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#2 CHT Higher than the rest

M

McPilot

Active Member
Hello...

my #2 CHT runs about 20-25 deg F higher than the other cylinders. I did a search and saw that a fellow VAF member did a baffling mod to correct this. It looks like his baffling may be a little different.

He drilled a hole in baffling to allow air flow to the lower fins on #2 cylinder. I am thinking that this is the reason for my issue. It is my thinking that even though the #2 cylinder is obviously in front that the lower fins get bypassed by the air flow.

It looks like his baffling does not cover the lower fins on #2 cylinder as mine does. Any suggestions?

IMG_3969_zpsvq8zi5ty.jpg
 
My #2 is also 20+ degrees hotter than my others. I just did the mod that a few others here did, directing flow to the lower fins. I hope to test fly tomorrow and will let you know if it worked for me as well. My baffling looks the same as yours? I will try to remember to snap a pic or two to show you what it looks like.
 
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lr172 said:
My #2 is also 20+ degrees hotter than my others. I just did the mod that a few others here did, directing flow to the lower fins. I hope to test fly tomorrow and will let you know if it worked for me as well. My baffling looks the same as yours? I will try to remember to snap a pic or two to show you what it looks like.
Click to expand...

That would be great. Thanks!
 
Other people such as Dan Horton have spaced baffle away from cyl. To allow more air flow around cyl. Notice how cooling fins are machined which leaves no fin area.
 
Dan's thread on baffle mods for cooling the finless area is here http://www.vansairforce.com/community/showthread.php?t=37835

Another thing to check is the fin area between the valves. Look down from the top of the engine, between the top spark plug and the valve cover. The cooling fins in this area are often somewhat plugged up with casting flash, and need a bit of touching up to let the air flow through.

rough%20flashing.jpg
 
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Mike,

I did the mod to route more air directly to the lower fins on #2. That cylinder had been running about 20* or so hotter than the next two. I did a test flight yesterday and #2 was the same as #4, so the mod dropped the temps about 20*.

Here are two pictures of the install. You can't see it, but I cut out a rectangle in the baffle about 3/4" high and covered most of the horizontal area of the cover. I am not sure that I need to route air to the upper fins, but did anyways. the holes in the top were 1/4". I figured that I would keep these minimal and drill more or larger as necessary. Overall, it was a simple mod. I chose not to remove any baffling and used rivets on top and just RTV below.

2meztp0.jpg


24oqeed.jpg


Larry
 
lr172 said:
Mike,

I did the mod to route more air directly to the lower fins on #2. That cylinder had been running about 20* or so hotter than the next two. I did a test flight yesterday and #2 was the same as #4, so the mod dropped the temps about 20*.

Here are two pictures of the install. You can't see it, but I cut out a rectangle in the baffle about 3/4" high and covered most of the horizontal area of the cover. I am not sure that I need to route air to the upper fins, but did anyways. the holes in the top were 1/4". I figured that I would keep these minimal and drill more or larger as necessary. Overall, it was a simple mod. I chose not to remove any baffling and used rivets on top and just RTV below.

2meztp0.jpg


24oqeed.jpg


Larry
Click to expand...


Thanks Larry,

This is a great help. I am at the airport now getting ready to do this... I can see that 3/4 cutout through the holes you drilled..
Thanks again! On top, my baffling actually has a stiffener "dam" in the area that has the problem with the fins. The left side facing plane does not have this dam. The cylinder fin profile is different on that side as well....

I will let you know how this works.. THANKS!!!

Mike
 
DanH said:
Larry, that's really very clever! My compliments....
Click to expand...

Thanks! It's really just an extension of pioneering work you and others have done on #3 airflow fix. That's the beauty of this community. As we share and learn, others can leverage that, as well as expand the knowledge or use cases.

Larry
 
OK guys..

Here is what the EASY fix was... I used a spacer about the thickness of 2 washers behind the baffle attach point on the #2 cylinder.

All of my CHTs are with a few degrees of each other now.

I am not so worried about a baffle leak as it does not appear to be clinically significant..

The OAT was 80 deg F in flight
Happy Cylinders:


IMG_3975-1_zpsa73dexnl.jpg
 
Mike, so far so good, but have you checked what happens to the temps when you are leaned out? That 10.6gph looks like a pretty rich setting. My numbers will vary significantly at different mixture (and throttle) settings.

That said, I made the same similar change first offered here on VAF for #2 by Toobuilder and it really helped my #2. Unfortunately not so much with my #3 which has always been my problem child.

Good luck as you test further.
 
alpinelakespilot2000 said:
Mike, so far so good, but have you checked what happens to the temps when you are leaned out? That 10.6gph looks like a pretty rich setting. My numbers will vary significantly at different mixture (and throttle) settings.

That said, I made the same similar change first offered here on VAF for #2 by Toobuilder and it really helped my #2. Unfortunately not so much with my #3 which has always been my problem child.

Good luck as you test further.
Click to expand...

Hi.. Good eye.. Yes, I was running at ~70% power and fuel flow was ~9.7 All temps below 360 throughout the flight... I notice my fuel flow creeps sometimes...
 
I had a similar situation with #2 on my carbed O-320. I read everything I could, and asked everyone I thought might have an answer. I checked for a sensor problem first. I tried several different modifications to the inlet ramp, sealed every hole and crack, assured myself that the baffling was as good and correct as possible. I installed bell washers between the rear of #4 and the baffle wall. Nothing I tried was working. Then, one day I was looking at the baffling on my friends 8. He had a small 1/4" gap between the baffling lower inlet ramp and the front of cylinder #2. Mine was flush up against the cylinder. I opened up that 1/4" gap on mine, and it worked like a charm. Obviously a certain amount of air can now flow down thru that gap and cool the forward lower portion of #2. Issue resolved. It only took 3 years of fiddling and step climbing to figure it out.
 
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