Hi Roy,
your pushrods alu or stainless ? Alu tube, any kind, is perfectly suitable in this application, Vincent types are very short, so no worries here. It is not the problem of straight load along the tube but the lateral motion at ends as these do a fraction of a circle together with the lever cups below and above. So at high speeds this is a sideload onto pushrods really and critical with long types as in BMWs and Horex, at 28 cm (280mm) compared to some 15 cm in Vincents. In this respect the E-module ( in English used, the stiffness under loads ?) is a factor, alu got one third of E-module compared to carbon steel. Stainless steel is a bit less E-module than carbon steel but we like the extra heat growth of factor 16 in stainless, carbon steel is 12 and alu is 24, so twice from steel. When this stiffness (correct term here? ) of material is critical you get a tube with three times wall thickness more than steel tube for same strength for side loads and bending.
Aliexpress got lots of nice thin wall stainless tubes at next to no money, or carbon steel if you prefer. I would not be willing to drill all tubes from solid rounds.
The problem of pushrods grinding on shrouds is the result of a design fault as the seal recesses in engine case do not lign up with the follower cup by at least one mm. Am I really the first to see the flaw ? That is why I did the excentric seal holder with small o-ring in it . The shroud can be shortened to end just above the end of the counterbore, no need to be any longer. An o-ring is nicer to have for shroud seal, some alignment range is in this and easier to slip in and out with a little lube. So in the end the 10x2 mm alu tube works allright with the Andrews Mk2 , 29 gr weight only ! Certainly 10 mm don´t drop through the rocker thread but this is no big deal to assemble pushrods first before you put heads over them - nothing I´d care much.
Vic
8x1 stainless tube
your pushrods alu or stainless ? Alu tube, any kind, is perfectly suitable in this application, Vincent types are very short, so no worries here. It is not the problem of straight load along the tube but the lateral motion at ends as these do a fraction of a circle together with the lever cups below and above. So at high speeds this is a sideload onto pushrods really and critical with long types as in BMWs and Horex, at 28 cm (280mm) compared to some 15 cm in Vincents. In this respect the E-module ( in English used, the stiffness under loads ?) is a factor, alu got one third of E-module compared to carbon steel. Stainless steel is a bit less E-module than carbon steel but we like the extra heat growth of factor 16 in stainless, carbon steel is 12 and alu is 24, so twice from steel. When this stiffness (correct term here? ) of material is critical you get a tube with three times wall thickness more than steel tube for same strength for side loads and bending.
Aliexpress got lots of nice thin wall stainless tubes at next to no money, or carbon steel if you prefer. I would not be willing to drill all tubes from solid rounds.
The problem of pushrods grinding on shrouds is the result of a design fault as the seal recesses in engine case do not lign up with the follower cup by at least one mm. Am I really the first to see the flaw ? That is why I did the excentric seal holder with small o-ring in it . The shroud can be shortened to end just above the end of the counterbore, no need to be any longer. An o-ring is nicer to have for shroud seal, some alignment range is in this and easier to slip in and out with a little lube. So in the end the 10x2 mm alu tube works allright with the Andrews Mk2 , 29 gr weight only ! Certainly 10 mm don´t drop through the rocker thread but this is no big deal to assemble pushrods first before you put heads over them - nothing I´d care much.
Vic
8x1 stainless tube