Genuinely disturbing piston behavior

GoldenMotor.com

Brass Mann

New Member
May 15, 2023
11
5
3
18
Howdy folks,
This is the third thread I've started about building this same bike which simply refuses to run at every corner (the others can be found here and here).
After a substantial delay waiting for my new CDI and spark plug to arrive (grabbed both because a new plug was inexpensive), these new components have still not allowed me to get a spark. I've done some more diagnostic and believe there is a serious problem with how the engine itself spins.
While examining my magneto with the cover off, I could notice it does not turn when I turn the pedals, despite the engine creating more resistance with the clutch engaged. I was able to turn the crankshaft by using a 13mm socket on a nut at the end of the magneto, at which point I could observe the piston going up and down its stroke by peeping through the spark plug hole. Curiously, whenever I would turn the pedals to recreate the same effect, the piston would slightly retract from top dead-center and then not move outright. I could still move the piston by using a socket wrench, but trying with the pedals seems to always create the aforementioned effect: the piston moves maybe half an inch before not moving at all.
Needless to say, this bike has caused me a substantial amount of grief, and these new findings leave the possibilities rather open-ended, hence why I'm posting yet another thread. I'm at a loss for what to do.

Attached is a picture of the magneto with the cover off. Prominently visible is the 13mm nut I've been using to turn the crank. I can provide more pictures, videos, explanations and clarifications as needed: I just want a running engine.
 
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Brass Mann

New Member
May 15, 2023
11
5
3
18
Howdy folks,
This is the third thread I've started about building this same bike which simply refuses to run at every corner (the others can be found here and here).
After a substantial delay waiting for my new CDI and spark plug to arrive (grabbed both because a new plug was inexpensive), these new components have still not allowed me to get a spark. I've done some more diagnostic and believe there is a serious problem with how the engine itself spins.
While examining my magneto with the cover off, I could notice it does not turn when I turn the pedals, despite the engine creating more resistance with the clutch engaged. I was able to turn the crankshaft by using a 13mm socket on a nut at the end of the magneto, at which point I could observe the piston going up and down its stroke by peeping through the spark plug hole. Curiously, whenever I would turn the pedals to recreate the same effect, the piston would slightly retract from top dead-center and then not move outright. I could still move the piston by using a socket wrench, but trying with the pedals seems to always create the aforementioned effect: the piston moves maybe half an inch before not moving at all.
Needless to say, this bike has caused me a substantial amount of grief, and these new findings leave the possibilities rather open-ended, hence why I'm posting yet another thread. I'm at a loss for what to do.

Attached is a picture of the magneto with the cover off. Prominently visible is the 13mm nut I've been using to turn the crank. I can provide more pictures, videos, explanations and clarifications as needed: I just want a running engine.
 

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Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
7,279
1,827
113
Los Angeles, CA.
I highly doubt that the piston itself has anything wrong with it... It sounds kinda like you either have a woodruff key missing somewhere, or (worst case scenario), the crank shaft is broken.

First... Take out the spark plug (so the engine can spin easily for testing purposes); Then remove all the engine side covers for more testing.

Next... Slowly roll the bike forward & watch all the sprockets & gears turn... The real test here is to make sure you also see the center shafts of each one turn with it!!! You're looking for a gear or sprocket that spins independently of it's center bolt.

Report back what you find.
 
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Brass Mann

New Member
May 15, 2023
11
5
3
18
I highly doubt that the piston itself has anything wrong with it... It sounds kinda like you either have a woodruff key missing somewhere, or (worst case scenario), the crank shaft is broken.

First... Take out the spark plug (so the engine can spin easily for testing purposes); Then remove all the engine side covers for more testing.

Next... Slowly roll the bike forward & watch all the sprockets & gears turn... The real test here is to make sure you also see the center shafts of each one turn with it!!! You're looking for a gear or sprocket that spins independently of it's center bolt.

Report back what you find.
I've found a couple of weird things.
For one, the whole thing seized up when I removed the sprocket cover - probably because it hold the clutch arm. The wheel would not turn at all, even when dragging the bike on the ground. Putting the cover back on resolved this issue.
The second is that my clutch does not turn with my wheels... kinda. On the attached image, you can see the pressure plate, flower nut, as well as what I've called "big gear" and "small gear". Both of these gears turn when I rotate the crankshaft by the magneto nut, but they spin independently from the pressure plate (and clutch, one would assume). I tightened the flower nut as hard as I could using my fingers, but the issue persisted. When rolling the bike, the opposite occurs: the pressure plate spins, but not the gears.
The pressure plate visibly moves when I clutch in, if that information is helpful. I'm guessing this is the broken part we're looking for?
 

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Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
7,279
1,827
113
Los Angeles, CA.
It really seems like you just started monkeying with it & making unnecessary adjustments while having zero mechanical skill or knowledge of how the clutch works. :(

There are several good videos on Youtube about how to repair & adjust these clutches.... I suggest you sit down & watch a few of them, (rather than spending weeks posting back & forth here).


Good luck (^)
 
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