaust valve in particular. Nothing to note that seemed out of the ordinary. Stems were clean looking in the ports. No burn marks of any kind near the seats and valve face.
Honestly, I believe in my case the loss of sealing is around the rings. You can hear the air out the breather. All the other cylinders are running 80/75 or better. Will pull the cylinder also and hone the bore and scotchbrite the piston and clean the ring grooves. My halfway, one cylinder tune up. Hopefully this will get me to my top end rebuild I'm hoping to do about 600hrs or whenever the engine tells me its time. I'm setting at 440 hrs now; other cylinders are doing fine.
Dropped my cylinder head off at a place that has considerable experience with Jab's locally. Having guides, valves and seats checked for peace of mind. Head looks very good and no signs of being overheated.
What I did find that didn't please me was the intake pipe leaving the plenum. It about fell in my hand when I undid the joiner hose section. Seal on the outside of the plenum was completely lost.
I looked that area over as thorough as one could do on the condition inspection and didn't catch this. Without some disassembly its pretty hard to detect this. It ended up being one of those "ahhah" moments. There was the source of the egt reading at low throttle settings. Probably had some effect at high throttle settings also?
When the head gets done, we'll bolt her back up and do some test flights with the plenum resealed. Hopefully, it will yield positive results and all will be well and good? Keeping my fingers crossed. I've had very few actual issues with this engine. One of the last of the solid lifter models. Mostly just worry about all the issues others have had. I keep on it like a fox. Looking for issues and occasionally finding something like this.
At the 1600 run up speed the egts all pretty much lined up. I made a mental note to check the egt on that cylinder next time I had the cowling off.
On the flight I was watching the egts and chts to see if there was any difference than what I was used to? Nothing out of the ordinary.
Just for reference, the #2 cylinder has aways been my warmest since day one. Number 5 and 6 have always been the most balanced and consistly run within 5-10 degrees of each other. Number 2 out front always runs about 15 degrees higher than the rest.
I began to notice on this last flight that making a couple different climbs and decents of over 3,000" each, the #2 was acting funny and getting hotter than normal. I got it up to 345 indicated on an extended climb. Now it is pretty warm out west but it still was off from the rest and by almost 35 degrees. Much more than I'm used to.
The following day I pulled the cowl and decided to run the valves at their normal 50 hr check and got that accomplished. While I had the shrouds off I decided to pull a "cold" leak down test on #2. Much to my displeasure I found it to run at 80/64. Down significantly from the last inspection. Factoring in the cold check it still seemed too much of a change for me. I pulled the head to look hard at the exhaust valve in particular. Nothing to note that seemed out of the ordinary. Stems were clean looking in the ports. No burn marks of any kind near the seats and valve face.
Honestly, I believe in my case the loss of sealing is around the rings. You can hear the air out the breather. All the other cylinders are running 80/75 or better. Will pull the cylinder also and hone the bore and scotchbrite the piston and clean the ring grooves. My halfway, one cylinder tune up. Hopefully this will get me to my top end rebuild I'm hoping to do about 600hrs or whenever the engine tells me its time. I'm setting at 440 hrs now; other cylinders are doing fine.
Dropped my cylinder head off at a place that has considerable experience with Jab's locally. Having guides, valves and seats checked for peace of mind. Head looks very good and no signs of being overheated.
What I did find that didn't please me was the intake pipe leaving the plenum. It about fell in my hand when I undid the joiner hose section. Seal on the outside of the plenum was completely lost.
I looked that area over as thorough as one could do on the condition inspection and didn't catch this. Without some disassembly its pretty hard to detect this. It ended up being one of those "ahhah" moments. There was the source of the egt reading at low throttle settings. Probably had some effect at high throttle settings also?
When the head gets done, we'll bolt her back up and do some test flights with the plenum resealed. Hopefully, it will yield positive results and all will be well and good? Keeping my fingers crossed. I've had very few actual issues with this engine. One of the last of the solid lifter models. Mostly just worry about all the issues others have had. I keep on it like a fox. Looking for issues and occasionally finding something like this.