Old timer's engine question

[garyahouse]

I know, this isn't an FJR question, but it is DEFINITELY a technical one. Can a two stroke engine run backwards? Many years ago, I owned a late 70's Rupp liquid cooled 440. Here's random pic from Photobucket of the pistons, though I'm not sure if this is the same exact year (or engine).

I was taking a short rest while out tearing up the ice late one beautiful crisp, moon-lit night. I went to start the engine and it kicked back, ripping the pull cord out of my right hand. What took place next was like a bad dream. The engine rocketed up to the highest rpm level I'd ever heard. It just sat there at a steady, even, stratospheric RPM. It scared me pretty good. I reached down and shut off the key.

No change.

I turned it on and then off again, just to be sure I'd actually shut it off.

No change.

I stood there wondering what to do. I hit the choke, which normally will force the engine to stall.

No change.

I lifted the cowl and pulled the rubber boots off of the spark plugs.

No change.

I stood back, wondering what to do. My mind was racing. Was I dreaming? Was this happening? I began asking myself some questions... if the engine is running so fast, why isn't the sled rocketing across the ice? It does after all have a centrifugal clutch, does it not? Is it running in reverse? Why won't it shut off? I was used to my 1974 Monte Carlo running and "deiselling" momentarily after I shut it off, but THIS... this was insane.

Then, finally, it just quit. That whole ordeal lasted for perhaps 30 seconds, it's hard to remember exactly.

It was dead silent out on the ice, except for the crackling of the metal bits under the cowl as the engine began cooling off. Jut at that moment, and this is the honest truth, I heard a loud cracking noise. At first I thought it was the snowmobile, but no, that was the ice beneath me. I'd been on the ice many times and recognized that sound. I looked down at the ice, and couldn't see much as it was too dark. I imagined myself plunging into the abyss. It was like my own personal nightmare, something ya might see in a horror movie. I mean, how many strange, unbelievable things could happen at one time?

The snowmobile was fairly new, and though I didn't know what had just happened, I KNEW I didn't want to stand around on the ice for one more second, so I put the spark plug wires back on, closed the cowl, hopped on the sled, flipped the key on, and pulled the cord. It started on the first pull, and ran perfectly as I headed for shore.

But I've never figured out just what happened to that motor that night. It never happened again, and the engine seemed to run just fine afterwards.

Anybody ever have something like this happen?

Gary

darksider #44

 

[ionbeam]

Yes, some older 2-Smoke engines can run backwards. Sometimes it is because of starter kick-back and sometimes it is timing related. A 2-stroke engine that has excessively retarded timing can run backwards on a 'normal' start. I have no experience with a pull start engine like yours, but I have seen a couple of kick start bikes run backwards. Some brands would readily run backwards if anything went wrong during the kick start. I don't think it's possible for a rotary valve 2-stroke to run backwards.

Antes Edit: Post below is the same but different, between the two it's pretty well covered.

 

[Fred W]

Gary, yeah two stroke engines can, and will readily, run backwards. Especially those with a points type ignition, which will also work in both directions.

But I cannot explain why it revved way up or any of the other crazy symptoms, like the inability to kill the ignition or choke it out. The intake would still work the same regardless of crankshaft direction.

I see ionbeam beat me to it (again).

 

[beemerdons]

Did you guys have Cox Model Airplanes when you were kids? As the .049 engine got some hours on it, about half the time it would fire up in reverse:

• You may also notice that, when your engine starts, the propeller is pushing wind forward instead of backwards! Sometimes, when starting by hand, the engine backfires and continues to run in the reverse direction. Reed valve engines will run equally well forward or backwards. Just pinch the fuel line and the engine will stop running. Repeat starting procedure.

 

[Pterodactyl]

Some current 2 stroke snowmachines reverse the engine in lieu of using a reverse gear. Works well

 

[dcarver]

Oh yeah they can. Had a Suzuki 90 with dead loss ignition and lightened flywheel.. I would purposely kick start it juuuuust right to get it running backwards... Then ask if anyone wanted to ride it.. Those in the know would encourage the target to really rev here up and make a 'race' start. The results still make mr grin, as the tank was

Raised in the rear, causing many a soprano voiced young men!

 

[CAJW]

A buddy's Hodaka Wombat back in the day did the same, it was a hoot trying to ride it backwards!

 

[lnewlf]

once had a Yammie DT400 rat bike with a Hooker expansion chamber-sounded like a hundred 12 gauges going off.

In front of some friends I kicked it once and it popped kind of funny...

kicked it again and it lit off...

revved the hell out of it and dropped the clutch planning on throwing an impressive roost for my buds...

went ass over teakettle over the handlebars..

damn thing was running backwards...

 

[timk]

Yamaha 2stroke golf carts all run backwards. The starter spins in both directions.

 

[Redfish Hunter]

I have heard stories of old Detroit Diesel engines running backwards. Detroit Diesel engines were two strokes, the only two stroke diesel engines I ever heard of. If they sputtered and popped on startup and wound up spinning backwards enough to fire and would run backwards. The part I never understood was that in every story I heard about these old Detroits running backwards they all revved really high. They would spin up beyond the normal RPM and would destroy themselves. The normal shut off method would not work and there would not be time to try anything else before they failed internally.

 

[J Paul]

The DDA 2 stroke engines would run backwards-I have personally seen it on old air compressors-they don't last long as the oil pump is also running backwards and the blower rather than supplying scavenging air is now a vacuum pump sucking exhaust. On a bike note the Scott water cooled 2 strokes could be reversed by bringing it to a slow idle and then going full advance on the timing at the right time.This was a sales feature when running a sidecar. Jeff

 

[FJRay]

I have worked on a lot of Detroit diesels and yes they are two strokes but I don't see how one could run backwards. The blower is for exhaust scavenging only and if it was turning the wrong direction it wouldn't run.It used to be a common problem if the Quill shaft broke there was no drive to the blower so it wouldn't run. It's a pain in the ass to change.

You are correct that they will run away on you if they have bad blower seals or some other way for fuel to get in the cylinders. The only way to get them to stop is shut off the air. Some had an air shutter that was spring operated so you could pull a cable and it would slam shut and stop the engine. The other way was to have pieces of plywood with rubber gaskets and you had to hold them on the ends of the air box until it died. It's not very comfortable sitting next to a screaming Detroit in the bilge of a boat.

The 71 series was only designed to turn 1700 RPM so when they spin up tight bad things happen. In landing craft they turned them up tighter but they were considered disposable. You still see them once in awhile with a battle govenor on them that needs to be reworked

There are a number of other two stroke diesels but that's a different story.

 

[Niehart]

Just a few years ago [okay maybe more that a few] my brother Bill and I were racing in the the Sugarloafer's Motorcycle Club's Cherry Creek National Hare and Hounds race. At that time, you had to run to your bike, kick start and go. The racier between Bill and I fired his bike, dropped the clutch and disappeared behind us. i don't remember what make or model it was but it was pretty funny at the time.

 

[Redfish Hunter]

FJRay, go to Google, start typing in Detroit Diesel and you will see plenty of examples of them running backwards. My Dad saw this himself back in the '60s with Detroits that were already old then. The ones he described were in old drag lines and cherry pickers of that era. I have no idea what series they were at that time.

Regarding Detroits in boat bilges, I have some experience crawling around 53, 71, and 92 series Detroits. Nothing like being the smallest and youngest one and therefore the best suited to pulling wires in tight, oily, greasy, hot bilges. I have never personally experienced them running backwards.

I have talked to some old captains who described the process of "Reversing the Engine" in old shrimp and oyster boats. I do not recall the bygone brand of engines they used. These early engines had no reverse gears in the transmission. The fuel flow was shut off to each individual cylinder to slow the engine and With Perfect Timing! the fuel was turned back on to cause the motor to turn backwards. This effectively allowed "reverse" for docking maneuvers. I cannot even imagine the crashes I would have caused had I been either the skipper or the deckhand.

 

[Queensland Ken]

Yep, they sure can.

Had a Bultaco and went over the bars when I gave it some gas.

 

[Donal]

Messerschmitt bubble cars were set up to reverse the engine to get the car to go backwards.......... Wiki link

Engine and transmission[edit]The KR200 ran on a 191 cc (11.7 cu in) Fichtel & Sachs air-cooled single cylinder two-stroke engine positioned in front of the rear wheel,[6] just behind the passenger's seat.[3] The engine had two sets of contact breaker points and, to reverse, the engine was stopped and then restarted, going backwards. This was effected by pushing the key further in the ignition switch than normal, whether intentionally or not. One result of this was that the KR200's sequential, positive-stop transmission provided the car with the same four gear ratios available in reverse as in forward movement.[6]

 

[garyahouse]

Thanks for the feedback guys. At least I know that my experience wasn't an isolated experience. The engine was running at such an unbelievably high rpm, I was sure it was going to destroy itself. I'm thinking that the combustion chambers must have gotten loaded up with deposits that glowed hot enough to cause ignition without the need for the spark plugs. As I said, the engine was fairly new. It never did that before or after that single incident. It was REALLY strange.

Everybody has a story or two that are just about unbelievable. That was the night when all the planets were aligned in my world I guess. Another interesting item from that experience was that the snowmobile didn't move. It just sat there. Apparently the clutch was designed to only work in one direction. None of it makes sense to me.

Gary

 

[fljab]

I have heard stories of old Detroit Diesel engines running backwards. Detroit Diesel engines were two strokes, the only two stroke diesel engines I ever heard of. <snip>

My first "big" job when I turned 18 was in a factory that built Detroit Diesels. I personally didn't work on them but did sweep the line at night.

We also made Ford I beams (for the trucks), pitman arms, thermostat housings, and other assorted bits. All gone now like much of the industry that fed the auto industry. General Products Corp, Jackson, Michigan.