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TECH & INSTALLATION TIPS TECH & INSTALLATION TIPS

CALCULATING COMPRESSION RATIO
SWEPT VOL. + TDC VOL.
CR =
TDC VOL.

Swept Volume = 3.1416 x Bore x Bore x Stroke ÷ 4
TDC Volume = Cylinder Head Volume + Gasket Volume + Deck Volume + Piston Dish (-Dome)
Volume
Gasket Volume = 3.1416 x Gasket Bore x Gasket Bore x Compressed Gasket Thickness ÷
4
Deck Volume = 3.1416 x Bore x Bore x Deck Clearance ÷ 4
Piston volume = as published in JE catalog x –.061
Head volume = as published in cc’s x .061
Always use cc’s or ci’s, do not mix the two. To convert cc’s to ci’s multiply cc’s by .061
HOW TO

Convert from Cubic Centimeters to Cubic Inches CALCULATING COMPRESSION HEIGHT/DISTANCE
Multiply by .0610237 .020
Example 1835cc x .0610237= 111.98 4.250 6. 385 1.270
2.125
Convert from Cubic Inches to Cubic Centimeters 9.800
Multiply by 16.387064 9.800 – 2.125 – 6.385 – 0.020 = 1.270
Example 350ci x 16.387064= 5735.47
Convert from Inches to Millimeters EXAMPLE: BLOCK 1/2 ROD DECK = COMPRESSION
Multiply by 25.4 HEIGHT – STROKE – LENGTH – CLEARANCE HEIGHT/DISTANCE
Example 3.189 x 25.4= 81.00mm FIGURE 3
Convert from Millimeters to Inches PISTON/DOME TO HEAD CRANK COUNTERWEIGHT
Multiply by .0393701 AND SPARK PLUG TO PISTON CLEARANCE Min. Clearance
Example 81mm x .0393701= 3.1889 Not to Scale! CLEARANCE Always check crank counterweight
Always check piston/dome to head to piston clearance at BDC. Min.
INSTALLING ROUND WIRE LOCKS and spark plug clearance to assure Recommended minimum is .060”. Clearance
proper clearance (See fig.1). Minimum
clearance for steel rod =.040”, CONNECTING ROD TO
Using the 4 o’clock position of the pick lock groove as a reference, install one end of the lock at 1 o’clock. (The end gap of the lock should aluminum =.060”. Check using clay
span from 1 o’clock to 3 o’clock) Position the rest of the lock as close to the wrist pin hole as possible. Insert a pick lock tool or small with piston installed on rod at TDC, PISTON CLEARANCE FIGURE 1
Due to the large variation in rod
screwdriver into the pick lock groove and leverage the lock into place. Once the first lock is in place, install the wrist pin. Seat the lock by be sure to rock the piston back and widths and material thickness Rock Piston
placing a brass or aluminum drift against the pin and strike the drift firmly with a hammer. Perform this function on a cloth towel or soft rubber forth in the bore to get total minimum above pin, always check
pad to prevent damage to the piston. Remove the pin and re-install with the connecting rod attached. Install and seat the second lock using running clearance. for proper piston to rod clearance
the same procedure, then re-seat each lock a second time. on OEM, aftermarket steel rods and
PISTON TO VALVE aluminum rods. Recommended
CLEARANCE clearance is .050” min per side .050 min. .050 min.
INSTALLING SPIRO LOCKS Piston to valve clearance is determined and .050” min from top of rod to
by cam lift, lobe separation, duration, piston. With the piston installed on
Begin with the leading tip of the lock in the 12 o’clock position. Insert your thumb through the center of the lock and hook it under your thumbnail at valve margin, head design, and the rod, rock the piston side to side
the 10 o’clock position (roughly 1/2” to the left of the leading tip). Install the leading tip into the 11 o’clock position of the groove. (If the wrist pin hole aftermarket milling of cylinder head. and rotate forward and backward .050 min.
ensure
proper
clearance.
to
intersects the oil ring groove, lock installation is slightly more difficult as the lock will catch on the bottom ring land) The leading edge of the lock should Minimum recommended clearance for See figure 2. Wrist
catch in the groove allowing it to stay on its own. Continue installing the lock by applying pressure in a circular, counter-clockwise motion (fig. 3) until intake & exhaust valve is .100” in Pin
depth and .050” radially. Check by
it fully snaps into place. Most pistons are made for double Spiro Locks, requiring 4 locks per piston (two at each end of the pin). For pistons made to using clay or follow cam manufacturers FIGURE 2
accept Round Wire Locks, see the installation instructions below. The correct number of Spiro Locks must be installed in each piston or severe engine recommendations for checking Rod
damage may occur. Do not over-stretch or re-use Spiro Locks. Do not install Spiro Locks in press-fit pin applications. clearance, making sure the cam is
degreed exactly as it will be during
operation.

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