Squish

[350BANSHEE350]

what is it and how do i check it

do i need to check it if i get my head shaved

BTW is milling the same as shaving

[jbooker82]

Get some solder. Take the spark plugs out. Bend the pice of solder in the shape of an L. Fish the solder down in to the spark plug hole so the one end goes over to the edge of the cylinder. Roll the motor over with the kick starter by hand. Bring the pice of solder back out and measure the thickness of the smashed pice with a calipar. That is how you check the squish.

 

Squish is the measurement of the clearance between the top of the piston and head. You want the solder to be parallel with the wrist pin so the piston doesnt rock back and fourth when smashing the solder.

 

josh

[350BANSHEE350]

okay sounds easy

so you need solder with flux cuz its weaker and you L shape it .. how big like 4 inches by 4 would work

and by in-line with the wristpin you mean from left to right inside the cylinder not north and south (from sitting on bike) and then just crank it by hand so it squishes it sounds easy

 

 

thanks josh

 

Mike

[jbooker82]

okay sounds easy

so you need solder with flux cuz its weaker and you L shape it .. how big like 4 inches by 4 would work

and by in-line with the wristpin you mean from left to right inside the cylinder not north and south (from sitting on bike) and then just crank it by hand so it squishes it sounds easy

thanks josh

 

Mike

 

It doesnt matter on the flux. The stuff I use has it in there. You only really need probably around a 2 in piece. you want to go straight over to the side of the cylinder (left and right like you said) and have it be up against the head when you roll the motor over. It would suck to get it in the transfer port and then when you roll the motor over you cut a pice off and have it fall down in the motor.

 

I believe most people shoot for .040 inch. Mine is at .035 kind of on the tight side but I dont have any problems with it.

 

josh

 

Ps you can also measuer the flattend solder in different places to see how well the shape of the combustion chamber is contured to the shape of the piston head.

[Lepew]

I heard the term squish came from the design in a head where there was minimal clearence between the piston and head. The piston on the compression stroke would "squish" the air from this area towards the opposite side of the combustion chamber near the valves and spark plug creating turbulence that would prevent detonation. It is very noticable if you look at a head on a common v-8. On a Banshee I don't know if the theory still holds but I know that squish clearance or clearance between the piston and head is critical. The rod will stretch at high RPM's and if there is not enough clearance than the piston will tap the head. The solder trick works very well to check squish. I always ckeck the squish when after assembling the top end. Shaving the head is just removing metal with a lathe or mill on the bottom to increase the compression, it will reduce you squish.

[350BANSHEE350]

okay now i am a little confused.. so the solder DOES need to go left or right

i want a peice long enough to hit the left or right side of the cylinder wall correct?

once i get a piece long enough i then crank it

i have 106 psi at 4000 feet which is stock compression (130 for sea level) so ill have save squish clearance if i mill it?

 

thanks

[Lepew]

Either left or right will work just make sure it is touching the cylinder wall when you crank it. When it is milled the machinist removes metal where it contacts the head, this causes the combustion chamber to sit lower the same amount the machinist removed from the surface of the head. Your squish clearance will be smaller by the same amount of material the machinist removed. For example if you squish clearance is .050" now then you have the head milled .010" you new squish clearance will be .040". This is in theory since you don't know if someone had cheap base or head gaskets that were not the right thickness in the motor to start so you must check your squish clearance again when you assemble the top end to know for sure it is not to small.

[jbooker82]

It doesnt matter witch way you go. Solder is cheap, so you could take a measuer ment on each side of each cylinder. You just want the solder to touch the cylinder wall on the sides (left or right not front and back) as if you were sitting on the seat.

 

The reason why you dont want to do the test on the intake or exhaust side of the cylinder is the solder might not get squished all the way since the piston can rock a tinny amout front to back. Your conecting rods would have to be egged out to get the piston to rock from side to side.

[350BANSHEE350]

okay got it now

so since the shee is a n 07 and its got the corrrect stock compression for my elevation well i really need to check the squish?

BTW what should stock squish be?

i want to run 91 high grade still so im thinking ill be safe with .030 correct?

or should i check squish before i mill the head?

okay so ill pick up some soder and a caliper to measure its

how think i solder should i guy does it matter?

 

thanks guys

[jbooker82]

I would check the squish befoer you mill the head. That way you know how much can be taken off before your head is milled down to much and the pistons hit the head. Squish is a good number to know on your engine.

[350BANSHEE350]

okay thanks