Breaking in and Operating an Allison

Discussion in 'Aviation' started by GregP, Mar 10, 2014.

  1. GregP

    GregP Well-Known Member

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    For all WWII V-12 engines I know of, the break-in procedure for a newly-rebuilt engine runs about the same.

    The Allison V-1710-90/100 series all have a 3,000 rpm max and usually a max of 57 inches of manifold pressure for normal operations. If you are a "war emergeny guy" you can use up to 75 inches MAP. Nobody is running early Allisons. Even the guys with the P-40B and C models are running -80 / -90 / -100 series Allison engines mated with the early nose cases, and they have to consiously use only the allotted amount of power the nosecase can handle.

    1) It is best to run straight oil and a club prop or real prop. We did it with straight 90 weight oil and a 6-blade club prop.

    2) You start the engine and let it idle until it is running smoothly at something like 800 rpm or so.

    3) Once running smoothly, advance to 1,000 rpm and let it idle until the temperature gets warm. That means an oil temp of maybe 85 - 90°C and continuous good oil presure. Look for leaks other than the test stand. There is usually minor seepage that quits as things warm up and seat in.

    4) Once warm, slowly advance to 1,600 rpm and let run for about 5 minutes on the test stand. Monitor temp and oil pressure for good values the entire time. Look for leaks.

    5) Shut it down, clean the engine, clean the screens and engine stand oil filters looking for anything other than tightseal (used to seal the gaskets). The cuno will have a lot of tightseal on the screens, so clean it up and clean the engine stand filters. Reassemble things. What you are looking to do is seat the piston rings. You must run the mixture at auto rich to start it (don;t HAVE to but works well), but you then lean it until the engine gets the smoothest. It sounds hard but isn't once you see it done or do it yourself several times. The exhaust flames tell the whole story and the ques to look for are well desvribed. Any veteran can help you out there. Mainly, avoid backfires. These can and WILL blow out gaskets requiring breakdown. Not usually, but it CAN happen.

    6) Always start and idle until warm. Change rpm very slowly. No WWII V-12 likes to accelerate or decelerate quickly. If you have the habit of accelerating or decelerating quickly, your engine life will be half of what it should be or less.

    7) Once warm run it up to 1,600 rpm slowly and run for about a minute at 15 - 20 inches MAP. Then advance to 2,000 rpm and maybe 20 - 25 - 30 inches of manifold pressure. Look for the exhaust stacks to turn a uniform dark grayish brown/black. If the color is uniform and the mixture is right, the rings and valves are seated. Continue running until almost seated as fuel and temperature allows. Look for leaks and clean the engine. Any leaks should be MUCH less or gone, or there is a problem that needs to be addressed. Better hope you paid attention when you installed the gaskets and seals.

    Clean the cuno and oil filters every hour or so to check for what is moving around in the engine. You should see lessening amounts of tightseal and no silver material. Tiny silver is usually bearings (lead or silver from the mains) and irregular bits can be broken rings. After maybe 4 - 6 hours, the tightseal will stop and the cuno should be clean or almost clean after an hour of running. That is what youa re looking for. You can now run it until broken in before cleaning the screens and filters again, but do that when the engine is ready to ship so the customer gets a fresh engine ready to run. If it is in the plane, you are ready to fly.

    9) Once the exhaust stacks are uniform, start and warm the engine, advance to 1,600 rpm, then to 2,000 rpm for about a minute, then to 2,300 to 2,500 rpm or so and up to 35 to 37 inches of manifold pressure. Run for several minutes, temperature permitting.

    10) Once the rings are seated you can do a short run to 2,500 rpm and maybe 35 - 40 inches or so. It depends on the prop used and the pitch. Can't do that too long or the test stand starts moving. Joe's test stand is a Ford dually truck and he can pull it backwards if he uses too much power. With a good club, you can load any V-12 so it can't get past 1,500 rpm, so the trick is to set the pitch. With a 6-blade Hamilton-Standard club, the correct pitch is about 23.5° or so, depending on model. With that we can get 2,500 rpm at 45 inches on the test stand. After seating, the owner usually wants to see a run or two and learn to start it and adjust the mixture himself / herself, and it's time to do that once the rings are seated. Sometimes they don't and we'd drain it, disassemble the test stand setup, and seal the engine for shipment. We leave oil in it so the owner doesn't have to pre-oil the engine unless it sits too long before use. Pre-oiling isn't tough, but you DO need the tools.

    They are easy. Get a small 5 - 10 gallon air tank and fill it with oil about 3/4 full. Pressurize it and insert the hose onto the oil intake galleys. Use air pressure of about 70 psi or so and let the oil flow with the valve covers off until oil comes out the heads all along the cam area. Re-install the valve covers, clean the seepage, and it is pre-oiled and ready for startup.

    11) Once in the plane, Joe would offer to come check it out and make sure the connections were correct. He would also offer to start it and warm it up for the new owner.

    12) Once ready for flight, the proedure is similar to a test stand run at first. Start it and let it warm up so the oil is at 90°C or better. The taxi out and fly. Set the prop to fine pitch, which gives 3,000 rpm once in governing range.

    13) On takeoff, roll onto the runway and SLOWLY advance to 45 inches, Let the plane accelerate to 45 - 55 knots and slowly advance to 50 - 57 inches. Lift off and climb for about a minute. Reduce to 35 - 40 inches or so and pull back to 2,100 - 2,500 rpm (we recommend 2,200) and cruise it around at low and medium power (600 - 850 HP or so, maybe 900 HP), occasionally going to 45 - 50 inches for a minute or so, until the bearings are thoroughly broken in. This usually takes anywhere from 15 - 20 hours. Once broken in, you can pretty much run it like you want as long as you warm it up gradually, advance AND retard the throttle slowly. If you are flying a P-38 DO NOT use the engines for steering on the ground and pay atention to the cylinder head temps. Forgetting to open the radiator doors after landing can toast an engine(s) on the ground taxi back to the hangar. Think of them as a single engine planes and use the brakes for steering. If you throttle-jockey the engines to ground steer your P-38, your main bearings will have a short, unhappy life ... they do NOT like quick acceleration to make a sharp turn. It is MUCH better to slowly accelerate the plane and use brakes for the sharp turn than it is to use throttle. Brkaes are WAY cheaper than Allisons, particularly the left hand turn Allisons. The P-38 and the sole Il-2 in Paul Allen's collection are the only planes that use a left turn Allison.

    If you follow these steps, you can get a long happy Allison life (or Merlin life). Oil changes and maintenance come at factory-recommended intervals. WWII engines like to run frequently rather than sit for a year and then run. If you can't fly it at least a few hours a month, preferably an hour a week, don't own one. Carburetors need overhaul every five years at a cost of around $5,000 each. If you can't afford that, don't own one. Mags sometimes fail; plugs sometimes foul or fail, and distributors sometimes develop issues.

    If your old wiring harness is more than 10 years old, get Joe or someone else to rewire it. Cracked ignition wires are a chief cause of rough running and ignition missing. Buy a few spare and learn how to install them correctly or have someone do it who KNOWS how to do it. WWII spark plugs are antiques. If you have WWII plugs, make them into a display ... but don't run them in your engine. Run new plugs. They may be $30 each or more, but if you can't afford good plugs, you can't afford to run an Allison or Merlin.

    By following these procedures and a few others, Joe Yancey has several customers with 1,100+ hours on their Allisons and they are still running smoothly and well.

    If you are running a Merlin, you have to do normal Merlin maintenance. You do NOT have to check the cylinder liner torque on an Allison but you re-torque every 25 - 30 hours for a Merlin. That's not a knock on a Merlin, just a different procedure to follow due to the design of the engine. Each one has many "special tools," and each one has its positives and negatives. Both will give good service if you treat them right, fly regularly, do the maintenance, and don't abuse them.

    Abused warbird engines can get VERY expensive instead of just expensive.

    If you think V-12's don't like to accelerate or decelerate quickly, radials are even MORE sensitive to that behavior. They really like to run at a steady speed and steady power setting. Abuse an R-3350 and it might bite you in one flight. Treat it well and it can last 3,000 hours between overhauls.

    The R-2800 is about as tolerant of abuse as any radial in the world. Treat a good one of those right and it will last a LONG time. Even the R-1340 in a T-6 / SNJ rewards gentle treatment with longer life. Of course, any radial will also oil down the engine compartment, belly, wheel wells, and lower sides of your plane ... but anyone who flies a radial knows that and accepts it. If they mind a bit of oil, they don't need a warbird, because all will reward you with oil as you run them. It's like a cat bringing you a dead bird or animal ... it goes with the territory.

    It helps to own a rag factory.

    If you abuse an engine too soon, it usually means a new set of main bearings, and that means engine removal and breakdown. Don't DO that. If you do, you will regret it, at least in the wallet, if not in flying time.
     
  2. GregP

    GregP Well-Known Member

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    #2 GregP, Mar 10, 2014
    Last edited: Mar 10, 2014
    In WWII the WAAF's and other production test pilots slow-timed the birds so they would be broken in right, here in the USA before line delivery. They pretty much adhered to good practices stateside except for young hotshots ... but most of THEM were away at the front lines. In combat if there was a scramble and you did what was necessary. And many P-38 jockeys didn't pay any attention to the crew chiefs or the training and operated them as they saw fit, thereby creating "war weary" engines well before their time.

    Generally, even in the Luftwaffe and Japanese air arms, the crew chiefs would start the birds early in the morning and warm them in preparation for the day's activities. If they didn't fly (but were fit to), they were warmed periodically throughout the day in anticipation. They tried very hard to operate the engines right but, in combat, you did what was required at the time. You can be sure they paid close attention to engine operation on an escort mission as they had the time and weren't going anywhere fast anyway. If they got bounced, then they usually went to combat power almost immediately as quickly as possible as part of a necessary survival reaction.

    WWII engines never reached wear-out. They were shot down, failed, or ran until overhauled at anywhere from 250 - 450 hours whether they needed it or not, usually back in depot maintenance areas set aside for aero engine overhaul. This is for Allisons and Merlins ... not all V-12's. This was a "military overhaul" and they were pretty good at it. Sometimes they did a front-line overhaul that was usually new piston rings and maybe a few other top end cylinder bank items, but rarely did they do main bearings in the field, though it was certainly possible if the need was pressing.

    Today owners want good engine life and pay attention. One way to know is when the oil pressure drops. If it is normally at 75 pounds per square inch and falls to 65 psi for some reason, with everything else being normal. you can bet the mains are at fault. The crankshafts are hollow and are oil pressurized, with small weep holes in the bearing journals for oiling the mains in operation. There was supposed to be a certain clearance, and that made the crankshaft operate on a thin film of oil under pressure. If the clearances get too big, then the oil shoots out into the open space and the oil pressure drops a bit. When it gets to certain limits, you KNOW it is time for mains. You can continue to operate it if you want, but you are playing with your life.

    Merlins had different limits and limitations, but were generally similar, being of similar material and design. They, too, either failed, were shot down, or operated until time for the prescribed military overhaul.

    You were always supposed to overhaul and engine when it received a prop strike, but sometimes this was bypassed. Sometimes they got away with it and sometimes they didn't. Bypassing safety precautions is never a good idea and can frequently be a very BAD idea. I'd rather be down here wishing I was up there than vice versa.
     
  3. GregP

    GregP Well-Known Member

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    I was reminded I strayed from the topic in the "First Generation Jet Bomber" thread, so here's a thread about breaking in a freshly-overhauled Allison.
     
  4. GrauGeist

    GrauGeist Well-Known Member

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    It is good information and gives a good idea of what all was involved.

    Thanks for sharing the info :thumbleft:
     
  5. GregP

    GregP Well-Known Member

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    You're welcome. If anyone is around southern California, it might be a neat thing to call up Joe Yancey, see if he is near running one, and go see a new baby Allison get broken in. He does about 4 - 8 engines per year, so at any given time, he might be running one or might not be.

    That would be Yancey Enterprises, Rialto, California.
     
  6. BiffF15

    BiffF15 Well-Known Member

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    GregP,
    Thanks again for the info! I'm spoiled by jet engines with FADECs on them! I had no idea that the engine break in period was as "involved" as it is.
    Cheers,
    Biff
     
  7. razor1uk

    razor1uk Well-Known Member

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    Just don't replace the word engine with something like 'other half'.
    *Ahem*
    I'll be going now *aribba aribba underray, fashooom, door closes*
     
  8. GregP

    GregP Well-Known Member

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    All piston engines of WWII vintage require a pretty lengthy break-in and demand proper operating procedures. If you are stupid, you can kill a new Allison in less than 10 minutes. But you can do that to a Merlin, R-2800, BMW 801, or any other engine, too.

    Jack Crowell owns a P-38 (one of two based at Chino) and he gave an event where Steve Hinton would check out 6 - 8 new P-38 pilots with it about 2 - 3 years back. Steve was on the radio screaming at one or two guys who were so happy to have flown it they were taxiing in with the radiator doors closed. If he hadn't been talking to them, they would have toasted the Allisons on the way in after a good flight!

    That's not something you should forget when using a powerful piston engine (or engines). The gauges are your life and your wallet ... WATCH them. In fact, that is one of the main things that new warbird pilots forget ... monitoring the engines on the way OUT to the runway and also on the way BACK IN to the hangar. We know of one guy who died in a P-51at Camarillo when he cobbed the power for a go-around and torque rolled it right in despite all the training during his checkout to the contrary.

    So warbirds may be forgiving of minor errors, but NOT of major lapses in judgement. They need to be flown with care and with forethought for what can go wrong. You should NOT be flipping through charts for emergency procedures if your engine quits, you should KNOW what to do. Know your systems and your emergency procedures by heart and be ready to use them. That way, you rarely HAVE an emergency that you aren't prepared for. Steve Hinton has told me of several former warbird pilots "retired" from flying warbirds when they got less than current on the systems and procedures. If you are flying a twin, like a Tigercat, and you have to declare an emergency for one sick engine, your procedures are too rusty to be safe. First fly the bird and second, try to handle the sick engine. You have plenty of power to get somewhere and land, so why crash trying to handle a sick engine instead of flying the plane?

    Chances are the engine is fine and you just need to adjust the mixture, change fuel tanks, pump the primer handle, or whatever.
     
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