Norton Twins Aluminium Barrels
Cast in fully heat treated L169 aerospace spec aluminium alloy, our Norton twin cylinder barrels have deeper, thinner fins than any others on the market, which makes them harder to cast but achieves superior cooling and a barrel that is visually closer to the original iron barrels. They save around 5kg in weight!
All variants, including the 650 & 750 models are of `through bolted` design, where the bottom fin joins directly to the cylinder flange, similar to original 850 barrels. We use different, coarser thread head bolts to optimise mounting to the alloy barrels.
These barrels are available in 68, 73, 77, 81 & 83mm bores. The 73 & 77mm barrels are offered in a choice of either spun cast iron liners or Nikasil ceramic coating direct onto the alloy casting. The 81 & 83mm sizes are only available with iron liners due to the thin nature of the spigots that project into the crankcases.
The lower section of our barrels are designed to fit standard `Commando` crankcases. If fitting to `Dominator` or `Atlas` cases, you need to talk to us before ordering because the opening in the cases is smaller, although the hole pattern is the same.
The 83mm (1,000cc) barrels are on wider centres to accommodate the bigger bores so require special cases, crankshaft & cylinder head in addition to the obvious parts.
Machined in our own workshop on modern 5 axis machinery to close tolerances, these are the optimum barrels for your Norton twin cylinder engine.
A few words about Nikasil ceramic bores: We are advocates of these bores wherever possible. The matrix of the plating is completely different to, say, chrome, and is designed to `hold` oil. Almost all modern automotive engines utilise ceramic bores The surface is extremely hard & 100,000 miles is perfectly possible with filtered air & oil. One of the big advantages on the Norton twin cylinders is that unlike for iron liners, where it is necessary to machine around 5mm bigger than bore size to accommodate liners that add nothing to the structural integrity of the component, with ceramic bores there remains a larger proportion of the casting carrying the load and therefore the stress on that material is reduced - so in simple terms the barrel is stronger. The bores can be replated once or twice for about 25% of the price of a new cylinder & can even be modified to accept iron liners. Nikasil bores run closer clearances, so the engine runs cleaner. Although any rings EXCEPT chrome can be used, TiN coated rings are the preferred choice for Nikasil bores, but these are not generally available for Norton twins. Note that because the piston clearances are tighter, the bores are `undersize` (around 2 thou/0.05mm under nominal bore size) so it is necessary to `gap` the piston rings to your desired end clearance before assembly.It should also be noted that because we are plating direct onto castings, not wrought billets as on our Manxes/G50`s, it is inevitable that there are some minor imperfections in the surface of the plating that will be visible - this is not a fault. Some variants of barrels cannot be offerered with Nikasil bores for a variety of reasons.