Full-Circle Crankshaft in Stihl Chainsaw

[Powerstroke Cowboy]

I'm in a few groups (not chainsaw related) and this is spot on. So much bad advice.

Indeed.

What's sad is when someone actually says the right thing, then gets trashed by all the "experts".

 

[Mastermind]

Indeed.

What's sad is when someone actually says the right thing, then gets trashed by all the "experts".

The worst advice I ever saw was on a thread about how to determine pushrod length in a performance engine.

 

[Powerstroke Cowboy]

The worst advice I ever saw was on a thread about how to determine pushrod length in a performance engine.

Well, that's over my education level. Never had to learn how. I'm sure it's simple but delicate.

 

[drf256]

Not in the mental image I'm seeing. The top of the crankshaft.....spinning rapidly toward the front....intake charge enters directly on top of spinning crank.....propels charge toward the front transfer entrance.

I used to thing the same thing, ‘cept it should pull it away at an equal rate. Look at the 462.

Steve did that pressure experiment a few years ago, around the same time he disproved the lack of impulse line need theory at WOT. IIRC, he showed positive case pressure with a bit of needle wiggling.

 

[Al Smith]

Forums in general you always can get one or two who try to blow smoke up somebodies azz .You have to seperate the wheat from the chaff or the horse chit from the gravey depending on how you look at it . It doesn't do any good to lock horns with them because it just drives you down to their level .If you can't ignore them , block them . Simple as that .

 

[huskihl]

Here we try our best to keep up on accurate info. Inaccuracies get called out for the most part. Most of the fb groups I’ve been in are phuked for correct info and can’t be fixed. Everything gets lost in the format because no one has to scroll through the whole thread to post.

 

[Stump Shot]

I used to thing the same thing, ‘cept it should pull it away at an equal rate. Look at the 462.

Steve did that pressure experiment a few years ago, around the same time he disproved the lack of impulse line need theory at WOT. IIRC, he showed positive case pressure with a bit of needle wiggling.

Gotta have them wiggles...

...I try and spread factual information when I can, doesn't matter much, no one listens to me anyways. LOL

 

[beaglebriar]

I'm in a few groups (not chainsaw related) and this is spot on. So much bad advice.

I'm in a couple non saw related groups as well. Mostly observe but the one lake/pond group has some good info. A lot of parrots though.

 

[82f100swb]

While I really have no clue in hell what I'm doing, I built this:


I filled in those areas that fed the open port transfers eventually too:


That's a Partner 5000 top end

 

[82f100swb]

Built this thing out of a box of parts I almost threw away multiple times in the past two years.


It runs like this:

That's a 3/8 20" setup in some white birch that's been drying 3-4 years.
It is unported in that video, just base gasket delete. .0465 squish, 105/119/74.

 

[Powerstroke Cowboy]

The mufflers been ported.

Did you get the crank balanced?

 

[Mastermind]

The mufflers been ported.

Did you get the crank balanced?

Balance on a single cylinder engine.....not actually possible.

Complete balancing of reciprocating masses by adding rotating mass is not possible. Complete balancing of single cylinder reciprocating engine is not possible.

 

[LBracing]

Balance on a single cylinder engine.....not actually possible.

Complete balancing of reciprocating masses by adding rotating mass is not possible. Complete balancing of single cylinder reciprocating engine is not possible.

Although balancing like a multi cylinder engine is not possible, it is crucial to have a correct balance factor wich is basically a ratio of reciprocating mass vs counterweight . That ratio is typically anywhere from 50-60% .

When modifying an original crank into full circle like posted above , it should be rebalanced as the mod reduces the balance factor and increase vibration , wich well ... cost power defeating purpose of said mod in the first place .

Husqvarna factory full circles on the other hand with their extra light cups only affect balance factor by around 3% wich is why they get away with using the same crank and only adding or removing cups .

Very first crank I built from scratch about 10 years ago I had no clue what balance factor was and covers would fall off the saw just blipping the throtle so bad it vibrated

2 stroke stuffing did a pretty simple easy to understand video on youtube showing what is and how to measure balance factor for ghose interested .

 

[Powerstroke Cowboy]

Learn something new everyday they say. Well, today I just learned something new.

 

[Mastermind]

Although balancing like a multi cylinder engine is not possible, it is crucial to have a correct balance factor wich is basically a ratio of reciprocating mass vs counterweight . That ratio is typically anywhere from 50-60% .

When modifying an original crank into full circle like posted above , it should be rebalanced as the mod reduces the balance factor and increase vibration , wich well ... cost power defeating purpose of said mod in the first place .

Husqvarna factory full circles on the other hand with their extra light cups only affect balance factor by around 3% wich is why they get away with using the same crank and only adding or removing cups .

Very first crank I built from scratch about 10 years ago I had no clue what balance factor was and covers would fall off the saw just blipping the throtle so bad it vibrated

2 stroke stuffing did a pretty simple easy to understand video on youtube showing what is and how to measure balance factor for ghose interested .

Thank you for posting this. Way above my pay grade.

 

[Stump Shot]

Thank you for posting this. Way above my pay grade.

I think when they talk about balancing a single cylinder crankshaft, that is a bit of a misnomer in that what is actually being balanced is the entire rotating assembly, the crankshaft along with complete piston with rings etc..

 

[82f100swb]

I actually got extremely lucky when it comes to the balance factor on this one. It vibrates considerably less than a stock saw, and I honestly didn't do anything beyond truing it on the lathe.

As for the muffler mod, what I meant is the cylinder itself is unmodified.

 

[Al Smith]

You can open a big can of worms if you get into balancing .Things like resonant frequency come into equation .You want to run something that will rattle the teeth out of your head try a 10-10 Mac and it's a rigid mount engine to boot .Odd though because a 700 Mac which just has a larger bore doesn't do that or at least not as badly .

 

[82f100swb]

You want to run something that will rattle the teeth out of your head try a 10-10 Mac and it's a rigid mount engine to boot . .

I have one of those... I don't know how many Mac guys have tried to convince me the 10-10 is smooth and doesn't need AV...

 

[Al Smith]

I have one of those... I don't know how many Mac guys have tried to convince me the 10-10 is smooth and doesn't need AV...

Not do or do as much .I have one of the last ever made which is 57cc instead of 54 .I don't use it that much because it's a show piece but it doesn't rattle as much . I'm not certain if the later models used the windowed pistons of the earlier or more like 700 .