Thread: Chainsaws aren't Dangerous...

Will double check tonight.

Well - without pulling it apart, mine certainly seems like a normal, hollow, muffler. Though mine is a few years old...

empty hollow muffler is the best.

cat mufflers build heaps of heat = not good

plus really restrict exhaust flow.

Serg

Originally Posted by uninformed

ben, widen the exhaust port on that saw, set squish band to piston gap at 0.5mm, and open the muffler outlet to 100-125% of the exhaust port, pull the limiters of the carb screws, retune and your good to go. dont need the planer then

Serg

Hey Serg - re-reading this, wtf is a "squish band"?

Any how-to's (with pics?) for doing the carby and piston mods?

My 357 xp definitely has less grunt atm than Andy's Dolmar, but it does desperately need both air filters and the spark plug replaced.

Originally Posted by isuzurover

Hey Serg - re-reading this, wtf is a "squish band"?
.....
....

The squish band is an area around the outside of the top of the piston which almost touched the head.
Thirty years ago it was considered desirable to get it right to improve the performance of two stroke engines. Apparently it still is.
The idea is that the combustion chamber at TDC is then a much smaller diameter and is closer to hemispherical.
This has the effect of shortening the flame front when combustion takes place, so combustion is improved.
I think part of the thinking thirty years ago was not only that it created a more compact combustion chamber, but that the air/fuel mixture close to the metal of the head and piston was harder to ignite. Getting rid of that thin part around the outside of the piston meant less of the fuel/air mix was partly wasted. Strictly speaking, you can't get rid of it completely, but you can make it so thin that it is practically non-existent.
We used to try to get the piston so close to the head that frequently cleaning the thin buildup of carbon was necessary to keep the piston from touching the head.

Originally Posted by isuzurover

Hey Serg - re-reading this, wtf is a "squish band"?

Any how-to's (with pics?) for doing the carby and piston mods?

My 357 xp definitely has less grunt atm than Andy's Dolmar, but it does desperately need both air filters and the spark plug replaced.

Needs a plug already, I've never put one in my dolmar yet

Ben, if you take your 357 cylinder off and look inside the head, you will see a flat band around the combustion chamber. this is the squish band.

im guessing the 357 has a one ring flat top piston.

use some soft solder(only needs to be about 1mm dia) cut 4 pieces about 5mm long. place these at 12,3,6 and 9 o clock ONTOP of the piston, (outside edges, so they will be compressed by the squish band) using a dab of grease to hold them there. 3 and 9 o clock being directly above the wrist pin ends and 12 and 6 = intake and exhaust port sides of piston

put the cylinder back on, you can do this with out the ring to make it easier. use the original gasket and torque down. pull the saw over and it will compress the solder between the piston top and the squish band. pull the cylinder off again and messure the flat spots of the solder.

on a worksaw you can run about 0.002 of an inch or 0.5mm squish band to piston gap, i wouldnt go smaller.

depending on how much you have to drop the cylinder, you may only have to remove the gasket, use some Pirmatex copper RTV silcone instead. but you may have to turn the base of the cylinder as well.

Racesaws

you can widen the exhaust port to 65% of the cylinder dia. measure the port straight across the opening. BUT your piston skirt may limit you, dont go closer than 1.5mm to the skirt edge, in other words the psiton skirt must still close the port completely. if you raise the exhaust port at all only rasie it the amount you drop the cylinder. if you dont raise it it will be a nice torquey saw.

open the muffler outlet to 100-120% of the exhaust port at the cylinder side.

you will need to retune the saw,

you dont need to mod the carb or piston for this sort of work, what you want is a good reliable, easy to start work saw....... racesaws are a whole different ball game.....

think tuned pipe and upto 20000 rpm

Serg

Get PULP next time Ben,makes a difference.
Use your Husky oil,or a very good semi synthetic or synthetic.
Tune to the book with the new fuel.
Should go well.
Air filters,should oly be rinsed in two stroke fuel,the oil is good to catch the dust.I do blow mine clean from time to time,but very carefully at 180deg to the filter and not close with the nozzel.
Chain sharpness is the key,if it isnt spitting big chips out,more a fine sawdust its blunt!!!
Let me know when you want some more
Andrew