From: John De Armond Newsgroups: alt.home.repair,misc.rural Subject: Re: 10.5 hp engine kicks-back when starting sometimes! Date: Sat, 26 Jul 2008 10:47:20 -0400 Message-ID: <oadm84ljpq25kqv8dg06vi9t0uffs2rs6q@4ax.com> On Fri, 25 Jul 2008 19:44:17 -0700, Don Bruder <dakidd@sonic.net> wrote: >In article <6evg09F97h1gU1@mid.individual.net>, > "Bill" <billnomailnospamx@yahoo.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. John |