can 80cc twostroke run backwards

[FurryOnTheInside]

The key is a 12:30 or 1 o'clock when the magnet is level so that you don't accidentally put the magnet on backwards, surely??
So the easiest thing is to grind a new keyway on the other side of the crank shaft. (EDIT: at 11, or 11:30, NOT 180° opposite!)
Is it possible to do that with the crankcase assembled?

I wouldn't mind having a go at an upside down engine in an upside down frame one day, just for fun.

 

[Frankenstein]

How about we stop asking why, and just do our best to answer. I would think a 2stroke could run backwards fine, but I don't know what changes you might have to make.

The question is fine, and leads to better solutions possibly, for all we know he wants to put it in his front wheel on its side, or modify some go kart frame, another reason could be to put it on a trike but the engine sits too far back or simply no good chain in location on the left side so hijacking the original right side drive may be in the works.

I ask questions all the time and a number of times doing so led to better results for the person simply because it uncovered a detail that enlightened them with a new idea that worked better than their original one would.

 

[Frankenstein]

The key is a 12:30 or 1 o'clock when the magnet is level so that you don't accidentally put the magnet on backwards, surely??
So the easiest thing is to grind a new keyway 180° on the other side of the crank shaft. Is it possible to do that with the crankcase assembled?

I wouldn't mind having a go at an upside down engine in an upside down frame one day, just for fun.

I don't think you need to cut opposite the keyway, timing is so the magnet is so the magnet is just a couple degrees past horizontal so the spark will occur just past TDC, if you cut a keyway at about 11 on the magnet you can flip the magnet over and the drop off should activate the CDI at the right time I think... I'm not totally sure

 

[Street Ryderz]

I don't think you need to cut opposite the keyway, timing is so the magnet is so the magnet is just a couple degrees past horizontal so the spark will occur just past TDC, if you cut a keyway at about 11 on the magnet you can flip the magnet over and the drop off should activate the CDI at the right time I think... I'm not totally sure

The spark occurs well before tdc etheir 18-20 degrees or 23-25 degrees deppending on the rotor cut position.

 

[FurryOnTheInside]

I don't think you need to cut opposite the keyway, timing is so the magnet is so the magnet is just a couple degrees past horizontal so the spark will occur just past TDC, if you cut a keyway at about 11 on the magnet you can flip the magnet over and the drop off should activate the CDI at the right time I think... I'm not totally sure

Okay I am confused lol ignore my previous post.
Um. Cut the crank at 11 o'clock, then just flip the magnet.

 

[Frankenstein]

The spark occurs well before tdc etheir 18-20 degrees or 23-25 degrees deppending on the rotor cut position.

Before TDC? Isn't that called knock or am I over hallucinating?

 

[Street Ryderz]

Okay I am confused lol ignore my previous post.
Um. Cut the crank at 11 o'clock, then just flip the magnet.

There you go!As Butre said it would easy with an old Manic Mechanic type rotor set up just on the flip side.They used to use a conicle washer made from aluminum and pres fit into the same cut in the rotor so you could retard or advance I geuss the timming.

 

[Street Ryderz]

Before TDC? Isn't that called knock or am I over hallucinating?

NO for real the latter ones arn't as bad but here's the epa tag showing the timming on a older engine.

 

[GreenMantis]

It takes a little bit of time for the flame front to fully propagate in the combustion chamber, so the spark has to be triggered a few degrees BTDC to compensate. Knock is when the ignition is too far advanced for (or for the volume of) the fuel you are using, higher octane burns slower, so it's less likely to knock. It means the flame front is propagating too soon, and colliding with the still up coming piston, and it's really bad for the engine. If the spark triggered at TDC, the flame front would barely catch up to the piston, and you make no horsepower.

 

[FurryOnTheInside]

It takes a little bit of time for the flame front to fully propagate in the combustion chamber, so the spark has to be triggered a few degrees BTDC to compensate. Knock is when the ignition is too far advanced for (or for the volume of) the fuel you are using, higher octane burns slower, so it's less likely to knock. It means the flame front is propagating too soon, and colliding with the still up coming piston, and it's really bad for the engine. If the spark triggered at TDC, the flame front would barely catch up to the piston, and you make no horsepower.

What are you quoting me for?