288xp cylinder decking

[troutfisher]

Hi folks, I'm porting my 281/288 Husky, here's what I came up with for decking the cylinder. Thats a piece of 1/4" steel plate, I cut a hole to match the cylinder. I stuck a piece of adhesive backed sandpaper to the plate. I stuck the cylinder into the plate and turned it by hand. I took the squish from .042" to .018", using the solder method. I degreed the saw before I started so I know how much to raise the ports to return to stock port timing. I will then widen the intake and exhaust ports to 70% of the bore (54mm bore, ports hopefully willl be 38mm wide) provided there is room. Opinions? Advice?

 

[Four Paws]

Nice enginuity - a poorman's lathe! I like it! Personally, I have no experience with these saws, but lots of guys like them. I am sure there is PLENTY of power to be had.

I know you said you took measurements, but I hope that you thought things through before you 'turned' your cylinder base down. On some saws, the piston skirt is not long enough to remove base material, and will open the bottom of the exhaust port at TDC - exposing the fresh fuel/air charge in the crank to the atmosphere.

You can take your intake port wider than 70% of the bore diameter. Up to .020" from the piston skirt is acceptable - I have heard some guys take it even closer. 70% on the exhaust is good. The single biggest piece of advice I can offer on porting is to concentrate on the shape of the port. Exagerate what is already there from the factory. Make sure you go easy on the rings and put a nice chamfer back in there.

Don't make the mistake of taking too much material out of the cylinder and opening those ports up - a little goes a long way. It is easier to open the saw back up and go in for more gains later, than it is to replace material which you have already removed.

A few final thoughts - .018" is a tad bit tight for a woods saw, but you should be alright! Make sure you burn premium fuel and watch it close for the first few tanks to see if it gets hot, and in what situations. Br sure to check your cranking compression after you get it back together. I say 175 psi is about right for a woods saw - your bearings will be much happier here. Remember you can adjust this value down to where you want it if it is too high.

Props for trying this on your own!

 

[blis]

Nice work, but i hope you made sure that metal piece was level before starting to lower your cylinder (thats why i use glass with sandpaper attached to when sanding heads)....

About the ports, I wouldnt take ports much beyond 70% of bore since it has 1 section exhaust, if it had 2 part exhaust you could widen em up to 80% or so... Thats becouse 70% is pretty much the max safe width of ports....

Oh, and remember this thumb rule, wider ports -> torque, higher ports -> hp

 

[troutfisher]

"I know you said you took measurements, but I hope that you thought things through before you 'turned' your cylinder base down. On some saws, the piston skirt is not long enough to remove base material, and will open the bottom of the exhaust port at TDC - exposing the fresh fuel/air charge in the crank to the atmosphere."

Thanks four paws, I had not taken this into consideration! I just put the cylinder back on the saw, brought the piston to TDC, and marked the piston with a pencil through the exhaust port. There is lots of room, about a 1/4 inch overlap between the piston skirt and exhaust port. This saw is a toy, I won't take it to the woods. I've had a couple different pipes on it, cracked the piston playing with the ignition timing. I've got a new piston kit from Bailey's, This is my first attempt at porting, thanks for the info.