Different Rotors.

[Theon]

These two rotors are over 20 deg apart in timing!
The more advanced rotor is coming out of the phantom and going on the goat, the Phantom is going to get the retarded magnet, as it is being detuned, but has a crank that's smooth to rev, so not a race bike , but will still rev out.
The Goat now has low gearing, big heat dispersal, only .2mm base gasket, high compression, reeds, heaps of advance and with a long freeflowing pipe, I want wheel stands!
I see the difference in these Mag Rotors as one of the biggest reasons one bike will behave totally different to another 'standard motor'.
Still if you have a choice of different Rotors, they can be used to give your motor a nudge in the direction you want.
Hopefully I have repaired my old timing light, and will soon be able to have these motors running and get some real timing numbers from these motors.

 

[Theon]

So now the Goat (blue frame), has the more advance, as the key way is more anti clockwise, the break in magnetic field which triggers the CDi to spark, will happen sooner, By about 20 deg!, and give this motor the low down punch I wan from it.

The Phantom, with the narrow cased '50' motor will be getting the revs, from the more retarded rotor.

 

[2door]

Theon,
That is an interesting find. Several years ago I was experimenting with different engines and I discovered the keyway in the crankshafts were cut differently. I can only imagine the impact that would have on engine performance if you combined the two; crank key and rotor indexing.

I made an adapter that would allow the use of a camshaft degree wheel on the crankshaft and used a dial indicator to get exact TDC through the sparkplug hole. I found from 3 to 7 degree differences in keyway locations on four different engines.
By the way, the most retarded of them was/is my best running engine. Both high and low end. It is also noticably quieter than other engines especially in terms of intake noise.

Thanks for sharing your finds.

Tom

 

[Davezilla]

I've seen similar issues over here between 2 different engines, the original one I got and the new Dax botttom end both have different timing, I remember reading where someone else discovered this and was making a conical bushing and cutting a conical hole in the rotor so he could lock the rotor dwn in any position without the woodruff key but I hadn't heard any more about it since then.

 

[Theon]

Yes I read that one too,
But thought to put this in a fresh thread.
As timing is a very important issue in us getting these to run right.
Timing Disc and Light will be coming soon, as will Modified rocket Cdi, with variable advance.
From what I've read and been told 20 deg advance is the magic number.

 

[BigBlue]

Good find. What are the measurements on the stepped part of the magneto core of both magneto rotors? Are they the same? Those stepped valleys are the timing advance waveforms. On most small engines, the stepped waveforms are outward, but since the China 2 strokes have less room, the waveforms are inversed. It would be interesting if someone could connect a oscilloscope to our engines. Maybe modify the waveforms.

Here's some more information on CDi units from Silicon Chip. See the Circut refinement section, figures 3 and 4: http://archive.siliconchip.com.au/cms/A_110499/article.html

Chris
AKA: BigBlue

 

[Theon]

There is only slight difference in the width of the gap in the rotors, typical of cheap manufacturing, but possibly filing the rotor back a little is another way of altering your timing a little. There might be a slight decrease in charge time but not significant if you were only looking for a couple of deg.

 

[Davezilla]

Yeah, I'd like to add in a timing disc and be able to check the timing with a light on my engines as well. Let me know what you come up with. I got a Rocket CDI and I opened it up and took several large high res pictures of it getting both sides of the board as well as closeups of all the resistors and components on the board. The SCR is the only thing I didn't get a picture of because I would have had to bend it or the capacitor over further than I felt safe bending them, but we all know which SCR it is anyway. For the timing disc, I was thinking about using a thin aluminum disc with timing marks going 30 degrees both ways past TDC, bolting it on over the magnet and just putting a pointer tab on one of the magneto bolts. I'll take some pics after I get one made as well.

 

[Theon]

M8 x 1mm nut, as used on the engine kit.
M5 nylock nut.
washer to suit.
Bit of tack welding, followed by a bit of filling and some 'persuasion'.
I got a new protractor today, but this is the old one.
then a washer, spring washer and a M5 screw.

 

[Davezilla]

Thanks for the close up of your degfree wheel... Cheap, but effective and I like it.
Here's mine, mine fits on the bevel gear side and I need to use a piece of solid wire for a pointer. Mine's dead simple as well because I googled "degree wheel" and selected images, the search brought up tons of different printable images so I found one that was real easy to read and set it up to be printed at 6" round on card stock. Next I got a piece of plastic sheet and cut it round, then used spray adhesive to glue the newly printed wheel to the p[lastic sheet. i then laid a phone book on top of it so the paper wouldn't wrinkle as the glue dried. After about an hour or so I driled an 8mm hole thru the center and used an M8x1.0 x30mm bolt with 3 nuts.

To mount the wheel to the engine, I take out the bevel gear screw and screw the wheel into it's place, use one nut as a jam nut to lock the bolt in position, then use the other 2 to lock the wheel into position once I decide where I want the Zero to point to.

 

[mech_engineer]

I use neodymium magnets and not a bolt

 

[Davezilla]

I really like the idea of the neo magnets, they'll stay put without the need to remove the bevel gear screw. I ended up making a better pointer out of a piece of aluminum and it can be mounted to the clutch cover bolt holes the same way with 1 jam nut to keep the bolt from moving, and 2 more jam nuts to lock the pointer into position. It's still real easy to set up as it can be put on and taken off in about a minute. The magnets would cut that time down to a few seconds tho...

After checking my port timings with my original jug on the new Dax bottom end, my durations are a bit longer than before with 116 degrees intake, 130 for the transfers, and 172 for the exhaust with 25 degrees blowdown. The intake duration is shorter because I cut out 5mm from my old piston and I was using a new uncut piston to take these measurements.
I'm thinking these numbers should work, but I do need to raise my jug by about 1mm to get my squish clearance acceptable, but I'll try a double head gasket first to see if it'll give me enough squish that way first. What's your opinions on this port timing?