How to start a 337

[kevin]

Ken's thread about fuel flow indications has a nugget in it about starting procedures. He refers to the book starting procedures. Those procedures never worked well for me. Below is the procedure that my mechanic taught me for a cold start. This procedure has worked very well for me for years, both on my '65 C337 and my '73 P337.

After master and mags and that stuff:

1.) Throttle full forward, mixture full forward.
2.) Electric boost pump to full until fuel flow reaches 80 lbs (on the '73. On the '65 I don't remember the figure, but the pointer is in the same place, about the four o'clock position for the rear engine, 8 o'clock for front). This should take two seconds or so normally, although for reasons I have never understood, sometimes it can take five or six seconds.
Now, quickly:
3.) Throttle to idle.
4.) Start.

My engines would both start in 2 or 3 blades most every time using this procedure.

Only exception is a hot start. If the engine had only been shut down for five minutes or so, or if it was a cool day, I would try the same procedure, but only blipping the boost pump for a second or so, to the 5/7 o'clock position on the fuel flow gauge. If that did not work (often), or if the engine was clearly hot, I would use the same procedures as above, except that at step 3, I would move the throttle to idle and the mixture to idle/cutoff, and start cranking. When the engine fires (in three to six blades), I quickly move the mixture to full rich, and blip the boost pump if the engine begins to falter, to keep it running. That procedure worked for a hot start every time for me.

My experience, for what it is worth to you. Use these procedures at your own discretion and risk.

Thoughts/suggestions from others?

Kevin

[WebMaster]

What I do, based on what John Black from TCM suggested, is Mix rich, throttles up some, both boosters on until good pressure/flow reading. Then boosters off, crack throttles up, 1/2 inch, start. Starts right up, cold or hot.

[Ken MacLean]

I know this is supposed to be about 337s, but 206s have big Continentals in them, and I fly them Part 135 occasionally. We were having lots of problems with cracked cylinders in those IO520s, and our inhouse genius, turned hero, suggested that a hot start with boost pump was pouring cold liquid on a hot head and starting the cylinder cracks that plagued us continually.

We implemented a hot start procedure that reduced our cylinder cracking problem by 2/3. When we know that we will be making a quick turn, we shut the engine off with the ignition switch while advancing the throttle to full forward, then retarding the mixture to cutoff, finishing the procedure just as the prop stops turning. This locks a fuel charge in the combustion chamber, and if a restart is attempted within a few minutes, hitting the starter and letting the engine catch and immediately returning the throttle to idle usually will do the trick. If not, go ahead and boost, but it usually will work.

We replace about 1/3 of the cylinders that we used to with this procedure.

Does this apply to 337s? If you are cracking cylinders, then maybe.

Another fellow applied the same logic to full rich mixture as part of the landing procedure. Same principle - introducing cold fuel to a hot surface starts a small crack around the exhaust valve and leads to eventual cylinder failure. So the suggested procedure is to leave the mixture lean on approach for smooth engine performance, and then on go around, if necessary, reach over and push ALL levers forward simultaneously to accomplish full power. A little different than we learned to fly, and certainly hazardous if it not practiced and well understood, but theoretically a cylinder saver.

Ken

[kevin]

I don't know about the shutdown procedure Ken, but leaving the mixture lean during descent and landing is a procedure I have followed for years. Go around is just everything forward, starting with mixture, as you said. I didn't know about the cylinder cracking aspect (and I have not had that problem, even with the 206 I used to own), but the 360s on Skymasters tend to load up at lower power/full rich and the spark plugs get fouled. Leaving it at cruise lean prevents that problem. Since the power is well back, there is no issue with running too lean.

Interesting point, thanks!

Kevin

[Ernie Martin]

Very interesting thread, especially the issue of hitting the boost pump to keep the engine from faltering immediately after start-up. And Ken's point about potentially causing cracks on the cylinder heads is worth pursuing.

With my background and location (at left) I know a little about this. I find that I need to hit the boost pump to keep the engine from dying after a hot start (typically after a 10-minute stop, whether at Customs or to refuel or to pick up passengers, in 90 degree weather). I had been under the impression that the principal purpose of the boost pump is really to get the right amount of fuel into the fuel injection system by pushing fuel past vapor locks which occurs on the fuel lines near the hot engine.

If my impression is correct and if you hit the boost pump for only a second or so (Kevin calls it a "blip"), turning it off as soon as the engine starts recovering, then I don't think you're pushing cold fuel into the chambers. For two reasons. First, the fuel that the boost pump is pushing into the chambers is the fuel in the lines near the hot engine (yes, there may be some vapor bubbles, but there is also fuel, and it's hot); in short, fuel from the tanks doesn't somehow somersault over the fuel in the lines near the engine. My second reason comes into play if I'm wrong about the lines having fuel inside them. Let's say the lines are essentially empty -- it's a huge vapor bubble inside. As long as the amount of fuel pushed by the boost pump is small (which comes from just blipping the pump), then when I look at the length of the fuel lines near the engines (hoses followed by thin tubes to the injectors), it seems to me that stretch of HOT fuel lines is going to warm the small amount of incoming fuel being pushed through.

I'm kind of out on a limb here. Sure would like for others to step in here and voice their opinion.

BTW, I'm a firm believer in Ken's last point, about leaning the engine on approach. I don't do it because of concerns of cold fuel into hot surfaces and cracking (and, to be honest, I don't quite understand the concern). I do it for a different reason: I'm concerned that I'll flood the relatively cool enginewith a full-rich mixture if I have to give it full throttle to go around. And it does require remembering that you have to push all levers forward simultaneously to accomplish full power.

Ernie

[Wayne Pearce]

I quite often fly from airfields with density alt of over 5000' in Australian bush and always approach at near full rich ready for go around and have never had a problem with cylinders or fouled plugs so I thought I should rethink this when reading this thread, this is what I came up with.............

*Always prime cold engine with 60lbs/hr fuel flow for one sec prior to start it will always start burnin & churnin within two revolutions

*Do same at 30lbs/hr with hot engine

*I quite often have to lean on climb above 5 or 6000' to keep the engine "tone" sounding correct

*I "gain control of the MP" and begin to enrichen prior to decent, I enrichen by 50'F before decent and keep it there until the circuit where on final I run nearly full rich depending on circuit density alt, this does not give thermal shock when done slowly

*If go around procedure is UP, UP & UP then I do not want to go from lean & hot upper cylinders to cold (thermal shock) just when I need full power. Saw a P68B damage a Lycoming 360 this way

*Have never had a problem with fouled plugs !!!!!!!!

*If we look at fuel line diameters and flows etc. we see that fuel velocity is around 520 mm/sec all things considered you are not going to heat the fuel appreciably with engine in the cruise getting fuel from a tank that is marginally above ambient because of return fuel

*vapour problems are either caused by low fuel flows & hot engine on the ground or cavitation or extreme temps where the fuel pressure is exceeded by vapour pressure

Hmmmm I am still rethinking my logic here whadya think

regards.............. Wayne

[Skymaster337B]

Speaking about starting procedures...the book mentions we should start the rear engine first. However, I start the front engine first because the battery is in the front. This saves the battery over time; so far, my battery has lasted almost 9 years now. Any one else do the same?

[Ernie Martin]

I always start the front first, but I thought that is what the book says. If I recall, it's because of the shorter run between the battery and the engine. If you happen to be in a highly marginal situation, where there is barely enough energy in the battery to barely turn an engine, then you want it to be the front engine, where you might get 3 or 4 revs before the battery dies, compared to the rear engine, where you might get 1 or 2 revs because of the higher cable resistance.

Ernie

[hharney]

My 1968 Owners Manual states that the front engine is normally started first. Rational is the battery cable length as Ernie states above.

I know I was always taught to start the front first and at one time I heard something about procedures indicating the rear should be started first because you can't see it and if the rear is started first you could hear it better.

But my book says the front should be started first.

[JeffAxel]

FWIW, they changed the wording in the first paragraph of the starting section in later POH's. My '77 POH says either engine can be started first, and mentions both arguments, the shorter cable run for the front versus the ability to hear the rear. I usually start the rear first, just because I like being able to hear it. If my battery was so drained that it couldn't start the rear engine, I would want to abort the flight, figure out why the battery was so low, and charge it properly with a charger, assuming the battery itself was okay. Recharging an almost dead battery with the alternators is tough on the battery and electrical system, and I am not sure I would feel comfortable relying on that system, especially in IFR or at night.

[Skymaster337B]

The only way we could resolve this topic is at the next Skymaster fly-in...at the hotel bar.

[skymstr02]

If you start the front engine first, how do you clear the rear engine?

I can yell "Clear Rear" thru the storm window, and some one will hear me, and then clear the front visually.

On my O-2, the battery is just inside the baggage door, so the rear starter is closer to the battery than a standard 337.

[JeffAxel]

Clearing the rear engine is a legit concern. I have gear mirrors on each wing so I can see the rear engine area pretty well from each side.

[Skymaster337B]

I say the only way to "clear" the rear prop is on the final walk-around. After that it's really an educated guess that it is clear. Starting the front engine should give enough notice to everyone to remain clear of the aircraft...and rear prop.

However, I've never heard of some one walking into the rear prop because they didn't know the aircraft was about to start-up. They typically walk into the prop getting in or out of a running aircraft.