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ENGINE SPECIFIC TECH SHEET FOR: BOX STOCK 6.5 OHV
Description: Single cylinder, 2 valve, OHV 4 cycle
Important Note: All parts must be Box Stock 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 known Box
Stock part (when performing a "stock part" 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. No
aftermarket coatings of any type are permitted on any part of
the engine(exception Blower Housing and Shrouds).
Combustion chamber volume: 26.5 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. Intake seat
maximum ID .897 , Exhaust seat maximum ID .862. Stock head
bolts only, must have four. Head gasket/s maybe after market,
must be of stock configuration, 2 gaskets permitted with a total
minimum thickness of .008 and maximum of .020. No copper or
aluminum gaskets allowed. Any stock configuration exhaust gasket
allowed no other sealer.
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.
Stock cylinder bore is 2.685" max. Stroke is 2.123" + .010" or -
.005". No piston pop-out allowed. Matting surface finish of
block and cylinder head is a non tech item, sufacing of both to
correct gasket failure and meet cc check allowed. May use 2 side
cover gaskets of stock configuration.
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. Venturi .615 NO-GO. Rear carb bore .751 NO-GO.
Main fuel jet .042 NO-GO. Low speed idle jet .019 NO-GO. Stock
emulsion tube must be used and unaltered, .066" max ID (no pass
through). Throttle shaft - .115 minimum. Butterfly - .037
minimum. Aftermarket air filter adapter allowed (max length of
1.375).
Valve Train: Stock valve cover only with any stock configuration
gasket, no sealer. Factory stock rocker arms 1:1 ratio and push
rods only. Stock valves only 45 degree angle only both valves,
Intake valve Max OD .985 +/- .005 and Exhaust valve Max OD
.948 +/- .005, no modifications allowed. Only Box Stock valve
springs. Max wire diameter on spring wire is .071 with a
maximum tension of 10.8 lbs. at a height of .850. Lash cap on
exhaust valve only. Valve stem seal allowed only on Intake
valve, maximun lip tickness of .027. Minimum thickness of
Intake retainer .230 , Exhaust retainer .250. BS lifters only,
no modifications allowed.
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(5lbs 4 oz minimum)
including plastic fins. No alterations of any type allowed.
Maximum ignition timing advance is 18° BTDC when a straight edge
placed on the outside of the right-hand coil leg is just
touching the right-hand edge of the metal magnet cover of the
flywheel. Flywheel key is non-tech.
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 1.180max - 1.168 min.
Camshaft Requirements: Stock camshaft cores only, ez-spin assy
must remain as stock. Cam lobe base circle diameter .865"
-.005/+.010 Duration check for Intake and Exhaust lobes (taken
off pushrod). Intake duration of 219 degrees at .050 lift/86
degrees at .200 lift. Exhaust duration of 222 degrees at .050
lift/97 degrees at .200 lift(All duration checks on intake and
exhaust allow +/- 2 degrees for wear and gauge variances). Max
Intake lift on cam .225 Min .215lift taken at the pushrod.
Max Intake lift at the valve .238 Taken on valve spring
retainer with zero lash. Max Exhaust lift on cam .232 Min
.222 lift taken at the pushrod. Max Exhaust Lift at the valve
.242 Taken on valve spring retainer with zero lash.
Blower Housing Assembly: pull starter must be present and remain
stock. Pull starter may be rotated for a better crank angle.
Header and Muffler Requirements: Any single stage, one piece
header made from .750 OD max and .635 ID max. steel tubing
allowed, with the RLV Mini B-91 Silencer (Optional 12-1-2010 and
mandantory 3-1-2011) installed at the end of pipe. The B-91
Silencer must be tread fitted to the pipe end. The entire
exhaust pipe including the muffler is 15 max length and 10 min
length. RLV Mini 91 Silencer Requirements: Part # 4117 Overall
Length 5.465 minimum 5.605 maximum. Threaded Nipple .690
maximum ID. Internal raised weld seam must be present. (ID as
Mfg. NO Grinding, Reaming, or Polishing Allowed) . Rear baffle
holes .1285 maximum, inner baffle holes .0965 maximum.
Silencer must be utilized as produced, with no modifications or
alterations permitted. Strap or brace required to silencer for
support, and to insure silencer does not turn and unscrew. (No
aftermarket coatings of any type are permitted.)
Fuel Tank Requirements: Floor Mounted fuel tank mandatory (stock
tank must be removed). Pulse type fuel pump allowed.
Fuel Pump Requirements: 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.
Clutches: Stamped steel drum shoe type clutches only, No
machined Billet drums allowed. No disc clutches allowed.
Important Note:Any attempt to increase the RPM s of the BOX
STOCK PROJECT,Stock
Classes,engine(example:stronger/non stock valve springs or
decreasing exhaust
restriction from stock levels)is strictly prohibited.Should this
be allowed or preformed
will mandate the use of an aftermarket Billet style flywheel for
high RPM use(Super
Box).ARC currently has these parts in their product line(part
#s 6618/6619)and they
are approved by AKRA for use,others may become available as
demand increases.Note:
Under no circumstances is this type of flywheel allowed in the
Box Stock Project (Stock
Classes),Stock Flywheel ONLY.
No other alterations to or from stock components are allowed
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