W

wizard

Active Member
Hi all. 9 months after my first flight I'm having a blast. Just got the flows balanced for LOP operation. Works great. Next issue is addressing a hot CHT...#1. On climb out and generally about 1,000 AGL, I'm hitting 400 which is what I have chosen to be my redline (yellow line is at 385). The rest of the cylinders are at around 360. Here is my approach:
1) Whittle down the air dam in front of #1
2) Seal baffles better
3) Fiberglass off one end of the inlet ramps (done)
4) ?

Am I the right track? Is there another approach that I should be looking at.
 
#1

If you haven't already, make sure the data is good. Have you swapped CHT senders? I have watched quite a few people chase instrumentation problems. If that isn't an issue, I had good luck "fine tuning" the CHTs with some careful trimming of the air dam in front of the cylinder. I also played with the location of the inlet ramps, since the cylinders on the right side are further forward and the rampsappear to restrict the air on that side. Good luck!

John Clark
RV8 N18U "Sunshine"
KSBA
 
Brian,
I had the same situation, #1 being the hottest.
I drilled out the rivets holding the air dam on with just the top cowling off.
If you try this slide a stainless steel scale or something behind the baffle so you don't drill into the cylinder fins.
I took the whole air dam off in front of #1.

CHT's are a lot more even now.

Mark
 
details

what's your typical temp spread?

I have stock baffle setup with the dams and such. #1 runs about 20 deg hotter than #3. #2 and #4 are about the same, somewhere in the middle.

I'm going to do the injector balancing thing too, but I was thinking I'd try to even the temps a bit first before fooling with the injector balancing. I guess the easy first step is to do what Mark suggests and see how it does if I take the right dam off altogether...
 
Follow ups

First thing I did was swap CHT probes...same result.

Typical temp spread: CHT 2-4 are within 10 degrees...CHT1 is 40 degrees hotter during climb and 30 degrees hotter in ROP cruise and 20 degrees hotter in LOP cruise. I know that we are probably talking "picky, picky", but I don't like having to limit my climbs when 3 of the 4 cylinders are okay. Love to be able to get CHT1 down a bit.

Interesting thing was that before I balanced injectors and running LOP, CHT3 was hottest...I had to buy a larger diameter restrictor to richen it up a bit. Once that was done, viola, CHT3 matched 2 and 4. I had to lean up cylinder 1 to match fuel flows at peak which didn't help matters. As I indicated earlier, CHT1 is hotter both on the ROP and LOP side of things.
 
Look down

at the fins at the top of the cyl head, between the intake and exhaust valves. I would not be surpprised to see some casting flashing blocking a few of the cooling channels betwen the fins..A few of mine were like this.

Take a punch and a file and remove this blockage..Makes quite a difference.

Frank
 
Trim the dam

I trimmed the dam in half and the temp came right into line.
 
Leaky intake?

Does a leak in the intake make sense? If that was the case, when I go LOP, wouldn't I see the CHT go way down as the fire goes out?

I checked for flashing on the fins but couldn't find any. Am I looking for bits of metal that cross from fin to fin or just excess that makes it look extra "bumpy"?

What about spark plugs? I regapped them a bit ago (didn't see any wear). They looked fine. I'm at about 160 Hobbs (130 tach). How long do spark plugs last?

As far as restrictors and injectors go, how does one clean them? And on what schedule?

I have learned alot in this process of building my plane, but the more I learn, the more I find I don't know.
 
wizard said:
Does a leak in the intake make sense? If that was the case, when I go LOP, wouldn't I see the CHT go way down as the fire goes out?

I checked for flashing on the fins but couldn't find any. Am I looking for bits of metal that cross from fin to fin or just excess that makes it look extra "bumpy"?

What about spark plugs? I regapped them a bit ago (didn't see any wear). They looked fine. I'm at about 160 Hobbs (130 tach). How long do spark plugs last?

As far as restrictors and injectors go, how does one clean them? And on what schedule?

I have learned alot in this process of building my plane, but the more I learn, the more I find I don't know.
Click to expand...

Wizard,

Fuel has a lot to do with cooling... not saying you have an intake leak, just pointing out areas to check. Also, when I fine tuned my cooling, I took the dams off and used aluminum tape. Easy to add or trim down, then build the dam to match later. Also, make sure the gap at the bottom of the dam is sealed off good. If this area is not sealed good, balancing the cylinders out will be difficult.
 
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Air dam

Any of you guys have a picture of the air dam installation you are referring to? I assume this is an add on deflector riveted to the lower inlet ramp. I am working on balancing my temps as well, and need a little help visualizing how others have added the deflector.

Thanks,
Chris
 
Deflector size

I found that the deflect in front of #1 was actually quite small (about 1 inch high max) and changing it's size made a far bigger difference than the one in front of #2. (about 2 inch's high)
My guess is that it's because it's on the exhaust valve side of the cylinder.

Cheers

Peter
 
Post a picture

Anyone have a picture of the modified #1 air dam and dimensions, after 90 hours I have the same issue, #1 CHT rapidly climbs into the 400's during full power climb out but all CHT's are fine in cruise. Happens at both high altitude and sea level airports both full rich and leaned out. I figured I would make the air dam removable so I could easily experiment with different sizes.
 
Check for exhaust leaks

I had about 400-410 on one cylinder. On investigation, I found an exhaust leak blowing on the CHT probe.
 
EGT and CHT just went high

On the last leg of a flight Sunday from IL to TX, the CHT and EGT on cyl 3 of my IO-360 parallel valve engine went high - to 428 and 1450 respectively. Normally they are <400 and <1400 during climb out. I reduced power, leveled out and got temps back down to the green and came on home.

Last night I pulled the cowlings and the spark plugs on #3 but both plugs look good - no fouling. I would have been surprised to see any because I've been flying long cross country legs with the plane leaned to about 75 ROP.

I checked the intake bolts at the cylinder but they are tight. Tomorrow I'll pull the injector nozzle and see if it has some dirt in it.

All the temps on the other cylinders were normal and oil temp was slightly elevated but still good. I have 80 hours on these cylinders and they've been performing beautifully.

Any other things I should be checking or looking for?
 
would

do a flow balance test..I.e see at what total fuel flow each of your cylinders peak..if it is injected they should all be pretty close., i.e peak EGT will be found at roughly 8.1 GPH at 24 squared.

If the #1 cylinder peaks first and you run ROP then this in theory would explain the high #1 cylinder temp..Its easier to do this check than to pull the cowl and will give you a data point.

If you run LOP the #1 cylinder will be the coldest cus it will be the first one to peak if you see what I mean..

What happens when you do lean aggresively?..I mean get to altitude and pull the red knob till it just quits and then enrichen till it JUST runs ok.....If #1 goes way cold compared to the others then I would suspect a injector to be partially plugged on #1.

Frank
 
Fixed!

Okay...so I removed the air dam in front of CHT#1 and temperatures came into line with one another. On climb-out, #1 and #2 hit 400 at the same time with #3 and #4 at 380. During LOP cruise, all four temps are within 5 degrees of one another, 349 to 354 at the LOP setting I was at. Awesome! Now on to the next item on my punchlist.
 
The injector nozzle for #3 cylinder was clogged. I will clean all four nozzles today and expect the temps will be back where they should be.

FWIW the fuel system in this -8 has a gascolator but no in-line filter. I will probably change that this winter. I trust the AFP people and they say that is the best arrangement. Who knows if an in-line filter would have caught the dirt that clogged this nozzle though.
 
Cleaned all 4 and did the oil and filter change at the same time. Temps on #3 are back where they were before the problem. All 4 injectors had some dirt in them.
 
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