Burris National Speedway Series – 2003 Season Rule Book


SECTION 10 - BRIGGS AND STRATTON 5HP TECHNICAL SPECIFICATIONS
General: All components must be OEM Briggs & Stratton unless otherwise specified. Gaskets
and fasteners non-tech unless otherwise specified. Gasket sealer on all machined surfaces
OK.

10.1  Cylinder head requirements: Machining permitted on the gasket mating surfaces and the
top of the post bosses only. Welding on the cylinder head is prohibited. Helicoil repair
of spark plug threads in original position permitted, no protrusion into combustion
chamber allowed. Bolt hole diameters .348" maximum. Combustion chamber depths:
piston area .011" minimum, spark plug area .408" minimum, valve area .300" minimum.
Head gasket material non-tech but must be stock configuration and .043" minimum
thickness. Eight stock head bolts required.
10.2 Bore and Stroke: 2.6025" maximum bore, 2.437 +/- .0l0" stroke. Protrusion of the piston above the top of the cylinder deck is .005" maximum parallel and inline with the wrist pin. *(See foot note)
10.3 Carburetor requirements: Stock Briggs & Stratton 5hp carburetor only. Filter adapter (if utilized) top surface must be flat and .250" maximum thickness from mounting face. Inside diameter of adapter may be radiused .250" maximum. No more than one filter adapter gasket may be used, thickness .075" maximum. One or two carburetor mounting flange gaskets may be used. Swirl non-tech. Throttle shaft washer and rubber seal must be in place and stock configuration. Throttle shaft leading edge .040" minimum, trailing edge .086" maximum. Butterfly must be unaltered stock with .059" minimum thickness at throttle shaft mating location. Butterfly screw must be unaltered stock, .322" minimum length. Except for outside end, needle screw must be unaltered stock with o-ring and washer present. Jet must have stock recess on backside with no funneling of hole allowed. Main metering hole diameter .062" maximum. Idle hole diameter .028" maximum. Air horn diameter 1.011" maximum. Recess at flange end must be as cast, .726" maximum diameter. Carburetor bore, from flange end recess to intersection of air horn diameter, .695" maximum diameter - must be straight, no tapering, no attempts to modify fuel/air flow permitted (rifling, dimpling, protrusions etc. not permitted). Diaphragm cover plate may be faced for proper sealing. Aftermarket diaphragm of stock configuration permitted. Spring and cup must be unaltered stock. Long fuel pickup tube may not be brass. Short tube inside diameter .066" maximum. Breather tube must be removed. Any stock, single hole, domed Briggs & Stratton fuel tank cap is permitted including those with integral splash shields.
10.4 Exhaust: See rule 8.3
10.5 Valve train: Stock, unaltered breather valve only. Two gaskets permitted. Grommet
and internal foam must be in place. Stock, unaltered, single angle valves only. Length
of flat from seating surface to end of valve .035" minimum. Intake valve angle 30º +/-lº,
1.115" minimum head diameter. Exhaust valve 45º +/- 1º, .990" minimum head
diameter. Stock valve springs and lower retainers required. Springs may be machined
to meet length requirements. Exhaust spring must be used on exhaust valve and may
be used on intake valve. One stock upper retainer may be used on either valve, .058"
maximum lip thickness. Intake valve spring length 1.240" maximum; .087" maximum
wire diameter. Exhaust valve spring length 1.300 “ minimum,1.500 “ maximum, .088 “
minimum wire diameter; inside spring diameter .625 “ minimum, .640 “ maximum. Both
upper valve chamber surfaces may be spot faced for valve spring stabilization. Depth
and geometry of spot face non-tech. Stock, single angle valve seats required. Valve
seat height to cam centerline 5.740" minimum, 5.775" maximum. Valve seat may not
protrude above cylinder deck surface.
10.6 Ignition systems: Stock, unaltered coil and coil air vane required. OEM plug wire only.
Connector and plug boot non-tech. Resistance from spark plug wire to ground is 2,000
ohms minimum, 5,000 ohms maximum. Stock, unaltered 5hp flywheel required.
Flywheel weight, 6.0 pounds minimum. Flywheel coating of any type is prohibited.
Revolving or adjustable flywheel screens are prohibited. Flywheel key is optional and
non-tech.
10.7 Piston requirements: Approved commercially available aluminum piston and ring
configuration permitted. (Briggs, Burris, Wiseco approved Super Stock type.) Length
from top of piston to top of wrist pin bore .925” minimum. (Decking of piston permitted
to adjust pop up within the .925” min.) Wrist pin outside Diameter .490 “ maximum,
inside diameter .290 “ maximum, length 1.727 “ minimum, 1.737 “ maximum.
10.8 Rings: All three required. Must be stock appearing.
10.9 Connecting rod requirements: Approved commercially available aluminum connecting
rod is permitted. Length from bottom of wrist pin bore to top of crankshaft journal bore
3.1233 “ minimum, 3.1333 “ maximum. Connecting rod bolts and dipper are non-tech.
10.10 Crankshaft requirements: Stock crankshaft required. Machining, polishing, addition of
material or otherwise altering of counterweights is prohibited. Stock timing gear in stock configuration required. Connecting rod journal diameter .990" minimum, Crankshaft journals may be clearance to .775" minimum diameter to facilitate bearing removal. Thermal treatment of crankshaft is permitted.
10.11 Camshaft requirements: Camshaft base circle is .770 “diameter maximum. Lifter
material to be ferrous steel only. Lifter head diameter .982”minimum, 1.005" maximum, Length 1.606" maximum. Cam profile check must be taken with zero (0) valve lash.
 
Camshaft profile limits
Lift
Exhaust degrees
Intake degrees
.050
38ºBBDC to 33ºBBDC
7ºBTDC to 0ºTDC
.100
21ºBBDC to 16ºBBDC
10ºATDC to 17ºATDC
.150
2ºBBDC to 3ºABDC
29ºATDC to 36ºATDC
.200
21ºABDC to 31ºABDC
55ºATDC to 64ºATDC
Max
.233 “ maximum
.233 “ maximum
.200
76ºBTDC to 65ºBTDC
43ºBBDC to 33ºBBDC
.150
48ºBTDC to 4OºBTDC
13ºBBDC to 6ºBBDC
.100
28ºBTDC to 21ºBTDC
6ºABDC to 13ºABDC
.050
10ºBTDC to 4ºBTDC
23ºABDC to 31ºABDC
  • EZ Spin: start 45º to 60º ABDC

• EZ Spin lift base: .013" minimum, .019" maximum, 30º minimum duration, .001"
maximum drop during duration.
10.12 Block requirements: Side cover must be stock. Stub for governor may be removed and hole plugged. Gasket mounting surface of side cover and block may be pin punched. Block must be unaltered stock with the following exceptions. The lifter bores may be countersunk to provide lifter head fillet radius clearance. Any means to raise the bottom of the lifter bore boss is prohibited. Welding to the block shall be for damage repair or lifter bore reinforcement only and may not constitute a functional modification. The cylinder deck may be machined, but cannot extend into the rear fin. Carburetor and exhaust pipe mounting surfaces must be unaltered stock. Alterations to inside surfaces of intake and exhaust ports are allowed so long as the intake port will not accept an .880 “ diameter No-Go plug gage and the exhaust port will not accept a 1.005 “ diameter No-Go plug gage. No addition of material is allowed. No additional holes may exist in the intake and/or exhaust ports. No alterations on the underside of the valve seats are allowed. Cylinder sleeve, if present, shall be ferrous material and uncoated.
   
*(Note: Areas wishing to allow IKF legal engines (w/ .015” popup) may do so as a local option. Participant must declare which rules the engine conforms to prior to teardown.)


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