Full-Circle Crankshaft in Stihl Chainsaw

[redneckhillbilly]

are these full circle cranks homemade? or is there a company that manufactures them?

 

[HumBurner]

That's a great way to describe it. There were some two-stroke motors in the 60's and 70's that had huge crankcases - mainly snowmobile engines. They were designed to produce a wide power/torque band and have good power in a lower RPM range. They were kind of lazier motors though - they didn't wind up well or even have the greatest acceleration. But they did make good, consistent power at a fairly low RPM range where the machine was designed to run.

It was the same situation with some two-stroke water pump motors used in the fire services - they would be run at a constant RPM that was fairly low (6-8,000 rpm).

Based on what you stated here, it seems like this would be an ideal setup for dedicated milling saws

 

[Ketchup]

Based on what you stated here, it seems like this would be an ideal setup for dedicated milling saws

First CSM I ever ran was two 076’s on a 60” bar. Big and slow but unstoppable. It made very consistent cuts and was reasonably fast considering the rpm. Unfortunately it was .404 skip. Half the log ended up as sawdust. And the boards had a texture that was probably 1/8” deep.

 

[MSaw]

What is a 'full-circle' crank?? Sorry, this has no meaning in the UK.

 

[jacob j.]

What is a 'full-circle' crank?? Sorry, this has no meaning in the UK.

This kind of crank:



Vs. this kind of crank (traditional):

 

[MSaw]

Is there a perceived benefit? They are just designed for different saws? Both will be dynamically balanced and well it's a toss-up on other matters. The top flywheel will give a more even chart on torque over a cycle and will run smoother whereas the more traditional crank probably has less overall rotating mass. Interesting, thanks.

 

[Loony661]

Is there a perceived benefit? They are just designed for different saws? Both will be dynamically balanced and well it's a toss-up on other matters. The top flywheel will give a more even chart on torque over a cycle and will run smoother whereas the more traditional crank probably has less overall rotating mass. Interesting, thanks.

It has more to do with case volume than balance. Therefore affecting throttle response and torque.

 

[Bjorn]

Husqvarna call it revboost. When full circle crank.

 

[srcarr52]

Husqvarna call it revboost. When full circle crank.

No, Revboost was a feature in the computer which would allow higher RPM for a short while after you first hit WOT before going to the normal rev limit. The idea was that you could nip small things off faster that way.

 

[cus_deluxe]

started on this crank months ago, maybe ill finish it someday. 394 crank for what will be a play saw

 

[Powerstroke Cowboy]

started on this crank months ago, maybe ill finish it someday. 394 crank for what will be a play saw
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Are you planning to fill it in with Epoxy?

 

[cus_deluxe]

Are you planning to fill it in with Epoxy?

yessir

 

[Ketchup]

started on this crank months ago, maybe ill finish it someday. 394 crank for what will be a play saw
View attachment 384733View attachment 384735View attachment 384734

What are you using for the outer band?

FWIW, the stuffers from a k970 crank look like they could fit 395 with a little work.

 

[cus_deluxe]

What are you using for the outer band?

FWIW, the stuffers from a k970 crank look like they could fit 395 with a little work.

i had wondered about the stuffers from bigger saws.
its fairly gangster, i think it was a 2 1/2” pipe coupler that had the perfect OD, i turned the inside diameter out a bit then turned down crank weights until the ring was a snug fit. plan is to tack it in place and fill w epoxy. i like the idea of the factory stuffers tho…