Engine timing misconceptions...Figured out!

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silverfox

New Member
Jun 29, 2012
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Rocky mountain house, Alberta
My engine just wasn't running right.
I had changed the bearings.I did some mild port matching...not timing..except..to relieve the bottom of the piston on the intake side.
Rings are great, but it just ran like a dog.
I kept doing what the timing references said to do and ...I shaved the key and advanced the timing, It got worst..
Problem solved...
I flipped the key around, which is contrary to the articles I had been linked to..
Well low and behold...The 2 stroke started sounding like a 2 stroke.
What an amazing difference guys,
I dunno if it had a badly machined keyway, as to over advance the timing to begin with, but for this crankshaft, it worked like a charm,
and i had to share it with you all..
Sometimes we all search for insight, and refuse to really want to try to step outside the box.
Well , in this case, I am sure glad i have.
I hope it works as well for You all as it has for me cause this 5000km motor just got a new lease on life.
Happy tweaking.
Just to be clear...I machined the key, and rotated the magnet clockwise on the shaft, contrary to all the posts i had seen on adjusting timing.
I wish you all , great results,
Happy trails,
Steve
dnut
 
crassius

crassius

Well-Known Member
Sep 30, 2012
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Is it just because it's way early in the morning for me, or does rotating clockwise on a shaft that is turning clockwise mean that you have advanced the timing rather than retarded it.
 
BigBlue

BigBlue

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Nov 29, 2011
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The Happy Time/China Girl magnetos have a lot of play and it is possible to advance or retard the timing by moving the magneto left or right.

Grubee even has information on his website about the magneto play:
http://motorbicycling.com/attachment.php?attachmentid=56740&stc=1&d=1361380143

Here's a video from one of our members, MultPaul, demonstrating the amount of play with the magneto mounted on a crankshaft with a degree indicator:
http://www.youtube.com/watch?v=FhvaNvT5NN4&list=UL8sKg6h9pDmw

For those that may be interested, my theory on how the ignition is advanced is by the shape of the magneto. If you look at the magneto it has two valleys. One on top and one on the bottom. I've found an article on CDI design that explains how the stepped design of a magneto coil can be designed to advance the timing. Rather than shaping the magneto coil in a step shape, the Chinese engineers shaped the magneto to be stepped, inverting the design. Look at figure 4 of the article:

http://archive.siliconchip.com.au/cms/A_110499/article.html

Good Luck,

Chris
AKA: BigBlue
 

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crassius

crassius

Well-Known Member
Sep 30, 2012
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Bikeguy Joe said:
It's early. He retarded the timing on his engine.
Click to expand...
I would agree if there were a set of points making a spark when the crank got to a certain point, but moving the magnet clockwise seems to bring it past the coil MORE before TDC than LESS.
 
biknut

biknut

Well-Known Member
Sep 28, 2010
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Dallas
The way you advance the timing on a china girl is, you rotate the magnet counter clockwise on the shaft.

Turning it clockwise retards the timing.
 
G

gokart25

Member
Sep 26, 2011
245
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Iowa
biknut said:
The way you advance the timing on a china girl is, you rotate the magnet counter clockwise on the shaft.

Turning it clockwise retards the timing.
Click to expand...
I took some advice from everyone on this forum, and it made my engine run way better. I turned my magnet counter clockwise on the shaft.
It didn't take much, just the a little wiggle room..like in the video link above.
Thanks everyone.
 
2door

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
I must be doing something right, or wrong depending on how you look at it but I've never had an engine that had enough slop in the key or keyway to move the magnet enough to change the timing by even one degree.

A coupls of years ago I did play with this on an engine that came from the factory gutless. I found it was retarded about 3 degrees compared to other engines I had at the time. I made my own off-set woodruff key and advanced the timing to match the other engines.
It helped a lot but that engine never performed like others I've had. Not unusual with the HT. Some perform, some don't.

Just an observation based on my experience with a number of engines, most from the same supplier.

I used a cam shaft degree wheel with an adapter I made to fit the crankshaft and set the piston at top dead center with a dial indicator to get magnet position indexed to piston position. I used an automotive timing light to compare where the magnet was when the plug fired and based it on piston position. I found that I got better results with the ignition at about three degrees before top dead center.

Don't know how it will work for anyone else and I'm not suggesting you start playing with off-set keys or changing your timing. Too far advanced or retarded and you can damage the engine/piston due to pre or post ignition. Be careful guys.

Tom
 
577-Jersey

577-Jersey

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Mar 23, 2013
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central western nj
biknut said:
The way you advance the timing on a china girl is, you rotate the magnet counter clockwise on the shaft.

Turning it clockwise retards the timing.
Click to expand...
How could that be if the crankshaft is spinning CW,,by rotating it CC wouldn't that fire after the piston hit TDC,,I may be missing something?

Regards

Tom :)
 
crassius

crassius

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Sep 30, 2012
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tried to point that out, but no one here seems to believe it - don't have time to make all those mods & do a video with a timing light on it
 
577-Jersey

577-Jersey

New Member
Mar 23, 2013
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central western nj
crassius said:
tried to point that out, but no one here seems to believe it - don't have time to make all those mods & do a video with a timing light on it
Click to expand...
I hear ya,,
Thought I had timing issues with this last build,,it was hard starting(alot of compression),,sluggish,4 stroking,missing,and pinging,,I took the nut off the crank and moved the mag a hair ccw(as far as the slop would let me go),then lessened the gap on the plug(.20),and moved the clip on the needle one up(last notch from top).Its running much better,no more ping,,but still misses and slobbers a little,,I think with a new NGK B6HS and after the break in tank it will clear right up though...
 
Toadmund

Toadmund

New Member
Jan 19, 2012
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Saint John, New Brunswick, Canada
So help me understand something people, the engine runs better retarded at higher RPM contrary to common sense, does that mean most, or all of these motors are far too advanced as stock to begin with, and must be retarded just a bit?


Hmmm, seems this explains it decently enough:
Goat Herder said:
AFFECTS OF THE IGNITION TIMING

Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.
Click to expand...
 
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577-Jersey

577-Jersey

New Member
Mar 23, 2013
293
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central western nj
If you rotate the magnet on the shaft it would be CCW retard CW advance,,if you elongate the holes in the magneto so you could twist it a couple mm.,,CCW would advance and CW would retard.
 
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