Why is everyone hung up on machining?

[Big_Wood]

you know, when it comes to this i agree fully. i talked to walkers saw shop who have been porting saws for far longer then anyone else here and they say they used to port saws like the guys here in the past but longevity becomes an issue. they now only do their race saws like the guys here. they are porting for guys who use their saws in some big wood compared to back east though. i'm not really sure what to think but what my buddies at walkers say but sounds about as convincing as it gets. how does a firewood hack who is constantly one AS test the longevity of a particular ported saw is what i think. it is why i will not send a saw away for porting, i am convinced on gains but not convinced at all on longevity. maybe one day i will be. i will say that there is a 660 in the walkers saw shop from a builder on here that barely made it 6 months before she was done. rod stretch and carbon build up is what mostly did her in apparently but the mains and big end weren't all that tight as well. it did have a sticker on it but i will not disclose any info on the builder. i'm still tempted to get a toy ported but will refrain from porting any work saws.

 

[blsnelling]

I'm not a fan of more than 180-190 PSI compression. I just haven't found more to be necessary for a strong dependable worksaw. On the other hand, I have not seen cylinders coming apart from builders that do like higher compression.

I've never seen a pitted piston crown either. On 50cc saw I'll run as tight as .016". 90cc saws I try to keep at .020". I personally owned a 066 for several years that only had .017 from the factory. I ran a ported topend on that saw and never saw signs of pitting. All I run is premium pump gas.

 

[Deets066]

On a ported saw that is tuned properly you will have less carbon build up than a stock saw

 

[zogger]

Seeing any difference in longevity with one ring versus two ring pistons?

I have a theory that two rings might keep the piston centered better.

Now how about strato engines and longevity, shouldn't they, by design, run cooler?

Not a porter or production cutter, notice my question marks.

 

[Termite]

Seeing any difference in longevity with one ring versus two ring pistons?

I have a theory that two rings might keep the piston centered better.

Now how about strato engines and longevity, shouldn't they, by design, run cooler?

Not a porter or production cutter, notice my question marks.

Good questions Zogger, I wish someone would have answered.
I think those big strato pistons need two rings because of there size.
And I think the big slug keeps them from accelerating as fast as the nonstrato saws.

 

[mdavlee]

Seeing any difference in longevity with one ring versus two ring pistons?

I have a theory that two rings might keep the piston centered better.

Now how about strato engines and longevity, shouldn't they, by design, run cooler?

Not a porter or production cutter, notice my question marks.

The skirts keep the piston centered for the most part. You only have a tiny bit of clearance between cylinder wall and piston. That's why oil is so important.

 

[blsnelling]

I didn't see where the OP ever said what oil or ratio they were using. It especially matters in the saws being discussed here, especially when ported.

 

[bitzer]

This is a bunch of horseshit. I put 1500 hours on a 390 every year and I have yet to have an engine fail. Our gas around here is half corn too. The problem with any work saw is the rest of it shakes apart. I'm not buying it.

 

[Rx7man]

Burnt bearings would give me the hint to run a little more oil, especially if it's happened on more than 1 saw... I've found a tweaked saw should have at least 1 step more oil in the mix.. IE, from 50 to 40:1, or from 40 to 32:1, and every saw is a little different on what it likes, but what all hot saws have in common is that intake velocities are much higher than stock and less oil stays in the crankcase.. if you put them through a piss revving contest in lean tune with 50:1 and go working them hard.. I certainly would EXPECT failures, and that's not necessarily the builders fault.

Cracked cylinders? I'd really like to see the pictures of where they cracked.. if it's at the base, perhaps its a torquing issue.. or using a better washer that could help it?

I find on my 65cc saws 180PSI is enough compression, and as you get bigger you're not going to want to pull on a 90cc with 200 psi.. That extra compression creates a lot of heat, and possibly detonation due to it...

 

[strtspdlx]

I just read through this. And I'm no rocket scientist but I'd think if your having consistent failures it because your trying the same thing over and over and expecting different results. If cylinders are cracking and bearings are coming apart. I'd think it has to do with heat input and Cooling (oil). So either your not using enough oil or the motor doesn't have the capacity to hold enough oil to properly cool. Especially if you're wasting crank bearing this could warp the cases and cause them to crack the heads. Also as mentioned improper torquing or poor choice of cylinder fasteners could be cracking the head. Have you tried checking the base of the head and the saw for flatness? I'd be almost willing to bet consistent failures would mean something in the case isn't right if they're always the same bottom end.


Regards-Carlo

 

[Heffalump]

One of the more interesting threads I've read in some time.

Obviously nothinglasts forever, but I want my current project to last a long as possible, while still being a beast. I'm repairing/refurbishing a Jonsereds 80 with a 90P&C. My understanding is that these old Jonny's were known for high compression, 200+psi. Granted, that is all anecdotal information. You know, "my saw had over 220psi!.....that's nothin', my dad's saw had 238psi the day he brought it home brand new!" This is a two-ring piston, and the saw body is overbuilt compared to today's offerings, and could likely handle high compression quite well. Still.....

The base gasket that I found on there is a sad little piece of crepe paper, about .005" thick. Since it had already blown out I was planning on deleting it. I will also be widening out the intake and exhaust just a few thousandths. Reading this thread, should I be thinking of perhaps cutting a thicker gasket to DECREASE compression? Perhaps, use the gasket thickness to dial in a compression level of about 200PSI?

I'm not a logger of any kind. We have some wooded property in the PNW that sees high winds pretty regularly. Storm cleanup and some firewood is what I do, and 24"+ trees are not at all uncommon for me. This saw runs a 32" bar with a 7pin sprocket It ain't for racin', nor do I call on it for full days of abusive use. But still, I very much like the saw and want it to be around for some time.

 

[blsnelling]

You'd be better served to start a new thread on the build of your Jonsered.

 

[Heffalump]

Fair enough.

http://www.arboristsite.com/community/threads/jonsereds-90-woods-port.279207/

Perhaps a better way for me to ask this question would be, what are the suspected limitations of the hardware that cause what @CanadianCarGuy refers to as premature failures? Lots of people are porting, squishing, and hot-rodding saws. As he said, most of these guys are weekend-warriors. GTG-Goliaths, if you will.

@CanadianCarGuy seems to imply, as I understand his posts, that there is a need to perform custom engine work on a saw in order to get it to perform at a level that will be acceptable to a full time logger. He also seems to indicate that there is a not-fully-understood predisposition to premature failure, but that does seem to be some correlation to high compression. Laws of thermal dynamics: More pressure equals more heat.

Multiple folks on this thread point out the importance of quality/quantity of oil with regard to cooling the engine. This would facilitate a need to flow enough new fresh oil through the system as is requried to adequately cool. So if there is more heat in the system from increased pressure, then the system needs increased flow for additional oil to cool properly.

So I am wondering, without any expectation of a completely defined answer from anyone, is there some sort of ideal flow and pressure that builders should shoot for instead of shooting for a minimum squish clearance, or a maximum opening of a port?

Again, this is one of the more interesting threads that I've come across on this site. I'm not trying to be a brainy geek, I just really enjoy digging into stuff like this!

And yes, I do see that most of the posts on this thread are from 2014.... It's still really cool stuff!

 

[Rx7man]

Well, the oil doesn't really do any significant cooling, the oil will help prevent heat from happening in the first place, but it can only prevent the heat caused by friction, and by helping the rings seal against the cylinder, so there's less hot blowby heating the piston from the sides. The heat caused by compression and burning fuel have to be dealt with in other ways.
FUEL cools the internals.. and it does that in 2 ways.. the first, which is most important to the bottom end, is the evaporation of the fuel causes a serious temperature drop in the air. the second way is it lowers the heat of the flame (when a richer mixture is used), which is probably more relevant to the P&C.

 

[Heffalump]

Interesting...

I think maybe I'm not understanding 2-strokes. Fuel is "aspirated" through the carb, and vacuum drawn into the crankcase as the piston rises through the cylinder on the compression stroke. As the piston falls on the power/exhaust stroke, combustion gasses exit via the exhaust port, and are propelled by A. The force of the combustion, and B. The pressure placed on the crankcase fuel vapors by the piston while it is moving down.

Where is the evaporation taking place?

 

[Heffalump]

Ok, I think I am getting this now. Did some more reading, the evap is just a function of the fuel/air mix running around inside the crank. There is no specific evap step or mechanism.
So as the fuel mix vapors enter the crankcase, it coats all the internals. As more vapor passes over the internals, some of the fuel evaporates and leaves the internals covered in oil. The oil protects the internals, and the fuel evaporation cools the internal temperatures.

With this in mind, I would think that maximizing flow becomes even more important with regard to longevity. Has anyone ever heard of someone hooking up a saw to a flow meter and turning the crank externally?

 

[Rx7man]

I think it would be hard to do and get meaningful results, as every 'section' of the engine affects the previous and the next, so a restrictive exhaust is going to affect the intake, and until you make some fire you're not going to have enough flow through that to be able to judge it.. I do want to build a dyno, because in the end, that's what can tell you what's going on.

Another note, As long as the fuel hasn't evaporated, the fuel/oil mix isn't very good at lubricating anything, it's only when all the fuel has evaporated and you have oil that it really starts to do it's job, thankfully this happens quickly. I won't go into more detail here, but this is where I learned this, and it makes sense in my mind http://forum.dirtrider.com/discussion/7169620/spooge-101-/p1

 

[mdavlee]

Daniel and those guys are cutting 6-7 hour days on steep slopes. They don't want to lug around any bigger powerhead like a 395, 3120, or 880.

 

[Heffalump]

I think it would be hard to do and get meaningful results, as every 'section' of the engine affects the previous and the next, so a restrictive exhaust is going to affect the intake, and until you make some fire you're not going to have enough flow through that to be able to judge it.. I do want to build a dyno, because in the end, that's what can tell you what's going on.

Another note, As long as the fuel hasn't evaporated, the fuel/oil mix isn't very good at lubricating anything, it's only when all the fuel has evaporated and you have oil that it really starts to do it's job, thankfully this happens quickly. I won't go into more detail here, but this is where I learned this, and it makes sense in my mind http://forum.dirtrider.com/discussion/7169620/spooge-101-/p1

That was a very cool article. Makes me feel better about running all my saws at 40:1.

Daniel and those guys are cutting 6-7 hour days on steep slopes. They don't want to lug around any bigger powerhead like a 395, 3120, or 880.

"The whole chainsaw is a compromise. You fix one problem and you create another. Sure you could design the 'perfect' chainsaw, but it would weigh 40 pounds!"
-Niels Hartz, Senior Product Engineer, Electrolux Motors AB

As previously mentioned, I have a bunch of old magnesium JonnySaws. When I use those things, they give me the impression that they'll never die. I have run one of my 70E's side by side with a more modern 60-70cc class saw and have not felt as though my old Jonny wasn't "pulling it's weight." That said, I could NOT imagine lugging that beast up and down the terrain of the PNW for a whole damn day, let alone something like my 80/90. And I KNOW that particular unit saw time in a logging camp. Mad respect to all those tough ol' bastards who lugged the heavy-ass Macs and David Bradley's and Homelites up and down the slopes of the western logging operations.

But I digress.

I'm gonna chew on all this a bit. I have no idea why I love this stuff so much......but I do!