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Hot #2 cylinder - options please

humptybump

Well Known Member
I've read many of the threads regarding hot cylinders. Now it's time to tackle my situation.

Engine is the 0320 with a carburetor. Cylinder #2 is the hottest. Cylinder #3 is the coldest. During climb and cruise the delta is 90-100 degrees F. I have tested the CHT's to verify they are pretty accurate.

Below is a picture. As mentioned on other threads, the #2 cylinder has an area on the front with very shallow fins and this not very efficient at shedding heat.


My guess at a solution is to reduce the amount of coverage of the aluminum shroud on the underside of the cylinder. This will only work on the portion of the cylinder closest to he engine case.

Is my solution correct? Is there a preferred solution given what I have described and shown in he picture?
 
Do not remove the lower shroud. Its function is to direct air all the way around the cylinder. If you open it up air goes straight down and you lose cooling for the very bottom. Do make sure air can get to the shroud from above. This is the same issue (search forums) some have had with the back of #3.
But first look for other causes. When leaning does #2 peak first? If so then it is running leaner than the others. Look for induction leaks on #2.
Also look for air leaks in the baffles, although that would affect #4, too.

My money is on an induction leak. Check all those flexible connections.
 
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Tank Bob for letting me know my idea is not a good one. I was thinking the lower shroud was a restriction rather than a funnel.

I've done a stepped leaning test and #2 does not peak significantly ahead of the others. It's just significantly hotter.

I have read the other posts on the subject. Most talk about creating a gap at the front face of cylinder #2 where there is no fin depth. If that is the best recommendation, then I can experiment with that area.

The only flexible connections are the small couplers at the start of the pipes (from carb to cylinder). You can barely see the #2 at the bottom center of the picture. I double checked all of those today for loose fit or loose clamps. They are very snug and very tight.

Since there is no visible induction leak, is there a test that I could do to find any non-visible induction leak?
 
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my #2 is hot as well

Hi Glen,

My #2 has been the hottest for over 1000 hrs now. Do you cruise ROP or LOP? I cruise LOP using carb heat and have found that by varying the position of the carb heat you can "steer" the CHTs - in my case, you move the knob towards the hot cyl pair (1/2 or 3/4) and they will cool down. This may just be jibberish if you are not LOP, but might be worth a try - all this said, I can get 1,3, and 4 at 280 in cruise and #2 will be at 300.

Drop me a line if you would like to discuss on the phone.
 
A 100 degree difference in CHT is huge, something is wrong. What are the actual numbers?
You said you checked the probes. Are the wires long enough to swap 2 and 4?
Are they all the same type (spark plug gasket probe on #2 only, for example)?
Is there any sign (deposits) of an exhaust leak, with the hot gases aimed at the #2 CHT probe?
I've seen mixture distributions improved a lot with a little carb heat on TCM motors; but usually not so much with Lycoming. But try it.

Simple test for induction leak: in cruise at > 7000' or so, full throttle, lean EGT 150 - 200 deg F rich of peak. Then pull throttle to idle. Does #2 EGT go up a lot more than others? (if there is a leak then at full throttle it doesn't leak much (MP is near the outside pressure). But at idle the MP goes low, big pressure difference, if there's a leak it will pull in extra air making that cylinder go lean (and hence EGT will rise).)

It might be useful to know the history. Has #2 CHT always been a lot higher than the others? Is the engine new, overhauled, ...? Steel cylinders?
 
air dams

Have you tried installing the air dams in front of the cylinder?
Without it ... it may be more difficult to get reasonable airflow around the cylinder.
 
Bob - #2 has always been hot but for the first 200hrs I only has a simple rotary switch to an analog gauge so I never had very accurate data. I've been flying an EMS for the past 25 hours. All the CHT probes are the same.

Dave - the air dams would help me if front cylinder were running cool but my front #2 is hot.

Bob - let me fly the induction leak test. It sounds pretty easy and will give me more clues.
 
Just for grins I would disconnect 1,3,and 4 just to verify you are actually looking at #2.
 
Hi Steve - I individually tested each probe so I'm pretty sure they are all reporting the correct cylinder :rolleyes:
 
1. Yes, put a spacer between the baffle and the cylinder where the screw holds the baffle to the cylinder. One or two washers will do the trick. This does create some gaps below the washers, a bit of RTV will keep the air "wrapping" around the cylinder.
2. Check the gap openings on the bottom of the cylinders for all the baffles. These are often not the same and it could be that this problem cylinder is too closed compared with the others. If the others are all cooler then you can slide a bit of aluminium in those gaps to close them a bit, thus forcing more air through the #3 cylinder, or open the opening on three slightly to allow a bit more air to flow.
3. Make sure that the baffle material that forms the gap seal between the cowling and the #3 cylinder is good. If air from the upper and lower plenum are allowed to mix at this location it will severely disrupt the airflow. A tight gap seal here is critical for proper engine cooling.
4. This happened to me a few years ago on some Lycoming cylinders. Look down between the fins of the cylinder at the sparkplug. You should be able to look straight down. On mine, and a few others, there was casting flashing and actual casting sand still in the fins at that location. Cleaning those fins dramatically lowered the cylinder temperature.
 
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Glen,

As recommended by Tom:

1. "Yes, put a spacer between the baffle and the cylinder where the screw holds the baffle to the cylinder. One or two washers will do the trick. This does create some gaps below the washers, a bit of RTV will keep the air "wrapping" around the cylinder".

I did this to my #2 cylinder on my carbureted 0-360 and it helped. However, most importantly, make sure that your mag(s) if you have magnetos, are correctly timed.

For quite a while I had been seeing my #2 cylinder running hotter than all of the others (which did not make sense), and during run-up with one lightspeed electronic ignition and 1 mag, I saw very little RPM drop (20 RPM) on the EI, and about THE SAME (about 20 RPM) drop on the mag. My mechanic very recently (last week) did my annual Condition inspection, we sent the mag off for its 500hr inspection (no issues). upon re-installing the mag (correctly timed), during run-up we saw the normal Lightspeed drop of about 20 RPM, and then saw a 75ish RPM drop running on the mag... I did research and learned that run-up on just the mag is supposed to have a normal RPM drop of about 75ish RPM. I did not realize that this was the correct RPM drop for a mag until I flew the plane with OAT of 100 degrees and saw that not only was my #2 cylinder no longer the hottest, but all of the CHTs were reading below 380 and within 5 to 7 degrees of each other, (with the exception of #1 which always ran cooler than the others)... We think that prior to removing the mag for service that the mag timing might have been a little too advanced which may have been causing the higher CHTs (especially #2), this was my very recent experience...

Good luck.

Victor
 
Be sure the baffles wrapped around the bottom of the cylinders are tight so the air flows through the vanes around the barrel. My RV7 had cooling issues and I tried everything but it wasn't until I tightened those up and sealed the outer edges with RTV (which I saw on a Tiger, known for cooling issues) that my temps dropped significantly.
 
#2

Since your problem seems focused on the #2 cylinder, I would propose you remove and inspect the intake tube/cylinder head junction. You will see the tube has a very small flange and being aluminum is subject to leaking. It is pretty easy to check and will give you peace of mind knowing it isn't leaking.
Good Luck.
 
Thanks Mike - the bottom aluminum shrouds were definitely tight. The safety wire went "prang" when I cut them and there were slight paint transfer marks where they made contact with the cylinder fins. (didn't look like rubbing, just a little mark when it was tightened up).

I said it "went" prang because I've pulled that part of the aluminum baffle to attempt DanH's metal work suggestion.
 
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Dave - the air dams would help me if front cylinder were running cool but my front #2 is hot.
If they have never been on and its always been hot ... may be worth adding some aluminum tape and see what happens.

As I understand it ... RV do their pressure recovery internal to the cowl.
The goal is to convert high velocity air as it enters to high pressure air inside the cowl which then passed through the cylinders.

If the high velocity air is disrupting the flow through the cylinders as it rushes past the fins in may actually make the cylinder hotter not cooler.

When it comes to cooling ... many things are not necessarily what one would expect.

We had the stbd side warmer... added a washer front and rear ...better....
 
I can help!

Call me, Dave Cicciari 513-259-7055. It's all about the pressure differenttail between the top and the bottom of the cylinders. Send me your email and I will send you some articles
Don't chop metal yet! Wont work!
 
Solved - just like everyone else

First, a little update for Bob. I ran the induction test and all the EGTs dropped together. I conclude there is no leak.

Now ... drum roll please ... my #2 temp is 372F ! Woohoo !

While we all think our problem is somehow unique, the odds are high it's not and someone has forged a path for us. In my case, appreciation once again goes to DanH. His metal forming solution was perfect.

 
The original builder likely was chasing the same high temp on #2 that I was reporting. It's clear he removed some of he material from the angle aluminum. An air dam on that side may have made things worse.

A text clip from Ironflight suggest that not all installations have air dams ...

"... the baffle kit back then didn’t have air dams as part of the stock setup, and the recommendation was to go without them, and add them if required. I never needed to, so I never did."​
 
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What is the consensus on max cylinder temp on break in of new cylinders (jugs)? Is it still the same temp. as once broke in?
Once a cylinder has reached say 460 degrees is the damage done or are we talking continuously running 460 . I'm not talking 10 hrs at 460 , I'm talking running 460 on all take offs. I'm just getting started breaking in my new Superior cylinders and only got 1/2 hr yet and it was hot so when my # 3 cylinder reached 430 I landed. I'm told for break in purposes 430 is OK but not to exceed 450.
Ron
 
First, a little update for Bob. I ran the induction test and all the EGTs dropped together. I conclude there is no leak.

Now ... drum roll please ... my #2 temp is 372F ! Woohoo !...

Just as a data point for you, I took off out of Parker AZ just a few hours ago and the OAT on taxi was 120 degrees! I climbed from 750 feet to 8500 at full throttle and best power EGT and my #2 and 4 CHT never broke 390. the other two just touched 405 right at the top of climb, but cooled instantly when I went LOP. Eventually, my #2 settled in at a too cool 295 for the cruise portion of the flight (71 OAT). I've been chasing this problem on my angle valve 200 HP engine and it is true, you need to get air down to the lower side of the head. Washers, "bulges" or plenums all work to varying degrees, but it is very clear that the stock vans baffles are seriously lacking.
 
Just clarify this for me, did you do that climb at Best power which I prefer to call Peak Power EGT, or 75dF ROP or did you mean doing the climb using a target EGT method?

Big difference in the result.
 
What is the consensus on max cylinder temp on break in of new cylinders (jugs)? Is it still the same temp. as once broke in?
Once a cylinder has reached say 460 degrees is the damage done or are we talking continuously running 460 . I'm not talking 10 hrs at 460 , I'm talking running 460 on all take offs. I'm just getting started breaking in my new Superior cylinders and only got 1/2 hr yet and it was hot so when my # 3 cylinder reached 430 I landed. I'm told for break in purposes 430 is OK but not to exceed 450.
Ron

I would be looking hard at that. I recall seeing up around 400 early in the first hour or two but we kept it under 410 and that was peaks, it was kept under 400 and usually 380ish from memory.

Check your timing!
 
Just clarify this for me, did you do that climb at Best power which I prefer to call Peak Power EGT, or 75dF ROP or did you mean doing the climb using a target EGT method?

Big difference in the result.

I maintain 100 degrees ROP until top of climb, then push over and go LOP.
 
Dan, thanks for the pressure graph in your thread. It explains why my rather small mod was so successful in bringing my #2 temp down.
 
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