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  #11  
Old 10-10-2017, 03:14 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by N941WR View Post
That would cause cylinder temps to drop, not rise, and then only if both ignitions stopped firing on those two cylinders.

Check you baffles, you might have a crack that is letting the cooling air out. Look around the corner of #4.
Actually losing one sparkplug/ignition source in a cylinder will retard the "effective timing" (the ultimate effect of timing is the occurrence of peak pressure relative to crank rotation and in a dual spark setup it is based on a combination of both spark events) in that cylinder. This should result in decreased CHTs and increased EGTs.

Larry
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Last edited by lr172 : 10-10-2017 at 03:18 PM.
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  #12  
Old 10-10-2017, 03:24 PM
lr172 lr172 is offline
 
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Originally Posted by Raymo View Post
Is your oil cooler mounted on the back of #4 and did you remove a winterization plate about 50 hrs ago? (sorry to state the obvious).
I had always assumed that the air flow past the engine was based on a pressure difference and not necessarily air flow. Given that the chamber is common, I would expect any leak would equally affect the cylinders. I am hoping an expert can chime in here, as I am struggling with a warmer #4 and would really like to understand if my assumptions were correct or incorrect. I suppose the effectiveness of the dams on #1 and #2 at least partially disproves my thinking.
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  #13  
Old 10-10-2017, 08:20 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by lr172 View Post
Actually losing one sparkplug/ignition source in a cylinder will retard the "effective timing" (the ultimate effect of timing is the occurrence of peak pressure relative to crank rotation and in a dual spark setup it is based on a combination of both spark events) in that cylinder. This should result in decreased CHTs and increased EGTs.

Larry
I may be a novice but by having a failed ignition timing does effectively retard the timing, as you mentioned; however, retarded timing typically reduces CHT's and increases EGT. Now, if it could advance the timing, causing more pressure in the cylinder, you will see CHT's go up and EGT's go down.
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  #14  
Old 10-10-2017, 09:10 PM
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Dbro172 Dbro172 is offline
 
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Quote:
Originally Posted by lr172 View Post
I had always assumed that the air flow past the engine was based on a pressure difference and not necessarily air flow. Given that the chamber is common, I would expect any leak would equally affect the cylinders. I am hoping an expert can chime in here, as I am struggling with a warmer #4 and would really like to understand if my assumptions were correct or incorrect. I suppose the effectiveness of the dams on #1 and #2 at least partially disproves my thinking.
This partially makes sense as you mention. I would agree about the common chamber but when people can improve cooling on #3 by adding a spacer or air dam behind #3 also proves that improving airflow in one particular area of the chamber can help. Likewise perhaps improving airflow too much at another area, in the wrong place can also hurt CHT’s.

For example, let’s say instead of adding airflow behind #3 you add airflow behind #4, and so much airflow that instead of going through the cooling fins of #4 its going out through the oil cooler, or a leak in the baffle?? Does path of least resistant rob cooling air from a nearby cylinder?

If so, and your oil temps are low, you can try and close off the backside of the oil filter. Less air through the oil filter should yield more air through the cylinders.

Baffles on the front of #1 and #2 cylinders seem to do two things, 1) raise the temp on the front cylinders 2) deflect more air to the rear cylinders. You should be able to toy with the front baffles enough to level the temps between 1 and 3 equally and 2 and 4 equally. But, if you have FI, there is no reason you shouldn’t be able to level the temps between all 4 cylinders by flow matching the injector orifaces. Is it possible #2 and #4 are currently blocked?

Lastly, a good set of mcfarlane cowl saver baffle material is far superior to the standard engine baffle rubber and if done right will provide a much better seal to the top cowl. http://www.vansairforce.com/communit...hlight=Baffled
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  #15  
Old 10-11-2017, 08:27 AM
LeMar LeMar is offline
 
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I flew the airplane yesterday (air temp was in the 50's) and the problem was not as severe. However, #2 and #4 were still the highest and in a 5,000 foot climb did reach 410. Until this issue started about 50 hours ago the CHTs never went over 390 even in mid-summer. Yesterday I checked the EGTs during that climb and they all stayed about the same, around 1250 which has been normal at full power(carbureted).
I'll cover the oil cooler and see if that makes a change. It's mounted behind #4.
My earlier thought about a primer system leak would seem to not make sense as the EGTs are normal so perhaps it is an air flow issue although I don't know what has changed to cause it.
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