High CHTs on engine break in

[carrollcw]

So, I hve high chts on cylinders 1 and 3 during my break in making it difficult to really run the engine hard. Someone mentioned I may want to trim down the vertical piece of aluminum in front of cylinder 1 (part of the baffle kit). My understanding is it helps hold in the cooling air, but on the other hand it makes sense that it might allow more air flow across that side of the engine if trimmed down. Thoughts?

[Ironflight]

Yes - those need to be trimmed to get the temperatures closer to one another. The tricky part is that the balance is very dependent on attitude/speed, so getting it perfect for cruise will make it off-point for climb. The early baffle kits didn't have the dams at all - and they actually worked pretty well.

[carrollcw]

CHT 3 is 30 deg hotter than 2 and 4, and 10 deg more than 1, so I think I'll trim it just a little. Sound like a good first step? Having trouble staying below 425.

[RV7A Flyer]

Originally Posted by carrollcw

CHT 3 is 30 deg hotter than 2 and 4, and 10 deg more than 1, so I think I'll trim it just a little. Sound like a good first step? Having trouble staying below 425.

What altitude/OAT/fuel flow?

FWIW, I removed mine entirely (they're removable via screws into nutplates rather than riveted on), and 2+ years later, have yet to put them back on...

[carrollcw]

Originally Posted by RV7A Flyer

What altitude/OAT/fuel flow?

FWIW, I removed mine entirely (they're removable via screws into nutplates rather than riveted on), and 2+ years later, have yet to put them back on...

All altitudes, oat, and fuel flows. I am trying to push the engine as hard as possible to break it in, but am having to run really rich and less than 23 man pres to keep CHT 3 below 425. The only time I don't have to worry about it is when I pull the power back. The engine seems to be starting to break in, I can run higher MP than before (first few flights had to run around 21 inches MP), but it is still running much hotter than the other side.

[carrollcw]

Maybe I should just drill the dam out on the right side and see what happens.

[hydroguy2]

Do you have the washer between the rear baffle and #3?

I never put on the front dams on. I do have a small piece of AL tape on the face of #1 to balance temps.

[Kyle Boatright]

Originally Posted by carrollcw

CHT 3 is 30 deg hotter than 2 and 4, and 10 deg more than 1, so I think I'll trim it just a little. Sound like a good first step? Having trouble staying below 425.

At least in the short term, 425F CHT's will not hurt your engine. However, running the engine gently those first few hours will. For break-in, I suggest running it hard and keeping the CHT's below Lycoming's 450 limit. That said, make sure you look for and eliminate leaks which waste cooling air.

Regarding the dams, the bigger they are, the cooler 3 and 4 will run and the warmer 1 & 2 will run. Sounds like you need to leave the dams alone or 3 will get even warmer.

As a data point, what type of CHT thermocouples do you have? The ring type tend to read higher than the bayonet type.

[BobTurner]

Might be worthwhile pulling the injectors, make sure #3 is flowing as much gas as the others.

[N941WR]

Originally Posted by hydroguy2

Do you have the washer between the rear baffle and #3?

...

That was going to be my recommendation.

Also, have you sealed all the gaps in the baffles? Even a small hole or gap will let a LOT of cooling air out.