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| High CHT http://t18.net/thorpforum/viewtopic.php?f=29&t=6363 |
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| Author: | gkerr [ Sun Oct 31, 2010 8:03 am ] |
| Post subject: | High CHT |
In my O-320 the rear aft cylinder, #4, runs hotter by about 50 plus degrees than the rest of them. It is always in the high green in cruise (385 if I'm lucky) and in a climb at full power I'm banging against the yellow (435). Compression's OK (70/80), can't hear any valve blow-by. I've improved the baffling and can't see anything wrong with it, I can't find any obvious induction leaks and finally, the ignition timing is dead on. In flight I occasionally get an almost undetectable roughness. It's really baffling (how about that for a pun) me! Any ideas? Graham Kerr (N444DD) |
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| Author: | fytrplt [ Sun Oct 31, 2010 9:28 am ] |
| Post subject: | High CHT |
I guess we can assume you have swapped leads with another cylinder and ruled out a sensor issue. Also, do the plugs indicate a lean situation in that jug? As my engine guy is quick to say, "Each cylinder is its own science project". |
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| Author: | Rich Brazell [ Sun Oct 31, 2010 10:40 am ] |
| Post subject: | High CHT |
You said you improved the baffling. How is the clearance between the rear of the cylinder fins and the baffle ? Some cylinders have a problem with the casting between the fins, creating an air flow problem. If this is the case a "spacer" may be in order to increase the clearance between the back of the fins and the baffle. Picked this little tidbit up on the Vans site. RB |
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| Author: | leewwalton [ Sun Oct 31, 2010 11:52 am ] |
| Post subject: | High CHT |
My number 4 used to run real hot (pre-rebuild). One day while looking at the baffles I noticed something odd about the back side of the number 4. I reached in there and pulled out a roll of electrical tape (looked about as old as the airplane) that had fallen behind the cyl and became lodged back there. Once I pulled it out it ran nice and cool. The roll of tape effectively reduced the clearance back there as Rich pointed out. It makes a big difference! |
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| Author: | admin [ Sun Oct 31, 2010 12:00 pm ] |
| Post subject: | High CHT |
Rich, The rear baffle actually is against the cooling fins. I'll try the spacer and report back to the group. GK *** admin posted for Graham Kerr *** |
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| Author: | Rich Brazell [ Sun Oct 31, 2010 1:54 pm ] |
| Post subject: | High CHT |
I doesn't need much clearance...1/8" to 1/4" I can't recall how the RV guys put in the spacer ? Seems a "thick" washer pop riveted between the fins and the baffle should work. Or a short piece of square alum. stock attached to the baffle to push it away from the cyl. fins. [;)] RB |
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| Author: | admin [ Mon Nov 01, 2010 9:15 am ] |
| Post subject: | High CHT |
These are some pics sent via Rich Brazell from the Vans site. Gary Green did a writeup a short while back on this very same subject regarding installing the Vans Baffle set and clearance behind the #4 cyl. If I can round it up, I'll post a copy here.       
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| Author: | admin [ Mon Nov 01, 2010 10:33 am ] |
| Post subject: | High CHT |
While mine is apart for paint, I'll be working on cleaning up the cowl, baffling and exhaust exit points. We'll have to wait for spring to see the outcome! Chuck *** admin posted for Chuck K *** |
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