Ross Racing Piston Installation Instructions

INSTRUCTIONS

FOR PROPER INSTALLATION OF ROSS

FORGED ALUMINUM AUTOMOTIVE PISTONS

IMPORTANT: Before balancing these pistons, be sure they are as you

ordered. Used or altered parts cannot be returned for refund, credit

or exchange regardless of the circumstances. In the event that your

pistons are not as ordered, contact the factory immediately as all

credits, exchanges, or repairs must be completed within 45 days of

purchase. All parts returned for credit must be in like new condition-

no scratches, dings or nicks.

BORE SIZE AND CLEARANCE

Before you attempt to set clearance of piston skirt to cylinder wall

you must first determine which skirt design your pistons have.

Failure to do this can result in piston scuffing, excessive oil

consumption, or a seized engine.

To determine which clearance instructions to use from this

instruction sheet, compare the lower sill of the oil ring groove of

your piston to be fitted against the illustrations below.

If the piston to

be fitted has a

step at this

corner, use

instructions ‘A’

on page 2.

If the piston to

be fitted has a

radius at this

corner, use

instructions ‘B’

on page 3.

* PLEASE NOTE: ALL DIMENSIONS IN THIS INSTRUCTION SHEET ARE FOR 74°

FAHRENHEIT TEMPERATURE. KEEP IN MIND THAT ALUMINUM EXPANDS WITH HEAT AND

CONTRACTS WITH COLD.

PAGE 2

INSTRUCTIONS ‘A’

Check piston diameter at the point indicated on drawing. Although the

piston skirt to the cylinder wall clearance preferences vary somewhat

among engine builders and designers, we recommend the following

minimum clearances for our pistons.

THE FOLLOWING RECOMMENDATIONS ARE FOR OUR STANDARD DESIGN

PISTONS FORGED FROM 2618 T-61 ALUMINUM. FOR MARINE

APPLICATIONS ADD APPROXIMATELY .001 CLEARANCE TO THE BELOW

CLEARANCES. MANY SOLID (WATER JACKETS FILLED) BLOCKS AND AIR

COOLED ENGINES WILL REQUIRE ADDITIONAL CLEARANCE AS WILL

ENGINES WHICH HAVE BEEN HONED WITHOUT TORQUE PLATES.

SET CLEARANCE AT BOTTOM SILL OF SIDE RELIEF

Blown gas street............................................................ .010

Blown fuel & blown gas competition.................. .012 to .014

Normally aspirated street cars....................................... .007

Blown alcohol................................................................ .011

Modified type engines, including drags,

circle track and road race................................... .008 to .009

* PLEASE NOTE: ALL DIMENSIONS IN THIS INSTRUCTION SHEET ARE FOR 74°

FAHRENHEIT TEMPERATURE. KEEP IN MIND THAT ALUMINUM EXPANDS WITH HEAT AND

CONTRACTS WITH COLD.

PAGE 3

INSTRUCTIONS ‘B’

Check piston diameter at the point indicated on drawing. Although piston

skirt to cylinder wall clearance preferences vary somewhat among engine

builders and designers we recommend the following minimum clearances

for our pistons.

THE FOLLOWING RECOMMENDATIONS ARE FOR OUR STANDARD DESIGN

PISTONS FORGED FROM 2618 T-61 ALUMINUM. MANY SOLID (WATER

JACKETS FILLED) BLOCKS AND AIR COOLED ENGINES WILL REQUIRE

ADDITIONAL CLEARANCE AS WELL AS ENGINES WHICH HAVE BEEN HONED

WITHOUT TORQUE PLATES. AIR-COOLED ENGINES WITH PLATED OR

SLEEVED ALUMINUM CYLINDERS MAY REQUIRE LESS CLEARANCE.

Normally aspirated street cars

Bore size 3.475 and under..................................... .003

Bore size 3.476 – 4.499......................................... .004

Bore size 4.500 and above..................................... .006

Modified type engines, including drags,

circle track, and road race.................................. .004 to .005

Turbo engines, small bore.............................................. .006

Marine applications add................................................ +.002

Nitrous over 250hp V-8 add.......................................... +.002

Nitrous over 100hp 4 cyl add........................................ +.002

* PLEASE NOTE: ALL DIMENSIONS IN THIS INSTRUCTION SHEET ARE FOR 74°

FAHRENHEIT TEMPERATURE. KEEP IN MIND THAT ALUMINUM EXPANDS WITH HEAT AND

CONTRACTS WITH COLD.

PAGE 4

VALVE POCKET DEPTH: Minimum acceptable valve to piston

clearance is dependent upon many factors, including cam lobe lift

rate, valve spring tension and valve actuation mechanism weight,

etc. However, we have found that .090 intake and .110 exhaust

clearance are sufficient in most instances, check valve to piston

clearance (using either clay or the light spring method) making sure

the camshaft is degreed as it will be operated, as a few degrees of

advance or retard at the camshaft can radically alter the valve to

piston clearance.

PISTON TO COUNTERWEIGHT CLEARANCE: A minimum of .060 is

acceptable. Check rod pin end to piston pin boss side clearance with

the piston in the bore and the rod installed on the crankshaft, to

insure that the side of the rod is not contacting the side of the piston

pin boss.

RING SIDE CLEARANCE: Check ring side clearance with feeler gauges

to be sure that it is between .001 and .004.

RING END GAP: Use the ring manufacturers recommendations.

CLEANLINESS: Scrub pistons and cylinder walls in hot soap and

water before installing. We recommend brushing a light coat of non-

detergent oil on pistons’ skirt and cylinder walls for initial

lubrication. DO NOT use detergent oil, synthetic oil, or an additive

until the rings have seated. Be sure to lubricate pins with lubriplate,

or an assembly oil to prevent galling on initial fire-up. Check forced

pin oilers for foreign matter.

When at all possible, use a moly top ring rather than chrome plated

rings. Chrome is a weldable material with very little surface porosity.

This can lead to premature cylinder wall wear and scuffing, as well

as prolonged break in periods.

OFFSET PINS: If this set of pistons has pins which are offset (side to

side) see separate instruction sheet concerning offset pins.

Spiro Lox installation may be facilitated by grasping each end of the

lox and pulling the ends apart a MODERATE (approximately ½”)

amount. This will cause the lox to resemble a small coil spring. The

lox can then be “spiraled” into place almost as if you were screwing

them into the groove. Be sure that all lox are properly seated and

* PLEASE NOTE: ALL DIMENSIONS IN THIS INSTRUCTION SHEET ARE FOR 74°

FAHRENHEIT TEMPERATURE. KEEP IN MIND THAT ALUMINUM EXPANDS WITH HEAT AND

CONTRACTS WITH COLD.

PAGE 5

that they exert radial pressure against the lox groove. You should

not be able to spin the lox by hand after they are installed. Most

Ross Racing Pistons come with double lox (four lox total per piston –

two at each end of the pin). Be sure that the correct number of lox

are installed in each piston.

Many Ross Piston designs have offset domes or valve pockets for

certain engines. Check to be certain the pistons are installed in the

correct cylinder numbers to ensure that the dome and valve pockets

match the combustion chamber and valves.

Many pistons (at the customer’s request) are made with hand fit or

marginal clearance domes for maximum compression and quench,

therefore check dome to head clearance with modeling clay with the

spark plug installed.

All Ross stocking pistons come from the factory pin fitted, however

many Ross custom pistons are shipped not pin fitted, as this is an

extra cost option. If the customer is going to pin fit the pistons, the

job should be done on a hone.

ALL ROSS PISTONS WITH THE OIL RING IN THE PIN HOLE

MUST USE EITHER OIL RING SUPPORT RAILS OR PIN BUTTONS.

IF THERE IS ANYTHING YOU DON’T UNDERSTAND ABOUT THE

ABOVE INSTRUCTIONS CALL THE ROSS TECHNICAL

INFORMATION LINE (310.536.0100).