The tappet guide block houses the tappets, or cam followers, and is pressed into the cylinder block in the intake position. Precise alignment is necessary to ensure the pushrods properly engage with the radiused ends of the tappet stems. This is the first iteration of the exhaust guide block with a machined groove to accept an o-ring, and the oilway for the tappets, as fitted to the 1966-1968 650 models. Check your parts book for compatibility.
The cast iron guide block is manufactured to original specifications in the UK by LF Harris. The O.D. measures .922″ 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″. There is a groove for an o-ring under the shoulder for oil sealing against the cylinder barrel flange. An oilway is machined into the lower half of the block to pressure feed the tappets.
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. Additional lubrication to the exhaust tappets is provided by the machined oilway which allows pressure-fed oil to pass to the tappet faces and camshaft lobes. 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. Installation of the guide block requires precision and skill and may be best left to a professional mechanic or machinist.
LF Harris motorcycle spares are produced to the highest quality standards possible utilizing original Triumph tooling, dies, factory blueprints & materials combined with modern manufacturing equipment, tolerances & techniques.