Measuring squish band and deck height

[Sci85]

Ok, here's my measurements. Like I figured, they are pretty close to Don's.

OEM Base gasket .020" compressed
Deck Height was .020'-.022"
Head Gasket compressed was .044"
.044-.022=.022" clearance.
Measuring clearance using pieces of solder measured .029" averaged

So, looks like I'm too tight as well. The .031" thick base gasket would give me an additional .011" of clearance for a total of .040" if using the solder measurement or .033" if using the piston above deck measurement. I will re-measure both to see why there is a .007 diff.

Does all the above look right and sound good?

Thanks.

[Sci85]

Ok, I measure everything one more time.

Base gasket .022"
Piston .022" above deck.
Solder laid across piston top - .028" at the flat part of the piston edge.
Head gasket quite thick - .044" compressed.

Now, with all that, looks like for optimum clearance of .035-.040", I need a base gasket that's .027-.029" thick correct?

What's the measurement for "squish"? I read somehwere that ideal it should be .043". Is that the same as the flat part of the piston to head distance?

Can someone double check my math?

Thanks.

[blowerbike]

.022+.022=.044
.044 would put you at zero deck...simple math...

[Sci85]

Ok now I'm confused BB. I may not be a master engine builder, but I can certainly add. The piston sits .022" above the cylinder. How is that zero deck height? Unless zero deck does not refer to the amount of piston above the cylinder...

[Suzuki_Don]

Ok, I measure everything one more time.

Base gasket .022"
Piston .022" above deck.
Solder laid across piston top - .028" at the flat part of the piston edge.
Head gasket quite thick - .044" compressed.

Now, with all that, looks like for optimum clearance of .035-.040", I need a base gasket that's .027-.029" thick correct?

What's the measurement for "squish"? I read somehwere that ideal it should be .043". Is that the same as the flat part of the piston to head distance?

Can someone double check my math?

Thanks.

Clay my calculation works out that you would need a .034" or .8mm base gasket.

[blowerbike]

Ok now I'm confused BB. I may not be a master engine builder, but I can certainly add. The piston sits .022" above the cylinder. How is that zero deck height? Unless zero deck does not refer to the amount of piston above the cylinder...

if your .022 above the liners then you need a .022 compressed base gasket for zero.
that would be if you checked it without a base gasket.
you checked it with a .022 base so you have .022 over and .022 under.
that means you need .044 to have the pistons even with the liners.
what don't you understand?

[boontonmike]

I retract my previous statment. That squish is damn tight. I'm curious now what mine came to as i just slapped it together. Anyone know how much the rods can flex on these motors? Also, would a roller bearing vs plain bearing have a different tolerance for squish? and last; would the bore size make a difference in prefered squish ( I would imagine smaller pistons could run a tighter number)?

[rapidray]

On a roller bearing GS motor, the pistons, rods & all the bearings clearances taken up, will see in the area of ABOUT .040, 40 THOUSANDTHS of an inch, stretch or growth in deck height at 12,500 rpm. With zero deck height and a .043 (standard copper or MLS) head gasket thickness, this leaves a .003 safety clearance between piston & head. Keep in mind this is based on a drag race engine & with less rpm you will be even safer. I recommend zero deck with a .043 thick head gasket on all the race engines I build for this reason. These numbers will keep just about any GS engine happy for a long time. That .003 may not sound like much but it really is at that rpm or less. With all the info above, keep in mind, the piston to valve clearance can be WAY more critical & give you bigger issues! Ray.

[GregT]

I retract my previous statment. That squish is damn tight. I'm curious now what mine came to as i just slapped it together. Anyone know how much the rods can flex on these motors? Also, would a roller bearing vs plain bearing have a different tolerance for squish? and last; would the bore size make a difference in prefered squish ( I would imagine smaller pistons could run a tighter number)?

Ray's said it all really. The only thing which raised my eyebrows was 12500RPM.... I use .040 as a base figure for most of what I build which includes quite a lot of roller bearing motors - from singles peaking at around 8000 to small twins doing 13000. But in the real world the GS components are on the heavy side and the crank is not very stiff so a tad extra is a safety margin.

Late plain bearing cranks are generally better supported, flex less and have lighter components. They can be squeezed a little tighter - judiciously and having regard to the use they'll get.

[Sci85]

With zero deck height and a .043 (standard copper or MLS) head gasket thickness

So, for my edification, when you say zero deck height that refers to the piston even with the cylinder top yes?

And squish is the measurement of the piston (at the flat) to the cylinder head correct?

And piston to valve clearance also needs to be measured as changing the base and/or head gasket will affect that clearance as well right?

Don - can you show me the math? I don't get where the .034" base gasket thickness was determined. If my current squish measurement is .028 and ideal is .043, then that's .015 difference. .015 + .022 = .037" base gasket needed for a .043" squish right?

To get the piston to be even with the cylinder, I need to add .022" more thickness to the base gasket for a total base gasket thickness of .044". Now, that would increase my squish clearance to .028 + .022 to .050". That's a little high yes? So, should I go with the piston .007" above the deck for a squish of .043 or should I shoot for piston even with the deck and use a thinner head gasket (or turned down piston flat)?

BTW, I do plan on revving it but not above factory redline.

Thanks again for the help and patience with me.

[blowerbike]

why don't you shoot for zero deck height and be done?
i never have the piston going into the head gasket (coming out of the cyl.).
.022+.022=.044
that's what i posted.
if you could get a .045 base gasket that's more than good enough.

[Sci85]

Oh ok, now I see what you meant. At first I didn't understand your ".022 under" comment in your original reply.

If I double up the base gaskets then that would bring me to zero deck but the squish would increase to .050. Is that a good squish number? I thought I read somewhere that .040-.043 is ideal.

[Suzuki_Don]

So, for my edification, when you say zero deck height that refers to the piston even with the cylinder top yes?

And squish is the measurement of the piston (at the flat) to the cylinder head correct?

And piston to valve clearance also needs to be measured as changing the base and/or head gasket will affect that clearance as well right?

Don - can you show me the math? I don't get where the .034" base gasket thickness was determined. If my current squish measurement is .028 and ideal is .043, then that's .015 difference. .015 + .022 = .037" base gasket needed for a .043" squish right?

To get the piston to be even with the cylinder, I need to add .022" more thickness to the base gasket for a total base gasket thickness of .044". Now, that would increase my squish clearance to .028 + .022 to .050". That's a little high yes? So, should I go with the piston .007" above the deck for a squish of .043 or should I shoot for piston even with the deck and use a thinner head gasket (or turned down piston flat)?

BTW, I do plan on revving it but not above factory redline.

Thanks again for the help and patience with me.

Clay, don't worry about deck height in this case. If you get zero deck height then you will have too large a squish measurement (.050").
The ideal squish measurement is .040", you have .028" so you need another .012" added to the base gasket to get it to .040". So existing base gasket at .022" + .012 = .034" for the new base gasket thickness. In my opinion .043" is too large for squish. In my experience .035" to .040" is ideal for street motors (stock). Some of the race boys use .025" but they like the piston to just about "kiss" the cylinder head.

You will never get the perfect squish as you are limited by the thickness of base gaskets you can obtain unless you start machining parts to accomplish what you are after. I did mine by only using standard parts and making my own base gasket from .8mm material to obtain the correct squish on my motor which is the exact conversion that you are doing and I know that it works with over 5000 miles on the motor. My squish for reference is .038" with no issues.

[Sci85]

Ok Don thanks. BTW, the gasket material you used, did it measure .034" before being compressed yes?

I have some felpro .030". Do you think that would be ok? My head gasket is a little thicker than yours was I believe. Uncompressed it measures .054". What do you think?

[Suzuki_Don]

Ok Don thanks. BTW, the gasket material you used, did it measure .034" before being compressed yes?

I have some felpro .030". Do you think that would be ok? My head gasket is a little thicker than yours was I believe. Uncompressed it measures .054". What do you think?

Clay I used .8mm thickness gasket material which is .0314". So your .030 material as close and with the head gasket a couple of thou thicker it will all average itself out ok.

You are on the money -- go ahead and make that base gasket. If you need any tips there is a tutorial as part of the thread that I sent you. Around page 15 or 16 I think.

Good luck