Full Circle Cranks photos

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Another tip on saw cranks,if you are building a high output saw for competition,I have welded the rod big end pin to the counterweights on each side to prevent the crank from "twisting",which can happen on pressed together cranks in high output engines,this is also performed on some Japanese 4-stroke motorcycle cranks for racing.
 
On a digital scale the stock crank weighed 696 grams,the Ti crank weighed 693 grams.
Interestingly when I conducted vacuum and pressure tests(Running,and static tests) on the crankcase of the engine with the stock and full circle cranks,the full circle crank actually created more pressure and vacuum in the crankcase.
I did cc the crankcase of the stock and Ti crank versions to calculate the actual crankcase compression ratio of both but I don't have that data right in front of me at this moment...
 
Crank and vac test doing more pressure is probably from the ti crank sealing better on the crank seals from having a rounder shaft or nicer surface finish. Or you just happened to seal the intake and exhaust better that one time.
 
@trappermike Here is a picture of a Husqvarna 562xp full circle crank. What type of material have you used to fill those voids when you were building crankshafts? Did you alter the cranks at all to improve crankshaft bearing lubrication?

562xp Crank.jpg
Echo crank stuffers.
Echo CS-355T Crankshaft.jpg
 
Best I could do with my phone.
 

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Full circle counter weights opens up a whole new problem area. The lower end assembly needs to be balanced.
 
They only need to be kind of balanced. 1 cylinder 2 stroke aren't very particular.
 
Adding weight to the crank and not balancing the complete rotating assembly means a lot more vibration at the higher rpm and premature bearing failure.
 
With the rotating assembly balanced better you might get more rpm at the high end. If your adding porting, a change in port timing and porting the piston. It all works together. Excess vibration can hold it back.

In building race engines tuning them to perfection is the toughest part.

What if those plastic pork chop pieces were removed from the crank and thinner steel pork chops were bolted in and tac welded then the rotating mass statically balanced.

I read where the dirtbike cranks are hollow inside the balances. I wonder if this design will hit the chainsaw engines too?
 
All I know is I did extensive crankcase vacuum and pressure testing on chainsaws. The full circle crank made higher tests than any stock crank,pressure and vacuum were higher,giving the saw considerably higher output. That's why the Japanese did this in racing engines. more vacuum,more pressure,more power, only one factory motor had a full circle crank stuffed from the factory (ever),and it was the fastest motorcycle in the world for 3 years.
 
Adding weight to the crank and not balancing the complete rotating assembly means a lot more vibration at the higher rpm and premature bearing failure.
You can't balance a single. If you balance the rotating assy to be perfect at TDC and BDC then you have a big imbalance at the 90 degree locations. It's all a compromise.
 
You can't balance a single. If you balance the rotating assy to be perfect at TDC and BDC then you have a big imbalance at the 90 degree locations. It's all a compromise.

I concur on this. A good example would be saws with the same chassis and different cylinder size. 362xp, 365sp, 372xp and 372xp xorq. They all have different rotating masses with the same crank assembly. To attempt to balance 1 would imbalance the others.
 
Going from pie shaped counter weights to full circle counter weights lessens the crankcase volume. Would it raise the transfer port pressure when the piston goes down?
 
Yes, the full circle crank fills the crankcase more creating a higher crankcase compression ratio,which forces more fuel up the transfer ports,which may only be open for .001" (one thousanths) of a second,so it definitely helps. My full circle counterweights were solid titanium,not a mash of parts,and they had "stuffed" counterbalance holes,which almost no factory did stock,to make crankcase comp. higher.
Yes how do you balance a 1 cyl. 2-stroke? I had no idea.What I did was made it "same as factory"-whatever the hell that is,and they were good. First time I revved the saw up I held it as far away from me as I could,I was afraid of the crank exploding at high rpm,but they proved strong.
I did modify the big end of the rod for better oiling,in the fashion motorcycles used,and drilled 2 small holes in the top of the rod for better pin oiling,no problems.
The saw factories today only use their "1/3 cranks today because they are much lighter and cheaper to make.
Aluminum flywheels? Considered it but just not strong enough,not even close. My full circle Ti crank was still a few grams less than stock,quite a feat I think.
 
I did purchase live centers to setup a crank balancer but got side tracked. Just been busy doing other stuff. I’m sure the balance matters when these engines go higher in rpm when we change the rotating element weights. I wonder how close there balanced from the factory?
 
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