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Help! Hot Cylinder?

rv7guy2

Active Member
Let me begin by apologizing for the length of this post but I am really hoping I can tap into the vast knowledge pool in the Van's community to help me with a very perplexing problem. Basically, sudden overheating with a cylinder during break-in.
in a nutshell, I am running an IO-360 in my RV-7 of 700 hours. I recently had to have Cy #1 and #3 re-honed due to vanishing. That's another story. Anyway yesterday I was finally able to go flying (cold, rain and snow for over a week). After preheating the engine I launched into a brilliantly clear cool day.
As I had been advised by a great many people, websites, books and a popular YouTube channel, I started flying a circular pattern around home airport at 26 in MP/2600 RPM (90% pwr according to Dynon Skyview EMS) at 3500 feet ASL. All was well for the first 1.5 hour with no surprises and very steady engine readings. Suddenly seemingly out of nowhere, the CHT of Cyl#1 quickly climbed over 400F and was rapidly going through 410-420-nearing 440 when I pulled the power back and pushed the nose over to get more air through the engine. The cylinder cooled and stabilized around 360 F so I slowly added power and was close to 90% again when second time, the CHT went through the roof. Again I pulled power and go it back under 400F. As the power was quite low, I added power and turned back towards the airport which was about 2 miles away. A third time the CHT climbed above 400F but I was quickly joining the circuit, called in "engine issue" and successfully landed. I ran fine during the landing circuit.
For those who might be asking, here's the engine readings for the first 1.5 hrs of break-in flight time., they were very steady.....MP 26.2 in/RMP 2600, HP-90%;CHT's-#1-357, #2-328, #3-343, #4-321 (remember #1 and #3 are the two cleaned and re-honed cylinders) EGT's 1153,1213,1125,1270 respectively; OAT 1C (33F) altitude 3500 FT, Baro setting 30.40; Oil PSI 83;Oil Temp 192F Fuel Pres 23; Amps 2, volts 14.1. Fuel Flow 15.9---full rich for the entire flight.
My local mechanic went over the engine and found NO induction leaks, a clean injection nozzle and no oil leaks. A few hours after landing on the advice of my local mechanic I switched the CHT's between Cyl 1 & 3 and went up for another flight, Again #1 CHT spiked, showing on CHT 3 after swapping with #1. I was anticipating it quickly landed.
So..question is...why would the CHT suddenly JUMP way over 400 F into the danger zone afterrunning for 1 1/2 hours when CHT temps are suppose to DROP during break in..and do it several times.?The other "newly reworked" cylinder behaved as expected.
I called the engine shop that performed the cleaning and re-honing work but had not heard back from them before end of business day yesterday.
Any thoughts? Ideas? Is my newly reworked cylinder pooched?
Thanks for your patience and taking the time to read all this.
Dave C
RV-7 C-GCPD
 
Dave

Do you have the egt readings when the cylinder was going over 400? And can you plot the cht’s and egt’s though this time period?

It would be interesting to see if this cylinder has gone really lean, possibly though a clogged injector.

Have you done a flow test on the injectors?

Regards

Peter
 
by saying you have an IO-360, is it a true IO-360 angle valve engine, or is it a (I)O-360 parallel valve engine with fuel injection?
Are you running stock mags or electronic ignition?
On the 200hp angle valve engines, Lycoming used to set the timing at the standard 25 degrees before top dead center, back in the days when the engine was designed for 100/130 fuel for the angle valve, and the old military "91" octane for the parallel valve 180 HP. With 100LL, depending on how the engine is being operated, the detonation boundaries become narrow, sometimes causing cylinders to run hot. In my case, I run a "pumped up" (I)O-360 parallel valve engine with dual "P" mags. With the normal timing of TDC, I found cylinder #1 to run 390 in cruise on a cool day. I retarded the timing one tooth (2.4 degrees) and under the same circumstances, #1 now runs about 365! Some angle valve 360's and 390's need 5 degrees after top dead center (which would equate to magneto engines of 20 degrees rather than the former 25 degrees before top dead center).
Regards,

DAR Gary
 
I agree with Ralph. I would take a good look to see if any of the baffles (especially the inter-cylinder baffles between 1 & 3 came off)...or at least came loose.
 
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Seating rings

I have several issues with Lycoming procedure. Probably fine for most production aircraft but not for closely cowled EAB. The ground runs are much too long.
I much prefer the Mahlon Russell protocol for ground runs and break in.
I do agree with Lycoming that 75% power is fine for break in, no need to run 90%.
The 140 degree minimum oil temperature is also counter to other Lycoming information that basically states when the engine will accelerate without stumbling you are good to go regardless of oil temperature.
Sustained CHT above 400 before rings are seated is almost a guarantee of glazing the cylinders. Then you pull the cylinders and start over.
 
Timing

The previous post does not explain this very well. For parallel valve set the timing at 22 degrees before top dead center for break in. For angle valve set the timing at 20 degrees.
If temps are good after rings are seated the parallel valve can be reset to 25 degrees. For the angle valve it can stay at 20 or you could go to 22.
The 22 degrees for the parallel valve was recommended by one of the top engines shops.
 
So..question is...why would the CHT suddenly JUMP way over 400 F into the danger zone afterrunning for 1 1/2 hours when CHT temps are suppose to DROP during break in..and do it several times.?The other "newly reworked" cylinder behaved as expected.

Thanks for your patience and taking the time to read all this.
Dave C
RV-7 C-GCPD

Detonation.

About the only thing that can raise CHTs 50* above normal temps at full power in 10-15 seconds is detonation or pre-ignition. I would start by looking for a spark that is jumping across a non-standard path (bridging across wires or carbon tracking in the cap/rotor). Also, get a borescope in the offending cylinder and look for a small piece of steel or carbon that could be getting hot enough to become a glow plug and pre-ignite the charge. Large chunks of metal can't get hot enough to glow. However, small pieces of carbon or steel that are mostly exposed (i.e. no heat sinking) can get hot enough to ignite things; This is classic pre-ignition and temps rise very fast and permanent damage comes quick. Wouldn't be overly surprising that the guys doing the cyl work left a small fingernail like piece of metal sticking out somewhere in the combustion chamber. Mechanic should have looked for this, but if the cyl shop pre-installed the pistons, not surprising that he didn't.

Larry
 
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I agree with Ralph. I would take a good look to see if any of the baffles (especially the inter-cylinder baffles between 1 & 3 came off)...or at least came loose.

If it gets better then gets worse and then better again, it can't really be baffling. If it fell off, it can't really put itself back in place.
 
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Could be worth checking the CHT probe in another cylinder. We had a probe that turned out to be reading 60F over temp this weekend. If all the EGT s are similar that may give you a bit of a clue.
 
Could be worth checking the CHT probe in another cylinder. We had a probe that turned out to be reading 60F over temp this weekend. If all the EGT s are similar that may give you a bit of a clue.

In the OP's original post he did try swapping CHT probes.

"A few hours after landing on the advice of my local mechanic I switched the CHT's between Cyl 1 & 3 and went up for another flight, Again #1 CHT spiked, showing on CHT 3 after swapping with #1. I was anticipating it quickly landed".
 
As others have stated this could be caused by a couple of things - partially blocked injector, missing baffling, detonation caused by lean mixture at high power setting, etc.

My money is on the plugged injector scenario, follow the best practices laid out in Lycoming Service Instruction SI-1275C (https://www.lycoming.com/content/service-instruction-no-1275c), and it might be a good exercise to pull the spark plugs from the offending cylinder and give them a once over (Ohms - 3K to 5K, Terminals snug, gap appropriate to ignition system.)

You didn't mention (or if you did, I missed it) what ignition system you have. What fuel delivery system you have. And, what the EGTs were during the over temp event.
 
My money is on the plugged injector scenario, follow the best practices laid out in Lycoming Service Instruction SI-1275C .

OP is breaking in a new cylinders at 90% power, so have to assume he is full rich. He is probably 200*-300* ROP. Peak CHTs are around 50-80* ROP (any leaner and CHTs drop). You can't get a 50* rise in CHT by leaning from 300 ROP to 80 ROP. Plugged injectors typically put a cylinder well LOP and show CHT reductions. OP also said his mechanic inpsected the injectors after the problem flight and found them clean.

Larry
 
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Engine break in

When receiving a factory overhauled engine, it has been run at least one hr.
Hence you can´t destroy things with 75 % power.
Replacing cylinders means that you are making the first run.
The goal is to cause wear between piston rings and cylinder without destroying things.
This is best accomplished running the engine at 1.000 rpm for 5 min.
let the engine cool completely. Next run the engine for 1.200 rpm for 5 min and let cool. Next, run the engine for 1.500 rpm for 5 min then increase to full rpm for 10 s and shut down and let the engine cool completely.
Now its time to fly the aircraft. Short ground run to do necessary checks.
Climb with full power to safe altitude, reduce power to 75 % as soon as possible, continue shallow climb. 75 % for first hour 65 % next hour.

Good luck
 
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