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  #1  
Old 10-08-2019, 05:24 PM
MartinPred's Avatar
MartinPred MartinPred is offline
 
Join Date: Nov 2005
Location: Overseas
Posts: 151
Default Engine Break-in—High #3 CHT

Greetings,

I could use some input. I recently rebuilt my Lycoming O-360-A1D (MA-4-5 carb) on my RV-4. About 15 hours into the break-in, all my CHTs have come down nicely except #3 (back right). It’s still consistently 40-60 degrees hotter than the other three.

Here’s the data from a flight I did this morning—run up plus three laps around the pattern.



At low altitude, even at WOT, I have no problem keeping 1, 2, and 4 below 380–either rich or LoP. But #3 keeps wanting to run away. I can climb out at full throttle, but #3 is usually hitting 440 F by the time I hit pattern altitude, so I have to pull back the throttle.

I’ve checked and rechecked, and reworked all my baffles. No air gaps. I’ve even added a spacer to the inter-cylinder baffle so more air can flow throw the short fins on the back.

The right side of the engine is consistently hotter than the left. So maybe fuel distribution needs work? Or maybe I’ve just managed to glaze #3?

Mike Busch has me scared to death of pulling a cylinder and replacing it with the engine on the engine mount. Too much risk of under-stretching the through bolts.

My plan is to keep flying and keep #3 to 440 or less, then monitor oil consumption for another 10-20 hours. But any thoughts would be appreciated.

Thanks,

-Matt Martin
N402BD
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  #2  
Old 10-08-2019, 06:49 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 3,882
Default

Do you have any air dams in front of #1 and #2? You might try some aluminum tape to see if that redirects air to #3. An air dam in front of #1 helped my #3 cylinder.
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  #3  
Old 10-08-2019, 08:14 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,281
Default CHT

Spacer between #3 cylinder and aft side baffle has been discussed many times. Also "flashing" from casting process between cylinder fins which obstructs flow of air.
Some have gone a step beyond the spacer and created a "bump" in the baffle behind #3.
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  #4  
Old 10-08-2019, 09:17 PM
calpilot calpilot is offline
 
Join Date: Aug 2018
Location: Independence
Posts: 14
Default HIGH EGT

The aft head from the spark plug hole to the cylinder fins on #3 and for forward or #2 have the well known lycoming curse....the fins narrow in the area where they need to be the deepest! I cut a 2" wide by 2" high square out of the baffle in that area, and made a cover with a 3/10 " stand off to allow air to pass from above the cylinder through the "fin wrap" on the baffle. I also went to a cooler plug (automotive) from an NGK BR8ES to a 9ES. Temps dropped quite a bit! Now on a hot day, I never see above 400 degrees! I also did the same thing on the aft of #4, since I rob a lot of air off that cylinder for the 3" scat duct for the remote oil cooler.

Regards,

Gary Brown
DAR - Pacific Northwest
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  #5  
Old 10-09-2019, 09:38 AM
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Raymo Raymo is offline
 
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Location: Richmond Hill, GA (KLHW)
Posts: 2,043
Default

Try adding a little carb heat, which may help with mixture distribution. Also consider a larger main jet (discussed many times here).
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  #6  
Old 10-13-2019, 05:30 PM
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TnMike TnMike is offline
 
Join Date: Nov 2009
Location: Lewisburg,Tn
Posts: 257
Default #3 Cyl Fix

Hi Matt,
I have made a few of these for myself and others as a great fix for #3 cyl. cooling issues.
Selling them for $25 each if you're interested. Covers fabrication costs.
Thanks,Mike
RV3B N931M







I could use some input. I recently rebuilt my Lycoming O-360-A1D (MA-4-5 carb) on my RV-4. About 15 hours into the break-in, all my CHTs have come down nicely except #3 (back right). It’s still consistently 40-60 degrees hotter than the other three.

My plan is to keep flying and keep #3 to 440 or less, then monitor oil consumption for another 10-20 hours. But any thoughts would be appreciated.

Thanks,

-Matt Martin
N402BD[/quote]
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Dues Paid
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  #7  
Old 10-13-2019, 10:01 PM
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GalinHdz GalinHdz is offline
 
Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 1,804
Default

TnMike; can you post more pics of your setup? Maybe a pic of the entire side of the engine showing cylinders #1 & #3. I am not smart enough to make out how or where it is attached with the one pic.

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  #8  
Old 10-14-2019, 11:03 AM
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MartinPred MartinPred is offline
 
Join Date: Nov 2005
Location: Overseas
Posts: 151
Default Many Ideas

I'm going to try the air dam and some of the other ideas posted. I'll take some more picture this weekend.

I was thinking that I managed to glaze #3, but no one has suggested that. So maybe it's airflow. Maybe it's poor fuel/air distribution. I'll keep trying different things.

-Matt
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  #9  
Old 10-14-2019, 11:07 AM
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Toobuilder Toobuilder is offline
 
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Location: Mojave
Posts: 4,409
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Do the bypass duct first. It may not fix your issue completely, but it is an effective fix for a known engineering deficiency. It is certain to help.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #10  
Old 10-14-2019, 01:06 PM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,895
Default

#3 has an intake gasket leak.

Look at the plots. #3 gets warmer than the others at full throttle, just because it's a little leaner. The signature is the larger EGT divergence from the others at part throttle.
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