Here's the tool:

Click to view attachment

Here it is in a cylinder as you would check deck height.

Click to view attachment

I've always wondered how that measurement should be taken. Thanks for the pics. How does this relate to the heads and how they are treated during a rebuild and how is compression affected by these variables? Also, don't forget to zero the caliper by extending the depth gauge slightly and then seating it against a perfectly flat and clean surface.

This necessarily the best way to measure deck height, but for most stock type rebuilds it will work fine.

This measurement * pi * cylinder diameter + head cc + piston pocket/dome volume will let you calculate compression ratio.

More deck height equals lower compression (fuel/air isn't compressed into such a small space). Less deck height equals higher compression.

The more your heads have been flycut (which removes material and reduces combustion chamber volume) the more deck height you'll need in order to compensate to keep the CR to 8.5:1 for stock FI.

here is a C/R calculator

http://www.wheelspin.net/calc/calc2.html

This is what I use, to bring it up to TDC, then I use a depth gauge.

if you have domed or dished pistons, I assume you would measure from the highest part of the piston, no?

that is calculated in Dome or Dish part of the calculator

I think Blair got some better photos, all I had was my cell phone. Here's Rich battling the ring compressor. Troy on the right.

How far did you guys get tonight?

I borrowed a depth gauge that was real easy to use.

NO, wether a dome or dish, for deck heigth, you would measure the flat side out side of the dome or dish. For the compression ratio, you would then either add -cc for a dome piston or +cc for a dish, to the chamber cc's, to figure the correct C/R.

Example: In my picture I have a flat top, the Deck Heigth, is .015", used for the C/R calculations, but I have +8cc in the valve reliefs, so I add the +8cc to the Head cc, which is 48cc, so for the C/R calculations the head cc is 56cc.

Hi Mark

I, dial indicate the piston to TDC, to get an exact reading of the deck heigth, I too have a depth gauge like yours, except it has a 6" base, what I used to do V8 motors.

Trying to eye ball TDC, you can be up to .001" to .003" off on TDC, which throws C/R calculations off.

the short block is together, the heads are coming offthe engine thats still in the car. between the shmucks ring compressor and spiro locks, we looked like the short buss brought us to school. spent to much time b.s'n!

I happen to be lucky and have a dial gauge and depth gauge in my garage. Thats what I used on my engine.

I'd also like to add the importance of torquing the cylinders to the block.

Mark, I know you're clear in what you say about it being fine for stock rebuilds, but I really dont think a caliper is the right tool for the job. There are many machine shops with depth gauges that would probably let you use them for free if you ask.

Good going you guys. I wish I could have come up. It looks like fun.

Dave

AAron,

Cowpullers are fine... With Starret's they are dead nuts, with el cheapo harbor freights, they are +/- .001.

You want to do two things. One, establish deck height depth more or less (for volume calcs) , and two, compare deck height on all 4 cylinders.

Remember this my friend, even if the calipers .... er Cowpullers are rated +/- .001, the variance from cylinder to cylinder are probably closer. Why? That tolerance is for any mesurement UP TO 6 INCHES. For measurements less than 6 inches, the readings should be better. Yes, I agree, on cheap stuff, there can be tolerances of +/- .001 on readings less than 6 inches, but if you are measuring approximately the same dimension from cylinder to cylinder, the readings should be tightly grouped for better accuracy than that.

Don't believe it? Sit down with a box of precison guage pins AND a caliper. Betcha you can get the same measurement off the same pin time after time. It may be off +/-.001 for el cheapo's but the same resut should show time after time. Go a little over or under on pin size and I bet it tracks off the original mesurement. That is, if the first pin diameter is .001 over, the next smaller pin diameter reading should also be .001 over as well, and the next pin size over original should track at .001 over.

Ken

Thanks to all that stopped by to pitch in (& McMark ) indeed after all the measuring math and assembly Blair came up with a 9.6 to 1 CR.
Im gonna spend today yanking out the 2.0 and stripping it and applying those heads to the 1911.
BTW the freaking Ring compressor experiance reinforces why you buy quality tools

after 0 decking it, what did you wind up with for a final deck height? what were the cc#s for the heads?

k

Sounds reasonable. Now use your numbers and the compression ratio calculator and change the deck height until you get the compression ratio you want. Looks like you'll probably need around a 1 mm shim to get 8.5:1, and half as much (0.5mm) for 9:1.

Did you compare the deck height readings for all four cylinders?

The tolerance is not dependednt on the length measured. If its rated up to 6" with a +/- .001" tolerance, that does not mean a 1" measurement is only +/- .00017". Thats how the system works...

The problem with calipers; they are an awkward tool to measure with in this application. They are perfect for measuring the length of a part or the diameter, but when you're trying to measure depth, there is no proper way to mount the caliper to get consistent readings. For example, your caliper can rock back and fourth because the reading surface is very narrow, which causes for huge discrepancies.

Like I said, a depth gauge sits perfectly perpendicular to the measuring surface and there is no room for human error.