circle crank ms660

[Deets066]

Guess im thinkin opposite on that for some reason

Let's look at this 660, Jason put a full circle crank in and it runs good.

Do you think it would still run as good if he took a stock crank and turned it down?

 

[Keith Gandy]

He can't raise the roof. If you see above, he had to drop it that much so the ring stayed tucked under it.

Ok gotcha. That would be a disaster! Maybe just widen and nip the lower and add transfer height and keep exhaust would be my thinkin then

 

[Keith Gandy]

Let's look at this 660, Jason put a full circle crank in and it runs good.

Do you think it would still run as good if he took a stock crank and turned it down?

Depends on the topend I would think and what u were workin with. In my mind a hybrid gets peaky and sacrafices some torque

 

[drf256]

Let's look at this 660, Jason put a full circle crank in and it runs good.

Do you think it would still run as good if he took a stock crank and turned it down?

No. But I bet an 064 with a 660 jug would.

 

[drf256]

I agree with KEITH.

 

[Keith Gandy]

I am too.

A heavy rotating assembly stores kinetic energy that's released in the first second the bar hits the wood. Then it's gone. A lighter assembly will lack that, but should spool up faster and have more rpm.

On our bigger cc enduro bikes we went with flywheel weights to prevent stall in a low rpm turn and also added torque and smoother power delivery on the bottom kinda like a metal flywheel vs poly on our saws I guess. So on this crank adding rotating mass should give more torque ?

 

[drf256]

On a car, a heavy flywheel gives you smoother idle and better launch. It take longer to rev though.

Everything has its place, and there's a lot more engineering in the crank and case than I understand.

 

[mdavlee]

I still think raising the exhaust 2 or 3 degrees would be my first try.

 

[Keith Gandy]

On a car, a heavy flywheel gives you smoother idle and better launch. It take longer to rev though.

Everything has its place, and there's a lot more engineering in the crank and case than I understand.

Ok so this fullcircle should make a better entry into the wood at wot for a cookie cuttin setup if it was ported for cant? It would have extra torque at entry but the effect would fall off after the saw really started pulling?

 

[Keith Gandy]

I still think raising the exhaust 2 or 3 degrees would be my first try.

It sounded in the video like it would really cut with more rpm but seemed to have good torque. It was really cuttin!!

 

[mdavlee]

Cold start racing might not be as good if it's not to full revs when it hits the wood.

 

[Deets066]

I agree with KEITH.

Which Keith?

 

[Brewz]

I think what ever is done with the top end needs to take into consideration the most significant change and that is reduced case capacity.

The motor needs air and fuel, and there will be less of it in the bottom end to push up into the top end.
I dont know enough about porting dynamics to make wild stabs in the dark, so I wont, but my advice is to look at what has changed that will effect the air/fuel flow dynamics and adjust to suit.
I like the theory of less intake duration because you have less capacity, but wont the saw still me moving the same volume of air up the transfers into the combustion chamber?
This has not changed, only the volume held in the bottom end has been reduced.
So considering this, wont the saw still need enough intake duration to fill the case with the same amount of air as it would if it had a standard crank?

My thinking is that with the circle crank, there will just be less left over in the case at BDC than standard, the saw will still consume the same amount of air on each cycle.

 

[jmssaws]

The only real difference in the saw from any other is it's ability to carry rpm,it revs like any other saw.

 

[Stihl working Hard]

It runs!

Thats always a good start

 

[Stihl working Hard]

Well if it hasn't come apart yet, then it probably ain't gonna!

My thoughts exactly

 

[Keith Gandy]

I think what ever is done with the top end needs to take into consideration the most significant change and that is reduced case capacity.

The motor needs air and fuel, and there will be less of it in the bottom end to push up into the top end.
I dont know enough about porting dynamics to make wild stabs in the dark, so I wont, but my advice is to look at what has changed that will effect the air/fuel flow dynamics and adjust to suit.
I like the theory of less intake duration because you have less capacity, but wont the saw still me moving the same volume of air up the transfers into the combustion chamber?
This has not changed, only the volume held in the bottom end has been reduced.
So considering this, wont the saw still need enough intake duration to fill the case with the same amount of air as it would if it had a standard crank?

My thinking is that with the circle crank, there will just be less left over in the case at BDC than standard, the saw will still consume the same amount of air on each cycle.

But wouldnt taking anything from the bottomend to the end of the transfer uppers be adding capacity back? I can see the rotational kinetic energy on bottomend being beneficial jason but does it help on topend rpm also? I know just taking up real eatate into the bottomend is gonna make rpm but im thinkin rotational energy on topend?

 

[Stihl working Hard]

Here's the first start up. Wood in a hour,gotta run to town.

Sounds normal so far

 

[Stihl working Hard]

Wonder if one of these fancy full circle cranks would work on my pipe and head saw

Would definitely rev

 

[Brewz]

The only real difference in the saw from any other is it's ability to carry rpm,it revs like any other saw.

Yep.

So standard port timings for a saw like this should apply.
Its just a 660 with a 288 piston, which is nothing new.
Difference it is will spin faster and smoother, so I guess you need to decide if you want torque for work or RPM for piss reeving and play and port appropriately.