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That tip about using a penny for gap checks on turbine blades is overblown
I overheard a new guy at the shop last week saying he read online that you can just use a US penny to check turbine blade tip clearance on a CFM56. Look, I get it's a quick field hack (and pennies are cheap) but the tolerance on those HPT blades is like 0.030 to 0.060 inches. A penny is about 0.060 inches thick on its own, which barely covers the upper limit. You'd need to measure the penny with a micrometer first and even then you're guessing. I'd rather spend the 2 minutes grabbing the proper feeler gauge set than risk a blade rub on a hot day. Has anyone else seen someone get burned by guessing clearances with coins?
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david_hayes4d agoMost Upvoted
Read a article once where a mechanic did that on a Rolls Royce Trent engine and ended up with a tip rub on takeoff. The penny was old and worn down to about 0.055 inches, but he didn't check it. Cost the airline a full engine swap and a few days of downtime over saving maybe 30 seconds. Not worth it when the feeler gauge is right there in the toolbox.
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parker_jones504d ago
@david_hayes nailed it. I just grab the feeler gauge, no shortcuts worth an engine swap.
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