This is the aluminium head gasket of the type fitted to OHV engines (Model 18 and ES2) between 1948 - 1955 (although it is possible that some engines of this design continued to be sold through into 1956).
In the accompanying photograph you can see it fitted to an ES2 barrel of this type. These are manufactured for us by a well established UK gasket manufacturer. We have these head gaskets made to our own specification and are a very nice slide fit over the lip of this model of barrel (unlike some other head gaskets I have seen for this model over the years).
Fitment and Background Information:
The Norton Spare Parts List of 1948 first shows this head gasket fitted, and at that time both the barrel and cylinder head would have been cast iron. Sometime in the early 1950's an alloy cylinder head of the same shape and design was also offered - being substantially lighter than the iron version (these later alloy versions are now considered a rare and desirable head, difficult to find at autojumbles, possibly because they were sought for racing bikes and 500T replicas). This alloy head (with open pushrod tube cutaways as per the photos continued to approximately 1956/57 - when it was replaced with a head with the pushrod enclosure cast into the head. The head gasket shown here fits all 500cc OHV models between 1948 - 55.
If you have a head with the post 1955 cast in pushrod design - we also provide the alloy head gasket for that type - but it is marginally different to this type and is Item 0920.
If you are not sure which barrel is fitted to your model (and which gasket you need) - look carefully at the item photographs: the barrel shape of this barrel (48 - 55 type) has slightly less finning than the 56 - 59 type shown in Item 0920, this being particularly noticeable in the fin area between the two pushrod tubes - compared side by side, the 48-55 barrel fin there does not protrude as far.
If you are unsure, email us at email@example.com and we can confirm dimensions to ensure you order the correct gasket. Likewise, if you have a Model 19 600 Barrel these may also fit that model, but please email to confirm.
1938 - 47 Engines and Earlier OHV Engines:
Although the earlier OHV barrel and head design were similar to the 1948 OHV design - i.e. they employed both an inner barrel spigot, and an outer flat mating surface - the 1939 Spare Parts List for this model does not show a head gasket listed. I have also built and raced many of the 38-47 type engines in past years, and never used a head gasket on any of them. However, if not using a head gasket (which acts almost entirely on the outer mating face), it is important to ensure that you have a good fit on the inner spigot, as a 'Top Hat' principle is adopted - i.e. the head bolts pull down on the head around the wide mating face, which ideally should cause the inner barrel spigot to touch the inner recess of the cylinder head fully, just before the two mating outer faces touch. When racing these engines on methanol with high compression ratios - I always used to use valve grinding paste on both faces - and rigorously ground the head from side to side on a barrel for about 5 - 10 minutes. Finally I would use fine grinding paste on the inner spigot face, and rough grinding paste on the outer face - looking for an even 'greyness' to the mating surfaces all the way round.
Useful Hint when fitting cylinder heads - either with or without an alloy head gasket: It is important when fitting the head gasket to these OHV models to ensure a good quality spanner or socket is used on the head bolts and the bolts are tightened down in an even 'X' sequence. I have never used a torque wrench (either on OHV or SOHC heads), but continue to evenly tighten down until I am unable to apply any more pressure - this normally being with a 12" ring spanner or socket.
However, it is most important to go round the cylinder head bolts again, once the engine has been ran for a short time and is warm. I used to find this particularly true of those OHV models with aluminium cylinder heads fitted with an aluminium head gasket as listed here. This can sometimes be fiddly - and may even entail having to remove the petrol tank to get full access to the head bolts. This normally pays dividends, and I have found I could sometimes get another 1/4 turn of each head bolt when warm. I also found failing to do this could sometimes result in premature failure of the alloy head gasket - particularly the area between pushrod tubes - which seemed the area most susceptible to 'blowing' the head gasket out.