Husqvarna 445 clammy build

I'll blame Steve for all this. He talked me into posting a build on this saw since it was getting torn down completely to get sealed up anyway. I had put a carb on this saw but it ran worse with the "new" AM carb than with the OEM original. I rebuilt it (the OEM carb that is) and it still seemed to be sucking air once it warmed up. I'm not very good at troubleshooting saws, but I'm curious about playing with the insides anyways. I have had seals for it sitting here in the shop for 6 months or so and just haven't gotten to it yet...

SOOOOO... here we go although this may take a while to get through it.

I tore it down and saw no obvious issues with it. If I'm this far in I might as well see if I can warm it up a tad.

It's an x-torq with the strato ports.



I checked the numbers:
exhaust opens @ 105* ATDC duration of 150*
x-fers open @ 117* ATDC giving it a blowdown of only 12*
intake opens @ 71* BTDC for a duration of 142*

exhaust port is 20mm wide in a 42mm bore


Lower x-fer openings match up to the lower crankcase alcove pretty well, both are 20mm wide side to side (blue marks) and match up well at the outer edge of the crankcase (green marks). Those edges will not get touched.


The upper transfer roofs are angled a little downward and the roofs will not get touched because the blowdown is already very short. There is a slight burr or plating bulge along the roof of the upper x-fer that I can catch the tip of a small screwdriver on in places. I will take a very small diamond flat file to eliminate that imperfection at the cylinder wall to reduce any drag in the flow at that point. This picture shows the roof of the transfer (the bottom edge in the pic) angles towards the middle of the transfer port on the other side of the cylinder. It's not a lot of angle but just wanted to note that it isn't flat or 90* to the cylinder wall.


The red mark is the x-fer roof edge that has the slight imperfection. You can't really see it but you can feel it and even catch a tool on it. This will get eliminated and just a slight chamfer on it. this port isn't very wide so the ring can't flex into it very far so there is a low risk of hanging in this port unlike a WIDE exhaust port that is too flat across it's roof.


Enough for now. After dinner I'll try to post my plans for this cylinder so the folks that really know how to work on saws can keep me on track... I tend to do goofy stuff that might suck me into the ditch sometimes and someone needs to keep an eye on me... LOL

The wife is expecting me to make a Rueben casserole for dinner... She doesn't have to twist my arm very hard...

 

Cool!
Couple years ago, a friend found a Jonsered version of this saw in a box disassembled and destined for the trash. He gave it to me. Original p/c was trash, so I picked up the 450’s top end an put it on. It passed all my tests so I assumed it was straight gassed. No mods since it went to dad, he appreciates the blue button.

It’ll be fun to follow along.



Edit: oh btw, that original cylinder cleaned up pretty good so if you finding yourself wanting to go nuts experimenting, I’ll send it to ya.

 

I'll take the blame. The more saw build threads the better in my opinion.

You plan on widening the exhaust? I usually go to 65% of the bore diameter and keep a rounded profile. Have hung a ring yet.

 

Some random thoughts while the casserole is in with awesome smells wafting through the house.

Yes, the exhaust will get widened to 27 or 28mm and it will have an arched roof. The roof will NOT get raised cuz on a 45cc saw I think we'll want all the torque we can keep. I'll get deeper into the plan later when I can doctor some pix to explain what I'm thinking.

Unfortunately this saw came to me not running so I won't have the chance to see if I manage to get some gains out of it... Or oopsies...

 

I agree on the exhaust roof height staying the same. Widening it plus lowering the intake some will probably make a nice power change.

 

I'm a bit more interested in the casserole....love me a good reuben.

 

MAF143

Im I seeing this right?
There is no bottom metal crankcase on these Husqvarna clamshell saws? Every clammy I've been in has a metal bottom to the crankcase that bolts into the plastic chassis, even the cheap poulan saws. Interesting.

 

Unfortunately this saw came to me in a non running condition so I don't have a "before" to compare it to. The goal is to at least get it running and hopefully get it to outperform my MS250 that I'm pretty happy with. The other part of this quest is to learn more about these clammy saws so when my MS250 gives me a reason to open it up I'll know how to "enhance" it some.

EXHAUST
The exhaust port will get widened. If it wasn't a clammy, I'd have the base and squish cut, raise the exhaust roof and lower the upper transfers to get some more blowdown. But on a budget, that's not an option.
I'm thinking widening to 27 or 28mm keeping the arc going with rounded corners (I was a draftsman, not an artist, pardon the crappy markings in the pix). Then when lightening the piston, putting a matching arc on it so it opens much wider to let more high pressure gases out quicker before the transfer ports open. I did the piston arc to match the exhaust port on my 357 and that saw runs ok. I'll blend the inner port to the opened up outer side of the port as well, then match the gasket, heat shield, and muffler opening to it.



Here's the piston arc I did on the 357 and I'm planning the same on this saw only maybe a little wider. I just don't want to get too close to the ring groove but I want it to match the port roof for as wide as I can. This mimics having a flat exhaust port roof without the risk of hanging a ring.

Not a great pic but hopefully you get the idea.


INTAKE
Duration seems kinda short to me, but I'm not sure of all the relationships that may get shifted when the strato ports come into the picture. I have increased the intake duration to upper 150's or even to 160 on the couple of non strato saws that I've done but with this being a strato AND having very short blowdown, I'm thinking that increasing it too much will to little to improve performance but may do a lot to just dump unburned mix out the exhaust.
I plan on blending it a little wider, but not lowering the intake floor. The strato ports in the upper part of the pic will not get touched. While lightening the piston I will shorten the skirts about 1.5mm to gain duration instead. Adding duration is on hold till I learn more about the blue piston port that I have questions on below.


PISTON
The skirt on exhaust side of the piston can be shortened to match the intake without free porting. I am planning on taking a few grams off the piston. This pic is the 445 piston. More on lightening it later when I have a little more info in my head.
I have questions on this.
The area with the red mark I understand. That opens the strato ports to the upper bypass ports so straight air can be loaded down the transfer tunnels a little way so the first part of the charge entering the combustion chamber and exits the exhaust port is straight air as opposed to fuel / air mix that won't get stuffed back in since there is no tuned pipe on a saw. That function of the strato design to save gas and lower emissions I get... not like a pro porter or good engine builder, but enough to know why they are there and how they work.

The area marked in blue I'm not quite sure about. I have a couple guesses but that is all they are... I'm hoping someone who understands its' function steps in and enlightens us about it. I would like to understand it better before lightening this piston to the point of making something not work as intended. If not, I will just not go crazy on the piston...
As the piston is going up in compression the blue area short circuits the upper transfer port to the crankcase right before the strato ports are opened to the transfer ports by the red area. And as the piston is coming down in the power stroke, the blue area opens the upper transfer port to the crankcase via the hole in the piston after the stratos charged the upper transfer tunnels with air. I see what it does, but I'm not sure what purpose it serves and how this timing and the size of the hole in the piston acts to improve the functionality of the saw.

Two stroke basics I kind of understand and I even get the strato stuff that blew me away when I first encountered them, but this blue piston port thing is over my head at this point and I would love to learn more about it.



LOWER X-FERS
Access to the lower transfers as the piston compresses the mix down into the crankcase looks to me like the mix has to make a 180* transition up into the transfer tunnels around 2 90* corners. I'm thinking that knife edging the divider between the two tunnels (blue mark) is a start and rounding the 2 edges from the crankcase at the entrance (red line) would be helpful while not increasing crankcase volume very much.


IGNITION TIMING
I'm planning on shaving the flywheel key for about a 5 or 6* timing advance.

My brain is smoking from thinking too much and my belly is full of Rueben casserole so I may have to grab a bowl of ice cream to cool things down for the evening.

 

You're seeing it just like I saw it... No metal bottom. not a mag source...

12* blowdown gave me a double take also... I measured it several times, had another beer and measured it again...

 

Many years ago as a youngster someone told me about Rueben sandwiches and it kinda turned my stomach... Wasn't crazy about swiss cheese, hated sauerkraut, threw away Rye bread, didn't really care for corned beef, and was grossed out by Thousand Island dressing. But all together in a sandwich... WOW.

Changed my life... along with many other things...

 

This was me too. I like kraut and corn beef now but still don't do swiss and rye bread. Lol

 

Cool build. I'll be watching since i own a 445. I'll just throw this out there but if we both make it to Dennys GTG in May i could bring mine with for a comparison if you're interested. It's bone stock. Not even a muffler mod.

 

I haven't ported a strato saw yet Monte. This will be interesting to learn.

 

MAF143

Your turn. My junk is running. Not cutting, but running.

 

OK, OK...
Been over on another site checking in with the big brain porters to ensure I'm not totally losing it... LOL

The area of the piston that I was questioning (marked in blue above) is just a void to shed piston weight. Turns out I was way overthinking again... The red void as mentioned is the Strato port to transfer tunnel pass through link. I did find some other port jobs on the internet on the 450 big brother to this saw. I'm getting a better fix in my head of where I want to go with this cylinder and piston. It's been a busy day today and work is demanding 10-12 hour days this week, NO FUN... All work and no play makes Monte a dull boy...

I'll try to get back on tomorrow evening as the plan comes more in focus and hopefully get the carbide to the Loom-numb this weekend.

 

1. Widen exhaust, blend and match muffler opening as described above. Of course a muffler mod.
2. Arc on the piston crown to match the exhaust port roof.
3. Lighten the piston as much as I am comfortable with. I'll try to get some weights B4 and after. I'm no longer worried about the blue void in the piston.
4. Trim the skirts of the piston to equate to lowing the intake port floor 5* to get the duration up into the 152* range. I'm thinking conservative here.
5. Trim the lower transfer tunnel up maybe a 1/4" and round it to get the square corners that cause eddy currents gone. I want to increase flow by reducing corners, but don't want to increase CC volume any more than needed.
6. Clean the flash out of the upper transfers to clean up the flow, but don't raise them or change the angles. I don't really want to open much up in transfer tunnels or crankcase to keep volume down and velocity up. Blowdown is already shorter at 12* than I like, but I don't want to raise the exhaust port to increase it for fear of losing any torque this saw has.
7. Trim the flywheel key for a 6* ignition timing advance.
8. Widen the intake port but not lower the floor, the piston skirt trim will handle the timing change, but the intake port widening will allow more flow. Again, I'm thinking to not increase the crankcase volume so the velocities and pressures stay up as much as possible.
9. Small carb on these so I may look at some carb work to smooth flow there.

 

A 550xp only has 10° bd. Just the way they’re designed. A Dolmar 7900 likes 28° and 20 will kill the power. No idea why they do what they do, just gotta try new things to see how it affects the outcome. Don’t get lost in a “supposedly better numbers” game or a “this worked great last time” mindset as you’ll only end up more confused. Just roll with what they gave you and make small mods here and there

 

Thanks Kevin. Sounds like great advice.



Maybe I should stick to the stuff I understand well... Muffler Mod, timing advance, square filed chain, Drinking PBR, Swedish Candles, peeing the bed, etc...


But I won't...

 

And magnesium fires?

 

I got a chance to play last evening...

Trimmed the piston skirts and cut some flash off the inside of the piston. The skirt is marked with my target to grind off. I ended up with the intake timing going from 71* with a 142* duration to 77* with a 154* duration.

This raises a question for me though with this being the first strato port saw that I have ever messed with the intake timing. I'll have to sit down and go through the cycles with the timing wheel and think through the relationship between intake port opening to the crankcase vs. the intake timing of the strato window of the piston opening to the upper transfer port of the cylinder to insert ex purge air into the tunnels. At first take, I'm thinking I should raise the strato window on the piston the same amount that lowered the intake (6*). The raising of the strato window (in my brain) isn't really to improve overall performance, but to maintain the strato's objective of saving gas and lowering emissions. But if you open it too much it would hurt performance.

So if this thread ends abruptly, you can assume my brain exploded thinking about this relationship...

Skirts and innards of the piston after lightening it up some.


Piston weighed in at 56 grams stock. I was only able to take off a single gram where I feel comfortable with keeping strength and longevity of the piston. This is a working firewood saw after all.

I couldn't let the wife see me using her nice scales in my shop!!!

Widening the intake port turned out to not really be an option after comparing the width of it to the width of the piston between the strato windows. Camera angle isn't lined up perfectly but you get the gist. Gotta have coverage of the port!