Stop torquing spark plugs on cold engines like it's a car

I keep seeing guys in here torquing turbine igniters at ambient temp and then wondering why they back out after 20 cycles. If you aren't heat-soaking the housing first, that torque spec is off by at least 15 percent - seen it cause a hot start failure on a Pratt 1000 series last month. Has anyone else noticed this or am I the only one reading the maintenance manual past the torque value?

2 comments

2 Comments

jesser7926d ago

Damn, that's wild! I never even thought about heat-soaking the housing before torquing igniters. Is that really a 15% swing? I've seen guys just yanking on a cold engine and calling it good, but I bet that explains why some of those Pratt 1000s have such a bad rep for backing out. I'd have thought the manual was just covering their ass with the temp note, not that you'd actually see a hot start failure from it. That's scary man, glad you caught it before it got worse.

holly_henderson8626d ago

That little detail about the Pratt 1000s is actually pretty spot on, but I gotta push back a bit on the 15% swing. In my experience with those engines, the thermal growth on the housing is more like a 10-12% difference from cold to hot, not a full 15. I’ve seen guys torque them cold and then check it after heat soak, and the torque drops off by about that much. The real issue is that the housing is aluminum and the igniter is steel, so their expansion rates are totally different. That mismatch is what causes the backing out, not necessarily a straight 15% error. Take this with a grain of salt, but I’ve had better luck torquing after a 15 minute heat soak at idle, then running it and rechecking. YMMV though, especially if you’re working on a different series.