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  #71  
Old 03-23-2019, 07:07 PM
sglynn's Avatar
sglynn sglynn is offline
 
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Default metal forming baffle for #3

Dan
I'm looking at your post in 2008 about metal forming the baffle to make room for air to flow top to bottom for cylinder #3. Your photo shows a pretty small gap, maybe 1/8". Is that enough space to cool #3 or do I need about 1/4" inch of space?

I did first flight of my 7A with IO360 and CS. All went well except #3 ran hotter than the other cylinders. It was about 415 CHT and 1499 EGT at 24x24. More power and the temps would raise. All other cylinders were cool.

thanks
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  #72  
Old 03-23-2019, 07:50 PM
j-red j-red is offline
 
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Default

I?d like to know the experience of others too. Mine has been that with about 1/8th inch on the #3 and #2 cyls temps have been quite cool (low 300?s at similar power settings). The high egt would suggest to me a lean condition.
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  #73  
Old 03-23-2019, 08:14 PM
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Ironflight Ironflight is offline
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Default

As many have written here many times, the “high” EGT doesn’t mean anything, other than that your probe is drilled a little closer to the exhaust flange than you might like. Absolute value of a single EGT means nothing - EGT is used to find peak for a cylinder, and to notice trends. A very small difference in probe to flange distance can make a noticeably difference in absolute values.
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  #74  
Old 03-24-2019, 07:06 AM
BillL BillL is offline
 
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Default Tell us more Sam . . .

Quote:
Originally Posted by sglynn View Post
Dan
I'm looking at your post in 2008 about metal forming the baffle to make room for air to flow top to bottom for cylinder #3. Your photo shows a pretty small gap, maybe 1/8". Is that enough space to cool #3 or do I need about 1/4" inch of space?

I did first flight of my 7A with IO360 and CS. All went well except #3 ran hotter than the other cylinders. It was about 415 CHT and 1499 EGT at 24x24. More power and the temps would raise. All other cylinders were cool.

thanks
Sam, please tell us all the CHT's. Cooler could be 80 or 20F less. I ran .2 gap on #2 and .25" gap on #3. My #4 is actually a little higher (+20F) and nearly all conditions. I concluded #4 is due to the exit gap of the baffle opening at the bottom of the head. You can look back at my plot in post #56 for area. Lots more variables than area, though, so don't get hung up on a single variable. RE: Cutting out the fin flashing around the spark plug helped my CHTs about 15-20F.

EDIT: Sam, do you have any gap on the back of #3??
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  #75  
Old 03-24-2019, 11:34 AM
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DanH DanH is offline
 
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Steve, I later built a bypass for #3 with more area. #2 remains a 1/8" or so.

See post #24, this thread.
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Last edited by DanH : 03-25-2019 at 08:02 AM.
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  #76  
Old 03-28-2019, 10:42 AM
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sglynn sglynn is offline
 
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Default #3 baffle mod

Quote:
Originally Posted by DanH View Post
Lycoming cylinders have a classic baffle problem. I don't know if anyone else has taken this particular approach to solving it (lots of ways to skin a cat), but maybe the pictures will help the new guys understand the issue.

Here's the root of the problem. The intake side of the head has no fin depth in the area indicated by the pencil. but standard baffles for the left front and right rear cylinders place a plate directly against this area. There is plenty of air at "A", but there is no way for air to circulate down to area "B"



Details:



Here's the standard baffle (right rear) against the head. Flow to the lower fins and baffle wrap is blocked by the zero-depth fin area identified by the green tape. The standard "cure" is to place a washer or some other spacer between the head and the baffle, but that opens a gap along the entire length of the baffle plate.....in particular the area outlined in a black rectangle above. Any air sneaking past the area in the rectangle is pure leakage.



It is quite easy to hammerform a small duct of sorts in the baffle plate. The "duct" is nothing more than a fancy dent knocked in the sheet.



The result is a passage to bypass the no-depth fin area (arrow). Now air can flow down the back of the head and pass in between the lower fins where you have a baffle wrap. The reminder of the baffle plate is not spaced away from the head and cylinder, reducing undesired leakage. Any air not passing between fins is pure drag; it didn't do any cooling work.



Not all builders have metal forming hammers, or may not want to try beating on an expensive baffle part as their first metal forming experience. I'll do the left front baffle using an alternate method and get it up here soon.

Have fun.

----->>>>POSTSCRIPT: See posts 24 and 25
So did this work well? If the dent in the baffle is made too large will that lower the pressure on upper side of engine and make all air flow worse?
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  #77  
Old 03-28-2019, 01:52 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by sglynn View Post
So did this work well?
Pretty well, but I tend to experiment. I enlarged the bypass for #3 and got some further reduction. This photo was taken while making that mod; I've cut away the hammered duct:



A larger bypass was riveted on:



Quote:
If the dent in the baffle is made too large will that lower the pressure on upper side of engine and make all air flow worse?
No. The throttle is the lower fin wrap, just like the other cylinders.

This mod dates from summer of 2013: http://www.vansairforce.com/communit...3&postcount=24
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Last edited by DanH : 03-28-2019 at 09:46 PM.
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  #78  
Old 03-28-2019, 03:40 PM
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sglynn sglynn is offline
 
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Default

Quote:
Originally Posted by DanH View Post
Pretty well, but I tend to experiment. I enlarged the bypass for #3 and got some further reduction. This photo was taken while making that mod; I've cut away the hammered duct:



A larger bypass was riveted on:





No. The throttle is the lower fin wrap, just like the other cylinders.
Oh, great point about the throttle being by the fin wrap. Great. Thanks for your quick and helpful reply. My second test is tomorrow with slightly opened baffle slot. thanks
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  #79  
Old 03-28-2019, 06:26 PM
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Checkmate Checkmate is offline
 
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Default Another Option

I did this on my #3 cylinder baffle for my new engine install but have not flown it to test yet. Might be an option for someone.
Hopefully the google link works below for pics.
https://lh3.googleusercontent.com/Rv...=w1605-h903-no

https://lh3.googleusercontent.com/oy...=w1605-h903-no

https://lh3.googleusercontent.com/4u...u=w509-h903-no
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  #80  
Old 03-29-2019, 11:03 AM
Monkey Monkey is offline
 
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Default Intake side

The intake side of the head doesn't need as much cooling air flow as the exhaust due to the incoming air being cool. That's why the fins are shorter on the intake side but I think it needs more that it gets when the baffles are up tight against the head. Probably needs to be the same clearance as between the two cylinders. I wonder if too much cooling air going around the cold side would be a bad thing as in making the cylinder have a 'cool' spot or the head not being a more uniform temp all the way around? I guess the head needs several CHT probes around it to see what is really going on.
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Last edited by Monkey : 03-29-2019 at 11:13 AM.
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