Reducing Squish on a Poulan Clamshell

[Chris-PA]

just a question. i'm stoked with what you're trying to do, but are you working at the wrong end? might it be easier to cut the top off the cylinder and machine a new head with the desired squish/compression ratio? it would make it easier to mod the transfers too. my understanding was that the mission was to reduce the .040" squish. we all get a little crazy at this time of year.

Well, setting aside the case stuffer thing, so far dropping the cylinder has been pretty easy. It's hard to imagine cutting off the top would be easier - and since this is a clamshell there are no through bolts, so I don't know how you'd reattach it.

Of course I have not done the real cylinder yet and put it back together, so we'll see!

Yeah another victim of running with the brake on.
Surprisingly the crank seal wasn't melted, Saw actually cranked pretty easily.
It's all there, just got that melted problem.

I have to point out this is the ONLY Poulan or Husqvarna plastic cased saw with an inboard clutch. It's a change they made at the time they changed the 42cc model over to strato - now it has the Stihl melted case disease too. They didn't make that mistake twice though, and the PP5020 has an outboard clutch and metal cover.

 

[Chris-PA]

Maybe not so complex ........... ???

I think I remember that there is more to those crank stuffers than just epoxy, but I have not found the thread. 10,000rpm would put a lot of force on them!

 

[LegDeLimber]

I was wondering about the stuffers and that rpm too. Was also thinking of some sort of "rebar" scheme.
Can't recall if there has been a detailed description of how they're done.
The act of setting a mold ring around the weights is pretty much a case of make sure it's centered/true and will clear everything as the crank turns, yada yada...
But I cant recall if the mold wall is also a strap that gets left in place after filling in the large open areas that the crank weights don't occupy.

 

[heyduke]

Well, setting aside the case stuffer thing, so far dropping the cylinder has been pretty easy. It's hard to imagine cutting off the top would be easier - and since this is a clamshell there are no through bolts, so I don't know how you'd reattach it.

Of course I have not done the real cylinder yet and put it back together, so we'll see!.

yes, you're right. i was only brain storming although "brain" might be an exaggeration... i wasn't thinking about how the pan bolts up. a head gasket would be a challenge too.

 

[LegDeLimber]

Looking at Chris-pa cutaway pics, sort of leaves you thinking of a ring of
number 8 or 10 diameter screws to hold the head on one of these.
Would be a pretty slick task to align your drilling pattern to precisely hit the that cylinder wall with every hole.

 

[Chris-PA]

So I beveled the crank around the pin boss. It wasn't too bad, but I had to go very slow - it's a sloppy old lathe and I got a bit of chatter on one side. I probably had the cutter too high too. I matched the angle of the cutter to the bevel on the counterweights, and cut the pin boss until I heard it begin to touch the weights.

I also had some trouble epoxying the fillers in the cap, as the epoxy was so thick that the one filler did not seat well enough, so I had to do some sanding. I think I have it clearanced pretty well now, but may have to do a little more.

Here are some shots of the setup and the crank:





With this new piston the squish is now 0.043", so I know what I need to cut off the cylinder.

 

[LegDeLimber]

Change your tool bit to just cut with a smaller area
Set it like My childish looking sketch.
Keep the nose radius vs tool size proportional to what I scratched out
and You'll see a big improvement in the cutting action!

When you have a broad face cutting like you did there,
it will be really bad to cause chatter.

Edit: you'll need to rotate the compound and feed by hand,
in order to keep the tool at the angle I show.
Unless you have the odd/semi-rare lathe with with an angle drive
ability on the compound.

 

[Homelite410]

I would have set the compound to desired angle and used a .060" radius cutter. Just my .02

 

[LegDeLimber]

One other thought: If you have *any* of those chatter lines on the crankpin area,
You should file and smooth them off.
I cant tell from the pics if there are any.

 

[Mastermind]

Really cool thread Chris.

I raised the crank in a Wild thing once......just to see if I could. I milled the base, and used a boring bar to fly cut the bearing pockets. It was pretty simple really.

 

[fordf150]

Haha my dumb+ss remembered something. I knew it was a boring bar to cut the pockets

 

[Mastermind]

It worked well. I was able to spin a .030" popup on the piston.

It had an air leak here........but you get the idea.

 

[Chris-PA]

Change your tool bit to just cut with a smaller area
Set it like My childish looking sketch.
Keep the nose radius vs tool size proportional to what I scratched out
and You'll see a big improvement in the cutting action!

When you have a broad face cutting like you did there,
it will be really bad to cause chatter.

Edit: you'll need to rotate the compound and feed by hand,
in order to keep the tool at the angle I show.
Unless you have the odd/semi-rare lathe with with an angle drive
ability on the compound.

I would have set the compound to desired angle and used a .060" radius cutter. Just my .02

Thanks for the tips guys. I'll freely admit I don't know my ass from my elbow when it comes to cutters and lathes. I do normally use the corner of the cutter, but on this lathe I don't know how to adjust the compound angle and I didn't want to change the setup. I'll talk to the machinist today and ask him how to do it though - it was after hours when I turned it and he wasn't around.

 

[Homelite410]

Get us a picture of the carriage without a tool post on it I bet we can help you out!

 

[LegDeLimber]

Give him a few months on a universal mill ("Bridgeport") and
we'll have him able to freehand that 45deg with the saddle and cross slide!!

I'll say it again: I MISS being in a nice little machine/fab shop.

 

[old guy]

It worked well. I was able to spin a .030" popup on the piston.

It had an air leak here........but you get the idea.

Is that chuckleing sound as the saw decelerates an indication of an air leak? any saws I heard do that always cut very well and I thought it was a good state of tune. I fear my ignorance is showing.

John

 

[Moparmyway]

I was able to spin a .030" popup on the piston.

BLASPHEMY !!!!!
YOU did WHAT ???????
My world now stands crushed !!!!!

 

[Chris-PA]

OK, I know how to adjust the angle on the lathe now!

 

[Mastermind]

Is that chuckleing sound as the saw decelerates an indication of an air leak? any saws I heard do that always cut very well and I thought it was a good state of tune. I fear my ignorance is showing.

John

That is a classic air leak sound. It had a crack in the JB Weld external transfers.

BLASPHEMY !!!!!
YOU did WHAT ???????
My world now stands crushed !!!!!

Yeah.....when I was a newbie I used popups. I'm not a newbie anymore......

 

[Chris-PA]

Yeah.....when I was a newbie I used popups. I'm not a newbie anymore......

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