[7c Wanna Be]

I was just wondering if Ski-doo comes out with a 4 stroke sled would they be able to use their electronic reverse or is the vavle train on a 4 stroke not capable of running backward.
Sorry guys but I'm bored.Maybe I'll go wipe down my sled.

 

[Rocketman]

I don't think a 4 stroke can run in reverse without damage...not sure though. I suspect that is one thing holding Doo's 4 stroke back.

 

[mxz7]

I can't see a 4 stroker running in reverse.Unless Rotax can figure out how to make an oil pump,pump in reverse.

 

[Wolfman]

RER will not work with a four stroke engine.  The engine would then start to intake air from the exhaust, and then exhaust it out the carbs.

 

[paul yarek]

wolfman,
 back when i was an ankle biter there was a guy with a late 50's honda. this guy would sit on the bike while his buddies pushed him backwards and it started, then the guy rode sitting backwards on the bike but facing his direction of travel.
 now i am not saying the new doo 4 stroke will acompany RER but i have seen a few 4 strokes run backwards.

 

[Wolfman]

Not discounting what you've seen, but I would have to see it to believe it.  Drawing on my mental image on the mechanics of a 4 stroke engine, I cannot see how it would be able to get fuel to run in reverse.

 

[paul yarek]

wolfy,
 i have seen lots of diesels run backwards also. ask a few guys on this site this was discussed awhile ago and i was not the only one to see a 4 stroke do that. believe me i wanted to post it and i hovered around the post until i seen a few others put the topic up.

 

[GC motorsports]

think of it like this.  4 strokes to the engine are starting at top dead center, 1)piston goes down, intake valves open, suck in air and fuel, 2) piston goes up, compression stroke then fire from plug 3) piston goes down, power stroke 4) piston goes up exhaust valves open and pushes exhaust out, then back to top dead center and stroke 1 again.

Now backwards  4) exhaust stroke, 3) power stroke, 2) compression stroke, and 1) intake stroke then back to 4 again

With the exhaust stroke coming immediately after the intake stroke, that would empty the cylinder of fuel leave nothing to combust and burn in strokes 3 and 2.

I honestly dont see how it would work unless the crank could turn backwards and the valve train would still be going forward.  If that happened it would be the same and workable.  Not saying it cant be done, it would be tough.   Plus the point about the oil pump pumping backwards would have to be addressed also.

 

[paul yarek]

hey i am not going to concern myself with those that do or don't believe me. because my motto is believe none of what you hear since you can only believe half of what you see.

 

[mxz7]

Intake,compression,power,exaust.It does not seem possible,but my brothers little 1972 Harley 90 ran backwards.The same way Paul Y explained.

 

[Wolfman]

Paul, Bringing diesels into the equation changes the rules.  They run direct (or prechamber) injection, and the cylinder is basically a big air compressor.  The old Detroit V engines were famous for running backwards.  As for having fuel mixed outside the cylinder and then drawn in, this is where I'm drawing a huge question mark.  The machanics of gasoline powered 4 cycle engines do not support running in reverse.  I *can* understand how a 2 stroke would be easily capable of running backwards.  The piston itself is the "valve" here, and it can still draw fuel from the intake side of the port, and exhaust it out as normal.

 

[GC motorsports]

The only reason I can think of that it would work would be back then, engines were not that good at exchanging the gasses in the cylinder and there was enough of the residual left behind after the exhaust stroke there was something left to burn.  However, that was then and this is now.  With generally multiple intake and exhaust valves engines are very very good at getting out the old and bringing in the new.  That is one of the reasons that we get so much more power out of engines today.

 

[ZRT800]

98% sure it won't work.  Yes they can run backwards, as said above the old bikes could.  But, from what I understand, RER slows the engine down, then spins it backwards.  I think you'd be looking at a lot of bent parts if you did that with a 4 stroke!!!!

 

[Wolfman]

Not really.  If they found a way to keep up oil pressure in "reverse," as well as found a way to supply fuel, and of course keep the timing chain (or belt) tension constant, then there really isn't much difference in which direction the engine will rotate.  The pistons will pump air, and valves will open and close with out any trouble.

 

[mxz7]

If you get right down to it,theoreticlly it cant happen due to the vavletrain.I wouldnt look for rer on a 4 stroke.If someone does figure it out and gets it on the market, he will probably win the Nobel Peace Prize.lol

 

[Golsovia]

A typical modern 4 stroke could not run in reverse no way - no how. However, I understand that there is technology being pursued which may replace the cam, that being electronically operated valves. I don't know what the status of these are but if they can make them work and then join that with electronic fuel injection, I see no reason why they couldn't run a 4-stroke in reverse. But then again, it would seem at this point in the game to be a lot simpler to use a mechanical transmission to accomplish reverse for the time being.