Reducing Squish on a Poulan Clamshell

[Mastermind]

So you've reached that age where pop ups just aren't happening any more?

I'm not saying that popups are a bad idea. They work just fine in many applications. I was pushed into cutting the squish bands by guys that wanted me to build them a saw without a popup. Some people just do not want a custom made piston in their engine.

After doing hundreds of saws with a cut squish band.......using a popup piston just seems like going backward rather than forward.

 

[Mastermind]

So you've reached that age where pop ups just aren't happening any more?

Oh wait........you were making a funny.

 

[Chris-PA]

OK, I hope to cut the cylinder down this evening, and I'm trying to decide how small to set the squish. My initial thought was to shoot for around 0.018" But then I got to thinking about how the crank is essentially mounted in rubber bushings, and I wonder if it moves at all? The rubber coating is pretty thin and clamped down well, so I'm hoping it doesn't move too much.

I guess if I go too far I can always take a little off the piston.

 

[Mastermind]

Chris, I would take off .040......then set clearance by cutting a popup.

 

[Chris-PA]

Chris, I would take off .040......then set clearance by cutting a popup.

Yeah, I've been toying with that. It gives me more to grind out the the bearing pockets, but that doesn't seem to be a big deal.

 

[Mastermind]

As large as that lathe is you probably could use it to cut the bearing pockets. Mounting the jug on a back plate wouldn't be as tough as you might think.

 

[Chris-PA]

As large as that lathe is you probably could use it to cut the bearing pockets. Mounting the jug on a back plate wouldn't be as tough as you might think.

Nah, I'm going to grind them out by hand with a Dremel like I did on the practice cylinder. It was easy to do using the sizing gauge I made.

I guess I won't be cutting the cylinder today - got a call that someone's been stealing my firewood, so I'm going home to find out what's up with that. Frozen green white oak isn't going to help them much.

 

[Chris-PA]

Well, it looks like it was a scrounger taking some punky, fractured stuff I had decided to leave next to the road. Doesn't look like he went back into the woods after my real stacks - what my wife thought was a trail to those stacks was just a deer path.

Now I wish I had stayed at work and cut that cylinder. Oh well, It's going down to -7 tonight so I got a head start on getting the stoves cranking. Hopefully the guy that took that wood needs it to keep warm tonight.

 

[Mastermind]

It's suppose to be -6 here tonight. Thanks a lot PA.

 

[Mastermind]

it was -7 several hours ago when I was running around doing errands. It is now -17 and the wind is blowing, had -26 last night, supposed to be colder tonight.
I can't bring myself to go to the barn to mess with saws in these temps.

I don't blame you.

We've got a good heater in the shop.......and the shop is small. Well insulated too.

 

[Mastermind]

12 degrees warmer than it was at daybreak.

 

[Mastermind]

We have lots of people with frozen water right now. I was able to get 16" minimum when I ran my line from the water meter. A lot of people have less soil than that.

We had to blast for the septic tank.

 

[Chris-PA]

Well, I cut 0.040" off the cylinder, and I'm happy with how it came out:

Tomorrow I'll try grinding out the bearing pockets.

I also cut both the new piston and the old one:


There's nothing wrong with the old piston, but there is a notch cut in the skirt and I think the intake duration will be too long now. After I get the bearing pockets done I can try mounting the pistons and measuring squish and timing.

 

[Chris-PA]

We have a scotchbrite belt at work, and I used it to smooth the crankshaft where I cut it, and the counterweights:

 

[Mastermind]

Chris did you get a benchmark to see if you will be getting good gains from this compression increase. I know you will.....but think the difference may be huge.

 

[Chris-PA]

Chris did you get a benchmark to see if you will be getting good gains from this compression increase. I know you will.....but think the difference may be huge.

I had run the saw a fair amount, but I don't have any consistent wood to use as a before/after benchmark. And I will have changed several things at once by the time it's back together. However, I did run it against my stock engined saw (in some very hard hickory ), so I can redo that comparison I suppose.

 

[Mastermind]

I do believe the first one had a better chain. Is that right?

 

[Flattop Burns]

Howdy,
Good read. I like the stuffers. Depending on how well it scavenges, you might want to put a rougher surface on them. Chris, it looks like you don't have any lack of tools. If you have the tools to do it, a cam ground crank pin will do the trick for adjusting squish on a clamshell.
Regards
Gregg

Was it just me but did that just seem like you and your buddies were camping and Lyle Alzado or Kent Tekulve walked out of the woods and sat down next to the fire said something and then walked off into the night?

 

[Chris-PA]

I do believe the first one had a better chain. Is that right?

That was a variable - the first was Carlton lo pro, and this one had Oregon 91PX. Generally I find them to be very close. I was disappointed that the ported saw was not faster - it felt faster and was more willing to rev, but it didn't show in the times. Chain could have been a factor.

 

[Mastermind]

Timed cuts really mean very little to me. There is too much emphasis put on the cut times has the only indicator of which saw is "better".

Like you said, the ported saw felt better.....that's what really matters. I've yet to meet a tree with a stopwatch.