Controlled Stock Motor

BRIGGA & STRATTON CONTROLLED STOCK

NOTE: All parts must be Briggs & Stratton factory production parts unless otherwise specified. No machining or alterations are permitted unless specifically noted. Any parts that are to remain stock are subject to be compared to a known stock Briggs and Stratton part. No reading between the lines. If it's not in the rules, it must remain stock. No titanium parts allowed, UNLESS OTHERWISE STATED ENGINE WILL BE TECHED AS RACED.

703.1 SHROUDS & COVERS: Engine shroud and covers must be intact and not modified, except Scatter Shroud made by W.E. Chapps may be used. This includes flywheel shroud unless there are no holes in block for it to be used. Taping of shroud housing allowed. Tape on block disallowed. Fixed screen must be affixed to shroud cool air intake area. Any bolt utilized to secure sheet metal, shrouding, etc. with the exception of sheet metal secured by the head bolts, may be replaced with large diameter bolt(s).

703.2 HEADER/SILENCER: Exhaust pipe/header must extend beyond gas tank but not extend past rear bumper (including silencer, where applicable) and have no exposed sharp edges. Loop Header pipes MUST be wrapped to protect driver from burns. Header/exhaust pipe MAY NOT PROTRUDE inside of exhaust port so as to alter port configuration for performance gain. Studs allowed for header pipe attachment to block.
NOTE: In events where silencing device is MANDATORY (Divisional, National, etc., points event and where required for non-points, local events), use of RLV 8-91 SILENCER IS MANDATORY. Silencer must be utilized as produced, with no modifications or alterations permitted.

703.2.1 Gasket and/or Silicone allowed to seal the header.

703.2.2 Header must be of fixed design, NO SLIPPY PIPES allowed. No extra tubes or extra holes allowed except hole for heat sensor probe if sensor is used.

703.2.3 All header pipes must be of continuous length from flange to end of pipe with stages or butt welds permitted (no chamber, infusers or covers of any type allowed on muffler etc.) Silencer must be visible when viewed from any angle. Header tube and silencer only legal parts.

703.2.4 Extra HEAT SHIELD above chain guard IS ALLOWED.

703.2.5 A header support brace and safety wiring of header bolts is MANDATORY to assure header bolts remain tight. It is recommended that the safety wire wrap around pipe to insure that bolts remain with pipe in case they are stripped out of block. Silencer must be tight, secure and completely intact on the header throughout the entire event. Silencer must be clamped to header tube and no welding of silencer in any area.

703.2.6 The use of exhaust block saver is allowed. It must be round with a 0.75 inches min. and 1" maximum thickness and be made of ALUMINUM. Must have a straight bore with a 1.005 MUST GO ID. Bolt holes must have stock cord diameter.

703.2.7 Silencer Baffle holes .1285" maximum all baffles.
NOTE... MRL allows the ues of the RLV Modified Muffler.

703.3 AIR FILTER: Any air cleaner permitted that is installed in a safe manner. Filter may not be used as an air ram and must filter from all areas as raced. Any open areas in filter must be covered with a filter sock. (No open areas allowed).

703.4 FUEL TANK: Tank cap MUST be stock and in the stock position. Brace on tank bracket IS permitted. Stock gas cap must be utilized. No overflow tube is allowed. Acceptable cap is stock Briggs & Straton domed cap with single vent hole and stock gasket or old style cap with metal insert (See Fig. 701.4). Cap splash shields are not permitted. Bungee-type strap may be used in ALL CLASSES to wrap around engine and fuel tank to prevent loosening of parts from vibration. One or two gaskets allowed on carburetor/tank joint. Only one gasket allowed Carb to tank with Blue Print-O-Seal is used in pick up cup of fuel tank, however an open a lot must be visible at the top of the pickup cup. (Min. distance of .062") (See Fig. 701.4)
NOTE: INSTALLATION INSTRUCTIONS FOR TANK REPAIR KIT: (See Fig. 701.4)
CAUTION: Fuel cup insert may have sharp edges, handle with care.
1. Remove fuel tank from engine and remove old gasket.
2. Roll fuel cup insert into a coil 1" in diameter or less with tab on outside of coil and insert into the fuel cup in tank, Fig. #1.
3. Tab should rest against edge of fuel cup. Push on insert at both sides of steam until seams butt against each other, Fig #2.
4. Reinstall tank and new gasket on engine.

703.5 FILTER ADAPTER: Filter adapter may not be funneled or tapered. Top of filter adapter must be flat. Adapter may not be run without an air filter. No sealer between carb and filter adapter allowed.

703.5.1 Adapter may have rolled edge not to exceed .250" from top.

703.5.2 Maximum thickness of filter adapter is .250", measured from the top of filter adapter to carb air horn mating surface.

703.5.3 One Briggs and Stratton stock gasket may be used under filter adapter, maximum thickness 075".

703.6 CONTROLLED CLASS CARBURETOR (SPEEDWAY DIRT ONLY): Must be Briggs and Stratton stock appearing carburetor and must have stock dual pick-up tubes. No material can be added to inside or outside of carb. No additional holes can be drilled in the "body ol" carb. "Area behind jet no a tech item". Both pick up tubes must work. Air must enter carb at air horn ONLY. One or two gaskets allowed. Only one gasket allowed when Blue-O-Print gasket is used. No sealer allowed on carb to block. Any attempt to bypass, gasket, bolts or bolt holes is prohibited. The butterfly must be held in place on throttle shaft with a screw. No other way of attaching is allowed.
703.6.1 Maximum bore at .715". (Full-length of bore) The carb bore is from the recess on the flange end (end that bolts to block) of the carb to the backside of the throttle shaft. Must be able to see some of the lip at between the recess area and the bore.

703.6.2 Diaphragm side CANNOT be used to create a pressure fuel feed. Diaphragm side of carburetor parts MUST be installed as supplied from the factory. Diaphragm cover plate MAY be surfaced to ensure a proper seal. No silicone or other material may be applied to diaphragm side of gaskets. After-market diaphragms, (including Teflon pumper diaphragm), allowed as long as it is of similar material and configuration of Briggs & Stratton diaphragm.

703.6.3 Breather tube must be removed from carburetor. The hole in the caburator may be plugged.

703.6.4 A tab to reinforce a broken tank bolt on the carburetor-to-tank flange of carburetor is allowed.

703.6.5 No after-market coatings are permitted.

703.6.6 Remote mechanical carb adjusters legal in all stock classes.

703.6.7 Holes left after removal of choke and threaded hole at floor of air horn may or may not be plugged so long as plugging does not protrude into air-horn area.

703.6.8 Felt or foam washer must be on carb shaft under lever. Rubber seal must be in proper location in carb body for air seal around throttle shaft.

703.7 HEAD BOLTS: Any stock head bolts may be utilized and eight are mandatory. Head bolt with stud allowed.

703.8 CYLINDER HEAD: Stock Briggs & Stratton 5HP cylinder head required. Head cannot be machined below the flat cylinder portion of the head. Machining of two pockets for valve clearance or a single, continuous relief area from side-to-side across valve area is permitted. In no instance may the relief area touch either the back or sidewalls of the head and should be done in a manner not to affect airflow. Head may not be O-ringed. Recess at deepest point of cylinder head must be a minimum of .400° (from gasket mating surface).

703.9 HEAD GASKET: Briggs & Stratton production head gaskets are approved and aftermarket gaskets of general stock configuration (accommodates all head bolts, follows general stock pattern; does not extend to form "heat sink," etc.) are acceptable. Gasket sealer must NOT be utilized on head gasket. NO aluminum or Copper gaskets allowed. (See Fig. 701.9)

703.9.1 Head gasket must be a minimum of .043" thickness at four points between head bolt holes, front, near and both sides.

703.10 CYLINDER BORE: No circular or machined grooving of cylinder is allowed in any position of cylinder (See Fig. 701.14.1)

703.10.1 Stock cylinder bore is 2.5625" and overbore is permitted providing it does not exceed 2.6025" (approximately .040" overbore).

703.11 CAMSHAFT: Cam can be of the type centered on each weld. Maximum running lift .265" no visual tech on lobes. Gear must remain as cast.

703.12 BREATHER VALVE: Crankcase breathers are allowed.

703.13 VALVES: Stock valves ONLY. No stellite type valve allowed, as found in industrial style engines. Must be one angle ONLY. Valves may not be polished or lightened. If working are (that portion of the valve stem translating with the valve guide area) of valve stem is cleaned, no material may be removed, such as linear grooves, cross hatching, etc. (See Fig. 701.11)

703.13.1 INTAKE VALVE: 30 degrees. Intake valve minimum diameter is 1.115".

703.13.2 EXHAUST VALVE: 45 degrees. Exhaust valve minimum diameter is .990".

703.13.3 Minimum thickness of valves between top (flat area) and seating surface to be minimum .035" (no "knife edging" of valve allowed). Valves will be checked with a NO-GO gauge for head thickness and legality will be determined by that gauge.

703.14 VALVE SPRINGS: Optional, including retainers. Back facing of upper portion of valve chamber to stabilize valve spring retainers and prevent spring bind is allowed.

703.15 VALVE SEATS: Valve seats must meet stock specs and can be replaced. Seats must have one angle only, 30-degree intake and 45 degree exhaust. Seats MAY NOT PROTRUDE above block casting or deck surface. PIN PUNCHING may be used to tighten a loose valve seat. No more than eight approx. evenly spaced pin punches per valve seat (see fig. 701.13 for locate and placement of pin punches). When re-facing valve seats it must be understood that if the tool for checking valve seat height enters valve seat, legality will be determined by that gauge.

703.15.1 Intake seat inside diameter, 1.004" (NO-GO).

703.15.2 Intake seat maximum thickness .215". Minimum thickness .199".

703.15.3 Exhaust seat inside diameter, .880" (NO-GO).

703.15.4 Exhaust seat maximum thickness .215". Minimum thickness .199".

703.16 DECK/PISTON CLEARANCE: Pop up not a tech item except Decking of the block cannot extend into the aluminum at rear of block (top of tin.)

703.17 IGNITION: Briggs & Stratton factory stock coils are MANDATORY and must be utilized in unaltered form (see photo). NO slotting of mounting holes or machining of attaching bolts is permitted. New style composite ignition is allowed. There must be resistance from ground to the plug wire. SPAR PLUG CONNECTOR must be stock factory type. Rubber plug boot is allowed. May be run with or without air vane (See Fig. 701.18).
NOTE: Coils may be rechecked for correct ohms reading after 2 minutes and 10 minutes.

703.17.1 Resistance from plug wire must be 2,000 ohms MINIMUM and 6,000 ohms MAXIMUM.

703.18 STARTER: New style recoil starter may be retained as produced and intact, however, if new style coil is removed, starter cup must also b removed. Old style recoil starter must be removed. If removed, crankshaft may be cut-off to facilitate any style nut and use of electric starter.

703.19 FLYWHEEL: ONLY stock, 5HP flywheel is permitted. Any flywheel key or NO flywheel key is allowed. Painting and coating of the flywheel (other than minimal factory over-spray) is not permitted. No machining, glass beading or sandblasting of flywheel is allowed. Chipped fins because of poor casting are allowed. However, completely broken fins are NOT allowed. Any screen or guard that fully covers the flywheel fins is allowed EXCEPT NO revolving screens. All screens must be bolted to blower housing. Flywheel washer must be stock

703.19.1 Weight of flywheel shall be 6lbs 4ozs MINIMUM.

703.20 CRANKCASE SIDE-COVER: Side-Cover must remain stock EXCEPT block and side-cover may be pin-punched to help prevent side-cover gasket failure and stub for governor may be removed and hole plugged to prevent leakage. Crankcase breather allowed.

703.20.1 After-market gaskets approved, however, must be same size and material as stock gasket(s). Up to three crankcase gaskets are allowed. Block and side-cover may be pin-punched to help prevent side-cover gasket failure. Fel-Pro Multi layer crankcase cover gasket is allowed for all classes.

703.21 VALVE LIFTERS: Optional. No titanium lifters allowed.

703.22 VALVE SEAT HEIGHT: Install a .500" rod in place of the cern and replace side cover. Measure through the valve guide from top edge of .500 rod to the top of the surface of the intake or exhaust valve seat. Minimum 5.485" / Maximum 6.520". Aluminum may be removed from top of seal to check seat height. Lifter bore and valve guide bore must except seat height gage rod.

703.23 CONNECTING ROD: After-market connecting rod may be used, but must meet stock specs No .020 undersize rods allowed. No under-sizing of connecting rod is permitted. However, rod may be clearanced providing that it is in stock configuration and finish with no "dimpling" or media blasting. Rod ends must be concentric with crankshaft journal end/or wrist pin with no chamfer or breaking if edges. Raptor III rod & dipper is legal: Dipper on Raptor III rod may be broken. However, it must be a natural break with no grinding, polishing or bead blasting visible. Old style rod (after market dipper) is a non-tech item in all classes.

703.23.1 Stock rod length is 3.120" minimum , 3.1333 maximum. Measured from bottom of wrist pin to top of crankshaft journal.

703.23.2 Oil hole opening. Raptor 3 or old style rod, is .185" NO-GO. New style cast Briggs & Stratton Raptor connecting rod approval (Part #555207). Oil hole and Chamfer no-go size to be established.

703.24 WRIST PIN: Wrist pin must not be altered and must be stock Briggs and Stratton pin.

703.24.1 Maximum inside dimension of wrist pin is .290".

703.24.2 Maximum outside dimension of wrist pin is .290".
RAPTOR II WRIST PIN SPECS

703.24.3 Maximum inside dimension of wrist pin is .291".

703.24.4 Maximum outside dimension is .490".

703.24.5 Length 1.732 + OR- .490".

703.25 RINGS Three rings are MANADATORY. Compression or top ring, if chamfered, may have either a beveled or chamfered inside face and must remain as manufactured. Scraper or second ring may only have an external circumference relief area. End of rings must remain flat. Mandrel check is no longer required. New factory rings from Briggs & Stratton without bevel on top ring and with relief around circumference of second ring are permitted. Excessive and gapping of rings not allowed. New style, beveled top compression ring (factory produced) is approved. Rings must conform to all listed factory specifications and be of stock configuration. Known, standards for piston/ring configurations and Briggs & Stratton factory approved parts. No machining of rings allowed. Exception; lapping and end gapping allowed, Shrinking of oil ring and low tension ring allowed. Rings must be in one piece when removed from block. With the exemption of the Raptor III oil ring, all broken pieces must be present in the ring land, if not the ring will be illegal. If stock rings are used they must meet the following specs.

703.25.1 Top two rings, .105" minimum width (for wear).

703.25.2 OIL RING must have minimum .085" width (for wear). Grove and six oil relief slots MUST be present on oil ring Groove must measure .083" minimum, regardless of condition of ring.

703.25.3 End gap with rings compressed on ring gauge cannot exceed .500".

703.25.4 Top ring cannot exceed standard Briggs and Stratton ring land width of .084 maximum.

RAPTOR III RINGS SPECS
703.25.5 Minimum width top two rings .090".
703.25.6 Thickness top two rings .058" + OR -.005".
703.25.7 Oil ring minimum width .070", ring groove must be present.
703.25.8 Oil ring Thickness .100" + OR - .005".

703.26 PISTON: After-market piston and stock rings may be used. No excessive cleaning oil top or skirt of piston allowed Piston Pin must be Briggs and Stratton Stock. Wrist pin hole must not be altered or relocated, minimum honing of wrist pin hold allowed, NO matching is allowed on piston. If stock piston is used it must meet the following specs.

703.26.1 From top of piston to wrist pin bore .937" minimum measurement

703.26.2 Minimum piston length is 1.869".

RAPTOR III PISTON SPECS

703.26.3 From top of piston to wrist in bore .937" minimum measurement.

703.26.4 Minimum piston length is 1.671".

703.26.5 Top two-ring land width .0603" .0612".

703.26.6 Oil ring land width .1020" .1032".

703.27 CRANKSHAFT Stock factory crankshaft mandatory. Stock factory timing gear mandatory and must be installed properly. Lightening, polishing of counter weights, addition of metal o other material is not permitted. Hardening of stock crankshaft is permitted in all classes to reduce premature journal wear. The power takeoff journal of a sleeve-bearing cranskshaft may be machined (turned-down concentrically) to permit its use in a ball bearing block. Offset crankshafts are not permitted. After-market bearing of non self-aligning type, with or without shield, is permitted. NO STROKER CRANKSHAFTS ALLOWED. (Se Fig. 701.28).

703.27.1 Minimum crankshaft journal diameter is .990".

703.27.2 Crankshaft may be clearanced to a minimum dimension of .775" to permit easier removal of the bearing.

703.27.3 STROKE: Stock stroke is 2.4370" plus .007" or minus .010" for wear. Stroke is checked by pushing piston down to take up play of rod clearance. Stroke is checked from bottom dead center (BDC) to op dead center (TDC). (See Figure 701.16).

703.28 PORTS: Porting Allowed. Ports surfaces are non-visual tech item. NO ADDITION OF MATERIAL ALLOWED. Block MAY NOT be machined or altered on intake or exhaust port "gasket mating" surfaces. NO GRINDING is allowed on underside of valve seat. No HOLES in ports allowed. If port is pin-punched, it may not be done in a manner to prevent entry of a NO-GO into port area. (See Fig. 701.29).

703.28.1 Intake port .880" NO-GO.

703.28.2 Exhaust port 1.005" NO-GO.

703.29 BLOCK Must be as produced, with no alterations or reworking, except block can be relieved for red clearance. Blocks repaired from broken rod damage, cracked lifter area, etc., are permitted providing that repair does not constitute a functional modification of original block. Porting of intake and exhaust ports allowed but block may not be machined on intake or exhaust ports gasket surfaces (See fig. 701.29). No bushings of any kind allowed except for bushings approved in this Tech Manual. DU Bearing may be installed in conventional block on flywheel side. Extra oil hole, 1/8" in diameter, may be drilled on flywheel side of block at crankshaft bushing to better lubricate crankshaft (applicable to all classes). Sleeving of cylinder block is permitted in all Briggs and Stratton engine classes. Regular ferrous sleeves only, with no coatings or plating, such as NicaSil, allowed. The repair of one coil post is allowed, as long as the remaining post is factory and unaltered. Valve guides may be replaced. Aftermarket valve brass or bronze guides allowed as long as they meet stock requirements. Valve guides may be stacked, No KNURLING of guides allowed. Minor grinding of block behind seal in a double bearing block where crank goes through block is allowed (to prevent crank from seizing). Chamfering at bottom of lifter bore for clearance purposes only allowed. Diameter of chamfer cannot exceed .500 and will be checked with a .505 no-go gauge, which measures .505. This applies to stock blocks that have been welded for strengthening purposes. No Undercutting of lifter bore permitted. (See fig. 701.30)

703.30 WELDING: No welding can be done to an engine from the cooling fins upwards except minor welding to lower exhaust bolt hole is allowed for repair (weld cannot protrude into exhaust port). The only welding permitted is to repair damage from a broken rod or cracked lifter bore. Welding of lifter bore for reinforcement or breakage allowed. Installation of bushing guide to help reinforce lifter bore area allowed.