The Making of a Full Circle Crank in a Homeshop

[awol]

The merits of using one have been and are beeing discussed in other threads, but here is a thread on how I have been able to use a stock crank, and turn it into a full circle.

I started this one by chucking on the pto end, and indicating to zero runout. A more accurate way would be to use a center in the headstock, and spin the crank between the centers.



After its centered, I run the tailstock up and put a little pressure on it. Then find the beginning point of cutting, zero the dial, and take light passes until we get contact on the throw side as seen here. This one only had to have .025 removed.



I used crank saver rings on the last one I did, but decided to make some from scratch for this one. I found a piece of old John Deere hydraulic cylinder tube, bored it for an easy slip fit of the crank, then turned down and polished the od. The rings are .025 thick, so with the loose slip fit the assembly will be a bit larger in diameter. Here are the rings getting parted off.




And the old crank with new rings slipped onto it.




And the crank fitted inside its case, just to see how it would look!

 

[awol]

Now the crank is machined, and the rings are done, but the real work has only begun. The next part is to slip the rings on the crank, and get all of the voids filled up with JB weld, and try not to get any in the rod bearing! I left the clearance between the crank and rings a little loose, because there needs to be a good film of epoxy between the two.

 

[jmssaws]

Slick freind, I am looking forward to seeing this develope and forward to receiving one to play with.

 

[jmssaws]

Awesome work

 

[Nitroman]

Why not weld thin plates over the ends rather than fill with epoxy? The mass of epoxy will affect performance, slower revs, but otherwise none. I can only think of flexing breaking the epoxy.

 

[awol]

Someone on here, I think it was Treemonkey, tried welding on his crank. It didnt work out. The epoxy fill will be lighter than steel plates anyway. I have not heard of one of these coming apart yet, but this could be the one. This saw ran upper 18000 rpms before the full circle, so it'll give it a good trieout!

 

[jmssaws]

Treemonkey said welding didn't work,I think jb weld will be fine,the ring contains it so there is really no force on the epoxy. What extra weight there is will be a plus.

 

[heimannm]

Watching and learning.

Mark

 

[Four Paws]

Someone on here, I think it was Treemonkey, tried welding on his crank. It didnt work out. The epoxy fill will be lighter than steel plates anyway. I have not heard of one of these coming apart yet, but this could be the one. This saw ran upper 18000 rpms before the full circle, so it'll give it a good trieout!

What Partner saw is that?

 

[Mastermind]

I'm here now.

 

[Lee H]

I've been a bit curious about full circle cranks. They have been used
in the karting industry for years. I even bought a Mac 101 with a full
circle and it was made just the way your doing yours. I understand it
is filling the crank case more so when the piston is on the down stroke
there is actually more pressure to charge the combustion area. But is it
that much of a difference. Much more power? Or is it going to let the
engine spin to higher rpm's with less drag around the crank.


Lee

 

[Mastermind]

Good questions Lee.

 

[paragonbuilder]

Simply awesome! Great job. Looking forward to more...


Sent from my iPhone using Tapatalk

 

[jmssaws]

Yeh this is great.
I'm sending one out tomorrow

 

[David Young]

P5k


That's slicker than deer guts on a doorknob. Nice job thanks for the thread

 

[angelo c]

Just sitting in the back of the room( thumbs inserted firmly in buttocks) trying to learn a new "language"...ifn y'all talk slow I might be able to follow....

so far all I learned to say is "wow"..

 

[Nitroman]

I've been a bit curious about full circle cranks. They have been used
in the karting industry for years. I even bought a Mac 101 with a full
circle and it was made just the way your doing yours. I understand it
is filling the crank case more so when the piston is on the down stroke
there is actually more pressure to charge the combustion area. But is it
that much of a difference. Much more power? Or is it going to let the
engine spin to higher rpm's with less drag around the crank.


Lee

But the volume in the case is reduced, so with less charge able to make its way in, would there really be more pressure built?

 

[cobey]

Neat stuff Alan

 

[Chris Zautner]

this is just awesome

 

[awol]

The saw this crank go's to is a 5000+ with 44mm jug. It has been a perpetual project of mine, but has taught me more about porting than most every other saw put together. Right now it has an intake block fitted, and running on a bored out WJ from an 066. It has 185 degrees of intake, 165 of exhaust, 20 blowdown.

But the volume in the case is reduced, so with less charge able to make its way in, would there really be more pressure built?

Remember that it will also provide a lower pressure negative signal when the port is open.