I'm in the process of obtaining my first 4 cycle engine (Saito 100) and have a few questions. Everyone keeps talking about "priming the engine". Can anyone give me some details on different ways of priming the engine. With a 2 stroke all I did was fill the plane with fuel and use the electric starter. On occasion I would need to put my finger over the carb intake and spin the prop a few time to sort of choke the engine. Other than that I never had any issues. I originally started my 2 strokes with a chicken stick (Just simply flipping the engine in the direction of travel), but later got an electric starter and consistanly used it.

Most of the guys at my club just start 4 stroke with their electric starter, but many on this thread are against it. I guess I'd almost need to see the reverse flip start in person because it's hard to picture how it's done just from rading a thread.

I just broke an APC 18x8 prop with chicken stick. When I did a normal flip, the engine backfired, and the trialing edge of the prop smashed against the chicken stick and broke a little section of the prop trialing edge.

There's props and cons to chicken stick and starter. Chicken stick can damage prop, while starter can damage spinner.

It's possible in an upright engine but you'd really have to be trying
Say you'd filled your tank then went off talking for 30 minutes and all the while the tank was syphoning into the carb. If the crank port was open then it'd run into the crankcase. Hit it with the starter and enough fuel might get thrown through the transfer port to fill the combustion chamber. All it takes is about 1cc of fuel for a .60 size engine. But that's one of the advantages of an inverted engine...any fuel that syphons through just dribbles straight out of the carb onto the ground (so long as the barrel is cracked open slightly).

Another way to lock up a up-rite engine is to refuel without taking off the pressure line to the muffler, fuel fills the muffler and back flows into the combustion chamber........DOH!

I wont be doing that again!

Regards
Mark

As an aside, hydrolock also plagues “round” engines on full-scale airplanes. You might have seen documentaries or newsreel films of ground crews pulling propellers through on B-17s and B-24s during World War Two. This was to ensure against hydrolock. Then, when the crew got on board and started the engine, one of the pistons wouldn’t hit a “brick wall” and damage a connecting rod, or something. Another term is simply “oil lock.” On radial engines the oil will tend to drain into the lower cylinders. If enough oil is in there during the compression stroke, the piston will hit a “brick wall.”

If you remember flying on DC-3s, DC-4s, DC-6s DC-7s or Lockheed Constellations (these were “top of the line” airliners at one time), then you might have noticed that the engines never started “right away.” This was because during the starting procedure the crew would count eight blades of rotation before turning on the magneto (“ignition”) switch. Once again, this was to prevent hydrolock. It took only six blades of prop rotation to clear all cylinders on the R-2800 engine that powered the DC-6, but it took eight blades of prop rotation to do the same for the R-3350 that powered the DC-7 - - which had a four-bladed prop. So, just for standardization, eight blades were counted during the starting sequence on ALL of the birds before turning on the magneto switch to provide ignition.

The same hydrolock problem can rear its ugly head on 4-stroke model engines. So, it’s best to rotate the prop through a couple of cycles prior to heating up the glow plug. This would be especially true on 4-strokes that are mounted inverted. You sure don’t want to hit a “brick wall” with the piston, right?

F-89 Driver

When the engine is hydro-locked due to flooding, it's difficult to turn with starter anyway. Usually it would throw the starter off and scratch the spinner. I always turn the props about 5~10 turns at 1/3 throttle before putting on the glow battery, which also helps to distribute the fuel evenly inside the engine for a sure start.

Hi seanychen ! Do you pre-turn your props with hand or the starter ? I have read elsewhere in this forum that an engine can pop prematurely without a glow igniter under the right conditions ! Haven't experienced that myself but worth the precaution............

I pre-turn with my hand slowly a few times by grasping the prop to reduce the hydro-lock. Only really high compression engines like Super Tigre ABC & Rossi can start w/o glow battery. OS and Saito are mostly what I use, and they should not start running w/o the glow battery.

I've heard this story about glow engines firing without the battery connected, a couple of guys who've mentioned it are very well respected so there must be some truth in it. However, in my 40+ years of messing around with various engines I've never experienced it and neither has anyone else that I know so I'd guess the chance of it happening is about as good as being hit by a meteor

Rossi, ST etc aren't what you'd call really high compression...they're about 11:1 where OS and so on are about 9.5:1 which isn't that much different. I run my Enya 60X at 13.5:1 and it definitely never shows any sign of kicking without the battery.