From: John De Armond
Subject: Re: 10.5 hp engine kicks-back when starting sometimes!
Date: Sat, 26 Jul 2008 10:47:20 -0400
On Fri, 25 Jul 2008 19:44:17 -0700, Don Bruder <firstname.lastname@example.org> wrote:
>In article <6evg09F97h1gU1@mid.individual.net>,
> "Bill" <email@example.com> wrote:
>> I have a 10.5 hp gasoline engine on my wood splitter which sometimes kicks
>> back when I pull the rope to start it. (Just once every few days, but that
>> is once too many times.)
>> This kicks back with a lot of force! And I am pulling with a lot of force as
>> well! Not good. (I've noticed this same problem with smaller engines too,
>> but not so much kick back force, so no problem there.)
>> My idea is to delay the spark just a little for starting. There could be a
>> switch to start an engine which delays the spark. Then once the engine is
>> running, you would flip the switch and it would spark and run like normal.
>> But when starting, kickback would be impossible because it would not spark
>> until the piston was its the way down.
Most, perhaps all modern engines already have electronic start retard built
into the electronic ignition module. (if your engine is old enough to still
have points, all bets are off.)
Start retard can only go so far. Many folks had their arms broken trying to
start Model As even with the manual retard set full retard. Ditto ankles and
old motorcycles with manual retard. I can count myself in the "almost"
category. Which brings me around to my main point.
The problem isn't with the engine. It's with the starting technique. Any
engine will kick back if the crankshaft is turning slowly enough when the
spark fires that it can't make it over TDC before burning gets underway. This
happens when you grab the cord and yank or stomp the kick starter from some
random engine condition without setting things up first. That's why one never
lets that happen.
The technique, developed around the turn of the previous century, is to slowly
rotate the engine until the piston is at top dead center on the power stroke.
That's where the crank suddenly rotates freely a little bit after the
resistance of compression.
After the engine is positioned that way, the cord is retracted (or the kick
starter returned to rest) and the strongest pull you can muster is given. The
engine has almost two complete rotations to store energy in the flywheel
before the compression stroke is encountered.
The result is an easier pull, no chance of kickback and usually, starting on
the first pull. One must be sure to immediately return the starter cord to
the rest position (don't let it fly - the recoil spring and/or rope will
eventually break from that abuse). If you hold onto the cord and the engine
doesn't quite start but fires in reverse, it'll yank the cord out of your hand
rather violently. Blisters and ripped skin can result.
I used to ride and race big single cylinder bikes before electric starters
become available. The "find TDC before cranking" became so second nature that
I now automatically do it even with tiny engines like the one on my weed
whacker. Not chance of kickback there, at least none that matters, but
pulling the cord is sooooo much less effort that way.