SOHC (and Early DOHC) Valves Section - General Information

The following listings show a variety of inlet and exhaust valves as commonly fitted to SOHC Norton engines.  However, before selecting the valves that best suit your needs - here is some general information about the valves we provide, and some useful information about SOHC Norton valves

(please remember - this information is based on our own experiences of stripping original engines - and should only be taken as useful information - not specific guidance for your own needs - it is always the customers responsibility to ensure they are comfortable with their choice and fitment of valves - and all responsibility of fitment lies with them). 

• Our valves - G&S:  Almost all the valves you see listed here are manufactured for us by G&S Valves - one of finest and longest established UK manufacturers of high quality valves.  All valves are manufactured to well established dimensions from a G&S drawing, to established SOHC dimensions and radiuses. 
• Because there were so many size variations offered over the years of manufacture - realistically we can only get each variation manufactured in small quantities - because of this the Unit Price of the valves shown here are far more expensive than some other valves for other marques or models you might find offered elsewhere - even other G&S valves - where they may have been manufactured for a more common engine model, in larger quantities.  Hopefully it goes without saying - it is better for a valve to be available, even if not cheap - rather than it not beint available at all.
• As of the end of 2023 - G&S valves (like so many UK manufacturing companies) had to announce heavy price increases following Covid and recession manufacturing cost incresases, particularly heat treatment costs.  Sorry - as of early 2024 we have had to raise our own prices considerably (but fyi - we have not passed on the full price/margin increase).
• Many of the following listings are 'multiple' listings - i.e. there is more than one variation for each listing.  To check availability - go to the lisitng, select the required valve in the 'dropdown' box - and if the valve is in stock it will show with a GREEN bar.  If out of stock - you can email us at paul.norman@racingvincent.co.uk to see if we have plans to get a new batch made (or if already in progress)
• Occasionally we may offer 'New Old Stock' valves if from a reputable source.  If so - we will clearly identify those valves - and make it clear if they are not of known G&S manufacture  

General Information for Norton SOHC (and early DOHC Valves):

• Generally - for most (Arthur Carrol designed) SOHC engines - a parrallel collet groove was used (this is different to most OHV and SV Norton models, which generally employed a conical collet groove)
• As a normal rule - SOHC inlet valves were of 11/32" valve stem diameter.  Exhaust valves were of 3/8" diameter (as were most OHV engines for both inlet and exhaust).  I am not sure at what point 5/16" valve stems were employed for the later SOHC (and early DOHC) Manx engines - but it it not unusual to find a later 'square' Manx head fitted with 5/16" stem valves for both inlet and exhaust.  We offer a small selection of 5/16" valves - which most have larger heads, more suitable for competition engines
• Normally - inlet valves had a concave valve head and exhaust valves had a flat valve head
• Some earlier SOHC Engines (i.e. Walter Moore CS1) engines look to have used valves fitted with a conical collet groove.  We are not experts on these earlier engines - but I am told it is not uncommon for early CS1's to be fitted with later ES2 valves and collets - which we can also offer, in our OHV section, or you can email us for more information before ordering
• Head Diameter:  There have been lots of variations in Norton SOHC valve head sizes - often with the inlet valve diameter being larger than the exhaust valve.  We offer many of the generally accepted 'standard' head sizes (i.e. 1.735"/1.750" being a common inlet head size on roadgoing 500cc Inter models) - as well as some of the larger sizes often found on those engines tuned for competition
• If changing your valve size as part of a rebuild or tuning exercise - remember you should always check clearances on rebuild - particularly valve to piston clearance if enlarging valve size.  As a general rule - I always used to look for a minimum 60 thou valve to piston clearance when building a competition engine
• Head diameter and valve seats:  Remember if replacing valves and unable to find the exact replacement valve diameter - that the cylinder head valve seat can be checked - as often the actual valve seat surface on the valve itself is far less than the width of the 'cut' valve seat - so you may find that a 1.750" valve will fit your cylinder head - even if the original valve was 1.735" - if the valve seat allows it.  But see point above about checking clearances etc
• Valve Length:  It seems that SOHC valves were supplied in variety of lengths - we believe this was mainly to allow for correct placement of the cambox - the ideal position of that being - where the rocker arm adjuster centre line (ideally) would be directly over the centre line of the valve, when the cam was at approximate mid lift.  In reality, this is often difficult to achieve - and some sort of slight compromise is required.  However - it was common practice to buy valves with a longer 'Blank Shaft', so the ideal height could be calculated by the engine builder, then cut to length and the collet groove cut.  I know that well known SOHC expert Stu Rogers always used to cut his own valves to length when building an engine (as do I, when not having the required length for an engine I am building).  Because of this - as well as supplying valves to a specific length (with collet already cut, ready to fit) - for most of the common valve types - we also provide a 'Blank Shaft' variant - where the customer can cut the valve to their own length.  If taking this option - for both inlet and exhaust variants we can provide the required collet groove dimensions - as used by G&S.  Sorry - but generally we no longer cut blank shaft valves to custom any more - the setup time for one valve is normally prohibitive to the customer!!  But feel free to email us if you require more information or advice
• Valve Caps:  As far as I know - Norton's did not originally offer valve caps in their SOHC Norton Spare Parts list - but we know that many customers and tuners have requested them and have fitted them over the years - we assume this is because it easily allows for small discrepancies in length between inlet/exhaust valve length, or cambox height discrepancies.  Because of this - we do offer both 11/32" and 3/8" valve caps in a couple of thicknesses - but fyi - it is up to the customer to decide if they wish to fit these - and at their own responsibility.  They are however, patterned on original 'Terry's' valve cap originals - using their dimensions.