Part Four: Compression

[deye223]

I did not. And yes....it needs it.

Thanks ....... no more derail I will pm you

Cheers D

 

[Mastermind]

Thanks ....... no more derail I will pm you

Cheers D

I'm only here for the derails.

 

[deye223]

I'm only here for the derails.

Me too it's where most of the good info is hiding

 

[Stump Shot]

Thought that this McCulloch Pro Mac 700 squish band and combustion chamber was interesting for being stock and forty years old.

 

[p61 western]

Thought that this McCulloch Pro Mac 700 squish band and combustion chamber was interesting for being stock and forty years old.

View attachment 184293

Is this something for you Steve?

 

[drf256]

They say McCulloch’s were “maxed out” from the factory. By the look of the factory jugs I’ve seen, I can understand why that has been said.

 

[mobilak]

sguish 0.3 is safe for it husgvarna 560xp?

 

[Wonkydonkey]

@mobilak If I read your question right, your asking is 0.3mm ok, which is 11.8 thou.
Have you checked the reading a few times ?

I think that’s a bit to small for my liking.
I'm sure Someone else will come along and maybe or maybe not confirm my answer.

Btw.... your English is better than my Greek language .

We have a few members from Greece, so I,m sure they will help you out if you need some translation

 

[mobilak]

sorry for my english but translate it is my fault

squish 0.3 itis safe? husgvarna 560xp

 

[drf256]

Probably not. You want closer to .5mm

Make some type of base gasket for it, or sand the squish band with any old flat topped 48mm piston until you get there.

As above, make sure your measurements are accurate before you give yourself a bigger problem.

 

[Nutball]

I haven't yet taken the time to get the tailstock on my lathe figured out and dialed in. It seems a bit low precision and clunky than what I've experienced on a big old LeBlonde. The clamping handle isn't even positioned right on the cam making it useless.

But I have settled on a solution that so far has worked out very well. I use a nylon rod, turn it to size, or in the case of the chucked mandrel shown below, I had to shim it slightly with tape instead of turning it down, and for the smaller one I use for 2511t's: it was a slightly loose fit, so I took a razor blade and cut shallow valleys which also formed ridges that now make it a very tight fit. Then, after putting the cylinder on, I drill a hole through the intake port such that I can drive a wood screw in at such an angle that it both prevents the cylinder from rotating, and clamps it onto the mandrel. I've never tried making big cuts with this setup, normally only .005" at a time, maybe .007-.010" at the most.

 

[Al Smith]

They say McCulloch’s were “maxed out” from the factory. By the look of the factory jugs I’ve seen, I can understand why that has been said.

The design of the 10 series is a study of it's own .With the staggered transfer ports it should scavenge very well . I had thought perhaps either a sweep or a little finger towards the intake .from the first transfer might make a little bit of improvement but never tried it .
I never claimed to be the best but have realized some gains from exhaust work ,type muffler etc .Much else than that would be a guess at best .

 

[Nutball]

They say McCulloch’s were “maxed out” from the factory. By the look of the factory jugs I’ve seen, I can understand why that has been said.

I need to run more Macs, the few stock ones I've run have not impressed me, but they didn't have the best of chains either. Videos I've seen haven't been impressive either. Modified is a whole different story.

Does anyone shave a little off the side of the crown above the ring when adding compression to compensate for more heat expansion? Maybe only for race builds? I came across a 026 piston that had a much tighter fit in the cylinder than most other models I've measured, and it got me wondering.

 

[Stump Shot]

I need to run more Macs, the few stock ones I've run have not impressed me, but they didn't have the best of chains either. Videos I've seen haven't been impressive either. Modified is a whole different story.

Does anyone shave a little off the side of the crown above the ring when adding compression to compensate for more heat expansion? Maybe only for race builds? I came across a 026 piston that had a much tighter fit in the cylinder than most other models I've measured, and it got me wondering.

That's done to help the ring expand tight to the bore I believe.

 

[Definitive Dave]

Compression is Silly!!! Most of my race saws run less than 170psi
Here is a Mac that has the power to impress anyone. @mdavlee and I had to tag team the saw to get it started and neither of us are exactly small guys
Mike took the first cuts and then @Lee H took the reins of this beast (it's his by the way) and gave the cant some hell. If you are wondering how strong the saw is, watch uncle Lee's upcut and how despite plenty of experience and a good solid stance it started to push him back a little.
Trust me, a well built McCulloch is a thing of beauty!!

 

[jacob j.]

Compression is Silly!!! Most of my race saws run less than 170psi
Here is a Mac that has the power to impress anyone. @mdavlee and I had to tag team the saw to get it started and neither of us are exactly small guys
Mike took the first cuts and then @Lee H took the reins of this beast (it's his by the way) and gave the cant some hell. If you are wondering how strong the saw is, watch uncle Lee's upcut and how despite plenty of experience and a good solid stance it started to push him back a little.
Trust me, a well built McCulloch is a thing of beauty!!

A well-built Mac is pretty amazing and Uncle Lee builds some of the best. If you guys want a good read from the archives on modified saws and compression, go here:

https://www.arboristsite.com/community/threads/biggest-perpetuated-myths-about-modded-saws.65396/

Brian (Timberwolf) built some good runners when he was in it.

 

[Mastermind]

A well-built Mac is pretty amazing and Uncle Lee builds some of the best. If you guys want a good read from the archives on modified saws and compression, go here:

https://www.arboristsite.com/community/threads/biggest-perpetuated-myths-about-modded-saws.65396/

Brian (Timberwolf) built some good runners when he was in it.

Thanks JJ, a past from the past. 2008.....that's when I joined AS.

Dennis Cahoon once told me that as long as there was no physical interference, the tighter the better on squish clearance. Brian (Timberwolf) once suggested .014 as a good starting point to me when I asked him directly.

Keep in mind that these are guys taking things over to the extreme side.

In my experience (and at this point I have a little) you need enough squish clearance to allow for carbon to build up. And it will in a real world working saw. Personally, I use .020" on a smaller saw, and .025" on a bigger saw.

Compression adds grunt. But....can be detrimental to RPM. You gotta build the saw to suit the end use. There are no one size fits all solutions. Which is why I try to refrain from wading in these days. I'd rather just read along....and be amused.

 

[jacob j.]

Dennis Cahoon once told me that as long as there was no physical interference, the tighter the better on squish clearance. Brian (Timberwolf) once suggested .014 as a good starting point to me when I asked him directly.

Keep in mind that these are guys taking things over to the extreme side.

I'm my experience (and at this point I have a little) you need enough squish clearance to allow for carbon to build up. And it will in a real world working saw. Personally, I use .020" on a smaller saw, and .025" on a bigger saw.

Compression adds grunt. But....can be detrimental to RPM. You gotta build the saw to suit the end use. There are no one size fits all solutions. Which is why I try to refrain from wading in these days. I'd rather just read along....and be amused.

Dennis and Brian both built some really great running engines. McBob also pointed out that in a higher compression engine, the higher compression will slow piston speed more after the exhaust port is closed, depending on
the weight of the reciprocating assembly among other factors, and can be important in larger engines, such as bikes. Like you say, you can have parasitic losses in a saw engine.

I've gone as tight as .016" or so in a couple of my worksaws and that was fine, but I'm typically working in cooler conditions where more oxygen is available. When I was doing the three-year hazard tree cutting
contract in the south Cascades, I ran a looser squish because it was in the heat of the summer at high altitudes with a lot less oxygen. That strategy worked well.

 

[Stump Shot]

In my experience (and at this point I have a little) you need enough squish clearance to allow for carbon to build up. And it will in a real world working saw. Personally, I use .020" on a smaller saw, and .025" on a bigger saw.

I too vary the squish tolerance for the size of the saw in cc's in my work saw's. I've been varying it even more for a milling saw or old man saw.
Compression(for the most part) seems to follow through this arc nicely, combustion chamber design will throw this off as well as band width, which should be taken into consideration before machining.
I believe the squish flow follows this arc as well and it would seem to prove out to me in my dickering to pan out, although I have no hard data to prove that, just the feel of the saw's and the note they make to give me an impression is all I have to go by.

 

[Al Smith]

A McCulloch engine can be a study all of it's own .I know more than most but I'm by no means a expert but I know one .My bud Louie who was a crew chief on a Huey gun ship in 'Nam and I went to apprenticeship with was number 2 in the nation several years in a row in the glory days of 2 cycle karting .He still has his notes and his port maps .Poor guy had a stroke though and I haven't made contact with him for several years .BTW he is exactly one day older than me .
Louie was on the watch for a decent 101 for me that didn't cost a kings ransom .There used to be a zillion of them but they went the way of the passenger pigeon .
Dan Henry sent me the bones of a super 44 I still haven't done anything to .I might be able to throw together a 5 cuber in vintage style .You never know until you try .Big kids toy more or less