SEMO Raceway Sikeston, Missouri
Rules for Clone Classes
Burris Tires Only
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ENGINE SPECIFIC TECH SHEET FOR: BOX STOCK PROJECT 6.5 OVH
Description: Single cylinder, 2 valve, OHV 4 cycle
Important Note: All parts must be Box Stock Project factory production parts unless otherwise specified in
this rules manual. No machining or alteration of parts is allowed unless specifically noted. All parts will be
subject to a comparison to a know Box Stock part (when performing a comparison check it is recommended
to use a + /- .005” tolerance). Engine will be teched as raced. There will also be a $200 claiming rule in place
for this engine. Refusing to accept the claimer will result in immediate disqualification of competitor along
with forfeiture of any points earned to date in class. Competitor will also not be allowed to compete any
longer in that class.
Combustion chamber volume: 27.5 cubic centimeter minimum, with piston at TDC, using prescribed procedure.
Cylinder Head Requirements: Must be OEM casting only. Porting and / or grinding are not permitted. Valve
seats are two angles 45 degrees valve face and 30 degrees top relief. Stock head bolts only, must have four.
Head
gasket maybe after market, must be of stock configuration. No copper or aluminum gaskets allowed. Stock exhaust
system only with no modifications. Any stock configuration gasket allowed no other sealer.
Bore and Stroke: Stock cylinder bore is 2.685” max. Stroke is 2.123” + / - .005”.
Carburetor requirements: Huayi OR RUI*ING model carb only. Carb to intake sealer is gasket only no other sealer
allowed.
Choke must be as supplied from factory, but may be fixed to stay in open position. Choke bore .810” NO-GO.
Venturi .615” NO-GO. Rear carb bore .751” NO-GO. Main fuel jet .028” NO-GO. Stock air cleaner assembly only.
Valve Train: Stock valve cover only with any stock configuration gasket, no sealer.
Factory stock rocker arms and push rods only. Stock valves only 45 degree angle only both valves, no
modifications allowed. Only Box Stock
valve springs only. Max wire diameter on spring wire is .0698” with a maximum tension of 10.8 lbs. at a height of
.850”.
Ignition system: Stock Box Stock system only and must be unaltered. Kill switch and low oil sensor may be
disabled and removed.
Flywheel: Box Stock flywheel only with plastic fins. No alterations of any type allowed. Must also run stock
flywheel key.
Piston and Rings: Must be unaltered Box Stock only. No machining of piston and rings allowed.
Connecting Rod: Stock Box Stock rod only. No machining of any type allowed. Stock rod bolts only.
Crankshaft Requirements: Stock Box Stock crankshaft required. Machining, polishing, addition of material or
other alteration of crankshaft is prohibited. Stock factory timing gear mandatory and must be installed in original
location. Crankshaft journal diameter is 1.180”- 1.175” min.
Camshaft Requirements: Stock as cast camshaft only. Cam lobe base circle diameter .865" -.005”/+.010”
Max Intake lift on cam .225” taken at the pushrod.
Max Intake lift at the valve .238” Taken on valve spring retainer with zero lash.
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Max Exhaust lift on cam .232” taken at the pushrod.
Max Exhaust Lift at the valve .242” Taken on valve spring retainer with zero lash.
(Additional cam checks will likely be added later)
Special note. Valve guide wear can give false valve lift readings when checking off the front of the valve spring
retainer. It is advised to take readings at several other points around the retainer (back, and both sides) if wear is
suspected of giving a false, unfavorable reading.
Block Requirements: Block must remain stock as produced. Stub for governor may be removed and hole plugged.
No machining of block allowed. Welding to the block shall be for rod damage repair only and may not constitute a
functional modification.
Quote:
The Following updates are optional changes as of September 1, 2008
Aftermarket air filter adapter allowed (max length of 1.375). Main fuel jet may be drilled to a no-go of .042 inch.
Stock emulsion tube must be used and unaltered.
Header and Muffler Requirements: Any single stage, one piece header made from .750” O.D. steel tubing allowed
with the BS tube style muffler part #89966 or it’s aftermarket equivalent(ex: rotary power) installed at the end of
pipe. The tube style muffler may either be welded or tread fitted to the pipe end. The entire exhaust pipe including
the muffler is 14” max length and 10” min length.
Claimer Rule: You must finish the race in the box stock class to purchase the winners engine for $200 (minus the
clutch/chain guard/throttle kit, header pipe/muffler, air filter adaptor/air filter, top plate & fuel pump).
The Following updates are mandatory changes as of January 1, 2009
Carburetor/Fuel Tank Requirements: Floor Mounted fuel tank mandatory (stock tank must be removed). Pulse
type fuel pump allowed. Fuel pump must be pulsed from either the crank case or the valve cover. You may install
a flat metal plate in the original tank location for the purpose of mounting the throttle linkage and fuel pump.
THESE R THE RULES FOR THE 2010 SEASON FOR CLONES- BLUES OR YELLOWS WILL BE ALLOWED -
AKRA RULES