- High quality inlet valves manufactured by G & S Valves - This valve is in one one the most common sizes - 1.750" head diameter, and with the groove machined, to an overall length of 4.650". We also sell exhaust valves in this common legth - standard Model 30\40 stem diameter : 11/32" - Stem length: 4.650". Price is Each.
These valves already have the collet groove machined and are ready to fit. Note: Norton cammy valves were made in a variety of lengths over the years, however, the- 4.650" is one of the most commonly used, Likewise - 1.750" Head Diameter is one of the most common head diameters found on Model 30 (500cc) International or early Manx models.
Note: 1.735" was a common Std SOHC inlet valve size - but it is not uncommon to find that the actual cylinder head valve seat will be expanded out to 1.750" already, or if requiring light re-cutting, to go out to 1.750" - making this 1.750" head size a very popular size fitting.
If you have an original you are looking to replace - then measure that first - 11/32" valve stem diameter and a concave valve head normallly denote an inlet valve.
The length of your valve is measured most eaily by placing the valve onto a flat surface valve head up, then run a digital caliper from the face of the valve head to the flat surface below. A few thou difference between inlet and exhaust valve length can easily be adjusted for by the adjustment in the 3 piece rocker adjuster - but when measuring valve lengths (particularly when building an engine from parts) - ideally the length is adjusted so the cambox height allows for the rocker pad to be centralised with the centreline of the valve, when the cam is at approximate half lit. Sometimes a slight compromise is called for
The head diameter should be measured across the overall diameter. 1.735" was an original standard Norton inlet valve size for SOHC 500cc engines - but 1.750" is a very common replacement - particularly if the valve seats have been re-cut - so it is always useful to measure the outer diameter of the inlet valve seat (particularly after re-cutting), as this will tell you the maxinum valve diameter that will fit your engine. Remember - if fitting larger valves than were previously fitted - always to plasticine the top of your piston on reassembly - to ensure you have sufficient valve to piston clearance. I always used to look for a minimum of 60 thou valve clearance when building a race engine.
If you are unsure you can email us for guidance and availability before ordering - on paul.norman@racingvincent.co.uk.