The tappet guide block houses the tappets, or cam followers, and is pressed into the cylinder block. Precise alignment is necessary to ensure the pushrods properly engage with the radiused ends of the tappet stems. This is the exhaust guide block with a machined groove to accept a sealing o-ring, and an oilway for tappet lubrication as fitted to the B-range 650 and 750 engines from 1969-1979. Check your parts book for compatibility. This cast iron guide block is manufactured to original specifications in the UK by Hepolite. The O.D. measures .985″ where the pushrod tube fits over the top of the block. Shoulder thickness is .187″, and the O.D. of the bottom of the guide block is .985″. Lubrication to the tappet stems is provided by drillings that pass through the block longitudinally, allowing oil to drain down the pushrod tube from the rocker box. The tappets are a sliding fit in the guide block bores and if the tappet stems or bores in the guide block become worn excessively, mechanical clatter may result. The guide block is an interference fit into the bore of the cylinder barrel. A special drift is used to set the block into its bore. It is advisable to freeze the guide block for several hours and to heat the bore surround under the cylinder barrel flange prior to fitting the block. It’s critical that the locking bolt hole in the guide block is in perfect alignment with the threaded hole in the cylinder flange. Reaming and honing of the tappet bores may be required in some cases to achieve the proper running clearance. Installation of the guide block requires precision and skill and may be best left to a professional mechanic or machinist. The product images shown are for illustrative purposes only and may not be an exact representation of the product received. Manufacturers occasionally make minor cosmetic changes to items, such as color, finish, label, or design. These changes do not impact the item’s function or compatibility. Please contact us if you have specific concerns regarding appearance.
