Running China Motor backwards ?? Successfully ??

[BigBlue]

All I ended up doing was removing the magneto and the woodruff key , then finding TDC working back to about 15 - 20 deg BTDC to find the position of the magneto when it fires for NORMAL engine rotation.

So then I moved the crank to the New 15 -20 deg BTDC for the new rotation and put the magneto on , remembering that the engine now spins the other way.

I am curious if you filed a new keyway in the magneto to change the new 15- 20 deg BTDC setting.

Chris
AKA: BigBlue

 

[ToyTruck]

Just removed the woodruff key

Marked the end of the crank shaft to be abled to reference the cranks position
With clutch engaged , rolled the wheel to get the crank at the new BDC firing position
Then held the magneto at its new spark firing position and tightened it up and it held ...

I was planning on a little fine tuning then I was going to loctite it ... But the motor died

Everything was still tight when I pulled it all apart to fault find the cause of motor lockup

 

[Fabian]

Fabian , do you really think port timing could affect anything ??

I'm not qualified to give a researched answer as i haven't studied the subject, but my suspicion is that the port opening and closing timing may very well have direction of crankshaft rotation taken into account.

I'm hoping that there are some other people on here who are qualified to answer this question, because it's sparked my curiosity.

 

[Fabian]

I should add that I had oil dripping of all over the motor ....

That's typical of these engines running high oil fuel ratios. I'm running and always have run my Chinese bicycle engines at 20:1 (for many reasons that i have gone through before) and they have all leaked oil from just about every corner of the engine; new or old.

These engines are like the WW2 air cooled radial's and there used to be a commonly known phrase back then:

"If it's not leaking oil,,, there ain't any"

Be thankful that your engine is leaking oil. It's a visual sign that you remembered to add oil to the fuel container. The day the engine stops leaking oil, you'll have a serious problem.

 

[ToyTruck]

Wouldn't reversing the engine rotation have the same effect as swapping the jug to get carb at front

I am not suggesting that I do it !

Just that as my motor reverses the motion of the piston , the same as a jug swap on a normal rotation motor ???

 

[Fabian]

I'm really hoping that someone with a strong technical engineering background can weigh in on this discussion and discuss the subject including the maths to make sense of it.

 

[ToyTruck]

I'm really hoping that someone with a strong technical engineering background can weigh in on this discussion and discuss the subject including the maths to make sense of it.

Haha , meanwhile , I will just replace the cooked bearing
Get it going again ..... And ride till it does it again lol

 

[keatonx]

I'm not qualified to give a researched answer as i haven't studied the subject, but my suspicion is that the port opening and closing timing may very well have direction of crankshaft rotation taken into account.

I'm hoping that there are some other people on here who are qualified to answer this question, because it's sparked my curiosity.

Im no engineer but ive put alot of research into 2 stroke engines. Rotation shouldn't affect port timing because no matter which way the engine spins, the piston still moves up and down by the same amount because the offset of the crank is the same. It may make a difference in the running characteristics though if the crank is offset (and i don't think it is).

However, it may affect the flow characteristics of the fuel mixture in the crankcase on some engines where reed valves are placed on the side of the crankcase, aiming downwards in the direction of crankshaft rotation. I have a 2 stroke lawnmower engine like this. In these engines the crankshaft's connecting rod bearing surface and counterweights may spin the fuel mix around in the case to assist in sweeping the fuel mix out of the reeds. If these engines are reversed, they might not run at very high speeds because of the crank offset it shoving fuel back up against the reeds as it passes by them, rather than creating turbulence that helps draw fuel out of them. Its hard to picture.

But a ht isnt like this so its not a problem. And even if it was this design, it wouldnt affect much because the crank is round, without a strange crank shape that has large counterweights and a finger sticking out for the big end bearing. So it wouldnt cause much turbulence anyways.

 

[ToyTruck]

BigBlue ... My timing wasn't set up like that...my motor would not fire as the magneto passes the blue and green ....

My engine was timed and firing as the green dot was passing where the top left screw is (using your pic to explain) remembering the magneto is spinning the other way and the spark fires as the magnetic field breaks.

What I THINK I have done , like you said is setup the timing way wrong , got it to run and backfire and not realise that it was cooking .... That timing that did the damage , didn't rev well and I went back and started from scratch and re timed it properly .... But the damage had already been done

Wouldn't there be more damage if I had been continuously running it with Hot timing ... Melted piston etc

I appreciate the help , don't really want to kill it again if it was my timing that did it

 

[ToyTruck]

It is the position of the magneto in relation to the magneto coil that is important.

In my opinion, you didn't change the timing by removing the Woodruff key and moving the crankshaft. What you described, every thing stayed the same as the stock position. To demonstrate, place your crankshaft keyway at the 12:00 again and it will look like the stock position.

With the crankshaft keyway at the 12:00 position, it will be at 15 deg BTDC, regardless of whether the engine is turning CW or CCW. Here's a picture to help explain what I am talking about.

View attachment 47415

Hope I didn't confuse you.

Good Luck,

Chris
AKA: BigBlue

Alright , the best way I can explain it without being able to take a pic is ...

In normal CW rotation , the spark fires when the Crank keyway is at 12:00 ..... TDC is 1:00

My setup is for CCW so my new 15degree BTDC is at 2:00 and at that point the rotor has to be leaving the magneto , so I set my Rotor keyway around at 7:00

Crank keyway at 2:00 rotor keyway at 7:00 ... No woodruff key , just tightened up the retaining nut and it held tight

Can someone verify for me that I got it right
Remembering that I am spinning the rotor backwards