Thorp Air Command - T18.net

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)

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".

_________________
Bob Highley
N711SH
SN 835
KLAL

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

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!

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

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 ***

_________________
Forum Administrator

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

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.

_________________
Forum Administrator

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 ***

_________________
Forum Administrator