rclement

My Feedback: (1)

One of the guys at the field yesterday was working on another guys engine and I noticed as he was starting it up that he was cranking it backwards. I asked him why he was doing it like that and he said that he always starts them backwards. (it was a Saito 4 stroke)
Question is, what's the point of doing that?

Hobbsy

My Feedback: (102)

Because it is a very easy way to start almost any engine especially big ones, roll it backwards a little rich and it will kick forward and start every time after you have the touch.

Dr1Driver

Cranking an engine backwards bounces the piston against compression rather than pulling it through compression. It's easier on high compression and 4 stroke engines. If the mix is right, it will start the engine reliably.

Dr.1

bkdavy

My Feedback: (1)

I was taught that flipping backwards also reduces the possibility of damaging an engine that might be flooded. Forcing the engine through the compression stroke in the forward direction if there is too much liquid in the cylinder can lead to bent connecting rods, cranks or worse. A flooded engine will start and run backwards. I can then get it to reverse direction or stall by dropping the throttle.

Brad

RaceCity

A flooded motor doesn't know which way it's turning if it hits a hydraulic lock. CW or CCW...it doesn't help anything. Moreover, once started the motor doesn't care how it got it that way.

The whole "bounce" start or "backflip" thing was in reality, a safety technique. Particularly with a 4 stroke, it was reasoned that the hand would be well away from the prop as the energy from a brisk back flip carried the motor backwards into compression where it would (hopefully) fire and take off in the proper direction.

There's a variety of techniques for hand starting. Any method that gets the motor started and leaves no body parts lying about is a good technique.

'Race

Dr1Driver

Race, rather than pulling the engine THROUGH compression (i.e., over TDC), the backwards flip brings the piston up AGAINST compression. The backwards flip does NOT go OVER TDC. If the engine is flooded, the piston will simply stop short of doing damage. The damage occurs when a flooded engine is FORCED OVER TDC, thereby pushing the piston against an incompressible fluid.

Dr.1

djlyon

While most start their pylon engines with an electric starter I bounce mine backwards off the compression with a chicken stick. First flip starts. I hand start (chicken stick)all my engines 2 or 4 stroke. Forward or backward depends on the state of the prime and often the engine. I resort to an electric starter only on occasion of difficulty in getting the fuel up from the tank or a hot engine that's soft on compression. A flooded engine gets back flipped until it starts.

Denis

B.L.E.

On a four stroke engine, you get the engine primed pretty wet, close the throttle to idle, light the glow plug, and then spin the engine backwards against the compression. The engine kicks back in the forward direction, has enough momentum to coast through the exhaust stroke, then the intake stroke, but because the throttle is almost closed, very little air enters the cylinder and at the end of the intake stroke, there is a partial vacuum in the cylinder as the intake valve closes and the compression stroke starts. Instead of resisting the compression, the vacuum actually sucks the piston up the cylinder until the piston is a considerable way up the bore and there is very little actual compression. Because there is very little effective compression, the fuel mixture does not ignite until the piston is nearly at the top of the stroke as the engine idles.

When using an electric starter, close the throttle to idle and then back the engine up as far as it will go before using the starter. The idea is to get a running start not just on the compression stroke but also on the intake stroke. The faster the engine is turning during the intake stroke, the higher the vacuum in the cylinder will be and the easier the compression stroke will be. Some people get the engine spinning with the throttle completely closed and then have someone open the throttle to idle while the starter is spinning the engine. This works very well but requires a second person.