Giorgio, yes most hand starters have a sprag clutch or one way bearing. However with a backfire it can injure you. When starting a Model T Ford they say to tuck the thumb away and not wrap around for risk of breaking your thumb.
On a kick starter they added a gear reduction and it locks in, making a backfire worse. With a hand starters it is usually just leverage advantage.
just in the moment i remembered, i have started also a tractor with hand cranc, but more than 35 years ago…it was the tractor of a friend where we stay for short time on his farm, and i hav e used the tractor two or three times… it was a güldner tractor with hatz diesel one cylinder motor, with two big fly wheels on every side, there was also the handle for cranking…with a claw to avoid a kick back…bevore starting it needs something like a starter cartridge, screwed in the cylinder head, what becomes glowing with the motor compression…
There were some American one cylinder tractors. I don’t remember ever seeing one. Maybe at the old engine shows and I didn’t know what I was looking at. Had a friend who restored a John Deere B. Looked like brand new. He just took it to shows. No work. Video of starting one.
Tone, l got nothing more to say to you but that you got too much fun 
Kick back is not at all pleasant… happens sometimes on the rope start BCS hay cutter too. If you knot the rope around your wrist and this happens, you are in for a real bad day…
Reminds me of a story l heared from my father in law. One day, he was at the bar with some friends, one of them drove there with a Tomo Vinkovič, similar to myne. They were rope start mostly at the time. When you got used to them, they were not hard to start. But at that time, there were some Bosnian road workers next to the bar. The tractor owner started placing bets, who can and who cant start the tractor. All the locals culd do it, with one hand. But the road workers got tossed and thrown around fron kickbacks like litle children. The guys drunk out a hell of a lot of bets, before the road workers figured out the tractor owner wound the rope the right way for the locals, and backwards for the poor Bosnians
Ai ai auw, I just threw away my handcrank for the Lister. I tried it a few times but the kickback can break a wrist (my wrists are not to big). No work, no money, no fun
Giorgio, you might be interested, yesterday I dismantled a lombardini 490 engine, here is a picture of the engine head, you can see the depth of the compression space, this engine should have a cr 1:6 or 1:7, I intend to increase the cr to 1:14, cut I will put one cooling rib on the head and thus lower the head by 10 mm, … I will report.
In the evening, when it gets dark, I take some time for this project, … well, let me describe the thing, it’s a Bertolini 490 cc lawnmower engine, the lawnmower was intended for waste, so the price was a good 200 Euros. I will restore the vital parts, this means changing the piston rings, grinding the valves, increasing the compression ratio, I am interested in how much power this wood gas engine will develop, I will do the measurements with the generator. Theoretically, I should get somewhere around 5 kW at 2000 rpm, if that works, I know I’m on the right track.
Well, let me support the above statement with numbers, the lap 490 engine has 12 hp at 3000 rpm when running on gasoline, or about 9.4 hp at 2000 rpm, if I calculate the power based on the torque (33Nm) at these speeds. A high-compression gasoline engine would have the ability to reach up to 50 Nm of torque and a power of 14.2 hp (10.5 kW) at 2000 rpm, so 5 kW on wood gas can be realistically expected.
Good Morning Tone,
May I suggest instead you target for this engine to operate at 2400-2800 RPM??
The concern is connecting rod self-lubricating.
I am assuming it had no oil pump pressure suppling to the eccentric spinning connecting rod big end.
Just splash lubricated this is the highest wearing weak point on all single cylinder engines.
Under a high pressure loading you combat this with more down into oil pulling up dipping events.
Regards
Steve Unruh
Im a little worried about that valve, I think you need to front face it completely. Remember if everything is working properly that valve will rotate around just a smidge at least at high rpm when the valve spring looses control and cant keep up with the speed of the valve opening and closeing (valve float)
Wow, Tone. Do you have trouble walking with that set of balls? 10mm is a man size cut on that head. How did you determine valve clearance before you decided on how much you could take off. Anyway, as usual, impressive. Angels go where wise men fear to tread.
I am very interested. I hope the starter motor will be strong enough? Also will the connecting rod bearing have a reasonable life?
Rindert
Rindert, this is a rope start engine talk about a big set of balls…
I tried to draw a sketch of the problem here, but I hope it’s fixed, otherwise this engine spins at 3000 rpm at most
tone, thanks for nice foto documentation how you fix the motorhead on the turner…
yesterday are arrived our new pocket tractors, we brought them up with the horse to our house in the mountains ,the work lasts more than 7 hours to bring all up here, finished at 4 o`clock in the morning…cold water shower restores the forces, but my son and i were really cooked…
Thanks GiorgioP,
I now know ACME actually means something significant, real. This name had been used decades here in the U.S. as children’s cartoons Do-All mechanical systems.
Your rotating external shaft looks to be the half speed camshaft end. Can be used as a slower speed accessory drive point.
Regards
Steve Unruh
Where the coyote buys all explosives and stuff for catching the roadrunner? 
Giorgio, now you have a serious machine, the Acme SAM 550 is probably the predecessor of the al 550 and the unmarked Lombardini is probably the predecessor of the la 490, 500 cc is a solid volume that will develop quite good power on wood. Lombardini probably has what you are asking about, a drive for lower power or for starting, there is also a centrifugal regulator. Engine 500 cc it already has good power, also for driving the generator and doing agricultural work .ACME engines
Intermotor engines
tone , thanks for the informations…the yellow engine-lombardini motor- has a reduction for the spark plug thread in the motorhead, made from brass, so the actual spark plug thread has small diameter…maybee they have made because of consumption of the original thread in the motorhead…
do you know such thread reductions exist to buy somewhere or is selfmade??
interested what comes out with your reduction of motorhead …will the ignition system have enough power than to produce the spark…? (interesting for my eventual diesel conversion…)
