How i measure squish

[NEIL31]

Hi guys i have been reading posts on squish gaps and see you all seem to use soft core solder, i do it a different way which IMO is more accurate.
you will need a reasonable quality dial gauge and extension and spark plug adaptor (i find a digital is easiest to use ) it is also easier if you have a spare piston of the same type dome.

1/ install plug adaptor into head dome and fit dial gauge

2/ with your dummy piston place centraly onto the squish part of the dome and zero the dial gauge (i always check the dome of my new pistons with that of my dummy)

3/place dome/gauge onto cylinder (i remove orings) and turn motor over and at TDC the smallest number you get is your squish

4/ on motors with 1 piece heads i assemble the topend and torque the head to the cylinder , install the dial gauge and slide my dummy piston into the cylinder till it bottoms out on the head and zero the gauge , then install cylinder and torque down and again turn motor over to TDC and the smallest # is your squish

[/URL][/IMG]

[/URL][/IMG]










i hope the pictures explain a little , a good dial gauge is worth its weight in gold if you do a little motor work also essential for zeroing degree wheels to work out the dwell at TDC

regards Neil

 

[sflsurfrider]

seems like a lot more work than sticking a piece of solder down the hole. :dunno:

 

[Mouthfulloflake]

maybe I dont understand squish correctly, but how does a dial guage in teh plug hole measure the squish?

going thru the plug hole, you are measuring the largest gap there is arent you?

the dome gets smaller as it goes away from that center section, and the methods of using solder reccommend going out towards the edge?

what sort of number would you look for using this method of greatest distance, VS smallest distance?

hell, I cant explain it...
:banghead:

 

[SJet]

Neil, you are right that is a dead nuts accurate way to measure the squish.

I would use your method if I was building a close squish motor.

For the average guy checking his .050'' squish motor, a piece of solder will do fine.

:biggthumpup:

 

[douglee25]

I think I understand correctly...

You put the dial gauge into the engine, turn the engine over, and record the number.

Then you install the gauge into the dummy head and....

ahh $hhiiit, I can't even figure it out now.

Doug

 

[Sanford]

NEIL31,

Your method isn't taking into consideration the angle of the squish band from the blending radius to the outer rim (taper - if there is one).

Also, some pistons have a tiny flat spot on the center of the piston dome where it came from machining or mold. This area is raised just a bit.

While I love calipers, dial-indicators, micrometers...there is a time when solder just works better overall. If this was a 4-stroke and you were trying to degree a camshaft, then a method like the one you outlined works perfectly. Let me guess, your background is mostly 4-stroke?

 

[SJet]

Okay,

The head is off the motor.
Screw the indicator in the plug hole.
Set the dome on the piston,(cyl. is removed at this point) and zero out the indicator.
Now, with the indicator still in the head put the motor together.
Spin the motor over slowly by hand.
Whatever the smallest # that the indicator reads, is going to be your squish.

Is this still clear as mud?:biggrin:

 

[Mouthfulloflake]

this was my concern Sanford.

you explained it MUCH better than I did though!

NEIL31,

Your method isn't taking into consideration the angle of the squish band from the blending radius to the outer rim (taper - if there is one).

Also, some pistons have a tiny flat spot on the center of the piston dome where it came from machining or mold. This area is raised just a bit.

While I love calipers, dial-indicators, micrometers...there is a time when solder just works better overall. If this was a 4-stroke and you were trying to degree a camshaft, then a method like the one you outlined works perfectly. Let me guess, your background is mostly 4-stroke?

 

[#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.

I like using the solder method because you can also check the bending radius of your squish band.

 

[egbrig]

The "squish" is the distance between the outer ring band and the distance to the piston crown. If you want to really do it correctly remove the head. Place 4 pieces of solder, (use some grease to hold them in place) place the 4 pieces at 12,3,6,9 o'clock intervals pointing toward piston center, retourque the head down as if you were putting it together to run. With the piston just slightly before tdc rotate the crank till the piston rotates through tdc and stop. Take the head off, measure the thinest portions of the solder. The reason you measure all 4 is because if your at tolerance at on side you may be over at an other side. Now your ready to determine the setup of your head.

 

[Mouthfulloflake]

so his method would work if you KNEW for sure the angle, and the bore size, and everything else were equal, it would basically tell you if the deck surface had changed or the thickness of the head gasket variance.

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.

I like using the solder method because you can also check the bending radius of your squish band.

 

[#ZERO]

Another thing you have to consider is that pistons will rock due to excessive clearances when cold and that's why you need to use four pieces of solder across the piston top. :wiggle:

 

[sflsurfrider]

the piston wont rock if you put once pc of solder parallel to the wristpins.

i check squish by putting the solder at the front of the front cyl, back of the front cyl, front of the back cyl, then back of the back cyl..... all using the same pc of solder.

theres no extra head or piston necessary and the only wrench you need is for the sparkplugs.

 

[norcal ex]

the piston wont rock if you put once pc of solder parallel to the wristpins.

i check squish by putting the solder at the front of the front cyl, back of the front cyl, front of the back cyl, then back of the back cyl..... all using the same pc of solder.

theres no extra head or piston necessary and the only wrench you need is for the sparkplugs.

how do you do it with the head on? angle the solder like an "L" ? ive never heard of it this way. please explain?

 

[douglee25]

how do you do it with the head on? angle the solder like an "L" ? ive never heard of it this way. please explain?

Precisely Marty! (Back to the Future) :biggthumpup:

Doug

 

[egbrig]

If you measure squish all the way around you will find that it is not the same on every side. If your building a surf boat and not a race boat you can get away with some slop. If building an all out race engine then everything must be taken into account.

 

[sflsurfrider]

how do you do it with the head on? angle the solder like an "L" ? ive never heard of it this way. please explain?

yes, i bend the solder into an L shape. i also bend the end of the solder into a U where it hits the cylinder wall as to not get a false reading from the clipped/broken/cut solder end.

 

[sflsurfrider]

If you measure squish all the way around you will find that it is not the same on every side. If your building a surf boat and not a race boat you can get away with some slop. If building an all out race engine then everything must be taken into account.

i can agree with that. checking clearance on an engine that is being held at WOT, on a high RPM engine, for long periods on a low-squish motor is a lot more important than engines that are built to brap around and never be held at WOT.

 

[Sanford]

Guess no one noticed that (picture) my solder test strip above was exactly the width of the bore and squished both ends evenly (laying opposite direction as piston pin).

 

[#ZERO]

Guess no one noticed that (picture) my solder test strip above was exactly the width of the bore and squished both ends evenly (laying opposite direction as piston pin).

I'm just curious what did you end up with on your squish measurement?

Did you see a difference in the bending radius or taper and what brand domes are you running?