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Very hot No.3 Cylinder

PH-SCP

Well Known Member
Hi guys,

After I had a sticking valve in the No.1 cylinder, I inspected all 4 on my RV-9, equipped with a Lycoming O-320-D2J. They were all found in a rather sorry state and I decided to replace all four with factory new cylinders.

The plane is equipped with a James Holy cowl and today I flew for the first time. Cylinder 3 is the hottest and won't cool down under 400F. In climb it went as high as 440F. Before the cylinder change, No.1 was the hottest but would cool down to be within 25F of the other cylinder head temperatures in cruise, all around 375F depending on OAT.

Oil cooler is behind No.3 cylinder and takes a chunk of the cooling air but this was never a big issue before.

Attached is picture in cruise of CHT's and EGT's.
What would be the best approach to solve this issue ?
Your advice would be very much appreciated.

Best regards.
 

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something wrong

You really don't want to see your CHTs over 400, particularly during break-in. How are your baffles? Are you sure you are getting enough fuel to the engine? How fast are you flying? Did your oil temp go up after the changes you made?
 
What you are seeing is not uncommon for brand new, or honed/ringed cylinders. They will be hot for a few hours. Temps need to be kept below 430 and you MUST do shallow climbs or whatever it takes to keep them under 430; lower is better. You should pull the plug on #3 and see if you glazed it. Best to address that early in the break-in if you did glaze it, so you don't have to repeat the process later. If you glazed it, a typical tell tale sign is wet, oily bottom plugs.

Larry
 
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Do a search for BAFFLE MOD. Dan Horton posted back in December 2008. I just did the same and brought my #3 down 15 degrees. U may have other issues, but this is definitely worth it.
 
CHT

You really don't want to see your CHTs over 400, particularly during break-in. How are your baffles? Are you sure you are getting enough fuel to the engine? How fast are you flying? Did your oil temp go up after the changes you made?
Totally agree with the break in part. Anything over 400 for more than a few seconds is completely unacceptable. Try retiming your mags to 20 degrees until you get the CHT under control.
Once the rings are seated 425 in climb should not hurt anything.
At 450 you have likely glazed that cylinder. Something is very wrong.
 
I’ll second the #3 baffle mod. Worked for me too - 15* decrease in CHT on that cylinder. Worth the effort.
 
For the sake of more accurate communication, the presence of the oil cooler near the hot cylinder doesn't "take" it provides an alternative path that reduces the "Delta P" in the vicinity of that cylinder.

Lyc Factory cooling spec is above 5" H2O, (the Delta P spec increases, more or less with engine displacement). I.E., the pressure differential needed to "push" enough mass through the baffles to cool the engine.

Please don't jump to the conclusion that by making this point I'm being critical.

If one uses "accurate" terminology, the path to the "answer" is typically shorter.

Onward and upward.
 
I see the photo shows a fuel flow of 8 gal/hr. For break in I think you want full rich or close to it to help control the CHT's.
 
You should consider the baffle mod, but there may be another cause here. I have a james cowl too, and know that James recommendations for lower baffle gaps for the head and barrels are smaller than standard Vans. This is typically a limiting factor for air flow and that jug/head might have the baffles settled in with a little more restriction (than others) in light of having all the baffles off for your repair. The intersection baffle can easily move 1/4", at least mine did.

When you look, it will be the head gaps that really matter, gaps on the barrel will make little (if any) measurable difference in CHT (I have data).

Edit: I am with Mark-and have data too, on the effect of oil cooler air flow. The location is no factor on any specific CHT, but the air consumed will affect upper pressure and may affect all CHT together, not just one.
 
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Lycoming Operators Manual 0-320...

For maximum service life, cylinder head temperatures should be maintained below 435°F (224°C) during high performance cruise operation and below 400°F (205°C) for economy cruise powers.

Doesn't sound like you exceeded that.
 
CHT

The standard Lycoming CHT limits do not apply to break in. The fuel flow looks low and may be a factor. I have the cooler behind #3 on a 0 320 with 10-1 pistons. No problem keeping the CHT below 425 in climb and 400 in cruise. NOT an RV
 
Assuming your engine installation used to run with acceptable temperatures I would be tempted to look at the inlet tract for that cylinder - it looks like it could have an air leak.

Did you use new hoses between the pipe and the 'sump tube'?
You didn't forget the inlet flange gasket or misalign it?
No offence intended - just covering all possibilities.

Another possibility I am dealing with right now is the intake flanges that join the intake tube to the cylinder head. I have ordered a new set of 4 a couple of hours ago.
One of the originals is like a banana and the others don't really lie properly flat.
Annoyingly one can't just grind them flat like one can an exhaust flange because of the machined recess.
Putting them through a machine shop to correct them would cost more than new ones.

I believe there is an alternative inlet flange connection available that cures these sorts of problems - I am in the UK and can't be bothered with the paperwork that would generate but you might be in a position to consider it.
 
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New cylinders on an engine see Lycoming SI 1427C.
Engine break in procedure is required.
This also means straight mineral oil in most cases.
 
Hi guys,

Thanks for all the response. Very much appreciated.
Today I was finally in a position to drive to the airport and open up the RV9.

As I am no aircraft mechanic, I had a certified company take care of the cylinder change. Maybe this was a mistake.

Looking at the bottom baffles, I saw this. Not sure if the picture is clear enough but it looks at the number 3 cylinder from the bottom. The baffles are open by about 1 cm (0,4 inch) and maybe even a bit more. They are not tightly rapped around the cylinder heads. The baffles consist of two parts, neither of which lay closely around the cooling ribs. Will rectify that tomorrow.

Will also look at the alignment of the inlet flanges and make sure there is no air leak there.

New hoses were used between the pipe and the 'sump tube', will look at those also.

I hope that with the baffles tightened up, I will see a significant improvemnet in temperatures.

Also discovered that EGT-3 sensor shows a wrong temperature. With the engine off, it shows -99F, the others are showing OAT. I have seen this during start up a few times and the mistake always corrected itself during engine warmup. Looks like time for a sensor change.
 

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It should be pulled tighter.

Looks like a Adel clamps are being used to hang a large wire from an oil drain tube, arguably a Bad Idea. And the hose clamp on the drain's rubber tube is too large. See Fig 11 here: https://www.danhorton.net/Articles/0414_Beads.pdf
.
 

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I just helped repair a baffle that looked just like this on a recently purchased RV-6. In his case, the end had cracked off, but it looked identical to yours, so assuming very little tension on it. He dropped around 40* CHT on the pair of cylinders after the repair.

Lary
 
Also discovered that EGT-3 sensor shows a wrong temperature. With the engine off, it shows -99F, the others are showing OAT.
From memory my Dynon D120 shows -99 when there is a probe/sensor failure OR a loose connection although I can't remember whether that was for EGT or CHT or both. You might want to check or replace the connectors where the EGT probe wire joins the wiring loom wire before spending any money.
The maintenance company probably left the probes in the pipes when they were removed and disconnected the wiring - it may not have been put back properly.
 
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