[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.

 

[RNB]

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

500 is redline.
435 is high performance ops
400 is economy cruise ops
per the O-360 manual.

 

[JonJay]

Those baffles look fine IF they are sealing to the top cowl. Witness marks will show where the baffle material is making good contact and also where it isn’t, and leaking. That’s why folks want to see the top cowl inside pics.
Set your engine timing per the manufacture. Probably 25d btc Retarding the timing is just a cover up.

 

[D-Dubya]

The only thing I might add is that it looks like you have a hole for a blast tube in the baffle wall behind #3 cylinder, but the blast tube is missing. If that's what that is, you have a big hole there that's doing nothing useful. And I'm curious as well to see what the fit of the flexible seals is at the D-shaped cowling openings. It's hard to visualize how that's working without the top cowling in place. If you have a borescope, you can look around at how everything seals against the top cowling. ANY gap that allows air to bypass the cooling fins is affecting your CHTs. One technique is to put a work light in the bottom half of the cowling and look for where you can see light. You'd be surprised how just a little bit of sealing up gaps will really help bring temps down to where you're more comfortable.

 

[Jeff Bost]

500 is redline.
435 is high performance ops
400 is economy cruise ops
per the O-360 manual.

Yes sir, I'm aware of those numbers. I'm used to flying big bore Continentals and temps over 400 are a no no. This engine has 1070 hrs and the previous owner replaced # 3 and 4 right before I bought it. I suspect the high temps might have contributed to their early exit. Thanks for your response. Jeff

 

[Jeff Bost]

Those baffles look fine IF they are sealing to the top cowl. Witness marks will show where the baffle material is making good contact and also where it isn’t, and leaking. That’s why folks want to see the top cowl inside pics.
Set your engine timing per the manufacture. Probably 25d btc Retarding the timing is just a cover up.

Yes sir .... I've been down the timing road with another engine without much success. I'll check top cowl soon, Jeff

 

[Jeff Bost]

The only thing I might add is that it looks like you have a hole for a blast tube in the baffle wall behind #3 cylinder, but the blast tube is missing. If that's what that is, you have a big hole there that's doing nothing useful. And I'm curious as well to see what the fit of the flexible seals is at the D-shaped cowling openings. It's hard to visualize how that's working without the top cowling in place. If you have a borescope, you can look around at how everything seals against the top cowling. ANY gap that allows air to bypass the cooling fins is affecting your CHTs. One technique is to put a work light in the bottom half of the cowling and look for where you can see light. You'd be surprised how just a little bit of sealing up gaps will really help bring temps down to where you're more comfortable.

Thanks. There is a blast tube on the other side that's aimed at the vacuum pump. Nothing but a hole on the right side. I almost duct taped it closed but decided that tape might not have enough heat resistance. Several holes where taped closed but had a higher quality tape in place. Jeff

 

[paulsmeds]

I’m chasing high CHTs on climb out as well. 430+ on #3 and #4 and I can’t stand it. I took both top and bottom cowling off then put the top cowling back on. In a semi-dark hanger, then I took a flashlight from the now open bottom and ran it along the edge of the baffle seals looking through the inlets in the front. It was obvious where it was not sealing - almost everywhere. I have big long stretches and a bunch of big open areas near the front. This is a new to me RV6A with an 80 SMOH as well and I believe these are original baffles. They are clearly too short to seal up. This weekend is a full replacement of all the baffling.

 

[RNB]

I am pretty new to aviation and lack any work experience. But I really hate to look for anything exotic before the obvious.
new baffling.
live with the numbers that are acceptable.

 

[DanH]

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

At a glance, this one needs a lot of seal work.

500 is redline.
435 is high performance ops
400 is economy cruise ops
per the O-360 manual.

Joe, it's good to see a new pilot memorizing the limits. Remember this too...four new jugs is about $10K installed.

 

[BH1166]

Jeff, what is the model number/data on your carb? Share please. Also, you are getting 2700 rpm on roll? If so, what is your engine info system saying about fuel flow while you climb, seeing your numbers you want down?

 

[Jeff Bost]

I’m chasing high CHTs on climb out as well. 430+ on #3 and #4 and I can’t stand it. I took both top and bottom cowling off then put the top cowling back on. In a semi-dark hanger, then I took a flashlight from the now open bottom and ran it along the edge of the baffle seals looking through the inlets in the front. It was obvious where it was not sealing - almost everywhere. I have big long stretches and a bunch of big open areas near the front. This is a new to me RV6A with an 80 SMOH as well and I believe these are original baffles. They are clearly too short to seal up. This weekend is a full replacement of all the baffling.

Thanks Paul. Take pics and let me know how you make out. Jeff

 

[storm_pilot]

Jeff, what is the model number/data on your carb? Share please. Also, you are getting 2700 rpm on roll? If so, what is your engine info system saying about fuel flow while you climb, seeing your numbers you want down?

I was about to ask the same question. Many carbs have an economizer function which leans the mixture as soon as you throttle back a bit. Climbing at WOT is best for cooling with a carb like that.

 

[Jeff Bost]

Jeff, what is the model number/data on your carb? Share please. Also, you are getting 2700 rpm on roll? If so, what is your engine info system saying about fuel flow while you climb, seeing your numbers you want down?

Yes on all counts….just under2700 and FF is book or better with boost pump on during takeoff and climb. I think the carb jet is ok. Jeff

 

[esco]

Jeff: before further flight I would closely inspect oil line over the top of the engine:
the baffle grommet is torn and shifted, and the line is discolored where it touches the edge of the hole.

As Jim & Aden noted, a high pressure oil leak at the engine can be catastrophic; I recommend inspection of the oil line is your priority.

 

[Jeff Bost]

Jeff: before further flight I would closely inspect oil line over the top of the engine:
the baffle grommet is torn and shifted, and the line is discolored where it touches the edge of the hole.

As Jim & Aden noted, a high pressure oil leak at the engine can be catastrophic; I recommend inspection of the oil line is your priority.

Thanks. I agree completely and I don’t intend to fly until I get this sorted. Jeff

 

[JonJay]

I’m chasing high CHTs on climb out as well. 430+ on #3 and #4 and I can’t stand it. I took both top and bottom cowling off then put the top cowling back on. In a semi-dark hanger, then I took a flashlight from the now open bottom and ran it along the edge of the baffle seals looking through the inlets in the front. It was obvious where it was not sealing - almost everywhere. I have big long stretches and a bunch of big open areas near the front. This is a new to me RV6A with an 80 SMOH as well and I believe these are original baffles. They are clearly too short to seal up. This weekend is a full replacement of all the baffling.

It would be tough to diagnose this way as the top cowl position is largely dictated by the bottom cowl. Also, too short on baffle material will typically cause them to “blow out”. This would be obvious if they were. Keep in mind the plenum gets its pressure from ram air which forces the baffle material up against the cowl to seal. It should lay against the cowl naturally and form a prroper “curl” against the top cowl when relaxed.
Not saying it isn’t an issue on yours but witness marks on the top cowl are a reliable indicator of how well they are sealing.

 

[Jeff Bost]

It would be tough to diagnose this way as the top cowl position is largely dictated by the bottom cowl. Also, too short on baffle material will typically cause them to “blow out”. This would be obvious if they were. Keep in mind the plenum gets its pressure from ram air which forces the baffle material up against the cowl to seal. It should lay against the cowl naturally and form a prroper “curl” against the top cowl when relaxed.
Not saying it isn’t an issue on yours but witness marks on the top cowl are a reliable indicator of how well they are sealing.

Thank you sir. Jeff

 

[Scott Hersha]

I agree with Dan, there’s a lot of baffle seal work that needs to be accomplished, including the area behind the starter ring gear - the vertical sections need to seal tightly against the cowl inlets and upper cowl ramps. I also see multiple holes in the back baffle. It looks like all of the openings for wires and the governer line are either not sealed, or not sealed properly. As others have said, make sure you secure the gov oil line where it penetrates that back baffle. It not only needs to seal air leakage, but it needs a robust soft material buffer against the aluminum baffle opening.
Years ago while working on the baffles/seals on my Cessna 170, I read a maintenance instruction that said a one square inch opening in your baffling can account for up to a 20% reduction in cooling efficiency. It doesn’t matter where the leakage is, it is reducing the pressure differential, and that affects the whole engine air cooling system.
Clamp a couple lights in the back area of the engine, put the cowl on in a dark hangar, and see if there is any light anywhere while looking in through the front cowl inlets. If you so, it deserves a look to see if you can at least minimize it.

 

[Jeff Bost]

I agree with Dan, there’s a lot of baffle seal work that needs to be accomplished, including the area behind the starter ring gear - the vertical sections need to seal tightly against the cowl inlets and upper cowl ramps. I also see multiple holes in the back baffle. It looks like all of the openings for wires and the governer line are either not sealed, or not sealed properly. As others have said, make sure you secure the gov oil line where it penetrates that back baffle. It not only needs to seal air leakage, but it needs a robust soft material buffer against the aluminum baffle opening.
Years ago while working on the baffles/seals on my Cessna 170, I read a maintenance instruction that said a one square inch opening in your baffling can account for up to a 20% reduction in cooling efficiency. It doesn’t matter where the leakage is, it is reducing the pressure differential, and that affects the whole engine air cooling system.
Clamp a couple lights in the back area of the engine, put the cowl on in a dark hangar, and see if there is any light anywhere while looking in through the front cowl inlets. If you so, it deserves a look to see if you can at least minimize it.

Thanks Scott. Agree with all and will get it take care of soon. Jeff

 

[blaplante]

1. By my eye there is absolute no sealing between the inboard side of the cowl inlets and the vertical section of baffling near the ring gear
2. It looks like a substantial leak area around the upper pilot's side engine mount and the back baffle
3. Check for presence of the upper cowl inlet 'ramps', should be bonded onto the cowl top
4. Can the cowl ramps bypass air? This is a common mistake where pressurized air can get into the inboard side of the ramp, and then exits outboard of the baffling. Unclear how this is done on this plane
5. Do you have a 4 point CHT monitor? What do the temp spreads look like between #1 and #3, and #2 and #4. If the front cylinders are 20F hotter, start adding some aluminum tape to the front face of the front cylinders. Plans call for a deflector here, which helps move some of the air aft. Some need it, some don't, some swear at it, etc.
6. Look down the back side of #3 at the base. Shine a light up from below. Very common to have a finger sized gap down in there.
7. As someone above noted, look at the inter-cylinder baffles. Shine a light from the top, and look at the bottom. High Temp RTV all gaps.

 

[blaplante]

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

We picked up a core engine. 700 hours in a flying club airplane. No engine monitor. All 4 cylinders were unserviceable due to cracks in the heads near the exhaust valves. Genuine Lycoming cylinders...

I can't say that this was from heat abuse or not. Maybe just fate. FWIW.

Edit:
I should add the engine was not pulled because of poor compression.

 

[JonJay]

Looking at the pics closer, you can see differences in sheen on the tops of the baffle material. You should see a relatively even “wear” or rub line along the length of the material. Shiny spots mean they are not making contact.
Also, like others mentioned, the front seal appears to have sections left out, even open rivet holes. This is a tough place to seal also. Takes some ingenuity as the plans are less than informative on these old builds.
The transition in the back left can be difficult. Many of us added a secondary piece of metal so the back baffle is straight and doesn’t make that jog as the jog is hard to seal with material. It looks like the builder just stuck a piece of material over the jog, which isn’t doing anything.
You can, and will, do better….

 

[jrs14855]

The comment on retarding the timing is ill informed. 20 degrees is optional per Lycoming and is mandatory on some engines. I suggested it as a means of lowering the CHT while working on the real cause.

 

[JonJay]

The comment on retarding the timing is ill informed. 20 degrees is optional per Lycoming and is mandatory on some engines. I suggested it as a means of lowering the CHT while working on the real cause.

Understood, but the OP is managing his CHT’s ok now, and is looking to get them better on climb out. He is reworking baffling to fix the problem. That’s the topic. But sure, reduce timing, reduce CHT’s a bit and reduce performance a bit. No “ill informed” comments there.

 

[Jeff Bost]

Looking at the pics closer, you can see differences in sheen on the tops of the baffle material. You should see a relatively even “wear” or rub line along the length of the material. Shiny spots mean they are not making contact.
Also, like others mentioned, the front seal appears to have sections left out, even open rivet holes. This is a tough place to seal also. Takes some ingenuity as the plans are less than informative on these old builds.
The transition in the back left can be difficult. Many of us added a secondary piece of metal so the back baffle is straight and doesn’t make that jog as the jog is hard to seal with material. It looks like the builder just stuck a piece of material over the jog, which isn’t doing anything.
You can, and will, do better….

I noticed the open rivet areas too. No baffling material at all. I’m thinking of having Base Leg Aviation redo all the baffling and rerouting my prop governor oil line. Jeff