Post by buttybach1932 on Aug 23, 2023 13:57:16 GMT
Ported Piston Villiers Mk VIII-A.
Having had an interest and worked on Velocette GTP's I was aware of the ported piston. The story goes that it was used in the 1929 247cc Six Port Levis engine to provide additional cooling to the underside of the piston crown. When Velocette's introduced the GTP in 1930 it developed a reputation for seizing and it was said that GTP stood for 'Generally Tight Piston'. To overcome the problem Velocette employed Levis engineer Alan Edwards who designed / developed a ported piston and redesigned cylinder barrel similar to Levis design, this was fitted to GTP's from 1934 on.
I was not aware the Villiers had ever fitted ported pistons to their engines but I noted that in 'Spares List No:22', Part No 79 is a ported cast iron deflector piston for a VIII-A engine. I have now found some pictures on an Austrian Vintage Motorcycle Web Site of a dismantled and rusty Villiers Mark VIII-A engine. The ported piston design is very similar to the Velocette except that it is manufactured in cast iron. The Mark VIII-A was the last 247cc engine to be fitted with a one piece cast iron cylinder head and barrel. Presumably by 1925 when the engine was introduced Villiers were having problems with the cast iron piston overheating and the ported piston provided additional cooling to the underside of the piston crown.
When the next version of the 247cc engine the Mark IX-A was introduced in 1926 it was based of the 342cc Mark VIII-B engine and 172cc TT Super Sports engine with a detachable sunburst aluminium cylinder head and aluminium deflector piston. Presumably the change to an aluminium cylinder head and piston solved the overheating problems because it reverted to a conventional transfer port fed directly from the crankcase.
Butty Bach
Having had an interest and worked on Velocette GTP's I was aware of the ported piston. The story goes that it was used in the 1929 247cc Six Port Levis engine to provide additional cooling to the underside of the piston crown. When Velocette's introduced the GTP in 1930 it developed a reputation for seizing and it was said that GTP stood for 'Generally Tight Piston'. To overcome the problem Velocette employed Levis engineer Alan Edwards who designed / developed a ported piston and redesigned cylinder barrel similar to Levis design, this was fitted to GTP's from 1934 on.
I was not aware the Villiers had ever fitted ported pistons to their engines but I noted that in 'Spares List No:22', Part No 79 is a ported cast iron deflector piston for a VIII-A engine. I have now found some pictures on an Austrian Vintage Motorcycle Web Site of a dismantled and rusty Villiers Mark VIII-A engine. The ported piston design is very similar to the Velocette except that it is manufactured in cast iron. The Mark VIII-A was the last 247cc engine to be fitted with a one piece cast iron cylinder head and barrel. Presumably by 1925 when the engine was introduced Villiers were having problems with the cast iron piston overheating and the ported piston provided additional cooling to the underside of the piston crown.
When the next version of the 247cc engine the Mark IX-A was introduced in 1926 it was based of the 342cc Mark VIII-B engine and 172cc TT Super Sports engine with a detachable sunburst aluminium cylinder head and aluminium deflector piston. Presumably the change to an aluminium cylinder head and piston solved the overheating problems because it reverted to a conventional transfer port fed directly from the crankcase.
Butty Bach
