Porting a Poulan 25da

[NPKenny]

I've read where a few of you have mentioned porting a Poulan 25da or some variant, yet I haven't been able to pull up a thread with any details shared. Anyone have any strategies that have worked out well? Any numbers?

I've never ported a reed valve saw and am not sure where I should be headed. My stock numbers are as follows.

Exhaust - 105*
Transfers - 119.5*
Squish - .052"
Base Gasket - .030"
Bore - 38mm
2-ring piston

 

[Eccentric]

Subscribed.opcorn:

 

[Rokon]

Huh, this should be interesting. opcorn:

 

[Eccentric]

Brad woke up an S25-CVA a while ago...

http://www.arboristsite.com/chainsaw/183478.htm

 

[blsnelling]

Not much blowdown and a huge squish. I'm thinking I would drop that squish down to .016"-.018" and maybe raise the exhaust to 100°.

 

[Rokon]

http://www.arboristsite.com/chainsaw/183478.htm

Too much bar on that thing. :msp_biggrin:

 

[NPKenny]

http://www.arboristsite.com/chainsaw/183478.htm

I had found that and saw where Brad only did a bit of muffler work. I've watched the video multiple times.

Not much blowdown and a huge squish. I'm thinking I would drop that squish down to .016"-.018" and maybe raise the exhaust to 100°.

I'll pull the gasket and probably leave the squish at the remaining 0.22" Glad for the insight about raising the exhaust slightly to get blowdown right. Not too often around here that this is suggested.

 

[Modifiedmark]

http://www.arboristsite.com/chainsaw/183478.htm

Brad had two of those to the Poulan GTG last year, and they both run great. There was a 200T there and it got owned pretty bad, but I dont know the details on that one.

 

[Mastermind]

I'll pull the gasket and probably leave the squish at the remaining 0.22" Glad for the insight about raising the exhaust slightly to get blowdown right. Not too often around here that this is suggested.

I'm gonna be building one of these in the next few weeks. I'll do a thread on it for sure. Even the carb has been over bored....

 

[srcarr52]

I've done a few. There is usually a nasty step in the squish band. I remove the step with sand paper on a mandrel. Then you can raise the exhaust port get the blowdown you want but it won't be too much that it will kill the torque.

 

[barneyrb]

Has anyone removed the two bridges in the exhaust port?

 

[rms61moparman]

I'm looking forward to this thread, and especially Randy's thread to follow!!!
Maybe I'll get one of mine ported someday!!:msp_wink:


Mike

 

[RedneckChainsawRepair]

I know that S25DA I redid for a customer put a smile on my face test cutting with it stock. Went with drum and 3/8LP rim set up too. :msp_biggrin:

 

[jropo]

Has anyone removed the two bridges in the exhaust port?

I'm not an expert by any means, but I'd rather work around the bridge and keep the rings where they belong, in the bore.

 

[Eccentric]

I'm gonna be building one of these in the next few weeks. I'll do a thread on it for sure. Even the carb has been over bored....

I'm looking forward to this thread, and especially Randy's thread to follow!!!
Maybe I'll get one of mine ported someday!!:msp_wink:


Mike

I think I just added another of my saws to my 'gotta send to Randy' list....

 

[NPKenny]

Some pictures!!

Here is the saw at tear down. Very small score in the piston, most likely caused from carbon / sawdust buildup in the crankcase.

I am glad I decided to tear this saw down completely... There was a ton of build-up material and slight pitting in the case halves that needed to be removed.

It is getting pretty tough to find pistons, so I tried my hand at cleaning this one up. I think it will work out just fine. I was surprised to find this to be a 38mm piston as it isn't labelled a Super or Deluxe model.

Here's the shot of the small step in the cylinder that srcarr52 mentioned. It is pretty small, but it's there. Once it's gone, it looks like the combustion chamber should be pretty tight.

I did a little bit of port matching at the base. I removed a flow channel from the support ridges on the PTO side case. They looked very restrictive, but who knows.

Here is another shot of the flowpath ground into the case ridges.

Ground a bit out of the bottom cylinder skirt on the flywheel side. It hung way into the case right into the flow-path.

 

[rms61moparman]

The piston looks great!
I hope you didn't go too far.
I just remove anything sharp or rough and don't worry about the scores. The rings will make up for the scores....................Won't they Jeremy?????:msp_wink:


Mike

 

[NPKenny]

The piston looks great!
I hope you didn't go too far.
I just remove anything sharp or rough and don't worry about the scores. The rings will make up for the scores....................Won't they Jeremy?????:msp_wink:


Mike

I went just far enough that nothing was protruding. There is just a bit of a score remaining, but I didn't want to get any deeper. The rest of the piston was just cleaned up with Scotch-brite.

 

[NPKenny]

Just to clarify the flow paths in the PTO case half.....

 

[srcarr52]

I hate to say it but when the transfers are open chances are one or both of your "flow paths" are blocked by the crank counter balances.