Poulan Pro 260 build

Anyone interested in seeing a hack possibly make a saw slower than it was stock? I dabble in saw hackery and I'd like to see more of you peeps try your own saw mods and share them here as well. Maybe this will spark that interest. I have gained my knowledge of the basics from a professional but anything you see here cannot be blamed on him, as I like to color outside the lines, so to speak. Anyway, here it goes...

 

This is what I'm working on. Since the pic I installed new fuel filter and lines, rebuilt the carburetor, put new bearings and seals on the crankshaft and started modification of the piston.

Eric Wanderweg

MAF143

 

Base numbers are...

Squish - .041
Exhaust - 108° After top dead center
Transfers - 125° ATDC
Intake - 66° Before TDC

More later. Stuffs to do.

 

Cool build Eggshooterist What are you modifying on the piston, the little windows next to the wrist pin or just smoothing the casting lines inside?

 

This is a windowless piston with no scallops out of the skirt bottom.

 

This is probably it's finished state.

 

The cut outs in the skirt, in my mind, facilitate flow into the lower transfers. I'll match the lowers best I can once I establish exactly where the skirt rests at bottom dead center. Its close in this picture based on where the ring has polished the bore.

There can be drawbacks to removing material in the crankcase and from the bottom of the piston, however. More case volume, as I understand, slows the charge going up the transfers. Hopefully what I do to the intake negates that plus adds more.

 

Experimenting on these cheap saws is a great way to see what works without wrecking your wallet or a nice quality oem saw.

 

Keep in mind, if this was a saw I cared about, my used 241 if I kept it, the 543xp...I wouldn't be hacking away at their pistons like this.

 

Clammys are a challenge because the bearings are the floor of the lower transfers so there is no grinding there to open them up, hence the piston cutting. You can see that here.

 

Cute lil bugger!
I have a number of those 4218s around here...that and a couple 5020s cut a lot of wood for me starting out. Can buy em cheap often times, I have several that I gave $20 for...the one was "locked up"...I asked him if he looked at it at all, he said nope, just wanna sell it...I clicked the chain brake off on the way to the car...ran great, just needed the chain sharpened!

 

Nice. When are you going to start a build thread?

 

Do you have a before and after weight of the slug?

What's the bore / piston size on this saw?

 

I'll get that information for you either today or tomorrow Monte. Until then, more on what I'm doing...

I'll be widening the exhaust out towards the bolt holes. Lines are for reference only. I go to 65% of bore diameter on port width. I think some go as far as 70% but I try to stay a bit conservative as to not snag a ballooning ring in the port.


Most of the saws I've messed with do not have that ridge all around the port and normally I don't remove any material off the floor but, I'm going to lower that ridge as far as I can without free porting. To those that don't know what that is, its when there is an opening under the piston in the exhaust port at tdc. It's not what you want for reasons that could be discussed later if necessary. This line on the piston indicates where that exhaust port floor lines up with the skirt which allows me to figure out how much I can remove from that ridge.

I'll also be lowering the intake floor to roughly that line, after doing some maffs to convert degrees to thousandths of inches. It usually comes out around 0.009-0.011 per degree depending on the engines stroke and where in the stroke you measure.

 

Sorry MAF143

I thought I had recorded the piston weight before grinding on it. It appears I did not. The other junk saw has a smaller bore.

 

NP, looks like you took quite a bit out of the piston. I always thin the skirt down some but it looks like you went a lot further on this one than I have ever gone. I'll be bolder next time...

 

Just remember, this isn't a "do what I do thread", it's a "this is what I did to this particular unit" type thread.

When I weigh them though, I usually can get 4-6 grams out of a stocker. That predator I did recently... I took 10 out of the piston. It was aftermarket and 12 grams heavier than stock. Combined with the original wrist pin I got to original weight compared to the new piston / pin.

 

For anyone that doesn't know what tools are needed for this type of thing, outside of basic hand tools, you need calipers for taking measurements. I have two pair. One is for outside and depth, the other for inside. The inside is a cheap $40 unit from Amazon. I use it to measure the port widths before and after grinding.

A degree wheel is a must as well to do accurate port timing. I made this one by printing it off the net, laminated it and glued it to this 8" aluminum disk I had. The drill chuck is a harbor freight unit.

Although not ideal, I'm still using this air pencil grinder that accepts 1/8 Dremel size bits. I buy quality cutters but cheap diamond bits from harbor freight. The far right cutter is wrecked. They make a 90° version of this grinder as well but I haven't purchased one yet as I may move to the traditional porting gear.


The Cratex bits are for polishing the exhaust port. They come in 4 grits.

 

Lots of cool stuff going on here.