My friend asks a question

In addition to the problems already mentioned there is the issue of the oil pump running backwards and not lubing the engine. I had a few bikes where the gas & oil went into separate tanks and a mechanical pump fed the oil to the engine. Art

I know even less of two stroke diesels than diesels in general. Can you explain why a blower is necessary? Could you not build the engine just like a gasoline one, except with a fuel injector in the cylinder head?

Is it about lubrication? You'd need to inject the lubrication oil into the intake air, but that can't be too difficult.

I understand that if you want to have the crank case oil filled, and avoid having lubrication oil in the exhaust, you certainly need a blower.

I seem to recall the old John Deere 2 cylinder engines that were being run on Diesel and were hot from being worked hard would sometimes run backwards when you shut them down.

Paul

Since it is 2 stroke there is only the compression and power stroke. a blower is necessary to blow the exhaust out of the cylinder and blow fresh air in when the piston drops below the ports.

Eng> > > And on a 2 stroke diesel a blower of some sort is not only an

No valves, just ports, you need a blower to clear the exhaust. No exhaust stroke after all and crankcase induction is a nogo with monster engines and multiple cylinders. These are not Lawnboys, they have a pressure lube system and probably a dry sump. Since they turn so slowly, they can have longer stroke/bore ratios than automotive diesels, adds to the efficiency. Probably closer to Diesel's original engine concept than a lot of the engines they call "diesel" these days. archive.org has some older books for download on diesels. Not a lot has changed to the basics.

Stan

snipped-for-privacy@g27g2000pro.googlegroups.com...

I had a neighbor with a story about that. For a while he had a boat with such a motor. He and a friend were out fishing, and had to navigate through some logs, or something. So there was a lot of backing- and forthing. They got out into the open river, and Lee made some comment about being happy they threaded their way through.

To which his friend replied "yup. And boy, the way the motor kept stalling had my heart in my throat, too".

It depends on the engine. Most model airplane two strokes (which is what I'm mostly familiar with) have crank-timed crankcase induction. So while the exhaust and transfer (from crankcase to cylinder) work the same forward and back, the intake into the crankcase is "one way" (some hot motors will run -- poorly -- backwards).

There are some itty-bitty reed valve engines that run quite happily in either direction -- in fact, a Cox 049 reedie will generally start the opposite of the direction you flip it, when you're trying to flip it forward. Flipping it backward, it generally starts in the same direction as the flip. Go figure.

Note that model airplane engines are mostly glow ignition -- that's a "sorta diesel" cycle where the ignition timing doesn't care about crank rotation.

Most chainsaw and weed-whacker engines, on the other hand, have a piston- timed crankcase induction (the piston uncovers a port between carburetor and case). These have less ultimate power potential than a crank-timed engine, but they're simpler to make. As mentioned elsewhere, even though the induction, transfer, and exhaust timing is the same forward and reverse, the spark will be off.

Scooter engines are probably mostly like chainsaw engines (if not entirely so). Large motorcycle two strokes often use reed valve crankcase induction, on the same principal as the little reedies for model airplanes, but considerably different mechanics. They would still run crappily, if at all, in reverse, because of spark timing.

Bigger engines start doing wacky (to me) things like running two pistons in one cylinder with offset cranks (Junkers Jumo), or running ports in the cylinder and valves in the head (I think it's usually transfer ports and exhaust valves), or other creative means of improving gas flow. Most of these are also going to run considerably less well in the reverse direction.

But my entire experience with bigger engines than weed whacker engines runs to reading Wikipedia pages.

So, the bottom line is: maybe it will, maybe it won't, and either way a motorcycle is a stable system moving forward but not back -- so you'd just fall off anyway.

If you are really dextrous you can catch them with the "spark lever" just as they come up on compression that last time and they bounce right back the other way.

They were also used in Maine where I saw one converted to a stationary engine and used to power an old fellow's boat building shop.

-- John B.

Is anyone familiar with the old drag-saws used to buck up logs. I remember the engine could be started either way, depending on the way you spun the flywheel.

Paul

Or the motor buggy used by maintenance crews on the railway? Gerry :-)} London, Canada

(...)

Ah! That explains why my long-lost 0.049 Cox 'Vette always ran backwards! The recoil starter rotated the wheels forward.

--Winston