measuring piston dome volume

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
\" how do you measure piston dome volume"
I just bought a 454 from a yard sale,

the seller has no clue as to the pistons used"

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ok first some facts
(1)cylinders will not be honed to true round as they will be in use with out the use of a deck plate to simulate and duplicate the bolt clamp stress on the cylinder walls, bores in blocks without a head or deck plate with the bolts or studs torqued to spec are not nearly the same shape before having the torqued studs bolts stress applied, theres almost no chance of getting a good ring seal without having the bores honed with a deck plate
always read, understand and follow the piston manufacturers guide for piston to bore clearance and how you measure that correctly
YOU NEED TO KNOW what is the piston to bore side clearance, where on the piston in relation to the pin,it will need to be accurately measured,in relation too the piston pin bore axis and piston top,surface, and how you measure it according to the manufacturer, and how did you measure both the piston and the bore and whats your ring gap supposed too be set at?
think carefully about both the initial cost and the structural strength of the engine block you select, the OEM blocks used in production car engines will RARELY accept a .030 plus over bore with out having one or more cylinders having marginally thin bore walls, this results in inadequate bore to ring sealing if its in the wrong area and promotes stress cracks. A .060 over bore in a SBC is rather commonly pushing that bore wall thickness up to or over a reasonable limit so you need to sonic and magnetically check the block for cracks and wall thickness.
you could easily dump $500-$1500 into machine work on a block that won't last more than a few months under high stress if its not carefully checked PRIOR to the machine work being done.

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be sure you, measure EACH bore and EACH piston,
(CORRECTLY with the proper tools in the way the tool and piston manufacturers suggested)
and number them on an engine build sheet indicating the bore and piston diam.
from large to smallest on each and install them on each cylinder to get the most consistent piston to bore clearance's
yes the difference may only be a few ten thousands if the bores are machined correctly, but you'll get the best results , most consistent lubrication, best durability and less heat build up that might result in detonation issues that way. its the little things that add up to making a good durable engine assembly,
BTW check rod orientation, so the beveled sides don't fact the adjacent rods, and check the bearing clearances with plasti guage

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btw
its standard practice to cc the combustion chambers, in the cylinder heads and the piston domes,(obviously check quenck and piston pin height, and clearances , mpisyton to head clearance, valve to piston cleances also,
(usually the piston domes volume is generally measured with the piston deck or quench surface rotated down the bore , exactly 1 inch) use your caliper or dial indicator and piston bridge)and the rings sealed temporarily with a bith of grease or paraffin to make sure you'll be dealing with as close as possible to the exact same compression ratio, in each cylinder, mark each piston with a indulable black magic marker A,B,C,D,E,F,G,H
and the bores 1-2-3-4-5-6-7-8 so you don't get measurements on the build sheet confused between bore diam and piston diam, and you can also not confuse dme volume on each piston
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ok you want to calculate your compression ratio,
be aware all BBC pistons will NOT work with ALL potential heads.
remember open and closed chamber heads on THE BBC.

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youll need to verify clearance in the combustion chambers and valve to piston clearance

http://garage.grumpysperformance.com/index.php?threads/vin-casting-info.10474/#post-44012

https://www.mortec.com/bbc.htm
and you bought a short block all ready assembled from some source that has no clue what the pistons used are.
they certainly have a dome volume that will take up space in the combustion chamber and raise effective
compression,
but are they 35cc-50cc, 64cc ?
you'll need a deck bridge and dial indicator lexan plate and cc burette


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dial indicator and ideally a lexan plate and a burret with cc measuring marks
watch the videos, the procedure is very similar to measuring combustion chamber volume
you push the piston down bore 1", using the deck bridge /dial indicator,
seal the piston to bore ring gap area with vasoline,over the rings, wipe excess away

the bore diameter must be measured accurately, a dial caliper can be used
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but a bore gauge is much more accurate
owler Full Warranty Extender Dial Bore Gage Set, 52-646-400, 1.4-6" Measuring Range, 0.0005" Graduation Interval: Bore Measurement Gauges: Amazon.com: Industrial & Scientific

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Fowler Full Warranty Extender Dial Bore Gage Set, 52-646-400, 1.4-6" Measuring Range, 0.0005" Graduation Interval: Bore Measurement Gauges: Amazon.com: Industrial & Scientific
www.amazon.com

6 Pcs Professional Premium Outside Micrometer Precision Machinist Tool Set 0-1"/1-2"/2-3"/3-4"/4-5"/5-6" Measuring Range Included 0.0001" Graduation: Amazon.com: Industrial & Scientific
6 Pcs Professional Premium Outside Micrometer Precision Machinist Tool Set 0-1"/1-2"/2-3"/3-4"/4-5"/5-6" Measuring Range Included 0.0001" Graduation: Amazon.com: Industrial & Scientific
www.amazon.com


Lexan Polycarbonate clear 1 sheet - 1/2" thick x 6 " x 6"

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I found two 1/2" thick 6"x 6" thick lexan clear sheet on scam bay for about $22 plus shipping that will allow me to fabricate,
TWO of the 6" x 6" COMBUSTION CHAMBER CHECKING AND CCING cover plates,
a step drill helps
http://www.harborfreight.com/catalogsearch/result?q=step+drill
by simply cutting into two equal pieces and drilling a counter sunk 3/16" hole in each half.
lexans a whole lot stronger than plexi-glass, and 6" x 6" allows more sealing surface options so thats the route I took
and its extra stiffness and weight helps seal the measuring fluids


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the formula for a cylinder volume is R sq times PI (3.147) times depth, 1"=25.4mm
R=1/2 the diameter of the bore.

yeah a pocket calculator may be helpful.
lets assume a 4.25" bore,and the piston 1" down bore,

4.25 bore x.5= R= 2.125 x 2.125 x 3.147=14.21067 cubic inches
theres 16.3871 ccs in a cubic inch, thus 14.21067=232.87 ccs



in this case lets say you fill the cylinder and it takes 189ccs,
you sub-track that from the potential max volume of 232.87 and see you have a 43.87 dome volume

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related threads YOU'LL NEED TO READ,
don,t skip the info links it great related info












 
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BTW the question always comes up, "how do you seal the rings/pistons to the bore so the fluid you use to measure the piston dome volume does not leak past the rings?

(DEPTH MICROMETER)
OK, most shops either use a piston bridge and dial indicator or maybe a custom fixture to place the flat or quench deck of the piston exactly 1" below the top of the cylinder bore, and they use a burette when ccing the bore volume vs the theoretical CC volume of a perfect flat bottom cylinder
most shops use a bit of moly grease, smeared 360
degrees around the and on the bore walls with the piston at bdc
and they rotate the crank up from BDC to 1" below TDC, then they use a few tissues and Q-tips to remove all excess grease above the piston or left on the bore wals , some shops pour a bit of melted PARRIFIN on the piston and wipe it into the piston to bore clearance and then they remove all excess off the piston before they measure the piston dome or recess in the piston, from that 1" down the bore location, with a burette of fluid, paraffin has the advantage that it rapidly melts and will burn off in use if a small amount is left in the oil, most oil already has a bit of paraffin in it,

you may need to use a floor jack to lift the engine to have the blocks deck read level, use a solid but reasonably soft spacer under the block if thats required to prevent damaging the blocks lower surfaces, a large block of wood may work,
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remember the formula for a cylinders volume is the radias (1/2 the diameter) squared times 3.147 times the depth (in this case 1"
1 cubic inch = 16.3871 cc's

so for example if the bore diameters 4.25" youll multiply 2.125 x 2.125 x 3.147 to get the cubic inch volume them multiply the result by 16.3871 to get the cc's
thats the expected volume above a flat top piston, you'll generally use a bit more because the valve clearance notches add 6-8 cc volume on a flat top piston or use a bit less fluid from the burret if the pistons got a dome.
obviously the difference is the dome volume
I generally use a 100cc-250cc BURRET and a 6" square sheet of LEXAN (they generally sell 12" square sheets so you get four to use to measure heads and piston volume ones you carefully saw then drill the 4 quarters) use with a small counter sunk hole drilled in the center over the bore for the burret to drip fluid through, a very small thin bead of grease or silicone around the bore to seal the lexan from leaking fluid is advised and of course the blocks deck must be both level and clean, before the blocks used to measure the piston dome volume,
this is a good time to use a 24" steel
carpenters square and a set of feeler gauges to verify the block decks square and level,
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you can purchase a 1/2" thick 6" x 6" lexan sheet you can drill and modify to cover a heads combustion chamber or a blocks bore to cc a combustion chamber volume or piston dome volume for under $16 on the internet/amazon /ebay
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read these links





you can purchase a 1/2" thick 6" x 6" lexan sheet you can drill and modify to cover a heads combustion chamber or a blocks bore to cc a combustion chamber volume or piston dome volume for under $16 on the internet/amazon /ebay
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What kind of engine are you building Grumpy when you need a 2000 cc Burette???

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I don't see the significance of the chart with RPM vs CID when it comes to overlap???

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