CHT during lycoming break in

[Notatestpilot]

I've started my break in post major overhaul of my O320.
During the 2 hour flight at 75% recommended power, my #3 & 4 CHT were at 415 to 420. The CHT for #1 & 2 were in the 375 to 385 range.
Is that normal for the back two cylinders?

 

[Jeff767]

I've started my break in post major overhaul of my O320.
During the 2 hour flight at 75% recommended power, my #3 & 4 CHT were at 415 to 420. The CHT for #1 & 2 were in the 375 to 385 range.
Is that normal for the back two cylinders?

It depends on your baffling and MAG timing. Lycoming recommends not exceeding 440 during break in but most other sources say do everything you can to keep temps below 400 if you want a low oil burning engine. Run it as hard as you can and as cool as you can. Don‘t however go below 75% unless your temps exceed 440.
In hot climates plan a break in flight for a dawn launch and minimize ground run time. Many oil burners are the result of owners who can’t resist long ground runs on a new or rebuilt engine. Never let the CHT’s exceed 300 on a ground run.

 

[Hang 4]

At some point, and you may have already passed it, you will see a drop in CHT when the rings seat. It's pretty noticeable. The rear cylinders do typically run hotter.

 

[MooneyDriver78]

Temperatures seem normal for back cylinders, the front seem too cool, but I don’t know what’s normal for your plane. What were the temperatures before overhaul?
Mine started in 420s, within 5 hours were 390s and after 10 hours were 370s.

 

[Domenick]

Did the temps come down during the 2 hour flight?

 

[Dan Thomas]

Don‘t however go below 75% unless your temps exceed 440.

From the Lycoming break-in instructions:





https://www.lycoming.com/sites/default/files/attachments/Lycoming%20Reciprocating%20engine%20Break-In%20and%20Oil%20Consumption.pdf

There is way too much made-up "advice" regarding engine operation. Lycoming built that engine, they do factory overhauls, they carry the liability for the thing, so what they say is what works for them and minimizes warranty claims and lousy oil consumption numbers. I broke in the flight school Lycs exactly as per that document and those engines used very little oil all the way to TBO.

And pay attention to the POH numbers for those power settings. You'll find yourself using nearly full throttle if you're high enough. For that last 30 minutes, if the airplane has the right prop on it, you will be at full throttle and 2700 RPM.

Too often, baffling is all beat-up and worn out, rotten or hardened seals and such, and it's all just transferred to the new/rebuilt engine. The increased friction of break-in generates more heat than the compromised cooling system can handle, and the cylinders and oil get hot. I have found the rear baffles not tied across the lower sides to keep them against the fins and make the air go where it should. Found intercylinder baffles missing altogether. Found seals not sealing against the cowl. It all adds up.

 

[Stewartb]

Nothing about those temps is alarming. Fly it per instructions and watch the temps. The easiest error to make is not tilting the baffle seals toward center when placing the top cowl, especially easy if the seals are new and stiff and haven’t taken a set. If those seals tilt out you lose the top cowl pressure. 3 and 4 will be warm as a result. Check simple things first.

 

[Jeff767]

Break in the engine by running it as close to maximum continuous power as possible without allowing any CHT to exceed 420 degrees Fahrenheit for Continental cylinders or 440 degrees F for Lycoming cylinders. Run it this hard for an hour or two, until you see the CHT come down noticeably, indicating that the break-in is mostly complete.

It’s very important to run the engine hard right from the outset. Keep ground running to a minimum, avoid a protracted preflight runup, and don’t cycle the propeller more than once (and as shallowly as possible). The reason for all this is that running a freshly honed cylinder at low power for any significant length of time can cause a condition known as glazing, in which a tough residue of carbonized oil builds up on the cylinder walls and stops the break-in process dead in its tracks. Once the cylinder has become glazed, it’s no longer oil-wettable, and the only solution may be to remove and re-hone the cylinder and start the break-in process all over again.

The above advice works great. Keep in mind the published lycoming procedures come from well before aircraft had CHT indications for one or all cylinders. To address CHT lycoming simply recommends a shallow climb.

 

[Stewartb]

To the OP, another item that makes break-in difficult is fine pitch props. It’s hard to get adequate cylinder pressures with a STOL prop on a hot day. Hopefully you have a cruise prop installed?

 

[Magman]

Regarding oil & procedures it is wise to listen to whomever has the warranty.

Often ignored is a long downwind taxi that provides very little cooling.

Easier to tow to position than pull jugs.

 

[Bell206]

Regarding oil & procedures it is wise to listen to whomever has the warranty.

^^^This. Its the most important item. You'll find most proponents of non-standard break-in procedures fail to mention this small detail. Even the infamous MB does not offer any warranty adjustments if you follow his advice over the OEM guidance and things go wrong. Something to keep in mind.

 

[Dan Thomas]

Break in the engine by running it as close to maximum continuous power as possible without allowing any CHT to exceed 420 degrees Fahrenheit for Continental cylinders or 440 degrees F for Lycoming cylinders. Run it this hard for an hour or two,

No. Do it as the manufacturer says. Using more power than necessary does no one any good. Running on straight mineral means that there are no ashless dispersants in it, so coking starts depositing varnishes and carbon everywhere when temps get high and stay there for awhile. The mineral oil is used because it has less lubricity and speeds break-in.

https://www.lycoming.com/content/hard-facts-about-engine-break
Each new or rebuilt engine is given a production test run at the factory before the engine is delivered to an aircraft manufacturer or customer. After installation in the aircraft, the engine is run again during the test flights. These test runs will ensure that the engine is operating normally and will provide an opportunity to locate small oil leaks or other minor discrepancies. In addition, these test runs do the initial seating of the piston rings. The rest of the break-in is the responsibility of the pilot who flies the aircraft during the next 50 hours.

A new, rebuilt or overhauled engine should receive the same start, warm-up and preflight checks as any other engine. There are some aircraft owners and pilots who would prefer to use low power settings for cruise during the break-in period. This is not recommended. A good break-in requires that the piston rings expand sufficiently to seat with the cylinder walls. This seating of the ring with the cylinder wall will only occur when pressures inside the cylinder are great enough to cause expansion of the piston rings. Pressures in the cylinder only become great enough for a good break-in when power settings above 65% are used.

Full power for takeoff and climb during the break-in period is not harmful; it is beneficial, although engine temperatures should be monitored closely to ensure that overheating does not occur. Cruise power settings above 65%, and preferably in the 70% to 75% of rated power range, should be used to achieve a good engine break-in.

Remember that if the new or rebuilt engine is normally aspirated (non-turbocharged), it will be necessary to cruise at lower altitudes to obtain the required cruise power levels. Density altitudes in excess of 8000 feet (5000 feet is recommended) will not allow the engine to develop sufficient cruise power for a good break-in.