Nik's Poulan Thread

[redunshee]

Most of the ones I have seen are around 125 psi. The 150psi is the exception for 3400 and 3800.

Agree. Seen a lot of them at 125. Even with gasket delete they don't get much higher. No big deal though as they run great atv120 to 125.

 

[fossil]

For whatever reason both my 3800's are at 140 while the 3400's are lower at 125 -130. Maybe less wear? One of my 3700's is at 170 which surprised me. It still has the base gasket in. Not sure what the other one is.

 

[redunshee]

For whatever reason both my 3800's are at 140 while the 3400's are lower at 125 -130. Maybe less wear? One of my 3700's is at 170 which surprised me. It still has the base gasket in. Not sure what the other one is.

Comp #s tend to vary for whatever reason. I would love to find out what a brand new 3400 or 3700 had for comps from the factory. Or better yet after it's broken in. Maybe we spend too much time worrying about compression.

 

[3000 FPS]

Well higher compression does give more torque. I have 2 3800 that we're at 125psi and I was able to get them up to 150psi. There is a noticeable difference in the way they cut, not that they did not cut good to start with, they are just better now.

 

[rms61moparman]

Comp #s tend to vary for whatever reason. I would love to find out what a brand new 3400 or 3700 had for comps from the factory. Or better yet after it's broken in. Maybe we spend too much time worrying about compression.

From what I've seen,

3400's USUALLY run 120-130
3700's from 130-140
and the 4000's from 140 to 150.

Now don't be beating me up about how you had a 3400 with 170psi and so forth.
There are exceptions to all of these but these ranges are for a normal, stock example of the respective group.


Mike

 

[redunshee]

Well higher compression does give more torque. I have 2 3800 that we're 125psi and I was able to get them up to 150psi. There is a noticeable difference in the way they cut, not that they did not cut good to start with, they are just better now.

Did you shave the cylinder base? I've considered doing the same thing but wonder if it would affect the timing due to the lowering of the intake and exhaust ports.

 

[3000 FPS]

Did you shave the cylinder base? I've considered doing the same thing but wonder if it would affect the timing due to the lowering of the intake and exhaust ports.

Yes I did shave the base by around .020". I did not change the timing on the ports after lowering the cylinder. I believe when I was done I had the squish down to around .025". They run good is about all I can say.

 

[fossil]

Comp #s tend to vary for whatever reason. I would love to find out what a brand new 3400 or 3700 had for comps from the factory. Or better yet after it's broken in. Maybe we spend too much time worrying about compression.

I think you're right. I can't complain about the way they run and enjoy every one of them. Easy to work on and super dependable machines.

 

[ImNotASwede]

Yes I did shave the base by around .020". I did not change the timing on the ports after lowering the cylinder. I believe when I was done I had the squish down to around .025". They run good is about all I can say.

Curious about the math to determine that

 

[ILikesEmGreen]

Curious about the math to determine that

.045-.020=.025.

Sent from my C811 4G using Tapatalk

 

[ImNotASwede]

.045-.020=.025.

Sent from my C811 4G using Tapatalk

Do you remove the cylinder, measure depth, measure top and bottom of stroke, and thickness of old gasket? Or....am I overthinking it?

 

[Acornhill]

I wish these were Poulan parts

Sent from my LG-D800 using Tapatalk

 

[PogoInTheWoods]

Do you remove the cylinder, measure depth, measure top and bottom of stroke, and thickness of old gasket? Or....am I overthinking it?

Do a search on "squish". It's a measurement of the distance between the squish band and the top of the piston usually measured by inserting pieces of solder on the top of the piston 90 degrees opposite each other in 4 locations and rotating the crank to and past TDC, then measure the solder thickness to determine what you can get away with regarding shaving the cylinder base and/or removing/modifying the desired thickness of the base gasket.

 

[3000 FPS]

Do you remove the cylinder, measure depth, measure top and bottom of stroke, and thickness of old gasket? Or....am I overthinking it?

Put a piece of solder down the spark plug hole and make sure it is facing the same direction as the wrist pin. Also make sure the end of the solder is touching the cylinder wall because the tightest section of the squish band is right next to the cylinder wall. Then grab the flywheel and turn it over to compress the solder. I usually rock it back and forth a couple of times. Then measure the solder with a dial indicator at the very end where it compresses the most. Also do both sides to get an over all reading. Then remove base gasket or shave cylinder and repeat the process until you get around .025".

 

[ImNotASwede]

Put a piece of solder down the spark plug hole and make sure it is facing the same direction as the wrist pin. Also make sure the end of the solder is touching the cylinder wall because the tightest section of the squish band is right next to the cylinder wall. Then grab the flywheel and turn it over to compress the solder. I usually rock it back and forth a couple of times. Then measure the solder with a dial indicator at the very end where it compresses the most. Also do both sides to get an over all reading. Then remove base gasket or shave cylinder and repeat the process until you get around .025".

As they say back home "that's wicked smuckin faht" clever. Where did .025 come from as the magic number? How much does the cylinder and piston shape affect that?

 

[ILikesEmGreen]

I can almost hear the accent while reading it. I'd figure the .025 would be about the tightest tolerance you'd wanna go with parts slinging around at close to 8-10k or better. Close enough to effectively squeeze the mix up into the combustion chamber...but enough distance to keep them from banging together.

 

[RedneckChainsawRepair]

They'll steal your Stihl, but they don't know enough to be Pullin your Poulan

Your sig reminds me of a guy I know who got his garage broken in. They stole his ms310 and left the poulan pro 325.

I ended up with the 325 on a trade in. Then passed it onto the next good soul I knew looking for one.

 

[ImNotASwede]

Your sig reminds me of a guy I know who got his garage broken in. They stole his ms310 and left the poulan pro 325.

I ended up with the 325 on a trade in. Then passed it onto the next good soul I knew looking for one.

I've lost count of how many times someone wants to talk saws and they talk like they're an expert because they own 1 stihl. Tell me how strong their "farm boss" and I mention I have some poulans that are decent and they laugh and laugh and tell me you can't beat a stihl...till I beat up on their 60cc stihl with my 330 or pull out my souped up 380 and really woop up on them....then the talk changes to..."well I mean, my stihl works for me and that's all that matters"....

 

[Tractorsaw1]

Ya know its a "farmboss" like that means something great, & I reply ya stihl kinda ruined that right there. I try to stay away from them, at least the stihl "farmboss"

 

[3000 FPS]

As they say back home "that's wicked smuckin faht" clever. Where did .025 come from as the magic number? How much does the cylinder and piston shape affect that?

We'll as you know the saw heats up and metal has a tendency to grow alittle. Actually the more CC's the engine has the more tolerance you need. .025" is a good tight squish but a good safe tolerance. I have gone as tight as .018" on a poulan 335 I have. The compression was up to 190 psi, but I do not recommend it.

The real pro saw builders will cut the squish band on a lathe making it wider and more uniform thus reducing the size of the combustion chamber and then drop the cylinder. The only other problem with to tight and to wide of squish is pre-ignition can occur. So there is a point where you can go to far. Then the pro saw builders will put a degree wheel on the crank and check the opening and closing of every port and making changes to those as they see fit for best performance.