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  #1  
Old 01-19-2019, 08:52 AM
Larry DeCamp's Avatar
Larry DeCamp Larry DeCamp is offline
 
Join Date: Apr 2010
Location: Clinton, Indiana
Posts: 884
Default Cyl #1 50F cold 😏

Need ideas, #1 CHT has always been significantly colder. Facts:
1-New 0320x150HP with perfect compression (180 hr)
2-Swap #1 TC with any other cylinder and the cold reading follows #1TC.
3-Replace #1 TC with new Alcor, still cold when flying.
4-Test all 4 TC in boiling water it reads 212F.
5-Used one TC in boiling water applied to all 4 panel inputs. All read 212F.
6-Installed a little deflector on #1 like #2 has from Vans baffle plans, no joy.
My concern with blocking #1 more radically to get a response is “What if the above is somehow flawed. Don’t want to cook a cylinder.
I noticed a Dave Anders pic with #1 cyl wrapped nearly to the top af the fins. OK, but why isn’t everyones #1 grossly colder ?

Ideas appreciated...Larry
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  #2  
Old 01-19-2019, 10:27 AM
Tom Martin Tom Martin is offline
 
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Location: Ontario, Canada
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Default

Check the bottom air outlet on the cylinder and compare with the others. A larger opening can be closed using
small inserts or even a bit of rtv for test purposes
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Last edited by Tom Martin : 01-19-2019 at 01:35 PM.
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  #3  
Old 01-19-2019, 01:05 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 5,129
Default Excellent thought +1

Quote:
Originally Posted by Tom Martin View Post
Check the bottom outlet on the cylinder and compare with the overs. A larger opening ca be closed useind small inserts or even a bit of rtv for test purposes
After checking absolutely everything else on my engine, I am pretty sure this is my issue for #4 running a tad hotter. I measure my opening and it is maybe 1/8" smaller yielding 20F hotter under nearly all conditions. I was very careful about the gaps and this one must have been on the small side.
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  #4  
Old 01-20-2019, 07:42 AM
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Larry DeCamp Larry DeCamp is offline
 
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Location: Clinton, Indiana
Posts: 884
Default Small opening ?

Thanks guys, great catch. I assume the small opening is the curved baffle under the cylinders connected by wire/bolt/ or spring to pull them together ??
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  #5  
Old 01-20-2019, 07:58 AM
BillL BillL is offline
 
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Location: Central IL
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Default Under the HEAD

Quote:
Originally Posted by Larry DeCamp View Post
Thanks guys, great catch. I assume the small opening is the curved baffle under the cylinders connected by wire/bolt/ or spring to pull them together ??
It is the opening under the HEAD not the cylinder/barrel that will affect CHT. My data indicates barrel opening will not affect your CHT.
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  #6  
Old 01-21-2019, 03:48 PM
odens_14 odens_14 is offline
 
Join Date: Jun 2007
Location: Alexandria, MN
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Quote:
Originally Posted by Larry DeCamp View Post
2-Swap #1 TC with any other cylinder and the cold reading follows #1TC.
Am i interpreting the quoted statement correctly: it's always the #1 thermocouple(TC) reading cool, even when that TC is connected to another cylinder?

if that's correct, it cant be anything with the baffling. You've replaced the TC with no change that tells me it must be the instrument itself? the fact they all read correctly in boiling water indicates it must be caused by the engine running, vibrating loose connection or something electrical possibly?
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  #7  
Old 01-21-2019, 05:22 PM
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AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,200
Default

Quote:
Originally Posted by Larry DeCamp View Post
Need ideas, #1 CHT has always been significantly colder. Facts:
1-New 0320x150HP with perfect compression (180 hr)
2-Swap #1 TC with any other cylinder and the cold reading follows #1TC.
3-Replace #1 TC with new Alcor, still cold when flying.
4-Test all 4 TC in boiling water it reads 212F.
5-Used one TC in boiling water applied to all 4 panel inputs. All read 212F.
6-Installed a little deflector on #1 like #2 has from Vans baffle plans, no joy.
My concern with blocking #1 more radically to get a response is “What if the above is somehow flawed. Don’t want to cook a cylinder.
I noticed a Dave Anders pic with #1 cyl wrapped nearly to the top af the fins. OK, but why isn’t everyones #1 grossly colder ?

Ideas appreciated...Larry
Fuel/air mixture is a strong driver of cht, and it is different for each cylinder. Have you done the cht/egt vs fuel flow curves? Run it at whatever power you are reporting the 50F lower, only go from quite rich (maybe 2-3 gph richer than where you run) to lean enough where it is running rough and losing noticeable power. Pause at every .1 or .2 gph to allow temps to stabilize perhaps 30s. Your cht variation might not be air cooling related, but simply where cylinder one reaches peak cht at a different point than the others.

Think about your engine as four separate engines, each developing a bit different hp, and each running a different fuel/air ratio.
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