10.5 hp engine kicks-back when starting sometimes!

[Bill]

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.)

I got to thinking that I was going to break or injure my hand/arm if I kept starting this engine. I searched the internet for injuries from starting these larger engines and there were in fact quite a few injuries including some broken bones. So I decided to solve this problem by installing an electric start. No more problem now for me...

But I got to thinking about this and why this happens. And could something be done to prevent this? (And the reason I am posting this.) A lot of you on these groups are quite clever, so maybe someone can come up with something...

I think the problem is that the spark is firing right when the piston reaches the top of the stroke or slightly before it reaches the top. Then sometimes this will cause the piston to go backwards instead of forwards. (And it needs to be this way of course to run properly.)

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.

Anyway I thought I would pass this idea along. Maybe some rocket scientist out there could come up with something which would attach between the spark plug and the spark plug wire???

[Don Bruder]

Good plan - Called "variable timing", and used on the Model T, for exactly the same purpose/reason, if I recall rightly. But I'll be dipped if I can tell you what the exact mechanism was.

But it's just plain NOT going to happen by putting something between the plug and the wire - It's something that has to be done at a "lower level".

Most "lawn-mower type" engines fire by way of a coil (or two coils, in the case of a two-cylinder rig) bolted solidly to the block (which means no adjusting of spark advance/retard is possible without major surgery) with a magnet in the flywheel passing under it. And since the flywheel is almost invariably keyed onto the crankshaft to maintain timing, that's also almost impossible to alter without major surgery.

Adjusting spark timing is dead-simple on a car, or other distributor-fed engine, since all it takes is twisting the distributor a bit. Doing it on a coil-and-magnet rig like most small engines is nearly impossible unless the capability was designed in right from the start.

[Sheldon]

You're having the same problem with other engines... so it's not the engines, it's you. Get yourself to a small engine repair shop and ask/ beg someone to instruct you in the proper method for pulling that rope.. Are you left handed?

[AZ Nomad]

Retard the ignition timing by rotating the distributor? Model T's used a buzzerbox to generate high voltage, so I don't know their mechanism exactly.

No, the location where the crank angle is detected (ie: where the points live or where there's a magneto) would have to be turned.

A fixed coil with a magnet on the flywheel would be difficult to modify. Maybe the flywheel or coil has shifted?

Maybe it's experiencing pre-ignition or incredibly late ignition. Replacing the sparkplug might be a good start.

[Steve Barker DLT]

is this only on a hot engine, or on a cold one also? If only on a hot engine, you might try a midgrade fuel. You may be getting some pre-ignition from the shitty fuel we have today.

steve

[ransley]

Maybe the timing is off from Pin Shear

[ransley]

By your lingo you are N. Canadian, I bet its Pin Shear =3D improper timing , a bad or loose Pin on the shaft . Timing as you see and know of is off, find out why , its mechanical. I bet it locked - knocked, a few degrees off on a previous stallout to zero rpm, forcing the pin or something else out of spec. A backfire never should happen, a Backfire is bad timing =3D maybe Pin Shear. But im guessing, and never worked on a motors issue. But I know fact of operation.. I still bet its the Timing Pin-key on the Fly wheel, but a motor pro will know.

[NapalmHeart]

By your lingo you are N. Canadian, I bet its Pin Shear = improper timing , a bad or loose Pin on the shaft . Timing as you see and know of is off, find out why , its mechanical. I bet it locked - knocked, a few degrees off on a previous stallout to zero rpm, forcing the pin or something else out of spec. A backfire never should happen, a Backfire is bad timing = maybe Pin Shear. But im guessing, and never worked on a motors issue. But I know fact of operation.. I still bet its the Timing Pin-key on the Fly wheel, but a motor pro will know.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The flyweights on the mechanical advance could be stuck in an advanced position.

Ken

[Steve Barker DLT]

Mechanical advance? On a single cylinder 10.5 HP?? Ya, oooooooook........

s

[Ann]

My grandfather's Model A pickup had a retard spark lever on the steering column. I Googled to confirm (yes) but didn't wade through the explanation(s).

[Dean Hoffman]

You need to teach that engine some respect. Some use big and bigger hammers. One guy used another way:

Dean

----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----

The #1 Newsgroup Service in the World! >100,000 Newsgroups

---= - Total Privacy via Encryption =---

[Kevin Ricks]

This is how I start a motor, maybe I just learned to do this to avoid kickback I don't know? Pull the rope full travel or as much as possible. Don't short stroke it. Let the starter rope retract quickly, Don't stand there holding the rope handle. On a no start don't start the next pull until the engine has completely stopped turning. If I sense a kickback, I just let go of the handle.

Also the starter catch mechanism may need to be lubricated so that it disengages properly.

Kevin

[Neon John]

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

-- John De Armond See my website for my current email address

[Sheldon]

Kevin Ricks wrote:

It's often more than a mere catch mechanism. With many of the pull start motors sold within the last ten years pulling the rope does not start the motor directly, pulling the rope winds a spring that once a particular pre-set tension is reached the spring releases and that's what rotates the flywheel... so that it rotates at a greater velocity than one can yank a cord by hand ... it's actually tantamont to electric start because pulling the cord essentially loads a starter motor, albeit spring loaded. With these motors the spring is wound with several short partial pulls of the cord and with progressively more pressure... with a little practice one will feel how progressively more pressure is required with each subsequent shorter pull as the spring tension increases and each subsequent pull should be shorter and shorter, it won't be too long before one will sense exactly when the spring will release (guys should be especially good at this sensing when it's approaching the point of no return, if yoose get my drift), if full pulls are made mindlessly the spring will release mid pull (prematurely) so kickback will typically occur, often painful. Read the manual paying careful attention to the section on starting... often manuals are not very clear so it's best to have someone at a small motor repair shop demonstrate. And typically lefties have trouble with pull start motors, not all, but generally, because like most all machine tools they are designed for righties.

[KLS]

I also learned this technique somehow; maybe a friend suggested I try it one time?

Exactly what I do, and works great for my small engines. That first pull is not a yank, it's a slow deliberate pull of the entire rope. Highly recommended.

[terry]

Old auto engines. Started by hand crank. Some had no electric starters at all. We had a

1926 Daimler hearse refitted with a 1938 Bedford (i.e. UK GMC). straight six engine, that had a defective starter AND a weak 1936 battery that had to be started by hand! Ignition off. Turn over engine slowly by hand through compressions of several or all cylinders to draw mixture into cylinders. Retard ignition timing; by the control often mounted on middle of the steering wheel. Pull compression up to near TDC. Ignition on. Pull by hand over TDC (watch your thumb position) and engine should start. Adjust ignition timing and drive off.

[Jerry - OHIO]

Bad points can cause this also.

[Jim]

[....]

good write-up John. facts are always useful.

[HeyBub]

Good point. The lower the octane the higher the volatility. Higher octane gas has a higher ignition point and is harder to detonate.

[Steve Barker DLT]

Very very few recoil starters work this way. In fact, i believe Stihl is the only one doing that on small chainsaws. And they only started that a couple years ago.

s