parrisw
Tree Freak
Cool thread!!
Porting a Poulan 25da
- Thread starter NPKenny
- Start date
Help Support Arborist Forum:
Squish Band
I move pretty slow on these things, usually because I end up improvising on the tools. Like my "squish cutter"... A 38mm bore means a 1.5" mandrel will fit very well. I sourced a 1.5" dowel and glued sandpaper to the end.
The first thought was to do it by hand, but it was very slow moving.... I chucked it up in the drill press and drove it with a drill bit. I started with 100-grit paper and ended with 320-grit. In hindsight, I switched grits way too soon. I could have centered the bit better as well.
I'm very happy with the results. I knocked off the step which was about .025" and then cleaned up the surface which amounted to a total cut of .030".
The squish was large enough that I needed to use the larger solder. It turned out to be .052" and is uniformly flat across the squish band. Seeing is believing in cutting a squish band.
I'm not exactly sure how I am going to drop the cylinder since the cylinder bore drops below the flange. I may pull the cylinder studs and drop the case .032" - .034" instead of the cylinder to get the squish to the .020" range..... Any suggestions?
I move pretty slow on these things, usually because I end up improvising on the tools. Like my "squish cutter"... A 38mm bore means a 1.5" mandrel will fit very well. I sourced a 1.5" dowel and glued sandpaper to the end.
The first thought was to do it by hand, but it was very slow moving.... I chucked it up in the drill press and drove it with a drill bit. I started with 100-grit paper and ended with 320-grit. In hindsight, I switched grits way too soon. I could have centered the bit better as well.
I'm very happy with the results. I knocked off the step which was about .025" and then cleaned up the surface which amounted to a total cut of .030".
The squish was large enough that I needed to use the larger solder. It turned out to be .052" and is uniformly flat across the squish band. Seeing is believing in cutting a squish band.
I'm not exactly sure how I am going to drop the cylinder since the cylinder bore drops below the flange. I may pull the cylinder studs and drop the case .032" - .034" instead of the cylinder to get the squish to the .020" range..... Any suggestions?
After partial reassembly, you are certainly right. I figure it can't hurt though as there is still a bit of time when they will be filling through that area.
parrisw
Tree Freak
You need acess to a lathe to turn the cylinder down, you also machine down the ears that protrude into the case. Yes you could also machine the case down.
srcarr52
We can't stop here, this is bat country.
It's best to use a mandrel in a lathe and cut both the flange and the extension of the cylinder. If you don't cut them both the extension will bottom out in the case before the sealing flange meets the case. I believe Mr. Snelling smoked a saw learning that lesson. :msp_w00t:
Nice work thus far with the improvised wooden squish grinder.
opcorn:
I've got access to a large lathe this afternoon. We'll see how this goes.
srcarr52
We can't stop here, this is bat country.
You need to make a mandrel to hold the cylinder. Here is a thread with the setup. http://www.arboristsite.com/chainsaw/174891.htm
I cut down the mandrel out of a random piece of fiber dowel. It worked incredibly well.
Then began cutting the base down. We sped up the the lathe quite a bit once we were confident in the mandrel. (Click for video.)
Here is the nearly finished product. All we had left was to cut the and bevel the cylinder insert.
The machine work gets to be as addicting as the saws themselves. With the time and concentration involved, $250 for a port job that includes machine work is a bargain if you can't do it yourself. Not to mention the expense and the volume of necessary tools.
I sacrificed my afternoon of work, so I have got to make up for it tonight. I probably won't even get to see if it fits.
Then began cutting the base down. We sped up the the lathe quite a bit once we were confident in the mandrel. (Click for video.)
Here is the nearly finished product. All we had left was to cut the and bevel the cylinder insert.
The machine work gets to be as addicting as the saws themselves. With the time and concentration involved, $250 for a port job that includes machine work is a bargain if you can't do it yourself. Not to mention the expense and the volume of necessary tools.
I sacrificed my afternoon of work, so I have got to make up for it tonight. I probably won't even get to see if it fits.
parrisw
Tree Freak
Nice work, you aint kidding about $250 being a bargin, that is why I don't do it for $$$ I've done the odd one as a trade/favour, but I'm just too dang slow. And yes I've got allot of $$$ tied up in tools here.
One tip, make the mandrel as short as you can get away with.
I cut down the mandrel out of a random piece of fiber dowel. It worked incredibly well.
Then began cutting the base down. We sped up the the lathe quite a bit once we were confident in the mandrel. (Click for video.)
Here is the nearly finished product. All we had left was to cut the and bevel the cylinder insert.
The machine work gets to be as addicting as the saws themselves. With the time and concentration involved, $250 for a port job that includes machine work is a bargain if you can't do it yourself. Not to mention the expense and the volume of necessary tools.
I sacrificed my afternoon of work, so I have got to make up for it tonight. I probably won't even get to see if it fits.
Excellent work. Way above my pay grade.
Mastermind
Work Saw Specialist
Getting in at midnight as never been a deterrent for an addiction... As such, I put the jug on to take some new measurements.
Squish = .023" ( I knew I could have gone tighter, but I am happy right here)
Exhaust = 111*
Transfers = 125*
With any luck, I'll be grinding tomorrow night. The plan is to take the exhaust to 100*, but I am not sure about how to approach the transfers. I haven't had the opportunity to maximize the flow area and blowdown on any other saws. Time to study a few posts.
Squish = .023" ( I knew I could have gone tighter, but I am happy right here)
Exhaust = 111*
Transfers = 125*
With any luck, I'll be grinding tomorrow night. The plan is to take the exhaust to 100*, but I am not sure about how to approach the transfers. I haven't had the opportunity to maximize the flow area and blowdown on any other saws. Time to study a few posts.
So which Poulan models in this family of saws are the "good" ones? Does 25da = s25 = xxv = ???
Mastermind
Work Saw Specialist
Getting in at midnight as never been a deterrent for an addiction... As such, I put the jug on to take some new measurements.
Squish = .023" ( I knew I could have gone tighter, but I am happy right here)
Exhaust = 111*
Transfers = 125*
With any luck, I'll be grinding tomorrow night. The plan is to take the exhaust to 100*, but I am not sure about how to approach the transfers. I haven't had the opportunity to maximize the flow area and blowdown on any other saws. Time to study a few posts.
I'm not sure I would go that high......:msp_unsure:
What were the numbers stock?
105* exhaust with base gasket in place.
119* transfer
.052" squish w/ gasket
What do you think??? Take it back to stock?
Mastermind
Work Saw Specialist
The transfers I would take to 120 and the exhaust to 103. That would give you more blowdown and you would net compression gains.
I've not ported one of these yet though.....so I may be just blowing smoke outta muh ass.
Very nice work and an excellent thread. I admire not only your ambition, but the fact that it is being applied to a great little saw that all too often seems to be overlooked as an ornery little performer even stock. Thanks for sharing!
srcarr52
We can't stop here, this is bat country.
The transfers I would take to 120 and the exhaust to 103. That would give you more blowdown and you would net compression gains.
I've not ported one of these yet though.....so I may be just blowing smoke outta muh ass.
I agree... don't go too high on the exhaust. These are not a high RPM saw so keep the torque. I left mine at 154 deg duration or 103 opening and it pulls a 16" with some authority. After truing the squish as you did and setting it at 0.018 it blew 180 psi.
How did you approach the exhaust width and the port bridges? I'll be leaving the bridges, but I'm debating how wide to go and how narrow to thin the bridges. Being a full circle piston and a brigded port, I bet I can go pretty wide. Here we are back at time/area.
