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Lycoming Cylinder Fin Dressing/Removal Limits

Captain Ron

PATRON
Les Cedres, QC, Canada
Hi Folks,

I have a cylinder sitting on a shelf collecting dust. It generally appears to be in useable/rebuildable condition aside from some damage to the two cooling fins closest to the rocker cover. It appears they've been dressed down in a triangular fashion. One fin is missing approximately 2" of its outer edge and the other about 1" with both having approximately 1/4" missing where they meet the cylinder head.

Searching online I've seen some mention of manufactures repair limits based on fin area or length but I've not been able to find any actual references in the usual places. Anybody know of guidance from Lycoming (or any other OEM out of curiosity)? Failing that, any unofficial wisdom on the topic?

Cheers,

Jeff
 
From my Lycoming IO-390 manual. Other manuals I’ve googled say the same. Look in the engine disassembly section- cylinders- visual inspection.

D. Look for cracked or broken fins and baffles (Figure 1). If a cooling fin adjacent to the exhaust port flange is cracked, a 3/16 in. diameter hole can be drilled as a stop, under the following conditions:
• The end of the crack is at least 1/4 in. from the base of the metal; or
• The cracked area can be removed from the fin, provided the maximum removal is no more
than one-half the total fin width; or
• No burrs or sharp edges are in evidence; or
• The minimum fillet at the root of the removed portion of the fin has a 1/4 in. radius, and the minimum corner at the top of the fin adjacent to the removed portion has a 1/2 in. radius; or
• There is no more than one crack per fin and its depth is not more than 1/4 in. from the base of the metal, and a fin stabilizer is used to reduce vibration and prevent further deepening of the crack.
• If a cooling fin is damaged, broken or bent, the bent area must not exceed 3/8 in. nor the break be 3/8 in. deep, or:
(1) There cannot be more than four blended fins on the push rod side of the head, or (2) No more than six blended fins on the anti-push rod side of the head.
 
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Thanks Stewart. Now that you point it out I can see it clearly in the overhaul manual. Always embarrassing when the answer was actually in the first place you looked :oops:.

Cylinder might be scrap based on that.

Another question for fun - anybody ever try to unscrew a head from the barrel? Always wondered what that would take to accomplish...

Cheers,
Jeff
 
Another question for fun - anybody ever try to unscrew a head from the barrel? Always wondered what that would take to accomplish...

Cheers,
Jeff

I've never done one on a small opposed engine, but I've done hundreds on radial engine cylinders. Pratts were usually pretty good, but the bigger Curtiss Wright cylinders always seemed to twist. The barrel sat on a plate with a propane torch coming up through the center. The plate had studs sticking up for the barrel to anchor to. We'd heat them up on the cylinder bench and had a "wrench" that fit the head, and when the heads were up to temp (I can't remember off the top of my head, just what that temp was, we'd "adjust" them to alignment like they were supposed to be. If we had a bad barrel or head, we'd sometime screw the head all the way off and put on a good one. It was actually very simple. Just takes heat and some muscle.
John
 
I've never done one on a small opposed engine, but I've done hundreds on radial engine cylinders. Pratts were usually pretty good, but the bigger Curtiss Wright cylinders always seemed to twist. The barrel sat on a plate with a propane torch coming up through the center. The plate had studs sticking up for the barrel to anchor to. We'd heat them up on the cylinder bench and had a "wrench" that fit the head, and when the heads were up to temp (I can't remember off the top of my head, just what that temp was, we'd "adjust" them to alignment like they were supposed to be. If we had a bad barrel or head, we'd sometime screw the head all the way off and put on a good one. It was actually very simple. Just takes heat and some muscle.
John

That's pretty cool, thanks for sharing.
 
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