Warbird Information Exchange

Hello all,

I'm new to the forum so I hope I didn't post in the wrong place.

I've read several accounts of WWII pilots "slow timing" a newly installed engine. If I recall correctly they describe flying it around at a reduced power setting for a number of hours until the required time had elapsed and then they were free to run it up to full power.

I've often wondered about the specifics of this:
What power settings MP and RPM etc. and how many hours/minutes were required?
I'm particularly interested in the R2800 and V-1650 engines.

Thanks

Steve

I'm curious now about this too as it is completely opposite of what you would do with a small engine. When we install a new lycoming, we run them for the first six to ten hours at 80% or more power to seal/set the rings.

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Aircraft: C47B, C-123K, Fairchild F-24, Funk Model B, L-21B, T-28B, T-34B
Static: F-4C Phantom II, F-15A, T-3 Provost

There was a good description of it in Bert Stile's Serenade to the Big Bird...but without the technical details. I had never heard of it, it sounded rather involved.

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doesn,t sound like good practise to me you need cylinder pressure to break in rings and rpm to break in cam lobes

That's always been my instinct as well. I've done many engine break-in flights on small Lycoming horizontally opposed engines and as described above by flightsimmer, we ran them very hard, on mineral oil for several hours in order to seat the rings.

Contrast that with:
Here's Frank Klibbe of the 56th Fighter Group describing the engine break-in of a new P-47 in the book "Gabby"... "And the engines had to be slow-timed. This meant you had to fly 10 hours of time at low rpms on the engine before you could really open up to it's maximum." He goes on to describe a major screw up that he made when he finally got to that magic time when he could open it up to full power...

It is called slow timing because while you are doing it, time seems to slow down to a crawl. You orbit the field for a hour or several hours, turning circles, never venturing further than you can glide.
The reason is to seat the rings and to see if the engine will stay together. To seat the rings, you run a higher than normal manifold setting for a given RPM than would normal, the higher the manifold pressure, the higher the pressure in the cylinders. Every 30 minutes to a hour, you adjust the manifold pressure to a different setting, repeat until bored out of your skull.
I used to slow time engines in spam cans at the FBO I worked at, I would bring breakfast and a audio book on every flight

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Matt Gunsch, A&P, IA, Warbird maint and restorations
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I remember my dad talked about "Slow Time" flights in the Mustang's after an engine change.
Robbie

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Thanks for that insight Matt. So it was still done at a fairly high power setting? Just not max power? I can see how the reduced rpm would help because it would increase BMEP. Just slow because it takes so darn long...

I am curious if "slow timing" is still used in large radials and inlines. In 30 years of light plane maintenance I have never seen it done in the air. We would make several ground runs beginning at idle and working up to a very brief full power run with more time shut down for cooling than we did running. The first flight was all about temperature management and keeping the engine at about 75 to 80% power and cylinder head temps below 400 F. This is considered the optimum power setting for seating the rings. Ring seating takes place with enough energy (if you will) to keep the rings in contact with the cylinder walls but without enough heat to anneal the rings or turn the oil into varnish. At power settings below 75% the rings don't make enough contact to seat and above that there is too much heat to prevent the oil cooking on the cylinder walls. Once the rings seat at 75-80% then they will seat at a lower power settings or higher settings. You can tell when the rings are seated when oil consumption stabilizes or when cylinder head temperatures suddenly drop with all else remaining equal. Some rings will seat in the first hour others take anywhere from 5 to 25 hours to seat. Engines that have been run on a dynomometer for a few hours before delivery often have the rings already seated.

I realise that the biggest Continental or Lycoming flat six is only a fraction of the size of a Merlin or R-2800 but since piston rings haven't changed much in 75 years I am betting that a modern rebuilder of large radials and inline engines doesn't require slow timing anymore.

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in my round engine freight dog days after an engine change with both the PW1830 (DC3),and R2800 (CV340), after a test flight that ensured temps and pressures were in the good green, and a final pull and check of the screens,the ships were signed off and sent on their way with blessings into normal service.

On C-124's with the R-4360-63a engines, we would install a new engine and operate the aircraft right away without any restrictions.

I remember going up to Suffolk County airport in New York from Dover AFB, to replace a #2 engine during a snowstorm. That evening I was at the FE panel checking out the new engine when the pilots came up the ladder and asked how it was going. I told them the job was done as soon as I finished the idle speed and mixture checks. They said, OK, when you've checked that, go ahead and start the other three engines and lets get out of here. (They were from Donaldson AFB, South Carolina and wanted to get home where it was warmer.)

We took off, at night, in the snow, with a full load of cargo, fuel, etc and stopped at McGuire AFB, NJ where I pulled and checked the oil screen. We took off again and we stopped at Dover, AFB, where I got off and went home.

This was a normal operation.