This is the aluminium head gasket of the type fitted to 500cc/600cc OHV engines (500cc ES2 and 600cc Model 19) between 1956 - 1959
In the accompanying photograph you can see it fitted to an ES2 barrel of this later type - and the accompanying picture from the 1957 Norton Spare Partts Catalog shows the OHV Head and Barrel design this head gasket is intended for. These are manufactured for us by a well established UK gasket manufacturer.
Fitment and Background Information:
This aluminium head gasket is visually almost identical to the earlier 1948-55 type OHV gasket we also sell (Item 0919), but the dimensions are actually slightly different to fit the later barrel design. If you look at the comparison photos of different type barrels, you will notice this engine type is identifiable by the fins being slightly wider than the earlier 48-55 barrel, particularly in the area between the pushrod tubes. Also the head on this engine type had cast in fins around the pushrod area on the cylinder head, and therefore pushrod tubes that only extended up to the top of the barrel (unlike the earlier design, where the pushrods went all the way up to the rockerbox. If you are unsure if your barrel/head requires this type of head gasket having looked at the photos - then email us at firstname.lastname@example.org and we can confirm dimensions from your engine.
Note: if you have a 350cc Model 50 engine of this same era, the head gasket for that model is also different to this one, but we sell that also - See Item 0921.
Another indicator of these later design engines is that the top of the crankcase at the point the pushrods come out, are sharper in profile than the earlier engine - see photograph attached of this later type 56-59 engine design. The reason we provide this detail, is that the period the engine design was changed to this later style is not entirely clear - it is listed as 1956, but I believe some bikes were still being sold with the earlier engine design in 1956 (and many owners swapped engines subsequently), so it is worth checking
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 most susceptible to 'blowing' the head gasket out.