When is Reverse Forward?

[Egon]

Airplanes may also have counter rotating engines or at least propellers.

Back in another time there were many small engines that would run in either direction. The railway cars that Track men used usually had this type of engine as well as many small boats.

 

[Predator]

I am not an engine expert, but I do know my way around one. I understand how it could run backwards, and how nothing good could come of exhaust going into the airbox. I also understand why you would want to change the oil after running it backwards and throwing all the crud the filter catches back into the oil pan. But I do have a question: Do you really think running an engine for 5 or 10 seconds with no oil pressure would trash it? I could understand the bearings and everything drying out after maybe 30 seconds, but will the damage be that severe in just a few seconds?

 

[tommu56]

my polaris sled runs backwards for reverse, hit the button, sled almost dies, then fires in reverse. of course it is a two stroke, but i never have had exhaust comin out the airbox,,,,,,,haha

maybe we have found somethin here,,,,fillin the fuel tank for free??!!!!!!

The reed valves would keep the flow in the correct direction no matter wich way it was turning.

tom

 

[Stimw]

They run small and big block Chevy and Ford engines "Left Hand" in boats all the time. All it takes for them is a LH starter, camshaft, distributor and oil pump.

 

[john_bud]

I am not an engine expert, but I do know my way around one. I understand how it could run backwards, and how nothing good could come of exhaust going into the airbox. I also understand why you would want to change the oil after running it backwards and throwing all the crud the filter catches back into the oil pan. But I do have a question: Do you really think running an engine for 5 or 10 seconds with no oil pressure would trash it? I could understand the bearings and everything drying out after maybe 30 seconds, but will the damage be that severe in just a few seconds?

The answer is a definite "it depends". Running at idle and no load for a few seconds, probably no damage. If you reversed due to lugging it down with super high loads and then continued to "give 'er heck" at 100+% load, then maybe to probably. Certainly you will do damage to the bearings, crank and rods. How much and how severe is the question as the oil film will dissipate pretty quick under full load. Typically, this happens when the user is operating at low throttle and then exceeds the torque capacity of th engine. The governor can't respond as the lever won't let it and the engine quickly stops. In the case of HST transmissions the power to lift the relief and hold it open just isn't there at low rpms and the engine has no choice but to stop. If you are lucky, it just stops. If you are unlucky it reverses.

NASCAR engines are pretty high strung beasties and making one go without oil at 9000 rpm for 2-3 seconds will result in sudden engine death syndrome. I also think that the valve clearance in them goes negative when reversed due to the valve train loosness going the wrong direction, resulting in the pistons spanking the valves. Not positive on that one.

Your best bet is to never lug down an engine so the load stalls it. If you are at PTO speed and the engine drops to 1/2 pto speed due to the load --> back off and take smaller bites etc. Your engine will thank you for it with thousands of hours of joyful labor. If you are at 1/2 throttle and the engine starts to lug down, you probably don't have time to respond before it dies. (that's a hint...)

jb

 

[Ray_Fort_White]

Back in the 60's while in Viet Nam, I spent a few days on an old sea-going tug. It had a small gas engine that ran an air-compressor. The compressed air was used for a pneumatic starter on each engine. When the bridge signaled the engine tender for reverse he would shut down that engine, move a lever controling the air and would crank the engine up in reverse.

The engines were open crankcase units that only ran a few hundred RPM. If a cylinder wasn't firing they could remove it and work on it and still use the engine.

The crew was Philapino. They didn't carry fresh water. They drank beer all day and hard stuff at night. They had sailed that rust bucket to Viet nam and probably sailed it back when their contract was up. I went up river with them pulling ammo barges going to the 9th Division Infantry. Ahhh, the good old days.

That engine seemed to run darned good backwards.

 

[paparammer]

Decades ago (early 60's) my uncle had a Mercury outboard (recollection says 60HP) that had no Neutral, i.e was direct drive. To go forward, you started by pressing the starter button on top of the shift lever and pushing lever forward. To reverse, you pulled the shift left back to what would be neutral, the engine stopped. You then pulled it slightly to the rear and pushed the starter button again and the motor was then going in reverse. Only got to drive it once as he lived on the opposite coast but did make holding a position difficult in a wind or current. It didn't seem to catch on, whatever the reason Mercury had for trying it.

 

[Heywood Jannockitov]

Remember the old beaters we all used to drive at one time or another, when you would shut them off and they would "run on" or "diesel" for awhile?
Chances are they were running backwards as well.

When the old GMC pickup I had would run on, I would stop it by dumping the clutch while in 4th gear with my foot on the brake. Guess what? The truck would lurch backwards.

 

[SPYDERLK]

NASCAR engines are pretty high strung beasties and making one go without oil at 9000 rpm for 2-3 seconds will result in sudden engine death syndrome. I also think that the valve clearance in them goes negative when reversed due to the valve train loosness going the wrong direction, [[[resulting in the pistons spanking the valves]]]. Not positive on that one.
jb

Tha would be due to valve float owing to steeper cam ramps present on the normal lift side.
larry

 

[john_bud]

Tha would be due to valve float owing to steeper cam ramps present on the normal lift side.
larry

Ahhhh.... that does make sense. I probably "knew that" but didn't think about it enough to realize it! Oh well, at least I was close, can't be right all the time. Thanks for the info.

jb