Baffling clean up

[Jeff Bost]

Guys,

I’ve been experiencing high CHTs on 3 and 4 during cruise climb. Having to indicate 140 mph to have a chance at 400 F. I removed the top cowl this morning and snapped some pics of the baffling. Some old RTF around but I see the need for more. Big holes where the ignition harness comes through the rear. Any advice would be appreciated. I have a cockpit control for the oil cooler but it’s wired full open in the summer position. Some have suggest partially blocking the oil cooler if oil temp in acceptable. Thanks.

Jeff

 

[Majorpayne317641]

ACS sells spark plug flange fittings to pass through the plugs while not leaking any air. I also have a controlled oil cooler door in my 8 but it has no affect on cylinder temps open or closed. I also have sufficient cooling.

 

[RNB]

Those baffles look old.
is this a new problem?
what engine?
what temp at desired climb?

I think folks get too worked up worrying over climb temps on lycoming engines.

 

[Jeff Bost]

Those baffles look old.
is this a new problem?
what engine?
what temp at desired climb?

I think folks get too worked up worrying over climb temps on lycoming engines.

I purchased the airplane 2 months ago. O-360 with CS prop. If I climb at Vy till 1000ft, then accelerate to 130-140, I’ll reach 430 CHT easily on #3 and 4. Reducing prop to 2500 rpm is minor help. Will cruise below 400, but won’t climb that way in warm weather. Seems like a baffling issue to me. Thanks, Jeff

 

[Webb]

Do you have a picture of the inside of the top cowl?

 

[Jeff Bost]

Do you have a picture of the inside of the top cowl?

No sir I don’t.

 

[Webb]

I suspect you will see dirty areas where air is leaking.

 

[mburch]

Do you have a picture of the inside of the top cowl?

Was going to ask the same thing. The way the vertical baffles behind the ring gear are cut real high makes me curious what the interface to the cowl inlet ramps looks like.

 

[Jeff Bost]

I’ll get a photo of top cowl and add it here in the next day or two. Thanks.

 

[RV8Squaz]

Check your ignition timing. An overly advanced timing will increase CHT significantly. Check for an induction leak especially on cylinders 3 and 4. A lean condition can drive up CHT’s. Replace intake tube gaskets if more than a few years old.

Your baffles really don’t look that bad. But it may be time to replace with new silicone seals. Make sure the seals are making contact all the way around. There appears to be some puckering.

Jerry

 

[Aden Rich]

You could use some front cylinder covers. They are a small place that is riveted to that angle going across the front of each cylinder. It helps push the air over the cylinder and back to the back cylinders on the engine. It keeps the air from diving right down the fins in the front there. It will also bring the front cylinder temps up if they are running cooler than the back ones.
Check each cylinder with a flashlight, between your pushrod tubes. Shine a light up from the bottom side of the cylinder in the area between the intake and exhaust valves. That area should not have any flashing in there. During the sand casting process, excess metal can get in that area and block off the air passages. You want all the flashing removed in there and have open passages so the air can get in there and cool between the intake and exhaust valves.
Also look up under the cylinders and make sure your inter-cylinder baffles fit snug up against the cylinders and don't have big open spaces. Sometimes they get hung up on the cylinder base nuts and are not install correctly, leaving large open gaps.
The underside of the cylinder baffles should also be pulled tight to the cylinder fins. They are the ones that wrap around the cylinders. It's a bugger to get them nice and tight. That will let a lot of air blow by and not go through the fin area.
Lastly, What is that oil line going over the top of the engine? Looks like it's going to your front crankcase and controls your C/S prop. I would highly recommend you ditch that non-standard piping arrangement and go purchase and new oil line from Superior or Lycoming. Texas Air Power has them or aerosport power in Kamloops, BC. It's a very specific line with some clips and clamps that attach and secure the line under the cylinders. That line you have could crack and break and then it will be a very bad day for you when you have oil going everywhere. Somethings you can alter and change due to it being experimental, however, I would error on the side of caution and purchase the correct parts on a critical oil line like that. The pressure coming out of that is like 300 psi, not 80 psi from your engine drive oil pump. IF you need me to help you look up that part number, I can do that.

 

[Jeff Bost]

You could use some front cylinder covers. They are a small place that is riveted to that angle going across the front of each cylinder. It helps push the air over the cylinder and back to the back cylinders on the engine. It keeps the air from diving right down the fins in the front there. It will also bring the front cylinder temps up if they are running cooler than the back ones.
Check each cylinder with a flashlight, between your pushrod tubes. Shine a light up from the bottom side of the cylinder in the area between the intake and exhaust valves. That area should not have any flashing in there. During the sand casting process, excess metal can get in that area and block off the air passages. You want all the flashing removed in there and have open passages so the air can get in there and cool between the intake and exhaust valves.
Also look up under the cylinders and make sure your inter-cylinder baffles fit snug up against the cylinders and don't have big open spaces. Sometimes they get hung up on the cylinder base nuts and are not install correctly, leaving large open gaps.
The underside of the cylinder baffles should also be pulled tight to the cylinder fins. They are the ones that wrap around the cylinders. It's a bugger to get them nice and tight. That will let a lot of air blow by and not go through the fin area.
Lastly, What is that oil line going over the top of the engine? Looks like it's going to your front crankcase and controls your C/S prop. I would highly recommend you ditch that non-standard piping arrangement and go purchase and new oil line from Superior or Lycoming. Texas Air Power has them or aerosport power in Kamloops, BC. It's a very specific line with some clips and clamps that attach and secure the line under the cylinders. That line you have could crack and break and then it will be a very bad day for you when you have oil going everywhere. Somethings you can alter and change due to it being experimental, however, I would error on the side of caution and purchase the correct parts on a critical oil line like that. The pressure coming out of that is like 300 psi, not 80 psi from your engine drive oil pump. IF you need me to help you look up that part number, I can do that.

Good info…thanks. The engine was assembled by a reputable builder and I’m surprised he’d set the supply line for the governor incorrectly. I’ll look into it. Thanks again. Jeff

 

[jrs14855]

That governor line was the starting point for an engine fire and fatal crash in an RV.
The sheet metal portion of the baffles may be too far from the cowl.
Install new silicone rubber all the way around. The baffle rubber at the front of the engine is not doing much.
45 degree angles on the sides and aft baffles would help to keep the rubber properly oriented.
If you do it right the silicon material should not need cuts to go around shallow bends.
If you set the timing to 22 degrees you should get a measurable drop in CHT.
Check the inter cylinder baffles that they are tight against the fins and have the proper gap.