ENGINE SPECIFIC TECH SHEET FOR: BOX STOCK 6.5 OHV
Description: Single cylinder, 2 valve, OHV 4 cycle engine.
Clones will run ARC restrictor plates.
Combustion chamber volume: 26.5 cubic centimeter minimum, with piston at TDC,using prescribed procedure. The Liquid CC check is the official check (IF THE ENGINE FAILS THE CC LIQUID CHECK AT ANY TIME DURING THE TECH PROCEDURE IT MUST BE CALLED ILLEGAL)
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, gasket thickness is a non tech item. Depth check between the valves, front to back and side to side may not vary by more than .005” max. No copper or aluminum gaskets allowed. Any stock configuration exhaust gasket allowed . Sealer allowed
Block Requirements: Stock cylinder bore is 2.715 max. Stroke is 2.123” + .010” or - .010. No piston pop out allowed. Matting surface finish of block and cylinder head is a non-tech item, surfacing of both to correct gasket failure and meet cc check allowed however, no piston pop out is allowed. May use 2 side cover gaskets of stock configuration. 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.
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 is a Non Tech item. Stock emulsion tube must be used and unaltered, .066’ max ID (no pass through). Side holes in E-Tube 4 holes max in bottom section and 20 holes max in top section. Minimum E-Tube length 1.092”. 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 .982” +/- .005” and Exhaust valve Max OD .948” +/- .005”, no modifications allowed. Only Box Stock valve springs. (Installed Height for valve springs .805, must be checked by using the .805 spring must go gauge with retainer seal in place on intake an exhaust valve if used.) Prescribed check procedure as follows – Remove valve spring, reinstall spring retainer, insert .805" must go gauge in spring location. Gauge must go in both locations Intake and Exhaust with any allowed retainers in place, as raced, during check procedure. Max wire diameter on spring wire is .071” with a maximum tension of 10.8 lbs. at a height of .850” and a maximum tension of 18lbs at .650 height. Lash cap on exhaust valve only. Valve stem seal allowed on Intake and Exhaust valve, maximum lip thickness 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: BSFW-1 and Dj-168F-16200-A steel billet flywheels alllowed at the same weight as stock flywheel( 5lbs 4oz min) including plastic fins. Also allowed Arc 6618,Arc 6619, Raceseng RSP-13-075, Rewheel NF-S1 & RSP-13-077, Rewheel F-S1, PVL 211-900. Non -fin flywheels must utilize stock plastic fins. No alterations of any type allowed. Timing and 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 1.180”max - 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.* (*+/- 2 degrees for wear and gauge variances) Max Intake lift on cam .225” – Min .215”lift 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. (To achieve zero valve lash for checking running lift, preload dial indicator by .001”.)
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: Open pipe, No loop pipes, RLV B-91 muffler required
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.
Unleaded gas only. A digitron fuel tester will be used.
Ikf or wka rules allowed. IKF APS flat restrictors,no funnelled plates
Stock Appearing: Clone/Predator engine. Any RLV muffler allowed. You may remove recoil and use starter nut. Electric starter may be used. Billet sidecovers are allowed. open fuel. Everything else will be stock appearing. No epoxy allowed on exterior of carb.
Flathead engine. Any RLV muffler allowed. No billet or cast aftermarket carbs allowed. Everything must be stock appearing.