Yet Another 42cc Poulan Porting Thread

[Chris-PA]

I did a thread some time ago when I first built this saw (http://www.arboristsite.com/community/threads/building-a-42cc-poulan.231308/), but the pictures are gone now. So is the engine that ended up in it, as it was really a rat and I kept playing with it until I eventually wrecked it. It's been on a shelf for a while, and I finally found part of a used 2001 PP260 saw on eBay with a good engine (well, other than being terribly carboned up). So I thought I'd take some pictures. I'll be trying to combine the best parts as I build it.

This is a 2001 engine, which is different than the final engines they installed before they went strato. This is a shot of the 2001 engine (left) and a 2004 model:

The transfers have larger volume and different shrouding at the bottom. The 2004 also has less aggressive timing, smaller ports and the exhaust does not have the steel insert. It also has a cat muffler. Here is the timing map I made of the stock timing:

Unfortunately these engines have a large (0.040") squish, probably so couch potatoes don't overexert themselves trying to start it. Since I don't have the means to weld a pop up, I just have to live with it. It means I will not be raising the exhaust, but then 155 is plenty anyway. The intake duration is small, and the case compression angle is too large - I would like it to be around 40deg.

I have had issues increasing the intake on these because of the location of the impulse port right below the intake, and I've made saddle shaped ports and such, but here I decided to just widen the intake, and flatten the lower edge (based on Mastermind's recent comments), and to increase the duration by notching the piston skirt. So both intake and exhaust got widened to 55%, but not intentionally changed in timing. Intake:


Exhaust:



Then I worked on the piston. I wanted to reduce the blow down to 20deg, but I've never been able to grind the transfers properly. Given the large squish, I decided to try a small bevel on the top of the piston:

Then I notched the skirt for the intake:


I had a really clean crank and bottom cap from the 2004 engine, so I used that. The later cap has a groove cast in for better sealing.

 

[Chris-PA]

So I put it all together, and checked how the timing came out - and I was disappointed. Basically, I learned that a little extra beveling and smoothing can easily add a couple of degrees, and before you know it you've gone much father than you planned. First, I should not have tried to increase the blow down - that went much more than I wanted. Then the intake went too far too, so here is where I ended up:

The good news was that all the error was on the piston, and I can get a piston kit for $19 shipped. But I decided to try it anyway, as the numbers are not that far from my Poulan 2775 and it runs great. So on with the assembly.

The earliest cases had a "turbo" scoop molded into the case, which they eliminated in the later ones, so I'm using the 1995 Craftsman case:

There are Walbro and Phelan flywheels - I'm using the Phelan (right) which has fewer, larger fins. Just because I like it better! I advanced the timing 6deg.

The later models with catalytic converters have a nice shield which also fits the earlier muffler - these are great as you can really open the outlet up and not melt stuff (well... more on that later):

Engine installed:


I used a larger Walbro carb (34/64" instead of the 28/64" that comes on these). This carb came off a 46cc Poulan, but there are various similar models used on Husky 142's, etc. It is a bolt on except that it has no purge bulb outlet nipple, so that is blocked off.


The muffler opened up - I cut out a large part of the internal baffle:
Assembled:

 

[Chris-PA]

It fired up and seemed to run quite well. So I used it to drop a dead white ash in my effort to increase the firewood pile for this winter. It ran great - it's certainly competent, although I can't say it's blazingly fast, and I'm sure that's mostly due to the large squish. It starts easily, will idle indefinitely, does not bog easily, and keeps pulling. Here it is trimming up a 14" round of white ash - it's an 18" bar with Carlton N1:

Not that fast, but in its defense that wood is pretty hard. I will also say that you can tell this is not a clean running strato engine - the thing certainly pumps out its share of fumes.

 

[Chris-PA]

When the daily thunderstorm hit I took it back to the barn, and noticed that the aluminum shield I had glued on the case by the muffler had come off. This showed the blistered edge of the case. Most of this is old damage from an earlier muffler:

I decided to add the shield from a later saw:

This has a clip that interferes with the non-brake cover I used:

I did not feel like notching it yet so I put on a chain brake cover. Every saw should have a purple chain brake.



So I'm happy with it, I'm glad it runs again, and I probably won't change the piston. I probably won't run it near as much as the GZ4000 saws as I like strato reduced fuel consumption and emissions.

 

[Four Paws]

Cool stuff! Happy to see someone working on their own equipment. Modifying the piston is always a safer approach and allows the builder easier experimentation. Thanks for sharing.

 

[Rookie1]

I like those saws. I usually open the muffler and run it. I'm not near as crafty as you with porting. I like the fact you took the time to show off a plastic saw.

 

[Chris-PA]

I ran it again today, and I have to say it's pretty strong. I guess I expected it to want to rev more, but instead it pulls pretty hard and doesn't want to bog down. I'll have to try it in some other wood besides this ash, and with a different chain too.

 

[Chris-PA]

I ran it against my other 42cc Poulan in really hard dead hickory today. Both saws have PP260 engines, the first is stock with only a muffler mod, and the second is the ported saw from this thread - it doesn't look like I achieved any speed improvement, although the ported saw feels stronger. The stock saw was wearing Carlton N1, while the ported saw had Oregon 91PX.

 

[ncpete]

Now if i was only smart enough to find a thread on porting the pp5020av.

 

[Chris-PA]

Now if i was only smart enough to find a thread on porting the pp5020av.

I have wanted to work on one of those - someday maybe I will find one cheap. I really don't need one, but the design impresses me.

 

[zogger]

I ran it against my other 42cc Poulan in really hard dead hickory today. Both saws have PP260 engines, the first is stock with only a muffler mod, and the second is the ported saw from this thread - it doesn't look like I achieved any speed improvement, although the ported saw feels stronger. The stock saw was wearing Carlton N1, while the ported saw had Oregon 91PX.

That is *real* dang good, especially in that hickory!

You do quite well with these inexpensive saws!

 

[angelo c]

Nice work bro !!!

 

[weimedog]

I read this thread again. This is an awesome thread! Have to figure out a way to connect at one of our GTG's. I have to wonder if we could find another piston with the same bore from another saw with a taller crown to take up some of that squish. Like we can with the Stihl 064 52mm in a 52mm Chinese BB 372 cylinder build. Meteor has an online catalog where they list piston dimensions. What was your concern about having 19degees blow down? That should be reasonable... even 17 or 18 on a little screamer like that. Or did I interpret that wrong?

 

[heyduke]

how do you think this saw compares with th later stratos?

 

[Chris-PA]

I read this thread again. This is an awesome thread! Have to figure out a way to connect at one of our GTG's. I have to wonder if we could find another piston with the same bore from another saw with a taller crown to take up some of that squish. Like we can with the Stihl 064 52mm in a 52mm Chinese BB 372 cylinder build. Meteor has an online catalog where they list piston dimensions. What was your concern about having 19degees blow down? That should be reasonable... even 17 or 18 on a little screamer like that. Or did I interpret that wrong?

Thanks! I wasn't real clear on my concerns about the timing - 19deg is OK, but it's the way I got it that I don't really like - those bevels on the edge of the piston mess up the squish area. Really the long intake duration concerned me, as combined with the advanced transfer opening it reduced the case compression angle more than I wanted. I try to remember that the ports are symmetrical, and and the closing event can be important too.

As for the squish - look at the first picture. I could take 0.020" off the base in a lathe, or frankly with a file. The bearing pockets on these engines are as-cast with no machining. They're nice, but there must be some slop. The bearings are covered with rubber all around - how many thousandths is that good for? When you take one apart there is a significant imprint of the bottom of the transfer in the rubber.

The point is that one could grind out the bearing pocket 0.020" with a Dremel and get close enough - the rubber coated bearing and the sealant will cover quite a few sins. I think if I turn a reference disk to the correct nominal diameter for the bearing pocket it would be a big help in grinding it. Unfortunately my intake duration is too long already and dropping the cylinder would probably put it up around 170, so I'll have to order a new piston.

And now I'm wondering if I can make a workable turning mandrel on the 3D printer......

how do you think this saw compares with th later stratos?

Unfortunately I have not (yet) messed with one of the later strato versions. I hope to do a 5020 one of these days.

 

[heyduke]

Unfortunately I have not (yet) messed with one of the later strato versions. I hope to do a 5020 one of these days.

i picked up a new 4218, the stato model, recently. i just wanted a strato to experiment with. there's a lot of room for improvement on what comes out of the poulan factory. it was poorly tuned and gutless. enriching low and high helped a little. i'm thinking about advancing the ignition. what are your thoughts there? i didn't realize that those fat rubber donuts were on the main bearings. thought maybe they were crank seals. that's sketchy. is the 2050 a strato?

 

[Chris-PA]

i picked up a new 4218, the stato model, recently. i just wanted a strato to experiment with. there's a lot of room for improvement on what comes out of the poulan factory. it was poorly tuned and gutless. enriching low and high helped a little. i'm thinking about advancing the ignition. what are your thoughts there? i didn't realize that those fat rubber donuts were on the main bearings. thought maybe they were crank seals. that's sketchy. is the 2050 a strato?

I been advancing the timing maybe 3 to 6 degrees- it seems to give them a little better throttle response. I figured it was appropriate given that a ported engine should hold a higher rpm.

The rubber coated bearing seem to work OK. They sure have made a lot of them, and it's not one of the things I read about causing trouble.

The PP5020 is a strato. The engine design looks to be very similar to the 4218, just a bit bigger. It has the same plastic transfer inserts that effectively make closed transfers out of a simple open casting, and similar port design.

 

[Chris-PA]

A couple of fun pictures from a cut-away engine I made of some scrap parts a while ago.

Big Squish:


Counterweights approaching the lower transfers:

 

[lwhaples]

Very cool project!

 

[Moparmyway]

Thanks for posting this ....... awesome work on what most consider "throw away" saws.
I have a few and they are pretty reliable !
What program did you use for the port timing charts ?