TECH MANUAL UPDATE 618.6 PRESSURE / VACUUM TESTING

April 11, 2016

CONCORD, NC - TECH MANUAL UPDATE 618.6   PRESSURE / VACUUM TESTING
Testing may be performed to insure extra air is not being pulled into the engine for a performance gain. Any means to bypass the intent of the class rules is illegal.  Both pressure and vacuum tests may be performed -- engine must hold 5 psi for 60 seconds and/or  5 HG of vacuum for 60 seconds.
 
-------------------------
 
Blowdown checking procedure for Yamaha engines --- (601.9 and Figure 606.2)
1 -- By a careful visual inspection (light check)  , identify the highest exhaust port and the highest intake port.
2 -- Using the Lad tool, zero the dial indicator on the highest exhaust port, taking care to hold the shaft  of the tool against the cylinder wall.
3 -- roll the crankshaft backwards five turns (.500" on the dial indicator)
4 -- insert the Lad tool into the highest intake port, holding the shaft of the tool against the cylinder wall.
5 -- roll the crankshaft forward until the piston stops on the Lad tool and note the value.
6 -- the value must be between .380" and .420" to be considered legal
7 -- engine to be checked as raced

BRIGGS AND STRATTON LO206 ENGINE RULES UPDATE

March 24. 2016

CONCORD, NC  
At  the WKA meeting March 6, 2015, the trustees voted to accept the Briggs and Stratton  LO206 engine rules -- some of these rules were not included in the 2016 techbook -- please note following clarifications and/or changes: 

708   BRIGGS LO206  
add -- all items may be compared to know stock parts to insure compliance.
The Briggs and Stratton 2016 LO206 Engine Class Regulations may be used in conjunction with rules listed here in section 708.
 
708.5.3   VENTURI:
The vertical dimension is 0.792" no-go.    Horizontal dimension is  0.615".  (delete 0.618') -- the gauge may not pass into the slide area.
"When the  0.602" gauge is inserted horizontally, it may not pass into the slide area at the narrow point formed by the overlap of the two venturi  circles"   (delete 0.605")
Venturi  idle  fuel  hole = .038" max
708.3  AIR FILTER
The only air filter permitted is the Briggs & Stratton Green Air Filter Part #555729. No modification to the filter element is permitted. A protective shield may be attached for wet-weather competition. It is not permitted for the protective shield to create any ram-air effect.
708.6.4   delete all
708.11   HEAD GASKET
Unaltered B&S part #555723 is the only head gasket allowed.
Minimum thickness allowed is .049" -- measurement must be performed using a
micrometer -- readings are taken from inside
the cylinder hole of the gasket closest to the
combustion chamber -- four measurements must be taken with 3 meeting
the minimum thickness of .049”
708.14    VALVES
Intake valve -- minimum weight of valve 27.80 grams -- diameter of valve stem = .246" to .247" --diameter of valve head = 1.055" to 1.065" -- diameter of valve seat = .972" inches ID maximum -- valve length minimum 3.3655" -- height from angle of valve face to top of the valve .057" minimum -- single angle only = 45 degrees
Exhaust valve -- minimum weight of valve = 27.20 grams -- diameter of valve stem = .246" to .247" --diameter of valve head = .935" to .945" -- diameter of valve seat = .850 inches ID maximum --  valve length minimum = 3.3655" -- height from angle of valve face to top of the valve = .060" minimum -- single angle only = 45 degrees
708.16   VALVE SPRINGS
Valve Springs are single coil stock, unaltered B&S part # 26826 -- must be identical in appearance to factory part and have 4.00 to 4.75 coils in stack -- Spring Wire Diameter .103" to .107" -- Valve spring length = .940" max -- Inside diameter = .615" to .635"
708.16.3   delete
708.5   CARBURETOR
The B&S stock carburetor part #555658 is the only carburetor permitted -- "Walbro", "Briggs" diamond logo and or #590890 etched in the body are additional visual indicators -- No alterations allowed unless stated below -- all parts will be compared to a stock known B&S part for eligibility -- this includes the nozzle, emulsion tube, jets, float, float needle and all other carb parts -- it will be allowed however to adjust the float height by means of bending the small tab on the float arm -- slide must remain B&S stock unaltered -- slide cutaway to be measured on flat surface = .075" no go -- B&S stock unaltered aluminum needle is required part number 555602 marked #BGB
708.9.1    ROCKER ARMS
Overall length 2.820" minimum
708.17.2   VALVE SEATS
delete -- "must have only one 45 degree angle on valve seats"
add -- Valve maintenance permitted (valve job). Valve seats must remain with the
factory specification of 30 and 45 degree angles only. Valve seats of additional
angles and/or excessive material removed when compared to the factory
stock is prohibited.