Reducing Squish on a Poulan Clamshell

[Chris-PA]

Where is that thread? i would love to read it. Im sure i could get my hands on a wildthing for around 30 dollars

No doubt, but Wild Things have no A/V system. They did make plenty of equivalent saws with quite nice A/V, often sold as Craftsman or Poulan Pro. The Poulan Pro versions further have chromed cylinders - at least the ones prior to the later strato engines did.

 

[auskip07]

No doubt, but Wild Things have no A/V system. They did make plenty of equivalent saws with quite nice A/V, often sold as Craftsman or Poulan Pro. The Poulan Pro versions further have chromed cylinders - at least the ones prior to the later strato engines did.

It looks like the one i have is just a nicer version of the Wild thing, it has a chrome cylinder and AV system. So i guess ill just keep modifying mine

 

[VinceGU05]

Great job. Did you use 4047 filler rod?

It seems like whatever size dome your minds eye predicts for these should be halved. I'm surprised you got only 185 psi with that dome. The chamber space much be rather large on a 390.

Did you relieve the piston under the dome at all? What weight difference did you come up with?

yes i used 4047 rod on it. and the dome ended up 5mm bigger in diameter. and .5mm higher than that shot.. i should have taken a final pic.
yes its a pretty deep chamber! i didnt relieve the piston. weight added would be 5 to 10 grams max i think.

 

[LegDeLimber]

i recently done up a MS390. being a clamshell. i went the easiest option to boost the comp.

ended up with something similar to this . and ended up with 185 psi. all standard port timing as nothing else was changed.

I gotta ask. What's the story behind the line (crack?) across the top of the piston in pic 3?

 

[LegDeLimber]

This project has me thinking of a couple of the Pre-strato, 46cc poulans sitting here that will need piston & ring(s), possibly a cylinder for a strait gassed one
(but that one will likely never get put back together - parts saw!)
So I looked at prices and see that the cyls are NLA on some sites and the pistons are hitting
$28~ 39, depending on the site.

 

[VinceGU05]

I gotta ask. What's the story behind the line (crack?) across the top of the piston in pic 3?

It's just a mark from when I cut the plasticine with a knife to see the cross section to check clearances from plug and chamber.
A bit like using solder to measure the squish.

 

[Chris-PA]

It's just a mark from when I cut the plasticine with a knife to see the cross section to check clearances from plug and chamber.
A bit like using solder to measure the squish.

I did consider having a buddy add some aluminum to the piston top so I could make bigger pop up, but in the end I decided not to risk the piston. This version of the Poulan cylinder has a decently small and well shaped combustion chamber (without having a boss cast into the top of the cylinder for turning, they were free to locate the spark plug there).

Also, I re-calculated the volume of my case inserts - they reduce the case volume by 5%. It's still not much, but a bit more than I first thought. I wish I had taken today off so I could run it!

 

[Chris-PA]

Well, I have a nasty head cold and sore throat, everything is coved with snow and I could not get the tractor back to the wood pile. But I trudged through anyway, and then I was out of storage space on my phone, but I got one poorly exposed video at least!



The thing actually ran really well, and I doubt the ring is seated yet. I'm pretty happy with it. This is frozen white oak, and I measure 3.5 to 4sec faster than my ported Earthquake in the same round (when it was not frozen):



Now I'm going to load the little stove in the living room and crank the heck out of it, and sit there and bake.

 

[auskip07]

very nice. Im assuming the earthquake is a lesser CC?

 

[Chris-PA]

very nice. Im assuming the earthquake is a lesser CC?

Thanks! The Earthquake is 38cc, but it is also ported and has the base cut for better compression.

 

[Chris-PA]

Well it's been a couple of weeks but the snow has finally melted enough that I could get to a wood pile, I'm mostly over the cold I had and it isn't pouring rain - which meant I could try out the saw a bit. In the mean time I got a new GB bar for it:


This bar is supposed to be 18" but is actually a full 19" from the case installed (19.5" with the chain), which is pushing it for a 42cc saw. The chain is 91VXL.

I don't like to waste wood cutting cookies so I noodled a few instead. I'm really pretty happy with this saw - it's got guts. This is noodling white oak with a knot, almost full bar:

It's working pretty hard but I think it's decent given the bar length.

Also, it illustrates how stupid the Piltz stuff is! This heavily modified 42cc saw can actually pull this bar with lo pro, but no way a smaller saw can handle a longer bar.

 

[bikemike]

This project has me thinking of a couple of the Pre-strato, 46cc poulans sitting here that will need piston & ring(s), possibly a cylinder for a strait gassed one
(but that one will likely never get put back together - parts saw!)
So I looked at prices and see that the cyls are NLA on some sites and the pistons are hitting
$28~ 39, depending on the site.

I was able to get a ring for my 46cc from jacks small engine. Shipping cost 3 times the price of the part

 

[bikemike]

Well, I have a nasty head cold and sore throat, everything is coved with snow and I could not get the tractor back to the wood pile. But I trudged through anyway, and then I was out of storage space on my phone, but I got one poorly exposed video at least!



The thing actually ran really well, and I doubt the ring is seated yet. I'm pretty happy with it. This is frozen white oak, and I measure 3.5 to 4sec faster than my ported Earthquake in the same round (when it was not frozen):



Now I'm going to load the little stove in the living room and crank the heck out of it, and sit there and bake.

Runs real nice

 

[Paragon Builder]

Well it's been a couple of weeks but the snow has finally melted enough that I could get to a wood pile, I'm mostly over the cold I had and it isn't pouring rain - which meant I could try out the saw a bit. In the mean time I got a new GB bar for it:
View attachment 412135

This bar is supposed to be 18" but is actually a full 19" from the case installed (19.5" with the chain), which is pushing it for a 42cc saw. The chain is 91VXL.

I don't like to waste wood cutting cookies so I noodled a few instead. I'm really pretty happy with this saw - it's got guts. The is noodling white oak with a knot, almost full bar:

It's working pretty hard but I think it's decent given the bar length.

Also, it illustrates how stupid the Piltz stuff is! This heavily modified 42cc saw can actually pull this bar with lo pro, but no way a smaller saw can cut a longer bar.

I was noodling today myself. Mostly with my 61, and a little with my 55. That saw is strong for 42cc!! Nice job, Chris!!!

 

[bikemike]

Runs real nice

Il have to get a vid of my poulan posted now that i got the new ring in it

 

[bikemike]

Poulan pro 46cc

 

[Chris-PA]

Poulan pro 46cc

Ha ha - very cool!

 

[bikemike]

Ha ha - very cool!

Its not bad for a old saw. Its got many hours on it and still runs like a champ. I did put the husky 136 clutch cover on it instead of the tooless crap

 

[old guy]

That clutch cover did catch my eye, I don't know if my stock 2900 will keep up wit dat saw.

John

 

[bikemike]

That clutch cover did catch my eye, I don't know if my stock 2900 will keep up wit dat saw.

John

What size is the 2900 in displacement?