I'm reading the break-in instructions for my Superior Millennium 0-320 cylinders and everything makes sense so far except: "At no time should cylinder head temperature be allowed to exceed original airframe equipment manufacturer recommended maximum cruise limit." Its one hell of a sentence that seems to mix CHT with cruise limits? I am confused. This engine is in a 74' Grumman AA5 Traveler. I am looking through the POH and can't find anything about CHT's and there is not a CHT gauge in the original equipment that the manual would refer to. (I am having one added for obvious reasons). It seems like Millennium would know at what temperatures their cylinders would melt away, more so then the engineers from 1974 proposing limitations on a different make of cylinder i.e Lycoming.
What's the airplane's maximum CHT for the cruise portion of flight? (not max CHT ever, which might be higher). Lacking anything specific to your airplane, I'd go with the engine manufacturer's limit for cruise (if any)... but, I'm not an A&P nor an aeronautical engineer... just a pilot who used to own a small aircraft.
I can't find any mention of CHT at all in the POH and there is no original CHT gauge in the plane to measure it.
You're screwed. (j/k) If it's not in any airframe manual then you might want to check the engine manual: https://www.lycoming.com/sites/default/files/O-320 Operator Manual 60297-30.pdf
Ah! Thanks to both of you. I did find that information in the Lycoming operators manual with very similar verbiage so that must be what they are referring too.
FYI: it's more a standard CYA statement as the airframe certification is boss when it comes to limits. Unless there are any limits listed in the AA5 TCDS the next step would be the engine limits as mentioned above. A quick call to the Superior tech support is also an option.
Did not see any CHT limitations in the TCDS. I may call a Superior Tech on Monday then just to make sure the Lycoming CHT limitations are valid for their cylinders. "For maximum service life, cylinder head temperatures should be maintained below 435°F. during high performance cruise operation" on page 3-6. On page 3-12 it states the maximum is 500°F with a footnote saying that for maximum service life use 150 to 435°F...
Keep it under 400 and roll on, you won’t have a issue if you stay away from Vx and Vy climbs, take your Vy speed and keep at least 5 knots over that, and faster if you climb up high for extended periods of time. I usually keep my altitude below 4,000 on a break-in. Don’t baby it too much or you won’t seat the rings.
If you’re at 500f, you’re close or about to hit complete cylinder failure. Stay under 400 for cruise, no more than 450 for climb. TCDSis for the airframe, not the engine. Search Lycoming’s website, there’s a great pamphlet for best use for engine longevity. Simplified notes from the engine manual.
FYI: there are engine and propeller operating limits in the airframe TCDS and the POH/AFM that must be followed as well. Some older model OEMs included more of these limits so a quick check is needed before looking to other ops limit references.
I would do everything possible during break to avoid exceeding 400 degrees and 380 would be better. The last thing you want is to glaze the cylinders and have to pull and rehone everything. Take off early when it’s cool and keep the speed in climb at whatever is needed to keep temps below 400. Run the engine hard to help seat the rings. Certainly not below 75% power. Depending on the type cylinders ring seating could occur anytime from 20 minutes to 5 hours unless they are chrome which could take longer. Ground runs should be very short and don’t let temps get above 350. Long ground runs are a sure fire way to glaze the cylinders.
