squish questions

[WaveDemon]

What is the acceptable range for squish clearance? What point do I want to measure on a piece of solder? Is the clearance the same on 701's and 760's? What effect on power does the squish have? Is there a perfect squish number?

 

[Matt_E]

The minimum squish you want to run on 81-84mm bore (not sure on the bigger ones) is 0.040.

Just stick a thicker piece of solder into the spark plug hole, finagle it so it touches the cylinder wall. Then rotate the crank one full revolution.
Pull the solder out, and you should be able to see where it was squished.
The hard thing (and important!) is to make sure the solder gets to the cylinder wall, and stays there.

 

[SUPERJET-113]

Yeah and dont use acid core solder!

 

[SUPERJET-113]

I posted this awhile back on this thread: http://www.x-h2o.com/threads/1121

Squish is basically a "ledge" projecting beyond combustion chamber area.
As the piston approaches the ledge, a rapid squeezing action is applied to the air/fuel mixture contained in the area between the piston dome and the ledge. This squishing action forces the trapped mixture rapidly into the combustion chamber area, creating a greater mixture turbulence. Additionally, the small volume and large surface area of the squish band allow a better cooling of the end gases to help prevent detonation.

The squish clearance can be measured by inserting a piece of resin core solder(no acid core!) into the combustion chamber, rotating the engine through Top Dead Center, removing the solder and measuring the thickness of the compressed solder.

 

[h2odesperado]

Hey I didn't know that! Thanks!

 

[madoyster]

That's a cool trick with the solder.:biggthumpup: Thanks now if I can only get my A.D.D. arse to remember it.:banghead:

 

[crammit442]

That's a cool trick with the solder.:biggthumpup: Thanks now if I can only get my A.D.D. arse to remember it.:banghead:

Make sure the solder is directly over the wrist pist when checking squish. Otherwise the piston may rock and your measurement will be bigger than the actual squish. It has to be INLINE with the pin. Does that make sense the way I'm saying it? Hope so.:smile:

Charles

 

[steve802cc]

Make sure the solder is directly over the wrist pist when checking squish. Otherwise the piston may rock and your measurement will be bigger than the actual squish. It has to be INLINE with the pin. Does that make sense the way I'm saying it? Hope so.:smile:

Charles

This may help too.
The wrist pins are parallel to the crankshaft meaning they run from front to back. When you put the solder in the spark plug hole it must go towards the front or back of the cylinder not towards one of the sides.

Steve

 

[Yamah0]

Ok so lets say squish is supposed to be 0.40, but when u measured, it came out to be bigger or smaller..

what does that say? What needs to be done to fix that?

Thanx
Zane...

 

[Matt_E]

Get new domes.

Or mill the cylinder down.

 

[Yamah0]

I see.. so if squish was smallerthan .40 then mill cylinder and if greater than .40 then domes..

So basically can u say its a manufactuing fault?

 

[Matt_E]

No..you misunderstood. If it's smaller than 0.040 (notice the decimal) then you machine the domes, run a thicker base gasker, or replace the domes.

If larger than 0.040, replace domes or machine cylinder (Realize your compression will go up)

 

[#ZERO]

When checking your piston squish the smallest area will be at the edge of the piston because the squish band width has a bending radius toward the dome. Most pump gas engines tend to like a couple of degrees of squish angle with a wide squish band widths and smaller diameter domes with more volume. Race gas engines like a narrow squish band widths and larger diameter domes with less volume.

 

[romack991]

The minimum squish you want to run on 81-84mm bore (not sure on the bigger ones) is 0.040.

Just stick a thicker piece of solder into the spark plug hole, finagle it so it touches the cylinder wall. Then rotate the crank one full revolution.
Pull the solder out, and you should be able to see where it was squished.
The hard thing (and important!) is to make sure the solder gets to the cylinder wall, and stays there.

do you just drop a pc in the cylinder and try to wiggle it around? Cut a longer piece and give it a 90deg bend. then just stick it though and hold it where you want it.

 

[SJ/XPBri]

Get a nice non acid core piece of solder



bend said piece of solder




put solder into cylinder




solder in place- make sure you have the end up against the cylinder wall- rotate engine over 1 revolution




measure the flattened piece of solder to get your squish #






This is just a pic of what the solders position is in relation to the head when being crushed



Hope this helps
Bri

 

[romack991]

nice work, another one ready for the TECH FAQ!

 

[steve802cc]

Nice!!:hail: :hail:
With that diagram and those pics this is a great example of what squish is and how to measure it.
Steve

 

[Phill]

I hate to ask a stupid question....but......whats up with the non-acid core piece of solder?? Will it eat at the cylinder??


Again sorry for the dumb question.

 

[madoyster]

NO Doubt that little trick:Banane01: is the Shiz!:cheer:

 

[#ZERO]

I hate to ask a stupid question....but......whats up with the non-acid core piece of solder?? Will it eat at the cylinder??

Acid core solder is only to be used on galvanized iron pipes that require etching for solder adhesion. It will damage the aluminum if used for a squish test, that’s why rosin core solder is recommended.