Full-Circle Crankshaft in Stihl Chainsaw

[cus_deluxe]

Your thinking is inline with mine. I also believe there is a case capacity to bore/stroke ratio that we should try and stay within for the task at hand. Too little case capacity could drive the rpm so high to where we’d be lowering exhaust and transfer heights to the point that one function would be fighting the others

572 vs 462: relatively small bore/long stroke/stuffers vs relativey big bore/short stroke/no stuffers. both good performers doin it differently. seems to jive with what ur sayin?

 

[Al Smith]

If a person were really into it online help and resources are many . .Gordon Jennings, Alexander Graham Bell and Macdizzy .I might also mention Fox Valley Kart in Indiana .Like I've said and will repeat there are no real secrets .It's all been done before at some time or another .Some worked some did not .

 

[cus_deluxe]

If a person were really into it online help and resources are many . .Gordon Jennings, Alexander Graham Bell and Macdizzy .I might also mention Fox Valley Kart in Indiana .Like I've said and will repeat there are no real secrets .It's all been done before at some time or another .Some worked some did not .

no one is disputing that, but theres a certain etiquette that goes along with stuff like what was posted earlier. as captain hook would say…

 

[Stump Shot]

It just could be possible that it's more than just a volumetric equation at work here. When ya think about it statically speaking, yes volume would seem to be the predominant thing. Think of it at say 10,000 RPM and it might be a bit different possibly. Think about that pork chop crank and the amount of disturbance it is causing compared to the relative calmness of a full circle(stuffed) crank inside the crankcase. The other thing is now picture that same commotion with a front feed transfer, when Husqvarna was mentioned this is what came to mind to me as the swirling effect would be going in the wrong direction to aid the transfer action up the front. So in other words, the transfer action could be smoother in a full circle crank along with having less area to try and push.
Could all be BS too, whatever the case may be, about the only time I really do anything to notice the difference, is when placing a 357xp cylinder on top of a 359 case and a 357xp is not what you get, more like a 358 or some such thing, not that that's all bad it can be a useful tool, just different than normal is all, which is no big secret, if it were however, I probably wouldn't even take a picture of it, let alone share it, as once you give it to someone, who knows where it may go from there. ...and yes Virginia, there really is a secret or two left out there on who did what on these saws(done before or not, matters little) or all them would run exactly the same and what fun would that be?
Interesting topic of conversation none the less and would like to hear what others think about it.

 

[Al Smith]

I'd say even if you port mapped a hotty cylinder no two would be exactly the same .For that matter although I've never built one I have made parts for them .Out of respect for the builder I won't specify exactly what they were .
Now rather than say "secret" perhaps little known would be more factual .Being more of a restorer /collector I've found replacement parts suggested to be NLA but it's not a secret just not well known



.

 

[Al Smith]

I just thought of another option not mentioned often .Kind of like extensions on the counter weights of a pork chop style crankshaft .Adds some width which would displace some volume and I think they used plastic or fiber glass to do it .How well they worked I haven't a clue

 

[huskihl]

572 vs 462: relatively small bore/long stroke/stuffers vs relativey big bore/short stroke/no stuffers. both good performers doin it differently. seems to jive with what ur sayin?

The way the 462 case is underneath the piston, I would almost bet that the 462 has less case capacity than the 572 though. Which is another thing that made the early ones higher strung.

 

[cus_deluxe]

The way the 462 case is underneath the piston, I would almost bet that the 462 has less case capacity than the 572 though. Which is another thing that made the early ones higher strung.

exactly. 572 without stuffers would probably feel pretty blah. 462 w full circle would prob be just about unusable

 

[huskihl]

exactly. 572 without stuffers would probably feel pretty blah. 462 w full circle would prob be just about unusable

Yep

 

[Al Smith]

Another option popped into my head .Some forum had a half-fast full circle done by thin machined steel rings that wrapped around the counter weights filled with some kind of epoxy .If it worked I have no idea .I had visions of the thing comming apart like a dollar watch and destroying the engine .

 

[drf256]

Comes down to physics as well. If a port can flow only X amount of air, and one has Y amount of volume, what’s the Z in the equation? It’s how many times it rotates to accomplish moving that amount of air (RPM).

HP is torque over time. Generally the more rpm, the more total power because it is an equation.

Bell’s book described it well. IIRC, it was Yamaha that started making smaller and smaller case volume in the early 70’s up to the point where they were overscavenging and losing power. This is where case volume/cylinder volume equations came into play.

I used to think that the crank weights would whip charge forward and create higher pressure at the front of the case. The 462 made me realize my theory was all wrong. If forward motion pushed charge forward, it also pulled it away. The 462 feeds the transfers from the bottom through long ass tunnels. Should add to torque, as the tunnels are part of the case volume.

Think we are all saying the same thing in different ways. I think the tight cased saws need less intake timing as well, otherwise they just get a ton of blowback. The bigger case saws, like a 660 Stihl for example, need more time to fill and have more time to compress charge so there isn’t as much spitback at more intake duration. Then they may huge uppers to flow that lazy charge into the cylinder.

 

[Dolkitafreak]

The way the 462 case is underneath the piston, I would almost bet that the 462 has less case capacity than the 572 though. Which is another thing that made the early ones higher strung.

7900 always makes me scratch my head, it’s a very tight case, tight trans, tight every port really, and torque for days!

 

[cus_deluxe]

7900 always makes me scratch my head, it’s a very tight case, tight trans, tight every port really, and torque for days!

ive never been in one of those, but ive always heard they have a lot of blowdown.

 

[Dolkitafreak]

ive never been in one of those, but ive always heard they have a lot of blowdown.

They do, I wanna say 26ish degrees stock and they like a couple more added to it, which is where I think their behavior comes from. Really shows why a good builder won’t approach two saws the same way.

 

[Stump Shot]

Comes down to physics as well. If a port can flow only X amount of air, and one has Y amount of volume, what’s the Z in the equation? It’s how many times it rotates to accomplish moving that amount of air (RPM).

HP is torque over time. Generally the more rpm, the more total power because it is an equation.

Bell’s book described it well. IIRC, it was Yamaha that started making smaller and smaller case volume in the early 70’s up to the point where they were overscavenging and losing power. This is where case volume/cylinder volume equations came into play.

I used to think that the crank weights would whip charge forward and create higher pressure at the front of the case. The 462 made me realize my theory was all wrong. If forward motion pushed charge forward, it also pulled it away. The 462 feeds the transfers from the bottom through long ass tunnels. Should add to torque, as the tunnels are part of the case volume.

Think we are all saying the same thing in different ways. I think the tight cased saws need less intake timing as well, otherwise they just get a ton of blowback. The bigger case saws, like a 660 Stihl for example, need more time to fill and have more time to compress charge so there isn’t as much spitback at more intake duration. Then they may huge uppers to flow that lazy charge into the cylinder.

Explains Big Bore kits too I would think.

 

[Al Smith]

It's all a bit theoretical however in reality it might not work as well as predicted .You want to be confused try to figure a resonance tuned intake and exhaust experimented with
by either Vickers or Villers some time in the 30's It worked but had limited success only within a certain RPM range .Had it been able to work full speed range it would have been the holy grail , push pull type thing .Saying that mouth full the average chainsaw owner is not going to be interested in a full circle crankshaft .

 

[huskihl]

7900 always makes me scratch my head, it’s a very tight case, tight trans, tight every port really, and torque for days!

Small tunnels limit some flow, which knocks the horsepower down but adds some torque just like a 372xpw. Lower upper transfer ports help with torque as well. And then 55° of case compression pushing it all makes them much more difficult to bog in the cut. And the narrow exhaust port also helps with torque.

 

[Redfin]

exactly. 572 without stuffers would probably feel pretty blah. 462 w full circle would prob be just about unusable

Dont believe. I filled front feed on one and added bottom lowers. Id hazard that be about the same volume.

 

[Ketchup]

Another option popped into my head .Some forum had a half-fast full circle done by thin machined steel rings that wrapped around the counter weights filled with some kind of epoxy .If it worked I have no idea .I had visions of the thing comming apart like a dollar watch and destroying the engine .

AWOL built several of those for 660. Never heard of one blowing up. I think JMS ended up with one. That was all on AS years ago. So often these types of experiments are poorly documented and flawed by other factors.

 

[Redfin]

Anyone hear from Alan lately?