running an engine in reverse

[gearhead2]

I have a small two-stroke 80cc engine. I'm wondering, is it possible to run it in reverse? The way i have to start the engine right now is to get the bike moving(the engine is directly connected to the wheels and it isn't a pull-start, so moving the bike is the only way to get the piston moving) and then apply the gas. So in theory, if i just cranked the engine(got the wheel moving backwards) backwards, wouldn't it start backwards?

 

[Old Bob]

The ignition timing has to be changed, if it sparks at lets say 20 BTDC with CCW rotation then it should spark 20 BTDC with CW rotation, so the magneto needs to be moved to the other side of 0 BTDC from where its at.

And it will run just fine.

 

[Zomby Builder]

For real

I have been thinking of mounting a HT upside down. To change the drive to the right. But I need it to go in reverse to work. How do you adjust the magnito timing

 

[Flapdoodle]

Long ago, you could buy offset keys for adjusting the timing. I had thought about making several for my HT 80 so I could play with the ignition timing.


They are small, so I imagine it would be fairly to make one by hand filing. All it does is turn the magnet so there should be very little force on it. Aluminum may work okay.

 

[gearhead2]

so how exactly would i need to change the magneto? Sorry, i don't really have any experience with engines.

 

[Old Bob]

A key could do it if the advance on the timing isn't more than the amount of material you have to remove on the key. A bracket to move magneto is used also.

 

[Zomby Builder]

W da Huh

I know how to change the timing on a car. Rotate the distributor. But key ?? What key? Pardon my ignorance, but please explain this..

 

[Flapdoodle]

The offset key rotates the magnet just like you do in the distributor.

 

[Zomby Builder]

So is the keyway on the crankshaft, or cam?

 

[Flapdoodle]

The rotating magnet is keyed to the left hand side of the crankshaft. It is doubtful that playing with the key offset could be of help if you want to reverse the rotation, but it is how I would change the timing. I have searched the forum for how many degrees before TDC the factory setting is without success. Anyone here know?

BTW, the smaller the shaft, the more degrees an offset key could do depending on the key size.