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When to start chasing CHTs?

A

alpinelakespilot2000

Well Known Member
I've only got two flights on the airplane with 1.5 hours total and it's grounded until Dynon sends me a replacement D180 after mine failed midflight on my second flight. However, I'm curious about when I should start trying to get my CHT's balanced. Do I wait until it seems like the engine is broken in or before? FWIW, I currently have no air dams on any cylinder, as none were recommended on my vintage of baffles.

On my last flight, cruising level for 50 minutes while circling the airport at 70-75% power, my oil temp was consistent at 190F (with OAT being 65F) and my CHTs stayed pretty consistently at:
#1 ~ 360F
#2 ~ 340F
#3 ~ 422F
#4 ~ 400F
Thus, it seems like the front cylinders are running about 60F cooler than the aft cylinders, which I assume is not all that out of the ordinary, sans air dams. I'd like to see #3 a bit cooler, though Aerosport only says to keep CHT's within Lycoming limits. For my 0-320-D2A, these are 525F max (at bayonet location) with recommended 435F and below for continuous operation "for maximum engine life." My #3 gets right up to the 430s on initial climb out. Not sure there's much I can do about that. I read a post from Paul Dye about his RV-3 that indicated he too had one cylinder up in the 430'sF pretty consistently before it all of a sudden dropped to below 400 after about 7 hours of flight, so I'm hoping my engine will follow the lead of his once I get more hours on it.

Anyway, back to my question, do I start trying to balance out the CHTs now with some air dams or just be patient and wait until I'm sure things have broken in?

Thanks.
 
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CHT's 1 & 2 are hot with air dams

I had almost the same problem today in reverse. This was my first flight and with the stock Van's air dams in place, I was getting about 423 degrees on Cylinder 2 and close to that on Cylinder 1 and increasing on climb until I throttled back to about 19 In and 2350 RPM at 3500 feet. The temperatures came down and stabilized at about 400 degrees. In the meantime, #3 and 4 were running about 380 degrees. I'm thinking of removing the air dams before I fly again. I'm also thinking about changing the front baffle so that I can attach the air dams with nut plates and screws to make them easily replaceable. That way, you could have a selection of dams of varying heights to fine tune your CHT cooling depending on ambient conditions.

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Let's not forget the RV Grin...
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I would recommend you not invest any major effort on a permanent type installation until after the engine is broken in, but in the mean time you can start experimenting with required sizes of air dams during your testing.
High temp. RTV will work fine to attach temp. dams to the front of the cyl.
I would recommend you start with dams trimmed to cover about the bottom 2/3s of the flat portion of the fin area on cyl. #1 & 2.
 
Is your plane fuel injected? If so, do not do any baffle work until (after break-in) you have done the mixture vs egt curves. Mixture has a huge effect on cht's, and balancing the mixtures by changing injector restrictors will go a long ways towards evening out cht's.

If it is carb'd, you can't really do much about imbalances, so the best thing will be to then look at baffling changes/dams/etc.
 
I believe the first thing you should do is find ALL the leaks in the baffles and seal them. We were amazed at the number of small leaks we found. We have about 70 hrs now and are now playing the dams in front of #1and #2 to balance the cooling. We are using metal tape to simulate the dams. The numbers we are getting are now just a tab over 400 during WOT climbs at 30C ancients. Watch the taxi time, because when we do a tough n go the numbers on climb out are all very acceptable below 380F
Phelps
 
Since your plane is currently grounded while waiting for your D180, I would suggest you scrutinize your airseals and baffles. You will be amazed at the number of locations you will be able to find where air is leaking in to the low pressure areas without providing any cooling.

Put a trouble light in the bottom of the cowl or through the oil door and then take a peek through the front of the cowl. Check the rear corner baffles to ensure an opening doesn't occur at the bottom of the corner. Use some high temp RTV to plug up any holes.

In most ships there is a significant gap in the front of the cowl, where there top and bottom halves mate, forward of where you secure the hinge. Some pilots have realized a 10 degree drop in CHT by covering this gap. If the tape test is successful then you can insert a lip in the inside of the cowl as a permanent fix.

Check the wear patterns on your airseal and top cowl and look at any missing segments.

A good posting by an RVer on typical areas of the baffling that can be improved. http://www.myrv10.com/N104CD/maintenance/20061022/index.html

In most RVs, the #3 cylinder is always the hottest. There are several good posting in the archives that will offer up some suggestions, the simplest is placing a washer where the baffle attaches to the aft end of the cylinder to increase the spacing.

I would bet that, given a few hours of work and a tube of RTV you could drop your CHTs by 10 degrees.
 
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