IHRA Official Rulebook
Figure 3 and 4: Bellhousing inspection hole cover
crankshaft flange diameter by more than one inch. FLYWHEEL SHIELD: TF, PFD, NFC: Cars equipped with a clutch must have a flywheel shield (bellhousing) that meets SFI Spec 6.2 and is labeled accordingly. A one-piece motor plate constructed of 1/4 inch minimum thickness 4130 chrome moly steel and fitting between the engine and flywheel shield according to the requirements of SFI Spec 2.2, 2.3 or 10.1 is required.The motor plate must be attached to the chassis at the four corners with at least two welded mounting points utilizing minimum 3/8 inch diameter grade 5 bolts and full nuts.The remaining two motor plate mounting points must be at least saddles fitting around the frame rails and secured with aircraft type clamps or bolts (hose clamps prohibited.) The flywheel shield and motor plate are to be fastened to the engine by at least seven high strength steel (or titanium) 7/16 inch diameter bolts on the the engine side of the motor plate and threaded into the engine (3/4 inch minimum) and nuts (of a similar metal) above the centerline of the crank shaft. The motor plate must be fastened to the flywheel shield with at least eight 7/16 inch diameter grade 8 bolts or high strength steel alloy (or titanium) studs and nuts below the centerline of the crank shaft. The flywheel shield must also be fastened to the motor plate by four 3/4 inch diameter grade 8 shoulder bolts or high strength steel (or titanium) fasteners and nuts; one in each quadrant as required by SFI Spec 2.3 or 10.1. A minimum .090 inch 4130 steel or titanium liner (or as required by the manufacturer) must be fitted to the flywheel shield that is the width of the round body surface of the shield. It must be welded together so that it will fit into the body of the flywheel shield and rotate in order to absorb energy. A 1/4 inch bolt may be threaded into the body of the flywheel shield to secure the liner(s) from movement during normal use. At least five fasteners, 3/8 inch diameter minimum, must be used to secure aftermarket planetary transmissions (and/or reversers) to flywheel shield. 1/2 inch thick rings, bosses, or nuts must be welded, or otherwise secured inside the back face of the flywheel shield through which the fasteners must be secured. Any modifications or alterations to the housing, by anyone other than the original manufacturer, are prohibited. Bellhousing must be re-certified by original manufacturer following modification. Clutch adjustment slots, maintenance holes and covers, etc., must be installed by the original manufacturer.
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