WKA Tech Update – Pressure / Vacuum Testing
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