Couple of ?'s about squish

[Beer Gut]

Just making sure I got this right, thought this weekend I might lower the squish on my MS460 to see what happens and learn something..

I want the finished solder height to be above .020 and around .024 would be great.. And when measuring I want to pull the saw around about 3 times and use 4 pieces of solder around the outside of the piston held in place by a little grease.

Depending on measurement I may or may not need a gasket but should use a fuel resistant gasket sealant to seal cylinder tight with or without gasket. I have access to Bridgeport Mills so if the base of the cylinder needs to be cut no problem. If gasket is made from a beer can or something else does sealant go on both sides of gasket? I'm guessing yes..

Before adding sealant and with new or no gasket in place check solder height again to make sure at desired squish. Do you compensate for sealant will it add a few thousandths?

Lowering squish on a stock saw will increase compression and horsepower and will not affect the transfer of the intake and exhaust ports correct? The saw does not need to be ported to have correct timing with lowered squish right?

For work saws that are heavily used will higher than stock compression take some life out of the saw causing the crank bearings to wear faster or affecting something else?

Does the carb need to be retuned will it change the RPM's?

Please read answer any ?'s you can and add anything else I missed.. This will be a good thread for future squish learning it should come up well with searches..

 

[nmurph]

Just making sure I got this right, thought this weekend I might lower the squish on my MS460 to see what happens and learn something..

I want the finished solder height to be abovee .020 and around .024 would be great.. And when measuring I want to pull the saw around about 3 times and use 4 pieces of solder around the outside of the piston held in place by a little grease...

I shoot for something bw .018-.020, but I wouldn't quibble if I hit .022 the first time; I would be happy. I prefer to stick the solder through the plug hole and jamb it against the cylinder wall. I usually only check it along the axis of the wrist pin but I repeat the measurement three or four times until I am gettting consistent numbers. If the numbers are less than .018", I will check it on four spots. .017 is OK with me, but anything less makes me worry. I know you can run .015-.016, but that doesn't leave much room for error. Make sure to measure the solder at the edge where the top of the cylinder meets the wall. Be careful not to mistake the tiny nib at the end that can result when the solder squeezes over the edge of the piston.

Depending on measurement I may or may not need a gasket but should use a fuel resistant gasket sealant to seal cylinder tight with or without gasket. I have access to Bridgeport Mills so if the base of the cylinder needs to be cut no problem. If gasket is made from a beer can or something else does sealant go on both sides of gasket? I'm guessing yes...

I usually use Coke cans (usually good for ~.003-.004") if I need some space. I also use gasket material if I need something thicker. I use a thin smear of Yamabond 4 (Hondabond/Tri-bond 1194) on both sides of the gasket.

Before adding sealant and with new or no gasket in place check solder height again to make sure at desired squish. Do you compensate for sealant? Will it add a few thousandths?

I measure bf I pull the cylinder and then measure the stock gasket. Then you can know what needs to go back in to come out with the correct squish. If you use aluminum can your measurement will be pretty accurate. Using paper gasket material means there will be some shrinkage due to the compression from the bolts that will need to be accounted for. A thin smear of sealant will hardly change the measurements. There will be more variation due to how much pressure you put on the calipers when you measure.

That brings up one more point: you need to be consistent with how you use the calipers. That is a skill that takes some time to master. I still struggle from time to time with this. When you get near the edge of the safety envelope, you need to be certain your numbers are valid.

Lowering squish on a stock saw will increase compression and horsepower and will not affect the transfer of the intake and exhaust ports correct? The saw does not need to be ported to have correct timing with lowered squish right?

You will raise the intake and lower the exhaust by a degree or so. These changes will usually offset each other and your gains are in raising the compression.

For work saws that are heavily used will higher than stock compression take some life out of the saw causing the crank bearings to wear faster or affecting something else?

I'm sure there is some additional wear, but I would be more concerned with running a clean filter, a sharp chain, and good quality mix, along with the correct tune.

Does the carb need to be retuned will it change the RPM's?

I check the tune everytime I cut wood.

Please read answer any ?'s you can and add anything else I missed.. This will be a good thread for future squish learning it should come up well with searches..[/QUOTE]

 

[Beer Gut]

What size solder do most start with? I have .050 at home here, to thick won't compress properly I would think and to thin may not even give you a reading with a stock saw correct? And after you lower it do you use a smaller diameter or stick with the same for accuracy?

 

[nmurph]

I think it is .05"; someone can correct me. It is not the big stuff used for pipes, it would be what you would use for electronics. I bought it at Lowe's. I have also bought a roll from WM when I couldn't find the first roll. I have seen squishes too tall to measure. I just grabbed the pipe solder to get started.

 

[WadePatton]

if your soldier is too thick, simply "pre-thin" it with your vice or c-clamp or a hammer.

if you can't make repeatable measurements, then you can't even start considering the accuracy of your measurements. it's not that hard if you tink about it.

carb tuning should be second-nature to folks who twiddle with saws. it ain't hard, can be done by the tone deaf now (tach), and even i learned it.

not picking, just sayin'.

 

[FATGUY]

squish should never be less than .0125 X stroke.

IE a 7900 has a 36.96mm stroke. Therefore squish should not be less than o.462mm (or ~ 0.018")

 

[chipper1]

squish should never be less than .0125 X stroke.

IE a 7900 has a 36.96mm stroke. Therefore squish should not be less than o.462mm (or ~ 0.018")

Have you measured the squish on a 7900, I've seen them tighter than .018.

 

[pioneerguy600]

Have you measured the squish on a 7900, I've seen them tighter than .018.

Unfortunately you will not hear back from Nick , FATGUY , has left this world.