Pocketbike Forum banner
1 - 9 of 9 Posts

·
Registered
Joined
·
122 Posts
Discussion Starter · #1 ·
The following is the video I am basing myself on.

Unlike the crank in the video , the fcc , on a balancing stand, will drop down on the rod end, so adding weights on the rod to get it to stay in any position ( like in the video ) …
Im guessing the balancing factor is off but on the opposite side than it is in the video? Can anyone help me on this?
 

·
Administrator
Joined
·
3,622 Posts
The FCC cranks balance factor is off by so much that it's not usable if you add tungsten to balance it out it increases the rotating mass of the engine and makes it kind of sluggish
 

·
Registered
Joined
·
122 Posts
Discussion Starter · #3 ·
The FCC cranks balance factor is off by so much that it's not usable if you add tungsten to balance it out it increases the rotating mass of the engine and makes it kind of sluggish
Oh man that sucks, is this something you know from personal experience?
 

·
Administrator
Joined
·
3,622 Posts
I tried to fix it three different ways

By adding tungsten only.
By adding some tungsten and then adding the rest of it in steel slugs in the flywheel.

The best results I had was I drilled out the one side and I had to drill out a lot and add a little bit of tungsten to get the desired 45% balance Factor the problem with this is I had to hog out so much that the crank lost its stuffer like ability what I mean by that is it no longer filled the entire void of the crankcase.

Moving along to problem two the FCC blocks a lot of the feed ramp area interrupting the flow of the engine.

And problem three the fuel charge has to be squeezed in between the connecting rod and the crank halves.

I have built about 12 of these engines over the years all different ways I speak from personal experience
 

Attachments

·
Registered
Joined
·
122 Posts
Discussion Starter · #6 ·
I tried to fix it three different ways

By adding tungsten only.
By adding some tungsten and then adding the rest of it in steel slugs in the flywheel.

The best results I had was I drilled out the one side and I had to drill out a lot and add a little bit of tungsten to get the desired 45% balance Factor the problem with this is I had to hog out so much that the crank lost its stuffer like ability what I mean by that is it no longer filled the entire void of the crankcase.

Moving along to problem two the FCC blocks a lot of the feed ramp area interrupting the flow of the engine.

And problem three the fuel charge has to be squeezed in between the connecting rod and the crank halves.

I have built about 12 of these engines over the years all different ways I speak from personal experience
Nice , and by the way no disrespect when i asked if it was from experience, that’s exactly why i asked so that id get that detailed explanation you gave me . That said.
First i thought we were aiming for 55 not 45,

2 i hogged out a pArt of the case in the feeding ramp.. basically widened the wholes case in the corners especially, im hoping to give more space for the charge to go past.
3 i guess you just dont use a fcc in a crank anymore?
 

·
Registered
Joined
·
122 Posts
Discussion Starter · #7 ·
cuz i have a half crank 12mm lying around here if your saying the fcc is just all around bad anyway ill still probably try it with other mods and see what it does .. i wanna try directing flow between the 2 crank halves by flipping an ada style reed block 90°
 

·
Registered
What's your poison? Mine is 40:1
Joined
·
1,439 Posts
A FFC is great for a low end engine, one that won't see high RPMs much. I have a half moon crank that had been lightened. In the middle there is 2-3mm of the crank machined down, much more open in the middle, that might work well for FFC.
I built a mild 44mm (1 pc) with FFC to sell. I broke it in on a bench was smooth but I didnt rev it up high. The guy that bought said it was a ripper and decently smooth. It was a mild port/blueprint job on the case and cylinder base. Rocket key (advanced), reed stopper modded, squish around 0.048", and HP clutch springs. Flywheel and clutch left stock otherwise.
 

·
Administrator
Joined
·
3,622 Posts
Hey I am all up for people trying new things just because my recipe was bad doesn't mean yours is going to be so give it a shot let us know what you did and how you got there.

45% balance Factor seems to be okay I agree with you 55% is the aim point anywhere between 45 and 55 is going to be the sweet spot for these engines sometimes getting them to 55 is just too much work.
 
1 - 9 of 9 Posts
Top